Evaluating the Effects of Clouds on Solar and Longwave Radiation From Moored Buoys in the North Pacific

NASA Astrophysics Data System (ADS)

Balmes, K.; Cronin, M. F.

2014-12-01

Clouds play a critical role in the ocean surface radiation balance, along with the solar zenith angle and the atmospheric moisture and aerosol content. Two moored buoys in the North Pacific - KEO (32.3°N, 144.6°E) and Papa (50°N, 145°W) - continuously measure solar and longwave radiation and other atmospheric and oceanic variables through two redundant systems. After identifying the primary system and constructing daily clear sky solar and longwave radiation values, the seasonal and regional clouds effects are quantified for the two locations. Situated south of the Kuroshio Extension, significant moisture content variability, associated with the Asian monsoon, affects solar and longwave radiation and cloud effects at KEO. Less seasonal variability is observed at buoy Papa located in the Gulf of Alaska. At KEO, the negative solar radiation cloud forcing outweigh the positive longwave radiation cloud forcing leading to ocean cooling, particularly in the summer. At Papa, the longwave radiation cloud forcing counteracts the solar cloud forcing during the winter, subsequently warming the ocean. The regional and seasonal variability of clouds represents a difficult aspect of climate modeling and an area for further research.

Radiative forcing perturbation due to observed increases in tropospheric ozone at Hohenpeissenberg

NASA Technical Reports Server (NTRS)

Wang, Wei-Chyung; Bojkov, Rumen D.; Zhuang, Yi-Cheng

1994-01-01

The effect on surface temperature due to changes in atmospheric O3 depends highly on the latitude where the change occurs. Previous sensitivity calculations indicate that ozone changes in the upper troposphere and lower stratosphere are more effective in causing surface temperature change (Wang et al., 1980). Long term ground-based observations show that tropospheric ozone, especially at the tropopause region, has been increasing at middle and high latitudes in the Northern Hemisphere (NATO, 1988; Quadrennial Ozone Symposium, 1992). These increases will enhance the greenhouse effect and increase the radiative forcing to the troposphere-surface system, which is opposite to the negative radiative forcing calculated from the observed stratospheric ozone depletion recently reported in WMO (1992). We used more than two thousands regularly measured ozonesondes providing reliable vertical O3 distribution at Hohenpeissenberg (47N; 11E) for the 1967-1990 to study the instantaneous solar and longwave radiative forcing the two decades 1971-1990 and compare the forcing with those caused by increasing CO2, CH4, N2O, and CFCs. Calculations are also made to compare the O3 radiative forcing between stratospheric depletion and tropospheric increase. Results indicate that the O3 changes will induce a positive radiative forcing dominated by tropospheric O3 increase and the magnitude of the forcing is comparable to that due to CO2 increases during the two decades. The significant implications of the tropospheric O3 increase to the global climate are discussed.

Airborne Solar Radiant Flux Measurements During ACE-2

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Russell, Philip B.; Jonsson, Haflidi

2000-01-01

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate in potentially significant ways. This aerosol radiative forcing is a major source of uncertainty in understanding the climate change of the past century and predicting future climate. To help reduce this uncertainty, the 1996 Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the 1997 Aerosol Characterization Experiment (ACE-2) measured the properties and radiative effects of aerosols over the Atlantic Ocean. In the ACE 2 program the solar radiant fluxes were measured on the Pelican aircraft and the UK Met Office C130. This poster will show results from the measurements for the aerosol effects during the clear column days. We will compare the results with calculations of the radiant fluxes.

Ultrasonic Power Output Measurement by Pulsed Radiation Pressure

PubMed Central

Fick, Steven E.; Breckenridge, Franklin R.

1996-01-01

Direct measurements of time-averaged spatially integrated output power radiated into reflectionless water loads can be made with high accuracy using techniques which exploit the radiation pressure exerted by sound on all objects in its path. With an absorptive target arranged to intercept the entirety of an ultrasound beam, total beam power can be determined as accurately as the radiation force induced on the target can be measured in isolation from confounding forces due to buoyancy, streaming, surface tension, and vibration. Pulse modulation of the incident ultrasound at a frequency well above those characteristics of confounding phenomena provides the desired isolation and other significant advantages in the operation of the radiation force balance (RFB) constructed in 1974. Equipped with purpose-built transducers and electronics, the RFB is adjusted to equate the radiation force and a counterforce generated by an actuator calibrated against reference masses using direct current as the transfer variable. Improvements made during its one overhaul in 1988 have nearly halved its overall measurement uncertainty and extended the capabilities of the RFB to include measuring the output of ultrasonic systems with arbitrary pulse waveforms. PMID:27805084

Technical note: Fu-Liou-Gu and Corti-Peter model performance evaluation for radiative retrievals from cirrus clouds

NASA Astrophysics Data System (ADS)

Lolli, Simone; Campbell, James R.; Lewis, Jasper R.; Gu, Yu; Welton, Ellsworth J.

2017-06-01

We compare, for the first time, the performance of a simplified atmospheric radiative transfer algorithm package, the Corti-Peter (CP) model, versus the more complex Fu-Liou-Gu (FLG) model, for resolving top-of-the-atmosphere radiative forcing characteristics from single-layer cirrus clouds obtained from the NASA Micro-Pulse Lidar Network database in 2010 and 2011 at Singapore and in Greenbelt, Maryland, USA, in 2012. Specifically, CP simplifies calculation of both clear-sky longwave and shortwave radiation through regression analysis applied to radiative calculations, which contributes significantly to differences between the two. The results of the intercomparison show that differences in annual net top-of-the-atmosphere (TOA) cloud radiative forcing can reach 65 %. This is particularly true when land surface temperatures are warmer than 288 K, where the CP regression analysis becomes less accurate. CP proves useful for first-order estimates of TOA cirrus cloud forcing, but may not be suitable for quantitative accuracy, including the absolute sign of cirrus cloud daytime TOA forcing that can readily oscillate around zero globally.

Polycyclic aromatic hydrocarbon optical properties and contribution to the acceleration of stellar outflows

NASA Technical Reports Server (NTRS)

Cherchneff, Isabelle; Barker, John R.; Tielens, Alexander G. G. M.

1991-01-01

The optical constants of four polycyclic aromatic hydrocarbon (PAH) molecules (benzene, pyrene, pentacene, and coronene) are determined from their measured laboratory absorption spectra. The Planck mean of the radiation pressure cross section is computed for each molecule and for amorphous carbon (AC) grains, and semiempirically estimated for large PAH molecules up to 400 carbon atoms. Assuming that PAHs are present in carbon-rich stellar outflows, the radiation pressure forces acting on them are calculated and compared with the radiation forces on AC particles. The results show that PAHs possess very different optical properties from AC grains. Small PAHs may experience an 'inverse greenhouse' effect in the inner part of the envelope, as they decouple from the gas close to the photosphere. The radiation pressure force on PAHs is always much less than the force at work on AC grains, and PAH molecules do not affect significantly the dynamics of the outflow.

Biomass burning aerosol transport and vertical distribution over the South African-Atlantic region: Aerosol Transport Over SE Atlantic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Das, Sampa; Harshvardhan, H.; Bian, Huisheng

Aerosols from wild-land fires could significantly perturb the global radiation balance and induce the climate change. In this study, the Community Atmospheric Model version 5 (CAM5) with prescribed daily fire aerosol emissions is used to investigate the spatial and seasonal characteristics of radiative forcings of wildfire aerosols including black carbon (BC) and particulate organic matter (POM). The global annual mean direct radiative forcing (DRF) of all fire aerosols is 0.15 W m-2, mainly due to the absorption of fire BC (0.25 W m-2), while fire POM induces a weak negative forcing (-0.05 W m-2). Strong positive DRF is found inmore » the Arctic and in the oceanic regions west of South Africa and South America as a result of amplified absorption of fire BC above low-level clouds, in general agreement with satellite observations. The global annual mean cloud radiative forcing due to all fire aerosols is -0.70 W m-2, resulting mainly from the fire POM indirect forcing (-0.59 W m-2). The large cloud liquid water path over land areas of the Arctic favors the strong fire aerosol indirect forcing (up to -15 W m-2) during the Arctic summer. Significant surface cooling, precipitation reduction and low-level cloud amount increase are also found in the Arctic summer as a result of the fire aerosol indirect effect. The global annual mean surface albedo forcing over land areas (0.03 W m-2) is mainly due to the fire BC-on-snow forcing (0.02 W m-2) with the maximum albedo forcing occurring in spring (0.12 W m-2) when snow starts to melt.« less

Radiative forcing of climate

NASA Technical Reports Server (NTRS)

Ramanswamy, V.; Shine, Keith; Leovy, Conway; Wang, Wei-Chyung; Rodhe, Henning; Wuebbles, Donald J.; Ding, M.; Lelieveld, Joseph; Edmonds, Jae A.; Mccormick, M. Patrick

1991-01-01

An update of the scientific discussions presented in Chapter 2 of the Intergovernmental Panel on Climate Change (IPCC) report is presented. The update discusses the atmospheric radiative and chemical species of significance for climate change. There are two major objectives of the present update. The first is an extension of the discussion on the Global Warming Potentials (GWP's), including a reevaluation in view of the updates in the lifetimes of the radiatively active species. The second important objective is to underscore major developments in the radiative forcing of climate due to the observed stratospheric ozone losses occurring between 1979 and 1990.

Does temperature nudging overwhelm aerosol radiative ...

EPA Pesticide Factsheets

For over two decades, data assimilation (popularly known as nudging) methods have been used for improving regional weather and climate simulations by reducing model biases in meteorological parameters and processes. Similar practice is also popular in many regional integrated meteorology-air quality models that include aerosol direct and indirect effects. However in such multi-modeling systems, temperature changes due to nudging can compete with temperature changes induced by radiatively active & hygroscopic short-lived tracers leading to interesting dilemmas: From weather and climate prediction’s (retrospective or future) point of view when nudging is continuously applied, is there any real added benefit of using such complex and computationally expensive regional integrated modeling systems? What are the relative sizes of these two competing forces? To address these intriguing questions, we convert temperature changes due to nudging into radiative fluxes (referred to as the pseudo radiative forcing, PRF) at the surface and troposphere, and compare the net PRF with the reported aerosol radiative forcing. Results indicate that the PRF at surface dominates PRF at top of the atmosphere (i.e., the net). Also, the net PRF is about 2-4 times larger than estimated aerosol radiative forcing at regional scales while it is significantly larger at local scales. These results also show large surface forcing errors at many polluted urban sites. Thus, operational c

Microbial network, phylogenetic diversity and community membership in the active layer across a permafrost thaw gradient.

PubMed

Mondav, Rhiannon; McCalley, Carmody K; Hodgkins, Suzanne B; Frolking, Steve; Saleska, Scott R; Rich, Virginia I; Chanton, Jeff P; Crill, Patrick M

2017-08-01

Biogenic production and release of methane (CH 4 ) from thawing permafrost has the potential to be a strong source of radiative forcing. We investigated changes in the active layer microbial community of three sites representative of distinct permafrost thaw stages at a palsa mire in northern Sweden. The palsa site (intact permafrost and low radiative forcing signature) had a phylogenetically clustered community dominated by Acidobacteria and Proteobacteria. The bog (thawing permafrost and low radiative forcing signature) had lower alpha diversity and midrange phylogenetic clustering, characteristic of ecosystem disturbance affecting habitat filtering. Hydrogenotrophic methanogens and Acidobacteria dominated the bog shifting from palsa-like to fen-like at the waterline. The fen (no underlying permafrost, high radiative forcing signature) had the highest alpha, beta and phylogenetic diversity, was dominated by Proteobacteria and Euryarchaeota and was significantly enriched in methanogens. The Mire microbial network was modular with module cores consisting of clusters of Acidobacteria, Euryarchaeota or Xanthomonodales. Loss of underlying permafrost with associated hydrological shifts correlated to changes in microbial composition, alpha, beta and phylogenetic diversity associated with a higher radiative forcing signature. These results support the complex role of microbial interactions in mediating carbon budget changes and climate feedback in response to climate forcing. © 2017 Society for Applied Microbiology and John Wiley & Sons Ltd.

A Finite-Element Method Model of Soft Tissue Response to Impulsive Acoustic Radiation Force

PubMed Central

Palmeri, Mark L.; Sharma, Amy C.; Bouchard, Richard R.; Nightingale, Roger W.; Nightingale, Kathryn R

2010-01-01

Several groups are studying acoustic radiation force and its ability to image the mechanical properties of tissue. Acoustic radiation force impulse (ARFI) imaging is one modality using standard diagnostic ultrasound scanners to generate localized, impulsive, acoustic radiation forces in tissue. The dynamic response of tissue is measured via conventional ultrasonic speckle-tracking methods and provides information about the mechanical properties of tissue. A finite-element method (FEM) model has been developed that simulates the dynamic response of tissues, with and without spherical inclusions, to an impulsive acoustic radiation force excitation from a linear array transducer. These FEM models were validated with calibrated phantoms. Shear wave speed, and therefore elasticity, dictates tissue relaxation following ARFI excitation, but Poisson’s ratio and density do not significantly alter tissue relaxation rates. Increased acoustic attenuation in tissue increases the relative amount of tissue displacement in the near field compared with the focal depth, but relaxation rates are not altered. Applications of this model include improving image quality, and distilling material and structural information from tissue’s dynamic response to ARFI excitation. Future work on these models includes incorporation of viscous material properties and modeling the ultrasonic tracking of displaced scatterers. PMID:16382621

Observationally derived rise in methane surface forcing mediated by water vapour trends

NASA Astrophysics Data System (ADS)

Feldman, D. R.; Collins, W. D.; Biraud, S. C.; Risser, M. D.; Turner, D. D.; Gero, P. J.; Tadić, J.; Helmig, D.; Xie, S.; Mlawer, E. J.; Shippert, T. R.; Torn, M. S.

2018-04-01

Atmospheric methane (CH4) mixing ratios exhibited a plateau between 1995 and 2006 and have subsequently been increasing. While there are a number of competing explanations for the temporal evolution of this greenhouse gas, these prominent features in the temporal trajectory of atmospheric CH4 are expected to perturb the surface energy balance through radiative forcing, largely due to the infrared radiative absorption features of CH4. However, to date this has been determined strictly through radiative transfer calculations. Here, we present a quantified observation of the time series of clear-sky radiative forcing by CH4 at the surface from 2002 to 2012 at a single site derived from spectroscopic measurements along with line-by-line calculations using ancillary data. There was no significant trend in CH4 forcing between 2002 and 2006, but since then, the trend in forcing was 0.026 ± 0.006 (99.7% CI) W m2 yr-1. The seasonal-cycle amplitude and secular trends in observed forcing are influenced by a corresponding seasonal cycle and trend in atmospheric CH4. However, we find that we must account for the overlapping absorption effects of atmospheric water vapour (H2O) and CH4 to explain the observations fully. Thus, the determination of CH4 radiative forcing requires accurate observations of both the spatiotemporal distribution of CH4 and the vertically resolved trends in H2O.

A numerical modeling study of the physical mechanisms causing radiation to promote the genesis of a tropical cyclone

NASA Astrophysics Data System (ADS)

Nicholls, M.; Pielke, R., Sr.; Smith, W. H.; Saleeby, S. M.; Wood, N.

2016-12-01

Several cloud-resolving numerical modeling results indicate that radiative forcing significantly accelerates tropical cyclogenesis. The primary mechanism appears to be differential radiative forcing between a relatively cloud-free environment and a developing tropical disturbance that generates circulations that influence convective activity in the core of the system, a mechanism first suggested by Gray and Jacobson. A dynamical perspective of this mechanism is taken by viewing it in terms of the lateral propagation of thermally driven gravity wave circulations. Numerical model experiments indicate that as an expansive stratiform cloud layer forms aloft the long wave cooling is reduced at low and mid levels. During the daytime there is not a very large differential radiative forcing between the environment and the cloud system, but it becomes significant at night when there is strong radiative clear sky cooling of the environment. Thermally driven circulations, are induced characterized by relatively weak subsidence in the environment but considerably stronger upward motion in the system core. This leads to a cooling tendency and increased relative humidity at night which appears to be a major factor in enhancing convective activity thereby leading in the mean to an increased rate of genesis. The increased upward motion and relative humidity that occurs throughout a deep layer is likely to aid in the triggering of convection, and provide a more favorable local environment at mid-levels for maintenance of buoyancy in convective cells due to a reduction of the detrimental effects of dry air entrainment. In order to clarify the effects of radiation the radiative forcing occurring in a fully physics simulation is imposed as a forcing term on the thermodynamic equation in a simulation without microphysics or radiation included to examine the induced circulations and the resultant thermodynamic changes that can influence convective development.

Aerosol Direct Radiative Forcing and Forcing Efficiencies at Surface from the shortwave Irradiance Measurements in Abu Dhabi, UAE

NASA Astrophysics Data System (ADS)

Beegum S, N.; Ben Romdhane, H.; Ghedira, H.

2013-12-01

Atmospheric aerosols are known to affect the radiation balance of the Earth-Atmospheric system directly by scattering and absorbing the solar and terrestrial radiation, and indirectly by affecting the lifetime and albedo of the clouds. Continuous and simultaneous measurements of short wave global irradiance in combination with synchronous spectral aerosol optical depth (AOD) measurements (from 340 nm to 1640 nm in 8 channels), for a period of 1 year from June 2012 to May 2013, were used for the determination of the surface direct aerosol radiative forcing and forcing efficiencies under cloud free conditions in Abu Dhabi (24.42°N, 54.61o E, 7m MSL), a coastal location in United Arab Emirates (UAE) in the Arabian Peninsula. The Rotating Shadow band Pyranometer (RSP, LI-COR) was used for the irradiance measurements (in the spectral region 400-1100 nm), whereas the AOD measurements were carried out using CIMEL Sunphotometer (CE 318-2, under AERONET program). The differential method, which is neither sensitive to calibration uncertainties nor model assumptions, has been employed for estimating forcing efficiencies from the changes in the measured fluxes. The forcing efficiency, which quantifies the net change in irradiance per unit change in AOD, is an appropriate parameter for the characterization of the aerosol radiative effects even if the microphysical and optical properties of the aerosols are not completely understood. The corresponding forcing values were estimated from the forcing efficiencies. The estimated radiative forcing and forcing efficiencies exhibited strong monthly variations. The forcing efficiencies (absolute magnitudes) were highest during March, and showed continuous decrease thereafter to reach the lowest value during September. In contrast, the forcing followed a slightly different pattern of variability, with the highest solar dimming during April ( -60 W m-2) and the minimum during February ( -20 W m-2). The results indicate that the aerosol microphysics as well as the types of aerosol undergo significant seasonal variations.

Variability of the contrail radiative forcing due to crystal shape

NASA Astrophysics Data System (ADS)

Markowicz, K. M.; Witek, M. L.

2011-12-01

The aim of this study is to examine the influence of particles' shape and particles' optical properties on the contrail radiative forcing. Contrail optical properties in the shortwave and longwave range are derived using a ray-tracing geometric method and the discrete dipole approximation method, respectively. Both methods present good correspondence of the single scattering albedo and the asymmetry parameter in a transition range (3-7μm). We compare optical properties defined following simple 10 crystals habits randomly oriented: hexagonal plates, hexagonal columns with different aspect ratio, and spherical. There are substantial differences in single scattering properties between ten crystal models investigated here (e.g. hexagonal columns and plates with different aspect ratios, spherical particles). The single scattering albedo and the asymmetry parameter both vary up to 0.1 between various crystal shapes. Radiative forcing calculations were performed using a model which includes an interface between the state-of-the-art radiative transfer model Fu-Liou and databases containing optical properties of the atmosphere and surface reflectance and emissivity. This interface allows to determine radiative fluxes in the atmosphere and to estimate the contrail radiative forcing for clear- and all-sky (including natural clouds) conditions for various crystal shapes. The Fu-Liou code is fast and therefore it is suitable for computing radiative forcing on a global scale. At the same time it has sufficiently good accuracy for such global applications. A noticeable weakness of the Fu-Liou code is that it does not take into account the 3D radiative effects, e.g. cloud shading and horizontal. Radiative transfer model calculations were performed at horizontal resolution of 5x5 degree and time resolution of 20 min during day and 3 h during night. In order to calculate a geographic distribution of the global and annual mean contrail radiative forcing, the contrail cover must be determined. Two cases are discussed here: a 1% homogeneous contrail cover and the contrail cover provided by Rädel and Shine (2008). In the second distribution case, a more realistic contrail cover is taken into account. This model combines the AERO2K flight inventory with meteorological data and normalizes it with respect to the contrail cover derived from satellite observations. Simulations performed by the Fu-Liou model show significant variability of the shortwave, longwave, and net radiative forcing with crystal shape. The nonspherical crystals have smaller net forcing in contrary to spherical particles. The differences in net radiative forcing between optical models reach up to 50%. The hexagonal column and hexagonal plate particles show the smallest net radiative forcing while the largest forcing is obtained for the spheres. The global and annual mean shortwave, longwave, and net contrail radiative forcing, average over all crystal models and assuming an optical depth of 0.3 at visible wavelengths, is -5.7, 16.8, and 11.1 mW/m2, respectively. A ratio of the radiative forcings' standard deviation to the mean value, derived using 10 different ice particle models, is about 0.2 for the shortwave, 0.14 for the longwave, and 0.23 for the net radiation.

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

PubMed Central

Sengupta, Kamalika; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim

2016-01-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol–cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20–100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m−2 (27%) to −0.60 W m−2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes. PMID:27790989

Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation

NASA Astrophysics Data System (ADS)

Gordon, Hamish; Sengupta, Kamalika; Rap, Alexandru; Duplissy, Jonathan; Frege, Carla; Williamson, Christina; Heinritzi, Martin; Simon, Mario; Yan, Chao; Almeida, João; Tröstl, Jasmin; Nieminen, Tuomo; Ortega, Ismael K.; Wagner, Robert; Dunne, Eimear M.; Adamov, Alexey; Amorim, Antonio; Bernhammer, Anne-Kathrin; Bianchi, Federico; Breitenlechner, Martin; Brilke, Sophia; Chen, Xuemeng; Craven, Jill S.; Dias, Antonio; Ehrhart, Sebastian; Fischer, Lukas; Flagan, Richard C.; Franchin, Alessandro; Fuchs, Claudia; Guida, Roberto; Hakala, Jani; Hoyle, Christopher R.; Jokinen, Tuija; Junninen, Heikki; Kangasluoma, Juha; Kim, Jaeseok; Kirkby, Jasper; Krapf, Manuel; Kürten, Andreas; Laaksonen, Ari; Lehtipalo, Katrianne; Makhmutov, Vladimir; Mathot, Serge; Molteni, Ugo; Monks, Sarah A.; Onnela, Antti; Peräkylä, Otso; Piel, Felix; Petäjä, Tuukka; Praplan, Arnaud P.; Pringle, Kirsty J.; Richards, Nigel A. D.; Rissanen, Matti P.; Rondo, Linda; Sarnela, Nina; Schobesberger, Siegfried; Scott, Catherine E.; Seinfeld, John H.; Sharma, Sangeeta; Sipilä, Mikko; Steiner, Gerhard; Stozhkov, Yuri; Stratmann, Frank; Tomé, Antonio; Virtanen, Annele; Vogel, Alexander Lucas; Wagner, Andrea C.; Wagner, Paul E.; Weingartner, Ernest; Wimmer, Daniela; Winkler, Paul M.; Ye, Penglin; Zhang, Xuan; Hansel, Armin; Dommen, Josef; Donahue, Neil M.; Worsnop, Douglas R.; Baltensperger, Urs; Kulmala, Markku; Curtius, Joachim; Carslaw, Kenneth S.

2016-10-01

The magnitude of aerosol radiative forcing caused by anthropogenic emissions depends on the baseline state of the atmosphere under pristine preindustrial conditions. Measurements show that particle formation in atmospheric conditions can occur solely from biogenic vapors. Here, we evaluate the potential effect of this source of particles on preindustrial cloud condensation nuclei (CCN) concentrations and aerosol-cloud radiative forcing over the industrial period. Model simulations show that the pure biogenic particle formation mechanism has a much larger relative effect on CCN concentrations in the preindustrial atmosphere than in the present atmosphere because of the lower aerosol concentrations. Consequently, preindustrial cloud albedo is increased more than under present day conditions, and therefore the cooling forcing of anthropogenic aerosols is reduced. The mechanism increases CCN concentrations by 20-100% over a large fraction of the preindustrial lower atmosphere, and the magnitude of annual global mean radiative forcing caused by changes of cloud albedo since 1750 is reduced by 0.22 W m-2 (27%) to -0.60 W m-2. Model uncertainties, relatively slow formation rates, and limited available ambient measurements make it difficult to establish the significance of a mechanism that has its dominant effect under preindustrial conditions. Our simulations predict more particle formation in the Amazon than is observed. However, the first observation of pure organic nucleation has now been reported for the free troposphere. Given the potentially significant effect on anthropogenic forcing, effort should be made to better understand such naturally driven aerosol processes.

Supercritical Accretion onto a Non-magnetized Neutron Star: Why is it Feasible?

NASA Astrophysics Data System (ADS)

Takahashi, Hiroyuki R.; Mineshige, Shin; Ohsuga, Ken

2018-01-01

To understand why supercritical accretion is feasible onto a neutron star (NS), we carefully examine the accretion flow dynamics by 2.5-dimensional general relativistic radiation magnetohydrodynamic (RMHD) simulations, comparing the cases of accretion onto a non-magnetized NS and that onto a black hole (BH). Supercritical BH accretion is relatively easy, since BHs can swallow excess radiation energy, so that radiation flux can be inward in its vicinity. This mechanism can never work for an NS, which has a solid surface. In fact, we find that the radiation force is always outward. Instead, we found significant reduction in the mass accretion rate due to strong radiation-pressure-driven outflow. The radiation flux F rad is self-regulated such that the radiation force balances with the sum of gravity and centrifugal forces. Even when the radiation energy density greatly exceeds that expected from the Eddington luminosity {E}{rad}≃ {F}{rad}τ /c> {10}2{L}{Edd}/(4π {r}2c), the radiation flux is always kept below a certain value, which makes it possible not to blow all the gas away from the disk. These effects make supercritical accretion feasible. We also find that a settling region, where accretion is significantly decelerated by a radiation cushion, is formed around the NS surface. In the settling region, the radiation temperature and mass density roughly follow {T}{rad}\\propto {r}-1 and ρ \\propto {r}-3, respectively. No settling region appears around the BH, so matter can be directly swallowed by the BH with supersonic speed.

Fire-induced albedo change and surface radiative forcing in sub-Saharan Africa savanna ecosystems: Implications for the energy balance

NASA Astrophysics Data System (ADS)

Dintwe, Kebonye; Okin, Gregory S.; Xue, Yongkang

2017-06-01

Surface albedo is a critical parameter that controls surface energy balance. In dryland ecosystems, fires play a significant role in decreasing surface albedo, resulting in positive radiative forcing. Here we investigate the long-term effect of fire on surface albedo. We devised a method to calculate short-, medium-, and long-term effect of fire-induced radiative forcing and their relative effects on energy balance. We used Moderate Resolution Imaging Spectroradiometer (MODIS) data in our analysis, covering different vegetation classes in sub-Saharan Africa (SSA). Our analysis indicated that mean short-term fire-induced albedo change in SSA was -0.022, -0.035, and -0.041 for savannas, shrubland, and grasslands, respectively. At regional scale, mean fire-induced albedo change in savannas was -0.018 and -0.024 for northern sub-Saharan of Africa and the southern hemisphere Africa, respectively. The short-term mean fire-induced radiative forcing in burned areas in sub-Saharan Africa (SSA) was 5.41 W m-2, which contributed continental and global radiative forcings of 0.25 and 0.058 W m-2, respectively. The impact of fire in surface albedo has long-lasting effects that varies with vegetation type. The long-term energetic effects of fire-induced albedo change and associated radiative forcing were, on average, more than 19 times greater across SSA than the short-term effects, suggesting that fires exerted far more radiative forcing than previously thought. Taking into account the actual duration of fire's effect on surface albedo, we conclude that the contribution of SSA fires, globally and throughout the year, is 0.12 W m-2. These findings provide crucial information on possible impact of fire on regional climate variability.

Net radiative forcing from widespread deployment of photovoltaics.

PubMed

Nemet, Gregory F

2009-03-15

If photovoltaics (PV) are to contribute significantly to stabilizing the climate, they will need to be deployed on the scale of multiple terawatts. Installation of that much PV would cover substantial portions of the Earth's surface with dark-colored, sunlight-absorbing panels, reducing the Earth's albedo. How much radiative forcing would result from this change in land use? How does this amount compare to the radiative forcing avoided by substituting PV for fossil fuels? This analysis uses a series of simple equations to compare the two effects and finds that substitution dominates; the avoided radiative forcing due to substitution of PV for fossil fuels is approximately 30 times largerthan the forcing due to albedo modification. Sensitivity analysis, including discounting of future costs and benefits, identifies unfavorable yet plausible configurations in which the albedo effect substantially reduces the climatic benefits of PV. The value of PV as a climate mitigation option depends on how it is deployed, not just how much it is deployed--efficiency of PV systems and the carbon intensity of the substituted energy are particularly important

Sensitivity of aerosol radiative forcing efficiency to the coarse mode contributions across aerosol regimes

NASA Astrophysics Data System (ADS)

McComiskey, A. C.; Telg, H.; Sheridan, P. J.; Kassianov, E.

2017-12-01

The coarse mode contribution to the aerosol radiative effect in a range of clean and turbid aerosol regimes has not been well quantified. While the coarse-mode radiative effect in turbid conditions is generally assumed to be consequential, the effect in clean conditions has likely been underestimated. We survey ground-based in situ measurements of the coarse mode fraction of aerosol optical properties measured around the globe over the past 20 years by the DOE Atmospheric Radiation Measurement Facility and the NOAA Global Monitoring Division. The aerosol forcing efficiency is presented, allowing an evaluation of where the aerosol coarse mode might be climatologically significant.

Radiative Forcing by Well-Mixed Greenhouse Gases: Estimates from Climate Models in the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4)

NASA Technical Reports Server (NTRS)

Collins, W. D.; Ramaswamy, V.; Schwarzkopf, M. D.; Sun, Y.; Portmann, R. W.; Fu, Q.; Casanova, S. E. B.; Dufresne, J.-L.; Fillmore, D. W.; Forster, P. M. D.;

Effect of single dose radiation therapy on weight-bearing lameness in dogs with elbow osteoarthritis.

PubMed

Kapatkin, Amy S; Nordquist, Barbro; Garcia, Tanya C; Griffin, Maureen A; Theon, Alain; Kim, Sun; Hayashi, Kei

2016-07-19

To determine if a single low dose of radiation therapy in dogs with osteoarthritis of the elbow joint was associated with a detectable improvement in their lameness and pain as documented by force platform gait analysis. In this cohort longitudinal observational study, five Labrador Retrievers with lameness due to elbow osteoarthritis that was unresponsive to medical treatment were removed from all non-steroidal anti-inflammatory and analgesic medications. A single treatment of radiation therapy delivering 10 Gray was performed on the affected elbow joint(s). Force platform gait analysis was used to assess the ground reaction forces of a limb affected with elbow osteoarthritis both before and after radiation therapy. Significant differences occurred in the weight-bearing on an affected limb with elbow osteoarthritis after radiation therapy at weeks six and 14. Change due to treatment was particularly apparent in dogs with unilateral elbow osteoarthritis. Administering a single low dose of radiation therapy may have a short-term benefit in dogs with elbow osteoarthritis, which is similar to the evidence supporting the use of radiation therapy in horses with orthopaedic disease.

An Experimental Investigation of the Role of Radiation in Laboratory Bench-Top Experiments in Thermal Physics

ERIC Educational Resources Information Center

Twomey, Patrick; O'Sullivan, Colm; O'Riordan, John

2009-01-01

A simple undergraduate experiment designed to study cooling purely by radiation and cooling by a combination of convection and radiation is described. Results indicate that the contribution from radiative cooling in normal laboratory experiments is more significant than students often realize, even in the case of forced cooling. (Contains 1…

Impact of Aerosols on Shortwave and Photosynthetically Active Radiation Balance over Sub-tropical Region in South Asia: Observational and Modeling Approach

NASA Astrophysics Data System (ADS)

Subba, T.; Pathak, B.

2016-12-01

The North-East Indian Region (NER) (22-30ºN, 89-98ºE) in south Asia sandwiched between two global biodiversity hotspots namely, Himalaya and Indo-Burma, assumes significance owing to its unique topography with mountains in the north, east and south and densely populated Indo Gangetic plains (IGP) towards the west resulting in complex aerosol system. Multi-year (2010-2014) concurrent measurements of aerosol properties and the shortwave radiation budget are examined over four geographically distinct stations of NER operational under Indian Space Research organization's ARFINET (Aerosol Radiative Forcing over India NETwork). An attempt has been made to lessen the ambiguity of forcing estimation by validating the radiative transfer modelled ARF with the CNR4 net radiometer measured values (r2 0.98). The Normalized Difference Vegetation Index and its dependence on the extinction of the photosynthetically active radiation (PAR) due to aerosol are assessed. The spring time enhancement of aerosols in the column has shown significant surface cooling (ARF = -48 ± 5 Wm-2) over the region, while the very high Black Carbon (BC) mass concentrations near the surface (SSA > 0.8) leads to significant atmospheric warming (ARF = +41 ± 7 Wm-2) in the shortwave range. Radiative forcing estimates reveal that the atmospheric forcing by BC could be as high as +30Wm-2 over the western part, which are significantly higher than the eastern part with a consequent heating rate of 1.5 K day-1 revealing an east-west asymmetry over NER. The impact of BC aerosols on the photosynthetic rate varies among different locations ranging from -5±2 Wm-2 to -25±3 Wm-2. Almost 70% of the total atmospheric shortwave radiative absorption is attributed to just 10% contribution of Black Carbon (BC) to total mass concentration and causes a reduction of more than 30% of PAR reaching the surface over Brahmaputra valley due to direct radiative effect. Comparison of previous and the present study shows highest surface dimming is observed in west-Asia followed by IGP and west-India. Surface radiative reduction over NER is comparable to south-India standing on the third place which is still higher than that of the Himalayan and Oceanic regions.

Cloud Radiation Forcings and Feedbacks: General Circulation Model Tests and Observational Validation

NASA Technical Reports Server (NTRS)

Lee,Wan-Ho; Iacobellis, Sam F.; Somerville, Richard C. J.

1997-01-01

Using an atmospheric general circulation model (the National Center for Atmospheric Research Community Climate Model: CCM2), the effects on climate sensitivity of several different cloud radiation parameterizations have been investigated. In addition to the original cloud radiation scheme of CCM2, four parameterizations incorporating prognostic cloud water were tested: one version with prescribed cloud radiative properties and three other versions with interactive cloud radiative properties. The authors' numerical experiments employ perpetual July integrations driven by globally constant sea surface temperature forcings of two degrees, both positive and negative. A diagnostic radiation calculation has been applied to investigate the partial contributions of high, middle, and low cloud to the total cloud radiative forcing, as well as the contributions of water vapor, temperature, and cloud to the net climate feedback. The high cloud net radiative forcing is positive, and the middle and low cloud net radiative forcings are negative. The total net cloud forcing is negative in all of the model versions. The effect of interactive cloud radiative properties on global climate sensitivity is significant. The net cloud radiative feedbacks consist of quite different shortwave and longwave components between the schemes with interactive cloud radiative properties and the schemes with specified properties. The increase in cloud water content in the warmer climate leads to optically thicker middle- and low-level clouds and in turn to negative shortwave feedbacks for the interactive radiative schemes, while the decrease in cloud amount simply produces a positive shortwave feedback for the schemes with a specified cloud water path. For the longwave feedbacks, the decrease in high effective cloudiness for the schemes without interactive radiative properties leads to a negative feedback, while for the other cases, the longwave feedback is positive. These cloud radiation parameterizations are empirically validated by using a single-column diagnostic model. together with measurements from the Atmospheric Radiation Measurement program and from the Tropical Ocean Global Atmosphere Combined Ocean-Atmosphere Response Experiment. The inclusion of prognostic cloud water produces a notable improvement in the realism of the parameterizations, as judged by these observations. Furthermore, the observational evidence suggests that deriving cloud radiative properties from cloud water content and microphysical characteristics is a promising route to further improvement.

Observational determination of surface radiative forcing by CO2 from 2000 to 2010

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feldman, Daniel R.; Collins, William D.; Gero, P. Johnathan

2015-02-25

The climatic impact of CO2 and other greenhouse gases is usually quantified in terms of radiative forcing1, calculated as the difference between estimates of the Earth’s radiation field from pre-industrial and present-day concentrations of these gases. Radiative transfer models calculate that the increase in CO2 since 1750 corresponds to a global annual-mean radiative forcing at the tropopause of 1.82 ± 0.19 W m -2 (ref. 2). However, despite widespread scientific discussion and modelling of the climate impacts of well-mixed greenhouse gases, there is little direct observational evidence of the radiative impact of increasing atmospheric CO2. Here we present observationally basedmore » evidence of clear-sky CO2 surface radiative forcing that is directly attributable to the increase, between 2000 and 2010, of 22 parts per million atmospheric CO2. The time series of this forcing at the two locations—the Southern Great Plains and the North Slope of Alaska—are derived from Atmospheric Emitted Radiance Interferometer spectra3 together with ancillary measurements and thoroughly corroborated radiative transfer calculations4. The time series both show statistically significant trends of 0.2 W m -2 per decade (with respective uncertainties of ±0.06 W m -2 per decade and ±0.07 W m-2 per decade) and have seasonal ranges of 0.1–0.2 W m -2. This is approximately ten per cent of the trend in downwelling longwave radiation5, 6, 7. These results confirm theoretical predictions of the atmospheric greenhouse effect due to anthropogenic emissions, and provide empirical evidence of how rising CO2 levels, mediated by temporal variations due to photosynthesis and respiration, are affecting the surface energy balance.« less

Infrared Radiative Forcing and Atmospheric Lifetimes of Trace Species Based on Observations from UARS

NASA Technical Reports Server (NTRS)

Minschwaner, K.; Carver, R. W.; Briegleb, B. P.

1997-01-01

Observations from instruments on the Upper Atmosphere Research Satellite (UARS) have been used to constrain calculations of infrared radiative forcing by CH4, CCl2F2 and N2O, and to determine lifetimes Of CCl2F2 and N2O- Radiative forcing is calculated as a change in net infrared flux at the tropopause that results from an increase in trace gas amount from pre-industrial (1750) to contemporary (1992) times. Latitudinal and seasonal variations are considered explicitly, using distributions of trace gases and temperature in the stratosphere from UARS measurements and seasonally averaged cloud statistics from the International Satellite Cloud Climatology Project. Top-of-atmosphere fluxes calculated for the contemporary period are in good agreement with satellite measurements from the Earth Radiation Budget Experiment. Globally averaged values of the radiative forcing are 0.536, 0.125, and 0.108 W m-2 for CH4, CCl2F2, and N2O, respectively. The largest forcing occurs near subtropical latitudes during summer, predominantly as a result of the combination of cloud-free skies and a high, cold tropopause. Clouds are found to play a significant role in regulating infrared forcing, reducing the magnitude of the forcing by 30-40% compared to the case of clear skies. The vertical profile of CCl2F2 is important in determining its radiative forcing; use of a height-independent mixing ratio in the stratosphere leads to an over prediction of the forcing by 10%. The impact of stratospheric profiles on radiative forcing by CH4 and N2O is less than 2%. UARS-based distributions of CCl2F2 and N2O are used also to determine global destruction rates and instantaneous lifetimes of these gases. Rates of photolytic destruction in the stratosphere are calculated using solar ultraviolet irradiances measured on UARS and a line-by-line model of absorption in the oxygen Schumann-Runge bands. Lifetimes are 114 +/- 22 and 118 +/- 25 years for CCl2F2 and N2O, respectively.

Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing

NASA Astrophysics Data System (ADS)

Etminan, M.; Myhre, G.; Highwood, E. J.; Shine, K. P.

2016-12-01

New calculations of the radiative forcing (RF) are presented for the three main well-mixed greenhouse gases, methane, nitrous oxide, and carbon dioxide. Methane's RF is particularly impacted because of the inclusion of the shortwave forcing; the 1750-2011 RF is about 25% higher (increasing from 0.48 W m-2 to 0.61 W m-2) compared to the value in the Intergovernmental Panel on Climate Change (IPCC) 2013 assessment; the 100 year global warming potential is 14% higher than the IPCC value. We present new simplified expressions to calculate RF. Unlike previous expressions used by IPCC, the new ones include the overlap between CO2 and N2O; for N2O forcing, the CO2 overlap can be as important as the CH4 overlap. The 1750-2011 CO2 RF is within 1% of IPCC's value but is about 10% higher when CO2 amounts reach 2000 ppm, a value projected to be possible under the extended RCP8.5 scenario.

Forcings and feedbacks in the GeoMIP ensemble for a reduction in solar irradiance and increase in CO2

NASA Astrophysics Data System (ADS)

Huneeus, Nicolas; Boucher, Olivier; Alterskjær, Kari; Cole, Jason N. S.; Curry, Charles L.; Ji, Duoying; Jones, Andy; Kravitz, Ben; Kristjánsson, Jón Egill; Moore, John C.; Muri, Helene; Niemeier, Ulrike; Rasch, Phil; Robock, Alan; Singh, Balwinder; Schmidt, Hauke; Schulz, Michael; Tilmes, Simone; Watanabe, Shingo; Yoon, Jin-Ho

2014-05-01

The effective radiative forcings (including rapid adjustments) and feedbacks associated with an instantaneous quadrupling of the preindustrial CO2 concentration and a counterbalancing reduction of the solar constant are investigated in the context of the Geoengineering Model Intercomparison Project (GeoMIP). The forcing and feedback parameters of the net energy flux, as well as its different components at the top-of-atmosphere (TOA) and surface, were examined in 10 Earth System Models to better understand the impact of solar radiation management on the energy budget. In spite of their very different nature, the feedback parameter and its components at the TOA and surface are almost identical for the two forcing mechanisms, not only in the global mean but also in their geographical distributions. This conclusion holds for each of the individual models despite intermodel differences in how feedbacks affect the energy budget. This indicates that the climate sensitivity parameter is independent of the forcing (when measured as an effective radiative forcing). We also show the existence of a large contribution of the cloudy-sky component to the shortwave effective radiative forcing at the TOA suggesting rapid cloud adjustments to a change in solar irradiance. In addition, the models present significant diversity in the spatial distribution of the shortwave feedback parameter in cloudy regions, indicating persistent uncertainties in cloud feedback mechanisms.

Can unforced radiative variability explain the "hiatus"?

NASA Astrophysics Data System (ADS)

Donohoe, A.

2016-02-01

The paradox of the "hiatus" is characterized as a decade long period over which global mean surface temperature remained relatively constant even though greenhouse forcing forcing is believed to have been positive and increasing. Explanations of the hiatus have focused on two primary lines of thought: 1. There was a net radiative imbalance at the top of atmosphere (TOA) but this energy input was stored in the ocean without increasing surface temperature or 2. There was no radiative imbalance at the TOA because the greenhouse forcing was offset by other climate forcings. Here, we explore a third hypothesis: that there was no TOA radiative imbalance over the decade due to unforced, natural modes of radiative variability that are unrelated to global mean temperature. Is it possible that the Earth could emit enough radiation to offset greenhouse forcing without increasing its temperature due to internal modes of climate variability? Global mean TOA energy imbalance is estimated to be 0.65 W m-2 as determined from the long term change in ocean heat content - where the majority of the energy imbalance is stored. Therefore, in order to offset this TOA energy imbalance natural modes of radiative variability with amplitudes of order 0.5 W m-2 at the decadal timescale are required. We demonstrate that unforced coupled climate models have global mean radiative variability of the required magnitude (2 standard deviations of 0.57 W m-2 in the inter-model mean) and that the vast majority (>90%) of this variability is unrelated to surface temperature radiative feedbacks. However, much of this variability is at shorter (monthly and annual) timescales and does not persist from year to year making the possibility of a decade long natural interruption of the energy accumulation in the climate system unlikely due to natural radiative variability alone given the magnitude of the greenhouse forcing on Earth. Comparison to observed satellite data suggest the models capture the magnitude (2 sigma = 0.61 W m-2) and mechanisms of internal radiative variability but we cannot exclude the possibility of low frequency modes of variability with significant magnitude given the limited length of the satellite record.

Amplitude-modulated acoustic radiation force experienced by elastic and viscoelastic spherical shells in progressive waves.

PubMed

Mitri, F G; Fellah, Z E A

2006-07-01

The dynamic acoustic radiation force resulting from a dual-frequency beam incident on spherical shells immersed in an inviscid fluid is examined theoretically in relation to their thickness and the contents of their interior hollow regions. The theory is modified to include a hysteresis type of absorption inside the shells' material. The results of numerical calculations are presented for stainless steel and absorbing lucite (PolyMethyMethacrylAte) shells with the hollow region filled with water or air. Significant differences occur when the interior fluid inside the hollow region is changed from water to air. It is shown that the dynamic radiation force function Yd deviates from the static radiation force function Yp when the modulation size parameter deltax = mid R:x2 - x1mid R: (x1 = k1a, x2 = k2a, k1 and k2 are the wave vectors of the incident ultrasound waves, and a is the outer radius of the shell) starts to exceed the width of the resonance peaks in the Yp curves.

The Impact of Desert Dust Aerosol Radiative Forcing on Global and West African Precipitation

NASA Astrophysics Data System (ADS)

Jordan, A.; Zaitchik, B. F.; Gnanadesikan, A.; Dezfuli, A. K.

2015-12-01

Desert dust aerosols exert a radiative forcing on the atmosphere, influencing atmospheric temperature structure and modifying radiative fluxes at the top of the atmosphere (TOA) and surface. As dust aerosols perturb radiative fluxes, the atmosphere responds by altering both energy and moisture dynamics, with potentially significant impacts on regional and global precipitation. Global Climate Model (GCM) experiments designed to characterize these processes have yielded a wide range of results, owing to both the complex nature of the system and diverse differences across models. Most model results show a general decrease in global precipitation, but regional results vary. Here, we compare simulations from GFDL's CM2Mc GCM with multiple other model experiments from the literature in order to investigate mechanisms of radiative impact and reasons for GCM differences on a global and regional scale. We focus on West Africa, a region of high interannual rainfall variability that is a source of dust and that neighbors major Sahara Desert dust sources. As such, changes in West African climate due to radiative forcing of desert dust aerosol have serious implications for desertification feedbacks. Our CM2Mc results show net cooling of the planet at TOA and surface, net warming of the atmosphere, and significant increases in precipitation over West Africa during the summer rainy season. These results differ from some previous GCM studies, prompting comparative analysis of desert dust parameters across models. This presentation will offer quantitative analysis of differences in dust aerosol parameters, aerosol optical properties, and overall particle burden across GCMs, and will characterize the contribution of model differences to the uncertainty of forcing and climate response affecting West Africa.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitri, F. G., E-mail: F.G.Mitri@ieee.org

This paper presents two key contributions; the first concerns the development of analytical expressions for the axial and transverse acoustic radiation forces exerted on a 2D rigid elliptical cylinder placed in the field of plane progressive, quasi-standing, or standing waves with arbitrary incidence. The second emphasis is on the acoustic radiation torque per length. The rigid elliptical cylinder case is important to be considered as a first-order approximation of the behavior of a cylindrical fluid column trapped in air because of the significant acoustic impedance mismatch at the particle boundary. Based on the rigorous partial-wave series expansion method in cylindricalmore » coordinates, non-dimensional acoustic radiation force and torque functions are derived and defined in terms of the scattering coefficients of the elliptic cylinder. A coupled system of linear equations is obtained after applying the Neumann boundary condition for an immovable surface in a non-viscous fluid and solved numerically by matrix inversion after performing a single numerical integration procedure. Computational results for the non-dimensional force components and torque, showing the transition from the progressive to the (equi-amplitude) standing wave behavior, are performed with particular emphasis on the aspect ratio a/b, where a and b are the semi-axes of the ellipse, the dimensionless size parameter, as well as the angle of incidence ranging from end-on to broadside incidence. The results show that the elliptical geometry has a direct influence on the radiation force and torque, so that the standard theory for circular cylinders (at normal incidence) leads to significant miscalculations when the cylinder cross section becomes non-circular. Moreover, the elliptical cylinder experiences, in addition to the acoustic radiation force, a radiation torque that vanishes for the circular cylinder case. The application of the formalism presented here may be extended to other 2D surfaces of arbitrary shape, such as Chebyshev cylindrical particles with a small deformation, stadiums (with oval shape), or other non-circular geometries.« less

Global upper ocean heat storage response to radiative forcing from changing solar irradiance and increasing greenhouse gas/aerosol concentrations

NASA Astrophysics Data System (ADS)

White, Warren B.; Cayan, Daniel R.; Lean, Judith

1998-09-01

We constructed gridded fields of diabatic heat storage changes in the upper ocean from 20°S to 60°N from historical temperature profiles collected from 1955 to 1996. We filtered these 42 year records for periods of 8 to 15 years and 15 to 30 years, producing depth-weighted vertical average temperature (DVT) changes from the sea surface to the top of the main pycnocline. Basin and global averages of these DVT changes reveal decadal and interdecadal variability in phase across the Indian, Pacific, Atlantic, and Global Oceans, each significantly correlated with changing surface solar radiative forcing at a lag of 0+/-2 years. Decadal and interdecadal changes in global average DVT are 0.06°+/-0.01°K and 0.04°K+/-0.01°K, respectively, the same as those expected from consideration of the Stefan-Boltzmann radiation balance (i.e., 0.3°K per Wm-2) in response to 0.1% changes in surface solar radiative forcing of 0.2 Wm-2 and 0.15 Wm-2, respectively. Global spatial patterns of DVT changes are similar to temperature changes simulated in coupled ocean-atmosphere models, suggesting that natural modes of Earth's variability are phase-locked to the solar irradiance cycle. A trend in global average DVT of 0.15°K over this 42 year record cannot be explained by changing surface solar radiative forcing. But when we consider the 0.5 Wm-2 increase in surface radiative forcing estimated from the increase in atmospheric greenhouse gas and aerosol (GGA) concentrations over this period [Intergovernmental Panel on Climate Change, 1995], the Stefan-Boltzmann radiation balance yields this observed change. Moreover, the sum of solar and GGA surface radiative forcing can explain the relatively sharp increase in global and basin average DVT in the late 1970's.

Radiative effects of light-absorbing particles deposited in snow over Himalayas using WRF-Chem simulations

NASA Astrophysics Data System (ADS)

Sarangi, C.; Qian, Y.; Painter, T. H.; Liu, Y.; Lin, G.; Wang, H.

2017-12-01

Radiative forcing induced by light-absorbing particles (LAP) deposited on snow is an important surface forcing. It has been debated that an aerosol-induced increase in atmospheric and surface warming over Tibetan Plateau (TP) prior to the South Asian summer monsoon can have a significant effect on the regional thermodynamics and South Asian monsoon circulation. However, knowledge about the radiative effects due to deposition of LAP in snow over TP is limited. In this study we have used a high-resolution WRF-Chem (coupled with online chemistry and snow-LAP-radiation model) simulations during 2013-2014 to estimate the spatio-temporal variation in LAP deposition on snow, specifically black carbon (BC) and dust particles, in Himalayas. Simulated distributions in meteorology, aerosol concentrations, snow albedo, snow grain size and snow depth are evaluated against satellite and in-situ measurements. The spatio-temporal change in snow albedo and snow grain size with variation in LAP deposition is investigated and the resulting shortwave LAP radiative forcing at surface is calculated. The LAP-radiative forcing due to aerosol deposition, both BC and dust, is higher in magnitude over Himalayan slopes (terrain height below 4 km) compared to that over TP (terrain height above 4 km). We found that the shortwave aerosol radiative forcing efficiency at surface due to increase in deposited mass of BC particles in snow layer ( 25 (W/m2)/ (mg/m2)) is manifold higher than the efficiency of dust particles ( 0.1 (W/m2)/ (mg/m2)) over TP. However, the radiative forcing of dust deposited in snow is similar in magnitude (maximum 20-30 W/m2) to that of BC deposited in snow over TP. This is mainly because the amount of dust deposited in snow over TP can be about 100 times greater than the amount of BC deposited in snow during polluted conditions. The impact of LAP on surface energy balance, snow melting and atmospheric thermodynamics is also examined.

Active control of sound radiation from a vibrating rectangular panel by sound sources and vibration inputs - An experimental comparison

NASA Technical Reports Server (NTRS)

Fuller, C. R.; Hansen, C. H.; Snyder, S. D.

1991-01-01

Active control of sound radiation from a rectangular panel by two different methods has been experimentally studied and compared. In the first method a single control force applied directly to the structure is used with a single error microphone located in the radiated acoustic field. Global attenuation of radiated sound was observed to occur by two main mechanisms. For 'on-resonance' excitation, the control force had the effect of increasing the total panel input impedance presented to the nosie source, thus reducing all radiated sound. For 'off-resonance' excitation, the control force tends not significantly to modify the panel total response amplitude but rather to restructure the relative phases of the modes leading to a more complex vibration pattern and a decrease in radiation efficiency. For acoustic control, the second method, the number of acoustic sources required for global reduction was seen to increase with panel modal order. The mechanism in this case was that the acoustic sources tended to create an inverse pressure distribution at the panel surface and thus 'unload' the panel by reducing the panel radiation impedance. In general, control by structural inputs appears more effective than control by acoustic sources for structurally radiated noise.

The effect of applied transducer force on acoustic radiation force impulse quantification within the left lobe of the liver.

PubMed

Porra, Luke; Swan, Hans; Ho, Chien

2015-08-01

Introduction: Acoustic Radiation Force Impulse (ARFI) Quantification measures shear wave velocities (SWVs) within the liver. It is a reliable method for predicting the severity of liver fibrosis and has the potential to assess fibrosis in any part of the liver, but previous research has found ARFI quantification in the right lobe more accurate than in the left lobe. A lack of standardised applied transducer force when performing ARFI quantification in the left lobe of the liver may account for some of this inaccuracy. The research hypothesis of this present study predicted that an increase in applied transducer force would result in an increase in SWVs measured. Methods: ARFI quantification within the left lobe of the liver was performed within a group of healthy volunteers (n = 28). During each examination, each participant was subjected to ARFI quantification at six different levels of transducer force applied to the epigastric abdominal wall. Results: A repeated measures ANOVA test showed that ARFI quantification was significantly affected by applied transducer force (p = 0.002). Significant pairwise comparisons using Bonferroni correction for multiple comparisons showed that with an increase in applied transducer force, there was a decrease in SWVs. Conclusion: Applied transducer force has a significant effect on SWVs within the left lobe of the liver and it may explain some of the less accurate and less reliable results in previous studies where transducer force was not taken into consideration. Future studies in the left lobe of the liver should take this into account and control for applied transducer force.

Arctic ocean radiative fluxes and cloud forcing estimated from the ISCCP C2 cloud dataset, 1983-1990

NASA Technical Reports Server (NTRS)

Schweiger, Axel J.; Key, Jeffrey R.

1994-01-01

Radiative fluxes and cloud forcings for the ocean areas of the Arctic are computed from the monthly cloud product of the International Satellite Cloud Climatology Project (ISCCP) for 1983-90. Spatially averaged short-wave fluxes are compared well with climatological values, while downwelling longwave fluxes are significantly lower. This is probably due to the fact that the ISCCP cloud amounts are underestimates. Top-of-the-atmosphere radiative fluxes are in excellent agreement with measurements from the Earth Radiation Budget Experiment (ERBE). Computed cloud forcings indicate that clouds have a warming effect at the surface and at the top of the atmosphere during winter and a cooling effect during summer. The net radiative effect of clouds is larger at the surface during winter but greater at the top of the atmosphere during summer. Overall the net radiative effect of clouds at the top of the atmosphere is one of cooling. This is in contrast to a previous result from ERBE data showing arctic cloud forcings have a net warming effect. Sensitivities to errors in input parameters are generally greater during winter with cloud amount being the most important paarameter. During summer the surface radiation balance is most sensitive to errors in the measurements of surface reflectance. The results are encouraging, but the estimated error of 20 W/sq m in surface net radiative fluxes is too large, given that estimates of the net radiative warming effect due to a doubling of CO2 are on the order of 4 W/sq m. Because it is difficult to determine the accuracy of results with existing in situ observations, it is recommended that the development of improved algorithms for the retrieval of surface radiative properties be accompanied by the simultaneous assembly of validation datasets.

Aerosol Absorption and Radiative Forcing

NASA Technical Reports Server (NTRS)

Stier, Philip; Seinfeld, J. H.; Kinne, Stefan; Boucher, Olivier

2007-01-01

We present a comprehensive examination of aerosol absorption with a focus on evaluating the sensitivity of the global distribution of aerosol absorption to key uncertainties in the process representation. For this purpose we extended the comprehensive aerosol-climate model ECHAM5-HAM by effective medium approximations for the calculation of aerosol effective refractive indices, updated black carbon refractive indices, new cloud radiative properties considering the effect of aerosol inclusions, as well as by modules for the calculation of long-wave aerosol radiative properties and instantaneous aerosol forcing. The evaluation of the simulated aerosol absorption optical depth with the AERONET sun-photometer network shows a good agreement in the large scale global patterns. On a regional basis it becomes evident that the update of the BC refractive indices to Bond and Bergstrom (2006) significantly improves the previous underestimation of the aerosol absorption optical depth. In the global annual-mean, absorption acts to reduce the shortwave anthropogenic aerosol top-of-atmosphere (TOA) radiative forcing clear-sky from -0.79 to -0.53 W m(sup -2) (33%) and all-sky from -0.47 to -0.13W m(sup -2 (72%). Our results confirm that basic assumptions about the BC refractive index play a key role for aerosol absorption and radiative forcing. The effect of the usage of more accurate effective medium approximations is comparably small. We demonstrate that the diversity in the AeroCom land-surface albedo fields contributes to the uncertainty in the simulated anthropogenic aerosol radiative forcings: the usage of an upper versus lower bound of the AeroCom land albedos introduces a global annual-mean TOA forcing range of 0.19W m(sup -2) (36%) clear-sky and of 0.12W m(sup -2) (92%) all-sky. The consideration of black carbon inclusions on cloud radiative properties results in a small global annual-mean all-sky absorption of 0.05W m(sup -2) and a positive TOA forcing perturbation of 0.02W m(sup -2). The long-wave aerosol radiative effects are small for anthropogenic aerosols but become of relevance for the larger natural dust and sea-salt aerosols.

A New Paradigm for Diagnosing Contributions to Model Aerosol Forcing Error: Diagnosing Model Aerosol Forcing Error

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, A. L.; Feldman, D. R.; Freidenreich, S.

A new paradigm in benchmark absorption-scattering radiative transfer is presented that enables both the globally averaged and spatially resolved testing of climate model radiation parameterizations in order to uncover persistent sources of biases in the aerosol instantaneous radiative effect (IRE). A proof of concept is demonstrated with the Geophysical Fluid Dynamics Laboratory AM4 and Community Earth System Model 1.2.2 climate models. Instead of prescribing atmospheric conditions and aerosols, as in prior intercomparisons, native snapshots of the atmospheric state and aerosol optical properties from the participating models are used as inputs to an accurate radiation solver to uncover model-relevant biases. Thesemore » diagnostic results show that the models' aerosol IRE bias is of the same magnitude as the persistent range cited (~1 W/m 2) and also varies spatially and with intrinsic aerosol optical properties. The findings presented here underscore the significance of native model error analysis and its dispositive ability to diagnose global biases, confirming its fundamental value for the Radiative Forcing Model Intercomparison Project.« less

A New Paradigm for Diagnosing Contributions to Model Aerosol Forcing Error: Diagnosing Model Aerosol Forcing Error

DOE PAGES

Jones, A. L.; Feldman, D. R.; Freidenreich, S.; ...

2017-12-07

A new paradigm in benchmark absorption-scattering radiative transfer is presented that enables both the globally averaged and spatially resolved testing of climate model radiation parameterizations in order to uncover persistent sources of biases in the aerosol instantaneous radiative effect (IRE). A proof of concept is demonstrated with the Geophysical Fluid Dynamics Laboratory AM4 and Community Earth System Model 1.2.2 climate models. Instead of prescribing atmospheric conditions and aerosols, as in prior intercomparisons, native snapshots of the atmospheric state and aerosol optical properties from the participating models are used as inputs to an accurate radiation solver to uncover model-relevant biases. Thesemore » diagnostic results show that the models' aerosol IRE bias is of the same magnitude as the persistent range cited (~1 W/m 2) and also varies spatially and with intrinsic aerosol optical properties. The findings presented here underscore the significance of native model error analysis and its dispositive ability to diagnose global biases, confirming its fundamental value for the Radiative Forcing Model Intercomparison Project.« less

Aerosol Radiative Forcing over North India during Pre-Monsoon Season using WRF-Chem

NASA Astrophysics Data System (ADS)

Misra, A.; Kumar, K.; Michael, M.; Tripathi, S. N.

2013-12-01

Study of aerosols is important for a fair understanding of the Earth climate system. This requires knowledge of the physical, chemical, optical, and morphological properties of aerosols. Aerosol radiative forcing provides information on the effect of aerosols on the Earth radiation budget. Radiative forcing estimates using model data provide an opportunity to examine the contribution of individual aerosol species to overall radiative forcing. We have used Weather Research and Forecast with Online Chemistry (WRF-Chem) derived aerosol concentration data to compute aerosol radiative forcing over north India during pre-monsoon season of 2008, 2009, and 2010. WRF-Chem derived mass concentrations are converted to number concentrations using standard procedure. Optical Properties of Aerosol and Cloud (OPAC) software package is used to compute extinction and scattering coefficients, and asymmetry parameter. Computations are performed at different altitudes and the obtained values are integrated to get the column optical properties. Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model is used to calculate the radiative forcing at surface and top-of-atmosphere. Higher values of aerosol radiative forcing are observed over desert region in western Indian state of Rajasthan, and Punjab of Pakistan. Contribution of individual aerosol species to atmospheric radiative forcing is also assessed. Dust radiative forcing is high over western India. Radiative forcing due to BC and water-soluble (WASO) aerosols are higher over north-west Indian states of Punjab and Haryana, and the Indo-Gangetic Basin. A pool of high WASO optical depth and radiative forcing is observed over the Indo-Bangladesh border. The findings of aerosol optical depth and radiative forcing are consistent with the geography and prevailing aerosol climatology of various regions. Heating rate profiles due to total aerosols and only due to BC have been evaluated at selected stations in north India. They show variation between various stations and seasons.

Vertical dependence of black carbon, sulphate and biomass burning aerosol radiative forcing

NASA Astrophysics Data System (ADS)

Samset, Bjørn H.; Myhre, Gunnar

2011-12-01

A global radiative transfer model is used to calculate the vertical profile of shortwave radiative forcing from a prescribed amount of aerosols. We study black carbon (BC), sulphate (SO4) and a black and organic carbon mixture typical of biomass burning (BIO), by prescribing aerosol burdens in layers between 1000 hPa and 20 hPa and calculating the resulting direct radiative forcing divided by the burden (NDRF). We find a strong sensitivity in the NDRF for BC with altitude, with a tenfold increase between BC close to the surface and the lower part of the stratosphere. Clouds are a major contributor to this dependence with altitude, but other factors also contribute. We break down and explain the different physical contributors to this strong sensitivity. The results show a modest regional dependence of the altitudinal dependence of BC NDRF between industrial regions, while for regions with properties deviating from the global mean NDRF variability is significant. Variations due to seasons and interannual changes in cloud conditions are found to be small. We explore the effect that large altitudinal variation in NDRF may have on model estimates of BC radiative forcing when vertical aerosol distributions are insufficiently constrained, and discuss possible applications of the present results for reducing inter-model differences.

Infrared Aerosol Radiative Forcing at the Surface and the Top of the Atmosphere

NASA Technical Reports Server (NTRS)

Markowicz, Krzysztof M.; Flatau, Piotr J.; Vogelmann, Andrew M.; Quinn, Patricia K.; Welton, Ellsworth J.

2003-01-01

We study the clear-sky aerosol radiative forcing at infrared wavelengths using data from the Aerosol Characterization Experiment (ACE-Asia) cruise of the NOAA R/V Ronald H. Brown. Limited number of data points is analyzed mostly from ship and collocated satellite values. An optical model is derived from chemical measurements, lidar profiles, and visible extinction measurements which is used to and estimate the infrared aerosol optical thickness and the single scattering albedo. The IR model results are compared to detailed Fourier Transform Interferometer based infrared aerosol forcing estimates, pyrgeometer based infrared downward fluxes, and against the direct solar forcing observations. This combined approach attests for the self-consistency of the optical model and allows to derive quantities such as the infrared forcing at the top of the atmosphere or the infrared optical thickness. The mean infrared aerosol optical thickness at 10 microns is 0.08 and the single scattering albedo is 0.55. The modeled infrared aerosol forcing reaches 10 W/sq m during the cruise, which is a significant contribution to the total direct aerosol forcing. The surface infrared aerosol radiative forcing is between 10 to 25% of the shortwave aerosol forcing. The infrared aerosol forcing at the top of the atmosphere can go up to 19% of the solar aerosol forcing. We show good agreement between satellite (CERES instrument) retrievals and model results at the top of the atmosphere. Over the Sea of Japan, the average infrared radiative forcing is 4.6 W/sq m in the window region at the surface and it is 1.5 W/sq m at top of the atmosphere. The top of the atmosphere IR forcing efficiency is a strong function of aerosol temperature while the surface IR forcing efficiency varies between 37 and 55 W/sq m (per infrared optical depth unit). and changes between 10 to 18 W/sq m (per infrared optical depth unit).

Force approach to radiation reaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

López, Gustavo V., E-mail: gulopez@udgserv.cencar.udg.mx

The difficulty of the usual approach to deal with the radiation reaction is pointed out, and under the condition that the radiation force must be a function of the external force and is zero whenever the external force be zero, a new and straightforward approach to radiation reaction force and damping is proposed. Starting from the Larmor formula for the power radiated by an accelerated charged particle, written in terms of the applied force instead of the acceleration, an expression for the radiation force is established in general, and applied to the examples for the linear and circular motion ofmore » a charged particle. This expression is quadratic in the magnitude of the applied force, inversely proportional to the speed of the charged particle, and directed opposite to the velocity vector. This force approach may contribute to the solution of the very old problem of incorporating the radiation reaction to the motion of the charged particles, and future experiments may tell us whether or not this approach point is in the right direction.« less

Evidence of a long-term increase in tropospheric ozone from Pic du Midi data series: Consequences: Positive radiative forcing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marenco, A.; Gouget, H.; Nedelec, P.

1994-08-01

The rate at which ozone is increasing in the troposphere is uncertain due to the lack of accurate long-term measurements. Old ozone measurements obtained at the Pic du Midi Observatory (3000 m high, southwestern France) were recently rediscovered. Four sets of data available at this station are presented. The results show an increase in ozone by a factor of 5 since the beginning of the twentieth century, corresponding to an exponential increase of 1.6% per year, although this trend is probably higher (2.4% per year) for the last few decades. A stable 10 ppb ozone mixing ratio is observed duringmore » the first 20 years of the series, which is representative to the preindustrial era ozone level. The increase is seen to start around 1895. Other data, obtained at various European high-altitude stations between 1920 and 1980, tie in closely with the Pic du Midi observations. A tentative evaluation of the impact of tropospheric ozone on radiative forcing confirms that ozone is currently the second most significant greenhouse gas, responsible for 22% and 13% of radiative forcing changes since 1800 in the northern and southern hemispheres, respectively. If these rates were to be maintained in the future, ozone would continue to evolve differently in the two hemispheres (maximum level in the northern hemisphere) and could make an even more significant contribution to the radiative forcing of the northern hemisphere.« less

Radiative forcing and rapid adjustment of absorbing aerosols in the Pearl River Delta Region of China

NASA Astrophysics Data System (ADS)

Liu, Z.; Yim, S. H. L.; Lau, G.

2016-12-01

Part of organic carbon defined as brown carbon (BrC) has been found to absorb solar radiation, especially in near-ultraviolet and blue bands, but their radiation impact is far less understood than black carbon (BC). Rapid adjustment thought to occur within a few weeks, induced by aerosol radiative effect and thereby alter cloud cover or other climate components. These effects are particularly pronounced for absorbing aerosols. The data gathered is from an online coupled model, WRF-Chem. A two-simulation test is conducted from July 8 to July 15. The baseline simulation doesn't account for aerosol-radiation interactions, whereas the sensitivity run includes it. The differences between these two simulations represent total effects of the aerosol instantaneous radiative forcing and subsequent rapid adjustment. In Figure 1, without cloud effect (clear sky), at the top of atmosphere (TOA), the SW radiation changes are negative in the PRD region, representing an overall cooling effect of aerosols. However, in the atmosphere (ATM), aerosols heat the atmosphere by absorbing incoming solar radiation with an average of 2.4 W/m2 (Table 1). After including rapid adjustment (all sky), the radiation change pattern becomes significantly different, especially at TOA and surface (SFC). This may be caused by cloud cover change due to rapid adjustment. The magnitude of SW radiation changes for all sky at all levels is smaller than that for clear sky. This result suggests the rapid adjustment counteracts the instantaneous radiative forcing of aerosols. At TOA, the cooling effect of the aerosol is 74% lower for all sky compared with clear sky, highlighting an overall warming effect of rapid adjustment in the PRD region. Aerosol-induced changes (W/m2) TOA ATM SFC Clear Sky -9.2 2.4 -11.6 All Sky -2.4 1.9 -4.3 Table 1. Aerosol-induced averaged changes in shortwave radiation due to aerosol-radiation interactions in the Pearl River Delta. The test shows the rapid adjustment of aerosols offsets part of the aerosol instantaneous negative radiation forcing, especially at TOA and SFC. The only absorbing aerosol species included in the test is BC. If absorption effects of dust and BrC are considered, the contribution of instantaneous radiative forcing and rapid adjustment may change.

Investigating the Linear Dependence of Direct and Indirect Radiative Forcing on Emission of Carbonaceous Aerosols in a Global Climate Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yanju; Wang, Hailong; Singh, Balwinder

The linearity of dependence of aerosol direct and indirect radiative forcing (DRF and IRF) on emissions is essential to answer the policy-relevant question on how the change in forcing would result from a change in emission. In this study, the forcing-to-emission relationship is investigated for black carbon (BC) and primary organic carbon (OC) emitted from North America and Asia. Direct and indirect radiative forcing of BC and OC are simulated with the Community Atmosphere Model (CAM5.1). Two diagnostics are introduced to aid in policy-relevant discussion: emission-normalized forcing (ENF) and linearity (R). DRF is linearly related to emission for both BCmore » and OC from the two regions and emission-normalized DRF is similar, within 15%. IRF is linear to emissions for weaker sources and regions far from source (North American BC and OC), while for large emission sources and near source regions (Asian OC) the response of forcing to emission is sub-linear. In North America emission-normalized IRF (ENIRF) is 2-4 times higher than that in Asia. The difference among regions and species is primarily caused by failure of accumulation mode particles to become CCN, and then to activate into CDNC. Optimal aggregation area (30ºx 30º) has been used to communicate the regional variation of forcing-to-emission relationship. For IRF, only 15-40% of the Earth’s surface is significantly affected by the two emission regions, but the forcing in these regions comprises most of the global impact. Linearity of IRF occurs in about two-thirds of the significant regions except for Asian OC. ENF is an effective tool to estimate forcing changes due to reduction of surface emissions, as long as there is sufficient attention to the causes of nonlinearity in the simulations used to derive ENIRF (emission into polluted regions and emission elevation). The differences in ENIRF have important implications for policy decisions. Lower ENIRF in more polluted region like Asia means that reductions of large amounts of OC in these regions would be relatively climate-neutral rather than causing significant warming via IRF reduction.« less

Impact of springtime biomass-burning aerosols on radiative forcing over northern Thailand during the 7SEAS campaign

NASA Astrophysics Data System (ADS)

Pani, Shantanu Kumar; Wang, Sheng-Hsiang; Lin, Neng-Huei; Lee, Chung-Te; Tsay, Si-Chee; Holben, Brent; Janjai, Serm; Hsiao, Ta-Chih; Chuang, Ming-Tung; Chantara, Somporn

2016-04-01

Biomass-burning (BB) aerosols are the significant contributor to the regional/global aerosol loading and radiation budgets. BB aerosols affect the radiation budget of the earth and atmosphere by scattering and absorbing directly the incoming solar and outgoing terrestrial radiation. These aerosols can exert either cooling or warming effect on climate, depending on the balance between scattering and absorption. BB activities in the form of wildland forest fires and agricultural crop burning are very pronounced in the Indochina peninsular regions in Southeast Asia mainly in spring (late February to April) season. The region of interest includes Doi Ang Khang (19.93° N, 99.05° E, 1536 msl) in northern Thailand, as part of the Seven South East Asian Studies (7-SEAS)/BASELInE (Biomass-burning Aerosols & Stratocumulus Environment: Lifecycles & Interactions Experiment) campaign in 2013. In this study, for the first time, the direct aerosol radiative effects of BB aerosols over near-source BB emissions, during the peak loading spring season, in northern Indochina were investigated by using ground-based physical, chemical, and optical properties of aerosols as well as the aerosol optical and radiative transfer models. Information on aerosol parameters in the field campaign was used in the OPAC (Optical Properties of Aerosols and Clouds) model to estimate various optical properties corresponding to aerosol compositions. Clear-sky shortwave direct aerosol radiative effects were further estimated with a raditive transfer model SBDART (Santa Barbara DISORT Atmospheric Radiative Transfer). The columnar aerosol optical depth (AOD500) was found to be ranged from 0.26 to 1.13 (with the mean value 0.71 ± 0.24). Fine-mode (fine mode fraction ≈0.98, angstrom exponent ≈1.8) and significantly absorbing aerosols (columnar single-scattering albedo ≈0.89, asymmetry-parameter ≈0.67 at 441 nm wavelength) dominated in this region. Water soluble and black carbon (BC) aerosols mainly dominate the both surface mass concentration and the columnar burden. The BC contributed only 6% to the aerosol mass loading, but its contribution to the total AOD and net atmospheric forcing were 12% and 75%, respectively. The mean radiative forcing was -6.8 to -8.7 W m-2 at the top-of-atmosphere and -28 to -33 W m-2 at surface. Furthermore BC aerosols contributed 45-49% to the surface radiative forcing along with the water soluble aerosols (49-52%), thus, significantly contributing to solar dimming

Long-term energy and climate implications of carbon capture and storage deployment strategies in the US coal-fired electricity fleet.

PubMed

Sathre, Roger; Masanet, Eric

2012-09-04

To understand the long-term energy and climate implications of different implementation strategies for carbon capture and storage (CCS) in the US coal-fired electricity fleet, we integrate three analytical elements: scenario projection of energy supply systems, temporally explicit life cycle modeling, and time-dependent calculation of radiative forcing. Assuming continued large-scale use of coal for electricity generation, we find that aggressive implementation of CCS could reduce cumulative greenhouse gas emissions (CO(2), CH(4), and N(2)O) from the US coal-fired power fleet through 2100 by 37-58%. Cumulative radiative forcing through 2100 would be reduced by only 24-46%, due to the front-loaded time profile of the emissions and the long atmospheric residence time of CO(2). The efficiency of energy conversion and carbon capture technologies strongly affects the amount of primary energy used but has little effect on greenhouse gas emissions or radiative forcing. Delaying implementation of CCS deployment significantly increases long-term radiative forcing. This study highlights the time-dynamic nature of potential climate benefits and energy costs of different CCS deployment pathways and identifies opportunities and constraints of successful CCS implementation.

Toric focusing for radiation force applications using a toric lens coupled to a spherically focused transducer.

PubMed

Arnal, Bastien; Nguyen, Thu-Mai; O'Donnell, Matthew

2014-12-01

Dynamic elastography using radiation force requires that an ultrasound field be focused during hundreds of microseconds at a pressure of several megapascals. Here, we address the importance of the focal geometry. Although there is usually no control of the elevational focal width in generating a tissue mechanical response, we propose a tunable approach to adapt the focus geometry that can significantly improve radiation force efficiency. Several thin, in-house-made polydimethylsiloxane lenses were designed to modify the focal spot of a spherical transducer. They exhibited low absorption and the focal spot widths were extended up to 8-fold in the elevation direction. Radiation force experiments demonstrated an 8-fold increase in tissue displacements using the same pressure level in a tissue-mimicking phantom with a similar shear wave spectrum, meaning it does not affect elastography resolution. Our results demonstrate that larger tissue responses can be obtained for a given pressure level, or that similar response can be reached at a much lower mechanical index (MI). We envision that this work will impact 3-D elastography using 2-D phased arrays, where such shaping can be achieved electronically with the potential for adaptive optimization.

Efficient finite element modeling of radiation forces on elastic particles of arbitrary size and geometry.

PubMed

Glynne-Jones, Peter; Mishra, Puja P; Boltryk, Rosemary J; Hill, Martyn

2013-04-01

A finite element based method is presented for calculating the acoustic radiation force on arbitrarily shaped elastic and fluid particles. Importantly for future applications, this development will permit the modeling of acoustic forces on complex structures such as biological cells, and the interactions between them and other bodies. The model is based on a non-viscous approximation, allowing the results from an efficient, numerical, linear scattering model to provide the basis for the second-order forces. Simulation times are of the order of a few seconds for an axi-symmetric structure. The model is verified against a range of existing analytical solutions (typical accuracy better than 0.1%), including those for cylinders, elastic spheres that are of significant size compared to the acoustic wavelength, and spheroidal particles.

Acoustic radiation force on a heated sphere including effects of heat transfer and acoustic streaming

NASA Technical Reports Server (NTRS)

Lee, Chun P.; Wang, Taylor G.

1988-01-01

A previous theoretical result on the subject of the acoustic radiation force on a heated sphere (Lee and Wang, 1984) is reexamined. For a more complete understanding, effects of heat transfer and acoustic streaming are taken into consideration. Essentially, it was found that, at high sound-pressure levels in a steady situation, the force is not affected significantly by the temperature profile, consistent with the result of an experimental work (Leung and Wang, 1985). This resolves the earlier apparent contradiction between the theory and the experiment. If excessive hot air is accumulated around the sphere, which can happen in transient situations, the force can be weakened or reversed in sign. A heat transfer model due to acoustic streaming was also found.

The Radiative Forcing Model Intercomparison Project (RFMIP): Assessment and characterization of forcing to enable feedback studies

NASA Astrophysics Data System (ADS)

Pincus, R.; Stevens, B. B.; Forster, P.; Collins, W.; Ramaswamy, V.

2014-12-01

The Radiative Forcing Model Intercomparison Project (RFMIP): Assessment and characterization of forcing to enable feedback studies An enormous amount of attention has been paid to the diversity of responses in the CMIP and other multi-model ensembles. This diversity is normally interpreted as a distribution in climate sensitivity driven by some distribution of feedback mechanisms. Identification of these feedbacks relies on precise identification of the forcing to which each model is subject, including distinguishing true error from model diversity. The Radiative Forcing Model Intercomparison Project (RFMIP) aims to disentangle the role of forcing from model sensitivity as determinants of varying climate model response by carefully characterizing the radiative forcing to which such models are subject and by coordinating experiments in which it is specified. RFMIP consists of four activities: 1) An assessment of accuracy in flux and forcing calculations for greenhouse gases under past, present, and future climates, using off-line radiative transfer calculations in specified atmospheres with climate model parameterizations and reference models 2) Characterization and assessment of model-specific historical forcing by anthropogenic aerosols, based on coordinated diagnostic output from climate models and off-line radiative transfer calculations with reference models 3) Characterization of model-specific effective radiative forcing, including contributions of model climatology and rapid adjustments, using coordinated climate model integrations and off-line radiative transfer calculations with a single fast model 4) Assessment of climate model response to precisely-characterized radiative forcing over the historical record, including efforts to infer true historical forcing from patterns of response, by direct specification of non-greenhouse-gas forcing in a series of coordinated climate model integrations This talk discusses the rationale for RFMIP, provides an overview of the four activities, and presents preliminary motivating results.

An Assessment of Radiation Modification from a European Perspective

NASA Astrophysics Data System (ADS)

Kristjansson, J. E.; Lawrence, M. G.; Boucher, O.; Haywood, J. M.; Irvine, P. J.; Muri, H.; Schmidt, H.; Schulz, M.; Vaughan, N.; Watson, M.; Born, W.; Schaefer, S.; Stelzer, H.

2014-12-01

The European Transdisciplinary Assessment of Climate Engineering (EuTRACE) project (2012-2014) is funded by the European Commission (EC). In EuTRACE, researchers from the natural sciences, social sciences and the humanities have joined forces to assess various proposed geoengineering techniques concerning their radiative forcing potential and side effects, ethical aspects, economics aspects, as well as governance and regulation aspects. A comprehensive assessment report will be submitted to the EC in autumn 2014. We will present some highlights of the part of the EuTRACE assessment that deals with the natural science aspects of proposed Radiation Modification (RM) techniques. The techniques considered are: a) Stratospheric Sulfur Injections; b) Marine Cloud Brightening; c) Desert Brightening; d) Vegetation Brightening; and e) Cirrus Cloud Thinning. A large number of publications in the scientific literature has been considered, as well as recently published assessment reports by the Royal Society in the UK and the German Federal Ministry of Education and Research. Some of the findings of the assessment are: Globally averaged, the current anthropogenic radiative forcing could conceivably be offset by the RM techniques considered. The RM techniques could have a significant global effect already after 1 year or less. Model simulations consistently show that Solar RM leads to regional imbalances due to different spatial footprints of solar and carbon dioxide radiative forcings. This may have significant consequences for precipitation patterns and the hydrological cycle. Very rapid warming is virtually certain if RM were to be stopped abruptly or over a period of one to a few years. Model studies of RM usually assume that the techniques are technologically feasible. In fact, the technological challenges are poorly known, and in many cases the physical processes involved are poorly understood. We will end by discussing key research questions and knowledge gaps.

Forced Gravity Waves and the Tropospheric Response to Convection

NASA Astrophysics Data System (ADS)

Halliday, O. J.; Griffiths, S. D.; Parker, D. J.; Stirling, A.

2017-12-01

It has been known for some time that gravity waves facilitate atmospheric adjustment to convective heating. Further, convectively forced gravity waves condition the neighboring atmosphere for the initiation and / or suppression of convection. Despite this, the radiation of gravity waves in macro-scale models (which are typically forced at the grid-scale, by existing parameterization schemes) is not well understood. We present here theoretical and numerical work directed toward improving our understanding of convectively forced gravity wave effects at the mesoscale. Using the linear hydrostatic equations of motion for an incompressible (but non-Boussinesq) fluid with vertically varying buoyancy frequency, we find a radiating solution to prescribed sensible heating. We then interrogate the spatial and temporal sensitivity of the vertical velocity and potential temperature response to different heating functions, considering the remote and near-field forced response both to steady and pulsed heating. We find that the meso-scale tropospheric response to convection is significantly dependent on the upward radiation characteristics of the gravity waves, which are in turn dependent upon the temporal and spatial structure of the source, and stratification of the domain. Moving from a trapped to upwardly-radiating solution there is a 50% reduction in tropospherically averaged vertical velocity, but significant perturbations persist for up to 4 hours in the far-field. We find the tropospheric adjustment to be sensitive to the horizontal length scale which characterizes the heating, observing a 20% reduction in vertical velocity when comparing the response from a 10 km to a 100 km heat source. We assess the implications for parameterization of convection in coarse-grained models in the light of these findings. We show that an idealized `full-physics' nonlinear simulation of deep convection in the UK Met Office Unified Model is qualitatively described by the linear solution: departures are quantified and explored.

Cloud and Radiation Mission with Active and Passive Sensing from the Space Station

NASA Technical Reports Server (NTRS)

Spinhirne, James D.

1998-01-01

A cloud and aerosol radiative forcing and physical process study involving active laser and radar profiling with a combination of passive radiometric sounders and imagers would use the space station as an observation platform. The objectives are to observe the full three dimensional cloud and aerosol structure and the associated physical parameters leading to a complete measurement of radiation forcing processes. The instruments would include specialized radar and lidar for cloud and aerosol profiling, visible, infrared and microwave imaging radiometers with comprehensive channels for cloud and aerosol observation and specialized sounders. The low altitude,. available power and servicing capability of the space station are significant advantages for the active sensors and multiple passive instruments.

Assessment of liver fibrosis with 2-D shear wave elastography in comparison to transient elastography and acoustic radiation force impulse imaging in patients with chronic liver disease.

PubMed

Gerber, Ludmila; Kasper, Daniela; Fitting, Daniel; Knop, Viola; Vermehren, Annika; Sprinzl, Kathrin; Hansmann, Martin L; Herrmann, Eva; Bojunga, Joerg; Albert, Joerg; Sarrazin, Christoph; Zeuzem, Stefan; Friedrich-Rust, Mireen

2015-09-01

Two-dimensional shear wave elastography (2-D SWE) is an ultrasound-based elastography method integrated into a conventional ultrasound machine. It can evaluate larger regions of interest and, therefore, might be better at determining the overall fibrosis distribution. The aim of this prospective study was to compare 2-D SWE with the two best evaluated liver elastography methods, transient elastography and acoustic radiation force impulse (point SWE using acoustic radiation force impulse) imaging, in the same population group. The study included 132 patients with chronic hepatopathies, in which liver stiffness was evaluated using transient elastography, acoustic radiation force impulse imaging and 2-D SWE. The reference methods were liver biopsy for the assessment of liver fibrosis (n = 101) and magnetic resonance imaging/computed tomography for the diagnosis of liver cirrhosis (n = 31). No significant difference in diagnostic accuracy, assessed as the area under the receiver operating characteristic curve (AUROC), was found between the three elastography methods (2-D SWE, transient elastography, acoustic radiation force impulse imaging) for the diagnosis of significant and advanced fibrosis and liver cirrhosis in the "per protocol" (AUROCs for fibrosis stages ≥2: 0.90, 0.95 and 0.91; for fibrosis stage [F] ≥3: 0.93, 0.95 and 0.94; for F = 4: 0.92, 0.96 and 0.92) and "intention to diagnose" cohort (AUROCs for F ≥2: 0.87, 0.92 and 0.91; for F ≥3: 0.91, 0.93 and 0.94; for F = 4: 0.88, 0.90 and 0.89). Therefore, 2-D SWE, ARFI imaging and transient elastography seem to be comparably good methods for non-invasive assessment of liver fibrosis. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Acoustic radiation force control: Pulsating spherical carriers.

PubMed

Rajabi, Majid; Mojahed, Alireza

2018-02-01

The interaction between harmonic plane progressive acoustic beams and a pulsating spherical radiator is studied. The acoustic radiation force function exerted on the spherical body is derived as a function of the incident wave pressure and the monopole vibration characteristics (i.e., amplitude and phase) of the body. Two distinct strategies are presented in order to alter the radiation force effects (i.e., pushing and pulling states) by changing its magnitude and direction. In the first strategy, an incident wave field with known amplitude and phase is considered. It is analytically shown that the zero- radiation force state (i.e., radiation force function cancellation) is achievable for specific pulsation characteristics belong to a frequency-dependent straight line equation in the plane of real-imaginary components (i.e., Nyquist Plane) of prescribed surface displacement. It is illustrated that these characteristic lines divide the mentioned displacement plane into two regions of positive (i.e., pushing) and negative (i.e., pulling) radiation forces. In the second strategy, the zero, negative and positive states of radiation force are obtained through adjusting the incident wave field characteristics (i.e., amplitude and phase) which insonifies the radiator with prescribed pulsation characteristics. It is proved that zero radiation force state occurs for incident wave pressure characteristics belong to specific frequency-dependent circles in Nyquist plane of incident wave pressure. These characteristic circles divide the Nyquist plane into two distinct regions corresponding to positive (out of circles) and negative (in the circles) values of radiation force function. It is analytically shown that the maximum amplitude of negative radiation force is exactly equal to the amplitude of the (positive) radiation force exerted upon the sphere in the passive state, by the same incident field. The developed concepts are much more deepened by considering the required power supply for distinct cases of zero, negative and positive radiation force states along with the frequency dependent asymmetry index. In addition, considering the effect of phase difference between the incident wave field and the pulsating object, and its possible variation with respect to spatial position of object, some practical points about the spatial average of generated radiation force, the optimal state of operation, the stability of zero radiation force states and the possibly of precise motion control are discussed. This work would extend the novel concept of smart carriers to and may be helpful for robust single-beam acoustic handling techniques. Furthermore, the shown capability of precise motion control may be considered as a new way toward smart acoustic driven micro-mechanisms and micro-machines. Copyright © 2017 Elsevier B.V. All rights reserved.

Clutter elimination for deep clinical optoacoustic imaging using localised vibration tagging (LOVIT)☆

PubMed Central

Jaeger, Michael; Bamber, Jeffrey C.; Frenz, Martin

2013-01-01

This paper investigates a novel method which allows clutter elimination in deep optoacoustic imaging. Clutter significantly limits imaging depth in clinical optoacoustic imaging, when irradiation optics and ultrasound detector are integrated in a handheld probe for flexible imaging of the human body. Strong optoacoustic transients generated at the irradiation site obscure weak signals from deep inside the tissue, either directly by propagating towards the probe, or via acoustic scattering. In this study we demonstrate that signals of interest can be distinguished from clutter by tagging them at the place of origin with localised tissue vibration induced by the acoustic radiation force in a focused ultrasonic beam. We show phantom results where this technique allowed almost full clutter elimination and thus strongly improved contrast for deep imaging. Localised vibration tagging by means of acoustic radiation force is especially promising for integration into ultrasound systems that already have implemented radiation force elastography. PMID:25302147

Bubble-based acoustic radiation force using chirp insonation to reduce standing wave effects.

PubMed

Erpelding, Todd N; Hollman, Kyle W; O'Donnell, Matthew

2007-02-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young's modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200 and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size.

Bubble-Based Acoustic Radiation Force Using Chirp Insonation to Reduce Standing Wave Effects

PubMed Central

Erpelding, Todd N.; Hollman, Kyle W.; O’Donnell, Matthew

2007-01-01

Bubble-based acoustic radiation force can measure local viscoelastic properties of tissue. High intensity acoustic waves applied to laser-generated bubbles induce displacements inversely proportional to local Young’s modulus. In certain instances, long pulse durations are desirable but are susceptible to standing wave artifacts, which corrupt displacement measurements. Chirp pulse acoustic radiation force was investigated as a method to reduce standing wave artifacts. Chirp pulses with linear frequency sweep magnitudes of 100, 200, and 300 kHz centered around 1.5 MHz were applied to glass beads within gelatin phantoms and laser-generated bubbles within porcine lenses. The ultrasound transducer was translated axially to vary standing wave conditions, while comparing displacements using chirp pulses and 1.5 MHz tone burst pulses of the same duration and peak rarefactional pressure. Results demonstrated significant reduction in standing wave effects using chirp pulses, with displacement proportional to acoustic intensity and bubble size. PMID:17306697

Easy Volcanic Aerosol

NASA Astrophysics Data System (ADS)

Toohey, Matthew; Stevens, Bjorn; Schmidt, Hauke; Timmreck, Claudia

2016-04-01

Radiative forcing by stratospheric sulfate aerosol of volcanic origin is one of the strongest drivers of natural climate variability. Transient model simulations attempting to match observed climate variability, such as the CMIP historical simulations, rely on volcanic forcing reconstructions based on observations of a small sample of recent eruptions and coarse proxy data for eruptions before the satellite era. Volcanic forcing data sets used in CMIP5 were provided either in terms of optical properties, or in terms of sulfate aerosol mass, leading to significant inter-model spread in the actual volcanic radiative forcing produced by models and in their resulting climate responses. It remains therefore unclear to what degree inter-model spread in response to volcanic forcing represents model differences or variations in the forcing. In order to isolate model differences, Easy Volcanic Aerosol (EVA) provides an analytic representation of volcanic stratospheric aerosol forcing, based on available observations and aerosol model results, prescribing the aerosol's radiative properties and primary modes of spatial and temporal variability. In contrast to regriddings of observational data, EVA allows for the production of physically consistent forcing for historic and hypothetical eruptions of varying magnitude, source latitude, and season. Within CMIP6, EVA will be used to reconstruct volcanic forcing over the past 2000 years for use in the Paleo-Modeling Intercomparison Project (PMIP), and will provide forcing sets for VolMIP experiments aiming to quantify model uncertainty in the response to volcanic forcing. Here, the functional form of EVA will be introduced, along with illustrative examples including the EVA-based reconstruction of volcanic forcing over the historical period, and that of the 1815 Tambora eruption.

Potential climate impact of black carbon emitted by rockets

NASA Astrophysics Data System (ADS)

Ross, Martin; Mills, Michael; Toohey, Darin

2010-12-01

A new type of hydrocarbon rocket engine is expected to power a fleet of suborbital rockets for commercial and scientific purposes in coming decades. A global climate model predicts that emissions from a fleet of 1000 launches per year of suborbital rockets would create a persistent layer of black carbon particles in the northern stratosphere that could cause potentially significant changes in the global atmospheric circulation and distributions of ozone and temperature. Tropical stratospheric ozone abundances are predicted to change as much as 1%, while polar ozone changes by up to 6%. Polar surface temperatures change as much as one degree K regionally with significant impacts on polar sea ice fractions. After one decade of continuous launches, globally averaged radiative forcing from the black carbon would exceed the forcing from the emitted CO2 by a factor of about 105 and would be comparable to the radiative forcing estimated from current subsonic aviation.

Spaceflight-relevant types of ionizing radiation and cortical bone: Potential LET effect?

NASA Astrophysics Data System (ADS)

Lloyd, Shane A. J.; Bandstra, Eric R.; Travis, Neil D.; Nelson, Gregory A.; Bourland, J. Daniel; Pecaut, Michael J.; Gridley, Daila S.; Willey, Jeffrey S.; Bateman, Ted A.

2008-12-01

Extended exposure to microgravity conditions results in significant bone loss. Coupled with radiation exposure, this phenomenon may place astronauts at a greater risk for mission-critical fractures. In a previous study, we identified a profound and prolonged loss of trabecular bone (29-39%) in mice following exposure to an acute, 2 Gy dose of radiation simulating both solar and cosmic sources. However, because skeletal strength depends on trabecular and cortical bone, accurate assessment of strength requires analysis of both bone compartments. The objective of the present study was to examine various properties of cortical bone in mice following exposure to multiple types of spaceflight-relevant radiation. Nine-week old, female C57BL/6 mice were sacrificed 110 days after exposure to a single, whole body, 2 Gy dose of gamma, proton, carbon, or iron radiation. Femora were evaluated with biomechanical testing, microcomputed tomography, quantitative histomorphometry, percent mineral content, and micro-hardness analysis. Compared to non-irradiated controls, there were significant differences compared to carbon or iron radiation for only fracture force, medullary area and mineral content. A greater differential effect based on linear energy transfer (LET) level may be present: high-LET (carbon or iron) particle irradiation was associated with a decline in structural properties (maximum force, fracture force, medullary area, and cortical porosity) and mineral composition compared to low-LET radiation (gamma and proton). Bone loss following irradiation appears to be largely specific to trabecular bone and may indicate unique biological microenvironments and microdosimetry conditions. However, the limited time points examined and non-haversian skeletal structure of the mice employed highlight the need for further investigation.

Monsoonal Responses to External Forcings over the Past Millennium: A Model Study (Invited)

NASA Astrophysics Data System (ADS)

Liu, J.; Wang, B.

2009-12-01

The climate variations related to Global Monsoon (GM) and East Asian summer monsoon (EASM) rainfall over the past 1000 years were investigated by analysis of a pair of millennium simulations with the coupled climate model named ECHO-G. The free run was generated using fixed external (annual cycle) forcing, while the forced run was obtained using time-varying solar irradiance variability, greenhouse gases (CO2 and CH4) concentration and estimated radiative effect of volcanic aerosols. The model results indicate that the centennial-millennial variation of the GM and EASM is essentially a forced response to the external radiative forcings (insolation, volcanic aerosols, and greenhouse gases). The GM strength responds more directly to the effective solar forcing (insolation plus radiative effect of the volcanoes) when compared to responses of the global mean surface temperature on centennial timescale. The simulated GM precipitation in the forced run exhibits a significant quasi-bi-centennial oscillation. Weak GM precipitation was simulated during the Little Ice Age (1450-1850) with three weakest periods concurring with the Spörer, Maunder, and Dalton Minimum of solar activity. Conversely, strong GM was simulated during the model Medieval Warm Period (ca. 1030-1240). Before the industrial period, the natural variation in effective solar forcing reinforces the thermal contrasts both between the ocean and continent and between the northern and southern hemispheres, resulting in millennium-scale variation and the quasi-bi-centennial oscillation of the GM. The prominent upward trend in the GM precipitation occurring in the last century and the remarkably strengthening of the global monsoon in the period of 1961-1990 appear unprecedented and owed possibly in part to the increase of atmospheric carbon dioxide concentration. The EASM has the largest meridional extent (5oN-55oN) among all the regional monsoons on globe. Thus, the EASM provides an unique opportunity for understanding the latitudinal differences of the monsoonal responses to external forcings and internal feedback processes. The strength of the forced response depends on latitude. On centennial-millennial time scales, the variation of the extratropical and subtropical rainfall tends to follow the effective solar radiation forcing closely; the tropical rainfall is less sensitive to the effective solar radiation forcing but responds significantly to the modern anthropogenic CO2 forcing. The spatial patterns and structures of the forced response differ from the internal mode (i.e., interannual variability that arises primarily from the internal feedback processes within the climate system). Further, the behavior of the internal mode is effectively modulated by changes in the mean state on the centennial to millennial time scales. These findings have important ramification in understanding the differences and linkages between the forced and internal modes of variability as well as in promoting communication between scientists studying modern- and paleo-monsoon variations.

Irrigation as an Historical Climate Forcing

NASA Technical Reports Server (NTRS)

Cook, Benjamin I.; Shukla, Sonali P.; Puma, Michael J.; Nazarenko, Larissa S.

2014-01-01

Irrigation is the single largest anthropogenic water use, a modification of the land surface that significantly affects surface energy budgets, the water cycle, and climate. Irrigation, however, is typically not included in standard historical general circulation model (GCM) simulations along with other anthropogenic and natural forcings. To investigate the importance of irrigation as an anthropogenic climate forcing, we conduct two 5-member ensemble GCM experiments. Both are setup identical to the historical forced (anthropogenic plus natural) scenario used in version 5 of the Coupled Model Intercomparison Project, but in one experiment we also add water to the land surface using a dataset of historically estimated irrigation rates. Irrigation has a negligible effect on the global average radiative balance at the top of the atmosphere, but causes significant cooling of global average surface air temperatures over land and dampens regional warming trends. This cooling is regionally focused and is especially strong in Western North America, the Mediterranean, the Middle East, and Asia. Irrigation enhances cloud cover and precipitation in these same regions, except for summer in parts of Monsoon Asia, where irrigation causes a reduction in monsoon season precipitation. Irrigation cools the surface, reducing upward fluxes of longwave radiation (increasing net longwave), and increases cloud cover, enhancing shortwave reflection (reducing net shortwave). The relative magnitude of these two processes causes regional increases (northern India) or decreases (Central Asia, China) in energy availability at the surface and top of the atmosphere. Despite these changes in net radiation, however, climate responses are due primarily to larger magnitude shifts in the Bowen ratio from sensible to latent heating. Irrigation impacts on temperature, precipitation, and other climate variables are regionally significant, even while other anthropogenic forcings (anthropogenic aerosols, greenhouse gases, etc.) dominate the long term climate evolution in the simulations. To better constrain the magnitude and uncertainties of irrigation-forced climate anomalies, irrigation should therefore be considered as another important anthropogenic climate forcing in the next generation of historical climate simulations and multimodel assessments.

Direct Radiative Forcing from Saharan Mineral Dust Layers from In-situ Measurements and Satellite Retrievals

NASA Astrophysics Data System (ADS)

Sauer, D. N.; Vázquez-Navarro, M.; Gasteiger, J.; Chouza, F.; Weinzierl, B.

2016-12-01

Mineral dust is the major species of airborne particulate matter by mass in the atmosphere. Each year an estimated 200-3000 Tg of dust are emitted from the North African desert and arid regions alone. A large fraction of the dust is lifted into the free troposphere and gets transported in extended dust layers westward over the Atlantic Ocean into the Caribbean Sea. Especially over the dark surface of the ocean, those dust layers exert a significant effect on the atmospheric radiative balance though aerosol-radiation interactions. During the Saharan Aerosol Long-range Transport and Aerosol-Cloud-Interaction Experiment (SALTRACE) in summer 2013 airborne in-situ aerosol measurements on both sides of the Atlantic Ocean, near the African coast and the Caribbean were performed. In this study we use data about aerosol microphysical properties acquired between Cabo Verde and Senegal to derive the aerosol optical properties and the resulting radiative forcing using the radiative transfer package libRadtran. We compare the results to values retrieved from MSG/SEVIRI data using the RRUMS algorithm. The RRUMS algorithm can derive shortwave and longwave top-of-atmosphere outgoing fluxes using only information issued from the narrow-band MSG/SEVIRI channels. A specific calibration based on collocated Terra/CERES measurements ensures a correct retrieval of the upwelling flux from the dust covered pixels. The comparison of radiative forcings based on in-situ data to satellite-retrieved values enables us to extend the radiative forcing estimates from small-scale in-situ measurements to large scale satellite coverage over the Atlantic Ocean.

North Atlantic Aerosol Properties for Radiative Impact Assessments. Derived from Column Closure Analyses in TARFOX and ACE-2

NASA Technical Reports Server (NTRS)

Russell, Philip A.; Bergstrom, Robert A.; Schmid, Beat; Livingston, John M.

2000-01-01

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate in potentially significant ways. This aerosol radiative forcing is a major source of uncertainty in understanding the climate change of the past century and predicting future climate. To help reduce this uncertainty, the 1996 Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the 1997 Aerosol Characterization Experiment (ACE-2) measured the properties and radiative effects of aerosols over the Atlantic Ocean. Both experiments used remote and in situ measurements from aircraft and the surface, coordinated with overpasses by a variety of satellite radiometers. TARFOX focused on the urban-industrial haze plume flowing from the United States over the western Atlantic, whereas ACE-2 studied aerosols over the eastern Atlantic from both Europe and Africa. These aerosols often have a marked impact on satellite-measured radiances. However, accurate derivation of flux changes, or radiative forcing, from the satellite measured radiances or retrieved aerosol optical depths (AODs) remains a difficult challenge. Here we summarize key initial results from TARFOX and ACE-2, with a focus on closure analyses that yield aerosol microphysical models for use in improved assessments of flux changes. We show how one such model gives computed radiative flux sensitivities (dF/dAOD) that agree with values measured in TARFOX and preliminary values computed for the polluted marine boundary layer in ACE-2. A companion paper uses the model to compute aerosol-induced flux changes over the North Atlantic from AVHRR-derived AOD fields.

Forced running exercise attenuates hippocampal neurogenesis impairment and the neurocognitive deficits induced by whole-brain irradiation via the BDNF-mediated pathway

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji, Jian-feng; Ji, Sheng-jun; Sun, Rui

Highlights: •Forced exercise can ameliorate WBI induced cognitive impairment in our rat model. •Mature BDNF plays an important role in the effects of forced exercise. •Exercise may be a possible treatment of the radiation-induced cognitive impairment. -- Abstract: Cranial radiotherapy induces progressive and debilitating cognitive deficits, particularly in long-term cancer survivors, which may in part be caused by the reduction of hippocampal neurogenesis. Previous studies suggested that voluntary exercise can reduce the cognitive impairment caused by radiation therapy. However, there is no study on the effect of forced wheel exercise and little is known about the molecular mechanisms mediating themore » effect of exercise. In the present study, we investigated whether the forced running exercise after irradiation had the protective effects of the radiation-induced cognitive impairment. Sixty-four Male Sprague–Dawley rats received a single dose of 20 Gy or sham whole-brain irradiation (WBI), behavioral test was evaluated using open field test and Morris water maze at 2 months after irradiation. Half of the rats accepted a 3-week forced running exercise before the behavior detection. Immunofluorescence was used to evaluate the changes in hippocampal neurogenesis and Western blotting was used to assess changes in the levels of mature brain-derived neurotrophic factor (BDNF), phosphorylated tyrosine receptor kinase B (TrkB) receptor, protein kinase B (Akt), extracellular signal-regulated kinase (ERK), calcium-calmodulin dependent kinase (CaMKII), cAMP-calcium response element binding protein (CREB) in the BDNF–pCREB signaling. We found forced running exercise significantly prevented radiation-induced cognitive deficits, ameliorated the impairment of hippocampal neurogenesis and attenuated the down-regulation of these proteins. Moreover, exercise also increased behavioral performance, hippocampal neurogenesis and elevated BDNF–pCREB signaling in non-irradiation group. These results suggest that forced running exercise offers a potentially effective treatment for radiation-induced cognitive deficits.« less

Greenhouse Effect, Radiative Forcing and Climate Sensitivity

NASA Astrophysics Data System (ADS)

Ponater, Michael; Dietmüller, Simone; Sausen, Robert

Temperature conditions and climate on Earth are controlled by the balance between absorbed solar radiation and outgoing terrestrial radiation. The greenhouse effect is a synonym for the trapping of infrared radiation by radiatively active atmospheric constituents. It generally causes a warming of the planet's surface, compared to the case without atmosphere. Perturbing the radiation balance of the planet, e.g., by anthropogenic greenhouse gas emissions, induces climate change. Individual contributions to a total climate impact are usually quantified and ranked in terms of their respective radiative forcing. This method involves some limitations, because the effect of the external forcing is modified by radiative feedbacks. Here the current concept of radiative forcing and potential improvements are explained.

Approaches on calibration of bolometer and establishment of bolometer calibration device

NASA Astrophysics Data System (ADS)

Xia, Ming; Gao, Jianqiang; Ye, Jun'an; Xia, Junwen; Yin, Dejin; Li, Tiecheng; Zhang, Dong

2015-10-01

Bolometer is mainly used for measuring thermal radiation in the field of public places, labor hygiene, heating and ventilation and building energy conservation. The working principle of bolometer is under the exposure of thermal radiation, temperature of black absorbing layer of detector rise after absorption of thermal radiation, which makes the electromotive force produced by thermoelectric. The white light reflective layer of detector does not absorb thermal radiation, so the electromotive force produced by thermoelectric is almost zero. A comparison of electromotive force produced by thermoelectric of black absorbing layer and white reflective layer can eliminate the influence of electric potential produced by the basal background temperature change. After the electromotive force which produced by thermal radiation is processed by the signal processing unit, the indication displays through the indication display unit. The measurement unit of thermal radiation intensity is usually W/m2 or kW/m2. Its accurate and reliable value has important significance for high temperature operation, labor safety and hygiene grading management. Bolometer calibration device is mainly composed of absolute radiometer, the reference light source, electric measuring instrument. Absolute radiometer is a self-calibration type radiometer. Its working principle is using the electric power which can be accurately measured replaces radiation power to absolutely measure the radiation power. Absolute radiometer is the standard apparatus of laser low power standard device, the measurement traceability is guaranteed. Using the calibration method of comparison, the absolute radiometer and bolometer measure the reference light source in the same position alternately which can get correction factor of irradiance indication. This paper is mainly about the design and calibration method of the bolometer calibration device. The uncertainty of the calibration result is also evaluated.

What is the impact of natural variability and aerosol-cloud interaction on the effective radiative forcing of anthropogenic aerosol?

NASA Astrophysics Data System (ADS)

Fiedler, S.; Stevens, B.; Mauritsen, T.

2017-12-01

State-of-the-art climate models have persistently shown a spread in estimates of the effective radiative forcing (ERF) associated with anthropogenic aerosol. Different reasons for the spread are known, but their relative importance is poorly understood. In this presentation we investigate the role of natural atmospheric variability, global patterns of aerosol radiative effects, and magnitudes of aerosol-cloud interaction in controlling the ERF of anthropogenic aerosol (Fiedler et al., 2017). We use the Earth system model MPI-ESM1.2 for conducting ensembles of atmosphere-only simulations and calculate the shortwave ERF of anthropogenic aerosol at the top of the atmosphere. The radiative effects are induced with the new parameterisation MACv2-SP (Stevens et al., 2017) that prescribes observationally constrained anthropogenic aerosol optical properties and an associated Twomey effect. Firstly, we compare the ERF of global patterns of anthropogenic aerosol from the mid-1970s and today. Our results suggest that such a substantial pattern difference has a negligible impact on the global mean ERF, when the natural variability of the atmosphere is considered. The clouds herein efficiently mask the clear-sky contributions to the forcing and reduce the detectability of significant anthropogenic aerosol radiative effects in all-sky conditions. Secondly, we strengthen the forcing magnitude through increasing the effect of aerosol-cloud interaction by prescribing an enhanced Twomey effect. In that case, the different spatial pattern of aerosol radiative effects from the mid-1970s and today causes a moderate change (15%) in the ERF of anthropogenic aerosol in our model. This finding lets us speculate that models with strong aerosol-cloud interactions would show a stronger ERF change with anthropogenic aerosol patterns. Testing whether the anthropogenic aerosol radiative forcing is model-dependent under prescribed aerosol conditions is currently ongoing work using MACv2-SP in comprehensive aerosol-climate models in the framework of the EU-funded project BACCHUS. In the future, MACv2-SP will be used in models participating in the Radiative Forcing Model Intercomparison Project (Pincus et al., 2016).

Seasonality of Forcing by Carbonaceous Aerosols

NASA Astrophysics Data System (ADS)

Habib, G.; Bond, T.; Rasch, P. J.; Coleman, D.

2006-12-01

Aerosols can influence the energy balance of Earth-Atmosphere system with profound effect on regional climate. Atmospheric processes, such as convection, scavenging, wet and dry deposition, govern the lifetime and location of aerosol; emissions affect its quantity and location. Both affect climate forcing. Here we investigate the effect of seasonality in emissions and atmospheric processes on radiative forcing by carbonaceous aerosols, focusing on aerosol from fossil fuel and biofuel. Because aerosol lifetime is seasonal, ignoring the seasonality of sources such as residential biofuel may introduce a bias in aerosol burden and therefore in predicted climate forcing. We present a global emission inventory of carbonaceous aerosols with seasonality, and simulate atmospheric concentrations using the Community Atmosphere Model (CAM). We discuss where and when the seasonality of emissions and atmospheric processes has strong effects on atmospheric burden, lifetime, climate forcing and aerosol optical depth (AOD). Previous work has shown that aerosol forcing is higher in summer than in winter, and has identified the importance of aerosol above cloud in determining black carbon forcing. We show that predicted cloud height is a very important factor in determining normalized radiative forcing (forcing per mass), especially in summer. This can affect the average summer radiative forcing by nearly 50%. Removal by cloud droplets is the dominant atmospheric cleansing mechanism for carbonaceous aerosols. We demonstrate the modeled seasonality of removal processes and compare the importance of scavenging by warm and cold clouds. Both types of clouds contribute significantly to aerosol removal. We estimate uncertainty in direct radiative forcing due to scavenging by tagging the aerosol which has experienced cloud interactions. Finally, seasonal variations offer an opportunity to assess modeled processes when a single process dominates variability. We identify regions where aerosol burden is most sensitive to convection and scavenging in warm and cold clouds, and compare seasonally modeled AOD with that retrieved by the Moderate Resolution Imaging Spectroradiometer (MODIS).

Acoustic Radiation Force Impulse Quantification in the Evaluation of Thyroid Elasticity in Pediatric Patients With Hashimoto Thyroiditis.

PubMed

Yucel, Serap; Ceyhan Bilgici, Meltem; Kara, Cengiz; Can Yilmaz, Gulay; Aydin, H Murat; Elmali, Muzaffer; Tomak, Leman; Saglam, Dilek

2018-05-01

To evaluate the parenchymal elasticity of the thyroid gland with acoustic radiation force impulse imaging in pediatric patients with Hashimoto thyroiditis and to compare it with healthy volunteers. Twenty-six patients with Hashimoto thyroiditis and 26 healthy volunteers between 6 and 17 years were included. The shear wave velocity (SWV) values of both thyroid lobes in both groups were evaluated. The age and sex characteristics of the controls and patients with Hashimoto thyroiditis were similar. The SWV of the thyroid gland in patients with Hashimoto thyroiditis (mean ± SD, 1.67 ± 0.63 m/s) was significantly higher than that in the control group (1.30 ± 0.13 m/s; P < .001). There was no significant difference between the thyroid lobes in both groups. A receiver operating characteristic curve analyses showed an optimal cutoff value of 1.41 m/s, with 73.1% sensitivity, 80.8% specificity, a 79.2 % positive predictive value, and a 75.0% negative predictive value (area under the curve, 0.806; P < .001). In patients with Hashimoto thyroiditis, there was a positive correlation between the SWV values versus anti-thyroperoxidase (Pearson r = 0.46; P = .038). There were no correlations between age, body mass index, thyroid function test results, and anti-thyroglobulin values and versus SWV values. Also, no significant differences were seen between the groups for gland size, gland vascularity, and l-thyroxine treatment. Acoustic radiation force impulse elastography showed a significant difference in the stiffness of the thyroid gland between children with Hashimoto thyroiditis and the healthy group. Using acoustic radiation force impulse elastography immediately after a standard ultrasound evaluation may predict chronic autoimmune thyroiditis. © 2017 by the American Institute of Ultrasound in Medicine.

Radiative Effects of Aerosols Generated from Biomass Burning, Dust Storms, and Forest Fires

NASA Technical Reports Server (NTRS)

Christopher Sundar A.; Vulcan, Donna V.; Welch, Ronald M.

1996-01-01

Atmospheric aerosol particles, both natural and anthropogenic, are important to the earth's radiative balance. They scatter the incoming solar radiation and modify the shortwave reflective properties of clouds by acting as Cloud Condensation Nuclei (CCN). Although it has been recognized that aerosols exert a net cooling influence on climate (Twomey et al. 1984), this effect has received much less attention than the radiative forcings due to clouds and greenhouse gases. The radiative forcing due to aerosols is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign (Houghton et al. 1990). Atmospheric aerosol particles generated from biomass burning, dust storms and forest fires are important regional climatic variables. A recent study by Penner et al. (1992) proposed that smoke particles from biomass burning may have a significant impact on the global radiation balance. They estimate that about 114 Tg of smoke is produced per year in the tropics through biomass burning. The direct and indirect effects of smoke aerosol due to biomass burning could add up globally to a cooling effect as large as 2 W/sq m. Ackerman and Chung (1992) used model calculations and the Earth Radiation Budget Experiment (ERBE) data to show that in comparison to clear days, the heavy dust loading over the Saudi Arabian peninsula can change the Top of the Atmosphere (TOA) clear sky shortwave and longwave radiant exitance by 40-90 W/sq m and 5-20 W/sq m, respectively. Large particle concentrations produced from these types of events often are found with optical thicknesses greater than one. These aerosol particles are transported across considerable distances from the source (Fraser et al. 1984). and they could perturb the radiative balance significantly. In this study, the regional radiative effects of aerosols produced from biomass burning, dust storms and forest fires are examined using the Advanced Very High Resolution Radiometer (AVHRR) Local Area Coverage (LAC) data and the instantaneous scanner ERBE data from the NOAA-9 and NOAA-10 satellites.

Radiation Force Caused by Scattering, Absorption, and Emission of Light by Nonspherical Particles

NASA Technical Reports Server (NTRS)

Mishchenko, Michael I.; Hansen, James E. (Technical Monitor)

2001-01-01

General formulas for computing the radiation force exerted on arbitrarily oriented and arbitrarily shaped nonspherical particles due to scattering, absorption, and emission of electromagnetic radiation are derived. For randomly oriented particles with a plane of symmetry, the formula for the average radiation force caused by the particle response to external illumination reduces to the standard Debye formula derived from the Lorenz-Mie theory, whereas the average radiation force caused by emission vanishes.

Interactive Soil Dust Aerosol Model in the GISS GCM. Part 1; Sensitivity of the Soil Dust Cycle to Radiative Properties of Soil Dust Aerosols

NASA Technical Reports Server (NTRS)

Perlwitz, Jan; Tegen, Ina; Miller, Ron L.

2000-01-01

The sensitivity of the soil dust aerosol cycle to the radiative forcing by soil dust aerosols is studied. Four experiments with the NASA/GISS atmospheric general circulation model, which includes a soil dust aerosol model, are compared, all using a prescribed climatological sea surface temperature as lower boundary condition. In one experiment, dust is included as dynamic tracer only (without interacting with radiation), whereas dust interacts with radiation in the other simulations. Although the single scattering albedo of dust particles is prescribed to be globally uniform in the experiments with radiatively active dust, a different single scattering albedo is used in those experiments to estimate whether regional variations in dust optical properties, corresponding to variations in mineralogical composition among different source regions, are important for the soil dust cycle and the climate state. On a global scale, the radiative forcing by dust generally causes a reduction in the atmospheric dust load corresponding to a decreased dust source flux. That is, there is a negative feedback in the climate system due to the radiative effect of dust. The dust source flux and its changes were analyzed in more detail for the main dust source regions. This analysis shows that the reduction varies both with the season and with the single scattering albedo of the dust particles. By examining the correlation with the surface wind, it was found that the dust emission from the Saharan/Sahelian source region and from the Arabian peninsula, along with the sensitivity of the emission to the single scattering albedo of dust particles, are related to large scale circulation patterns, in particular to the trade winds during Northern Hemisphere winter and to the Indian monsoon circulation during summer. In the other regions, such relations to the large scale circulation were not found. There, the dependence of dust deflation to radiative forcing by dust particles is probably dominated by physical processes with short time scales. The experiments show that dust radiative forcing can lead to significant changes both in the soil dust cycle and in the climate state. To estimate dust concentration and radiative forcing by dust more accurately, dust size distributions and dust single scattering albedo in the model should be a function of the source region, because dust concentration and climate response to dust radiative forcing are sensitive to dust radiative parameters.

Dynamic acoustic radiation force acting on cylindrical shells: theory and simulations.

PubMed

Mitri, F G; Fatemi, M

2005-05-01

An object placed in an acoustic field is known to experience a force due to the transfer of momentum from the wave to the object itself. This force is known to be steady when the incident field is considered to be continuous with constant amplitude. One may define the dynamic (oscillatory) radiation force for a continuous wave-field whose intensity varies slowly with time. This paper extends the theory of the dynamic acoustic radiation force resulting from an amplitude-modulated progressive plane wave-field incident on solid cylinders to the case of solid cylindrical shells with particular emphasis on their thickness and contents of their hollow regions. A new factor corresponding to the dynamic radiation force is defined as Y(d) and stands for the dynamic radiation force per unit energy density and unit cross sectional surface. The results of numerical calculations are presented, indicating the ways in which the form of the dynamic radiation force function curves are affected by variations in the material mechanical parameters and by changes in the interior fluid inside the shell's hollow region. It was shown that the dynamic radiation force function Y(d) deviates from the static radiation force function for progressive waves Y(p) when the modulation frequency increases. These results indicate that the theory presented here is broader than the existing theory on cylinders.

Experimental study of acoustic radiation force of an ultrasound beam on absorbing and scattering objects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nikolaeva, Anastasiia V., E-mail: niko200707@mail.ru; Kryzhanovsky, Maxim A.; Tsysar, Sergey A.

Acoustic radiation force is a nonlinear acoustic effect caused by the transfer of wave momentum to absorbing or scattering objects. This phenomenon is exploited in modern ultrasound metrology for measurement of the acoustic power radiated by a source and is used for both therapeutic and diagnostic sources in medical applications. To calculate radiation force an acoustic hologram can be used in conjunction with analytical expressions based on the angular spectrum of the measured field. The results of an experimental investigation of radiation forces in two different cases are presented in this paper. In one case, the radiation force of anmore » obliquely incident ultrasound beam on a large absorber (which completely absorbs the beam) is considered. The second case concerns measurement of the radiation force on a spherical target that is small compared to the beam diameter.« less

The Potential Radiative Forcing of Global Land Use and Land Cover Change Activities

NASA Astrophysics Data System (ADS)

Ward, D. S.; Mahowald, N. M.; Kloster, S.

2014-12-01

Given the expected increase in pressure on land resources over the next century, there is a need to understand the total impacts of activities associated with land use and land cover change (LULCC). Here we quantify these impacts using the radiative forcing metric, including forcings from changes in long-lived greenhouse gases, tropospheric ozone, aerosol effects, and land surface albedo. We estimate radiative forcings from the different agents for historical LULCC and for six future projections using simulations from the National Center for Atmospheric Research Community Land Model and Community Atmosphere Models and additional offline analyses. When all forcing agents are considered together we show that 45% (+30%, -20%) of the present-day (2010) anthropogenic radiative forcing can be attributed to LULCC. Changes in the emission of non-CO2 greenhouse gases and aerosols from LULCC enhance the total LULCC radiative forcing by a factor of 2 to 3 with respect to the forcing from CO2 alone. In contrast, the non-CO2 forcings from fossil fuel burning are roughly neutral, due largely to the negative (cooling) impact of aerosols from these sources. We partition the global LULCC radiative forcing into three major sources: direct modification of land cover (e.g. deforestation), agricultural activities, and fire regime changes. Contributions from deforestation and agriculture are roughly equal in the present day, while changes to wildfire activity impose a small negative forcing globally. In 2100, deforestation activities comprise the majority of the LULCC radiative forcing for all projections except one (Representative Concentration Pathway (RCP) 4.5). This suggests that realistic scenarios of future forest area change are essential for projecting the contribution of LULCC to climate change. However, the commonly used RCP land cover change projections all include decreases in global deforestation rates over the next 85 years. To place an upper bound on the potential radiative forcing from LULCC we create a 'worst-case scenario" in which all arable land is converted to agriculture by the year 2100. This scenario leads to a total radiative forcing of 4.3 Wm-2 (+/- 1 Wm-2) suggesting that well thought-out land policy is needed to minimize future increases in global anthropogenic radiative forcing.

Precipitation Response to Regional Radiative Forcing

NASA Technical Reports Server (NTRS)

Shindell, D. T.; Voulgarakis, A.; Faluvegi, G.; Milly, G.

2012-01-01

Precipitation shifts can have large impacts on human society and ecosystems. Many aspects of how inhomogeneous radiative forcings influence precipitation remain unclear, however. Here we investigate regional precipitation responses to various forcings imposed in different latitude bands in a climate model. We find that several regions show strong, significant responses to most forcings, but that the magnitude and even the sign depends upon the forcing location and type. Aerosol and ozone forcings typically induce larger responses than equivalent carbon dioxide (CO2) forcing, and the influence of remote forcings often outweighs that of local forcings. Consistent with this, ozone and especially aerosols contribute greatly to precipitation changes over the Sahel and South and East Asia in historical simulations, and inclusion of aerosols greatly increases the agreement with observed trends in these areas, which cannot be attributed to either greenhouse gases or natural forcings. Estimates of precipitation responses derived from multiplying our Regional Precipitation Potentials (RPP; the response per unit forcing relationships) by historical forcings typically capture the actual response in full transient climate simulations fairly well, suggesting that these relationships may provide useful metrics. The strong sensitivity to aerosol and ozone forcing suggests that although some air quality improvements may unmask greenhouse gas-induced warming, they have large benefits for reducing regional disruption of the hydrologic cycle.

Towards quantifying global aerosol radiative effects using lidar

NASA Astrophysics Data System (ADS)

Thorsen, T. J.

2017-12-01

Spaceborne lidar observations alleviate many of the limitations of passivesensors and have great potential to provide accurate global all-sky estimatesof the aerosol direct radiative effect (DRE). However, analysis of CALIPSOlidar observations show that CALIPSO does not detect allradiatively-significant aerosol, i.e. aerosol that directly modifies theEarth's radiation budget. We estimated that using CALIPSO observationsresults in an underestimate of the magnitude of the global mean aerosol DREby up to 54%. The CATS lidar on-board the ISS is shown to have a poorersensitivity than CALIPSO and the expected sensitivity of the upcoming ATLIDlidar on EarthCARE indicates that calculations of the aerosol DRE willcontinue to be significantly biased. Improvements to our knowledge of aerosol forcing, which contributes thelargest uncertainty to climate sensitivity, could be achieved by a futurespace-based HSRL mission. To this end, high-accuracy ground-based andairborne lidar datasets have been used to compute the detection sensitivityrequired to accurately resolve the aerosol DRE. Multiwavelength HSRLmeasurements also can retrieve vertically-resolved aerosol optical propertiesneeded for radiative transfer calculations which are not provided by currentsatellite observations. Current satellite observations also do not provideall the quantities needed to compute the aerosol direct radiative forcing,i.e. the radiative effect of just anthropogenic aerosols. A multiwavelengthHSRL allows for a more refined aerosol classification to be made enablingboth calculations of anthropogenic aerosol radiative effects and betterconstraints on global models.

The importance of the diurnal and annual cycle of air traffic for contrail radiative forcing.

PubMed

Stuber, Nicola; Forster, Piers; Rädel, Gaby; Shine, Keith

2006-06-15

Air traffic condensation trails, or contrails, are believed to have a net atmospheric warming effect, although one that is currently small compared to that induced by other sources of human emissions. However, the comparably large growth rate of air traffic requires an improved understanding of the resulting impact of aircraft radiative forcing on climate. Contrails have an effect on the Earth's energy balance similar to that of high thin ice clouds. Their trapping of outgoing longwave radiation emitted by the Earth and atmosphere (positive radiative forcing) is partly compensated by their reflection of incoming solar radiation (negative radiative forcing). On average, the longwave effect dominates and the net contrail radiative forcing is believed to be positive. Over daily and annual timescales, varying levels of air traffic, meteorological conditions, and solar insolation influence the net forcing effect of contrails. Here we determine the factors most important for contrail climate forcing using a sophisticated radiative transfer model for a site in southeast England, located in the entrance to the North Atlantic flight corridor. We find that night-time flights during winter (December to February) are responsible for most of the contrail radiative forcing. Night flights account for only 25 per cent of daily air traffic, but contribute 60 to 80 per cent of the contrail forcing. Further, winter flights account for only 22 per cent of annual air traffic, but contribute half of the annual mean forcing. These results suggest that flight rescheduling could help to minimize the climate impact of aviation.

On the causal structure between CO2 and global temperature

PubMed Central

Stips, Adolf; Macias, Diego; Coughlan, Clare; Garcia-Gorriz, Elisa; Liang, X. San

2016-01-01

We use a newly developed technique that is based on the information flow concept to investigate the causal structure between the global radiative forcing and the annual global mean surface temperature anomalies (GMTA) since 1850. Our study unambiguously shows one-way causality between the total Greenhouse Gases and GMTA. Specifically, it is confirmed that the former, especially CO2, are the main causal drivers of the recent warming. A significant but smaller information flow comes from aerosol direct and indirect forcing, and on short time periods, volcanic forcings. In contrast the causality contribution from natural forcings (solar irradiance and volcanic forcing) to the long term trend is not significant. The spatial explicit analysis reveals that the anthropogenic forcing fingerprint is significantly regionally varying in both hemispheres. On paleoclimate time scales, however, the cause-effect direction is reversed: temperature changes cause subsequent CO2/CH4 changes. PMID:26900086

Climate forcings and feedbacks

NASA Technical Reports Server (NTRS)

Hansen, James

1993-01-01

Global temperature has increased significantly during the past century. Understanding the causes of observed global temperature change is impossible in the absence of adequate monitoring of changes in global climate forcings and radiative feedbacks. Climate forcings are changes imposed on the planet's energy balance, such as change of incoming sunlight or a human-induced change of surface properties due to deforestation. Radiative feedbacks are radiative changes induced by climate change, such as alteration of cloud properties or the extent of sea ice. Monitoring of global climate forcings and feedbacks, if sufficiently precise and long-term, can provide a very strong constraint on interpretation of observed temperature change. Such monitoring is essential to eliminate uncertainties about the relative importance of various climate change mechanisms including tropospheric sulfate aerosols from burning of coal and oil smoke from slash and burn agriculture, changes of solar irradiance changes of several greenhouse gases, and many other mechanisms. The considerable variability of observed temperature, together with evidence that a substantial portion of this variability is unforced indicates that observations of climate forcings and feedbacks must be continued for decades. Since the climate system responds to the time integral of the forcing, a further requirement is that the observations be carried out continuously. However, precise observations of forcings and feedbacks will also be able to provide valuable conclusions on shorter time scales. For example, knowledge of the climate forcing by increasing CFC's relative to the forcing by changing ozone is important to policymakers, as is information on the forcing by CO2 relative to the forcing by sulfate aerosols. It will also be possible to obtain valuable tests of climate models on short time scales, if there is precise monitoring of all forcings and feedbacks during and after events such as a large volcanic eruption or an El Nino.

SOURCE ATTRIBUTION OF RADIATIVE FORCING FROM SHORT LIVED CLIMATE FORCING AGENTS

EPA Science Inventory

The immediate project result is quantification of the pre-industrial to present forcing for anthropogenic emissions, the radiative effects of natural emissions, and spatial distribution of the radiative forcing efficiency for key aerosol and O3 precursors (i.e., mW/m^2<...

Modes of interannual variability in northern hemisphere winter atmospheric circulation in CMIP5 models: evaluation, projection and role of external forcing

NASA Astrophysics Data System (ADS)

Frederiksen, Carsten S.; Ying, Kairan; Grainger, Simon; Zheng, Xiaogu

2018-04-01

Models from the coupled model intercomparison project phase 5 (CMIP5) dataset are evaluated for their ability to simulate the dominant slow modes of interannual variability in the Northern Hemisphere atmospheric circulation 500 hPa geopotential height in the twentieth century. A multi-model ensemble of the best 13 models has then been used to identify the leading modes of interannual variability in components related to (1) intraseasonal processes; (2) slowly-varying internal dynamics; and (3) the slowly-varying response to external changes in radiative forcing. Modes in the intraseasonal component are related to intraseasonal variability in the North Atlantic, North Pacific and North American, and Eurasian regions and are little affected by the larger radiative forcing of the Representative Concentration Pathways 8.5 (RCP8.5) scenario. The leading modes in the slow-internal component are related to the El Niño-Southern Oscillation, Pacific North American or Tropical Northern Hemisphere teleconnection, the North Atlantic Oscillation, and the Western Pacific teleconnection pattern. While the structure of these slow-internal modes is little affected by the larger radiative forcing of the RCP8.5 scenario, their explained variance increases in the warmer climate. The leading mode in the slow-external component has a significant trend and is shown to be related predominantly to the climate change trend in the well mixed greenhouse gas concentration during the historical period. This mode is associated with increasing height in the 500 hPa pressure level. A secondary influence on this mode is the radiative forcing due to stratospheric aerosols associated with volcanic eruptions. The second slow-external mode is shown to be also related to radiative forcing due to stratospheric aerosols. Under RCP8.5 there is only one slow-external mode related to greenhouse gas forcing with a trend over four times the historical trend.

North Atlantic Aerosol Properties and Direct Radiative Effects: Key Results from TARFOX and ACE-2

NASA Technical Reports Server (NTRS)

Russell, P. B.; Livingston, J. M.; Schmid, B.; Bergstrom, Robert A.; Hignett, P.; Hobbs, P. V.; Durkee, P. A.

2000-01-01

Aerosol effects on atmospheric radiative fluxes provide a forcing function that can change the climate In potentially significant ways. This aerosol radiative forcing is a major source of uncertainty in understanding the observed climate change of the past century and in predicting future climate. To help reduce this uncertainty, the International Global Atmospheric Chemistry Project (IGAC) has endorsed a series of multiplatform aerosol field campaigns. The Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) and the second Aerosol Characterization Experiment (ACE-2) were the first IGAC campaigns to address the impact of anthropogenic aerosols, Both TARFOX and ACE-2 gathered extensive data sets on aerosol properties and radiative effects, TARFOX focused on the urban-industrial haze plume flowing from the eastern United States over the western Atlantic Ocean, whereas ACE-2 studied aerosols carried over the eastern Atlantic from both European urban/industrial and African mineral sources. These aerosols often have a marked influence on the top-of-atmosphere radiances measured by satellites. Shown there are contours of aerosol optical depth derived from radiances measured by the AVHRR sensor on the NOAA-11 satellite. The contours readily show that aerosols originating in North America, Europe, and Africa impact the radiative properties of air over the North Atlantic. However, the accurate derivation of flux changes, or radiative forcing, from the satellite measured radiances or retrieved optical depths remains a difficult challenge. In this paper we summarize key initial results from TARFOX and, to a lesser extent, ACE-2, with a focus on those results that allow an improved assessment of the flux changes caused by North Atlantic aerosols at middle latitudes.

Hemodynamic Flow-Induced Mechanotransduction Signaling Influences the Radiation Response of the Vascular Endothelium.

PubMed

Natarajan, Mohan; Aravindan, Natarajan; Sprague, Eugene A; Mohan, Sumathy

2016-08-01

Hemodynamic shear stress is defined as the physical force exerted by the continuous flow of blood in the vascular system. Endothelial cells, which line the inner layer of blood vessels, sense this physiological force through mechanotransduction signaling and adapt to maintain structural and functional homeostasis. Hemodynamic flow, shear stress and mechanotransduction signaling are, therefore, an integral part of endothelial pathophysiology. Although this is a well-established concept in the cardiovascular field, it is largely dismissed in studies aimed at understanding radiation injury to the endothelium and subsequent cardiovascular complications. We and others have reported on the differential response of the endothelium when the cells are under hemodynamic flow shear compared with static culture. Further, we have demonstrated significant differences in the gene expression of static versus shear-stressed irradiated cells in four key pathways, reinforcing the importance of shear stress in understanding radiation injury of the endothelium. This article further emphasizes the influence of hemodynamic shear stress and the associated mechanotransduction signaling on physiological functioning of the vascular endothelium and underscores its significance in understanding radiation injury to the vasculature and associated cardiac complications. Studies of radiation effect on endothelial biology and its implication on cardiotoxicity and vascular complications thus far have failed to highlight the significance of these factors. Factoring in these integral parts of the endothelium will enhance our understanding of the contribution of the endothelium to radiation biology. Without such information, the current approaches to studying radiation-induced injury to the endothelium and its consequences in health and disease are limited.

Radiation force on absorbing targets and power measurements of a high intensity focused ultrasound (HIFU) source

NASA Astrophysics Data System (ADS)

Qian, Zuwen; Zhu, Zhemin; Ye, Shigong; Jiang, Wenhua; Zhu, Houqing; Yu, Jinshen

2010-10-01

Based on the analytic expressions for the radiated field of a circular concave piston given by Hasegawa et al., an integral for calculation of the radiation force on a plane absorbing target in a spherically focused field is derived. A general relation between acoustic power P and normal radiation force F n is obtained under the condition of kr ≫ 1. Numerical computation is carried out by using the symbolic computation program for practically focused sources and absorbing circular targets. The results show that, for a given source, there is a range of target positions where the radiation force is independent of the target’s position under the assumption that the contribution of the acoustic field behind the target to the radiation force can be neglected. The experiments are carried out and confirm that there is a range of target positions where the measured radiation force is basically independent of the target’s position even at high acoustic power (up to 700 W). It is believed that when the radiation force method is used to measure the acoustic power radiated from a focused source, the size of the target must be selected in such a way that no observable sound can be found in the region behind the target.

Experimental verification of theoretical equations for acoustic radiation force on compressible spherical particles in traveling waves.

PubMed

Johnson, Kennita A; Vormohr, Hannah R; Doinikov, Alexander A; Bouakaz, Ayache; Shields, C Wyatt; López, Gabriel P; Dayton, Paul A

2016-05-01

Acoustophoresis uses acoustic radiation force to remotely manipulate particles suspended in a host fluid for many scientific, technological, and medical applications, such as acoustic levitation, acoustic coagulation, contrast ultrasound imaging, ultrasound-assisted drug delivery, etc. To estimate the magnitude of acoustic radiation forces, equations derived for an inviscid host fluid are commonly used. However, there are theoretical predictions that, in the case of a traveling wave, viscous effects can dramatically change the magnitude of acoustic radiation forces, which make the equations obtained for an inviscid host fluid invalid for proper estimation of acoustic radiation forces. To date, experimental verification of these predictions has not been published. Experimental measurements of viscous effects on acoustic radiation forces in a traveling wave were conducted using a confocal optical and acoustic system and values were compared with available theories. Our results show that, even in a low-viscosity fluid such as water, the magnitude of acoustic radiation forces is increased manyfold by viscous effects in comparison with what follows from the equations derived for an inviscid fluid.

Experimental verification of theoretical equations for acoustic radiation force on compressible spherical particles in traveling waves

NASA Astrophysics Data System (ADS)

Johnson, Kennita A.; Vormohr, Hannah R.; Doinikov, Alexander A.; Bouakaz, Ayache; Shields, C. Wyatt; López, Gabriel P.; Dayton, Paul A.

2016-05-01

Acoustophoresis uses acoustic radiation force to remotely manipulate particles suspended in a host fluid for many scientific, technological, and medical applications, such as acoustic levitation, acoustic coagulation, contrast ultrasound imaging, ultrasound-assisted drug delivery, etc. To estimate the magnitude of acoustic radiation forces, equations derived for an inviscid host fluid are commonly used. However, there are theoretical predictions that, in the case of a traveling wave, viscous effects can dramatically change the magnitude of acoustic radiation forces, which make the equations obtained for an inviscid host fluid invalid for proper estimation of acoustic radiation forces. To date, experimental verification of these predictions has not been published. Experimental measurements of viscous effects on acoustic radiation forces in a traveling wave were conducted using a confocal optical and acoustic system and values were compared with available theories. Our results show that, even in a low-viscosity fluid such as water, the magnitude of acoustic radiation forces is increased manyfold by viscous effects in comparison with what follows from the equations derived for an inviscid fluid.

Radiative forcing over the conterminous United States due to contemporary land cover land use change and sensitivity to snow and interannual albedo variability

USGS Publications Warehouse

Barnes, Christopher A.; Roy, David P.

2010-01-01

Satellite-derived land cover land use (LCLU), snow and albedo data, and incoming surface solar radiation reanalysis data were used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 58 ecoregions covering 69% of the conterminous United States. A net positive surface radiative forcing (i.e., warming) of 0.029 Wm−2 due to LCLU albedo change from 1973 to 2000 was estimated. The forcings for individual ecoregions were similar in magnitude to current global forcing estimates, with the most negative forcing (as low as −0.367 Wm−2) due to the transition to forest and the most positive forcing (up to 0.337 Wm−2) due to the conversion to grass/shrub. Snow exacerbated both negative and positive forcing for LCLU transitions between snow-hiding and snow-revealing LCLU classes. The surface radiative forcing estimates were highly sensitive to snow-free interannual albedo variability that had a percent average monthly variation from 1.6% to 4.3% across the ecoregions. The results described in this paper enhance our understanding of contemporary LCLU change on surface radiative forcing and suggest that future forcing estimates should model snow and interannual albedo variation.

On the synchrotron radiation reaction in external magnetic field

NASA Astrophysics Data System (ADS)

Tursunov, Arman; Kološ, Martin

2017-12-01

We study the dynamics of point electric charges undergoing radiation reaction force due to synchrotron radiation in the presence of external uniform magnetic field. The radiation reaction force cannot be neglected in many physical situations and its presence modifies the equations of motion significantly. The exact form of the equation of motion known as the Lorentz-Dirac equation contains higher order Schott term which leads to the appearance of the runaway solutions. We demonstrate effective computational ways to avoid such unphysical solutions and perform numerical integration of the dynamical equations. We show that in the ultrarelativistic case the Schott term is small and does not have considerable effect to the trajectory of a particle. We compare results with the covariant Landau-Lifshitz equation which is the first iteration of the Lorentz-Dirac equation. Even though the Landau-Lifshitz equation is thought to be approximative solution, we show that in realistic scenarios both approaches lead to identical results.

Simulating Dust Regional Impact on the Middle East Climate and the Red Sea

NASA Astrophysics Data System (ADS)

Osipov, Sergey; Stenchikov, Georgiy

2017-04-01

Dust is one of the most abundant aerosols, however, currently only a few regional climate downscalings account for dust. This study focuses on the Middle East and the Red Sea regional climate response to the dust aerosol radiative forcing. The Red Sea is located between North Africa and Arabian Peninsula, which are first and third largest source regions of dust, respectively. MODIS and SEVIRI satellite observations show extremely high dust optical depths in the region, especially over the southern Red Sea during the summer season. The significant north-to-south gradient of the dust optical depth over the Red Sea persists throughout the entire year. Modeled atmospheric radiative forcing at the surface, top of the atmosphere and absorption in the atmospheric column indicate that dust significantly perturbs radiative balance. Top of the atmosphere modeled forcing is validated against independently derived GERB satellite product. Due to strong radiative forcing at the sea surface (daily mean forcing during summer reaches -32 Wm-2 and 10 Wm-2 in SW and LW, respectively), using uncoupled ocean model with prescribed atmospheric boundary conditions would result in an unrealistic ocean response. Therefore, here we employ the Regional Ocean Modeling system (ROMS) fully coupled with the Weather Research and Forecasting (WRF) model to study the impact of dust on the Red Sea thermal regime and circulation. The WRF was modified to interactively account for the radiative effect of dust. Daily spectral optical properties of dust are computed using Mie, T-matrix, and geometric optics approaches, and are based on the SEVIRI climatological optical depth. The WRF model parent and nested domains are configured over the Middle East and North Africa (MENA) region and over the Red Sea with 30 and 10 km resolution, respectively. The ROMS model over the Red Sea has 2 km grid spacing. The simulations show that, in the equilibrium response, dust causes 0.3-0.5 K cooling of the Red Sea surface waters, and weakens the overturning circulation in the Red Sea. The salinity distribution, freshwater, and heat budgets are significantly perturbed. This indicates that dust plays an important role in the formation of the Red Sea energy balance and circulation regimes, and has to be thoroughly accounted for in future modeling studies.

The Radiative Forcing Model Intercomparison Project (RFMIP): Experimental protocol for CMIP6

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pincus, Robert; Forster, Piers M.; Stevens, Bjorn

The phrasing of the first of three questions motivating CMIP6 – “How does the Earth system respond to forcing?” – suggests that forcing is always well-known, yet the radiative forcing to which this question refers has historically been uncertain in coordinated experiments even as understanding of how best to infer radiative forcing has evolved. The Radiative Forcing Model Intercomparison Project (RFMIP) endorsed by CMIP6 seeks to provide a foundation for answering the question through three related activities: (i) accurate characterization of the effective radiative forcing relative to a near-preindustrial baseline and careful diagnosis of the components of this forcing; (ii) assessment ofmore » the absolute accuracy of clear-sky radiative transfer parameterizations against reference models on the global scales relevant for climate modeling; and (iii) identification of robust model responses to tightly specified aerosol radiative forcing from 1850 to present. Complete characterization of effective radiative forcing can be accomplished with 180 years (Tier 1) of atmosphere-only simulation using a sea-surface temperature and sea ice concentration climatology derived from the host model's preindustrial control simulation. Assessment of parameterization error requires trivial amounts of computation but the development of small amounts of infrastructure: new, spectrally detailed diagnostic output requested as two snapshots at present-day and preindustrial conditions, and results from the model's radiation code applied to specified atmospheric conditions. In conclusion, the search for robust responses to aerosol changes relies on the CMIP6 specification of anthropogenic aerosol properties; models using this specification can contribute to RFMIP with no additional simulation, while those using a full aerosol model are requested to perform at least one and up to four 165-year coupled ocean–atmosphere simulations at Tier 1.« less

The Radiative Forcing Model Intercomparison Project (RFMIP): Experimental protocol for CMIP6

DOE PAGES

Pincus, Robert; Forster, Piers M.; Stevens, Bjorn

2016-09-27

The phrasing of the first of three questions motivating CMIP6 – “How does the Earth system respond to forcing?” – suggests that forcing is always well-known, yet the radiative forcing to which this question refers has historically been uncertain in coordinated experiments even as understanding of how best to infer radiative forcing has evolved. The Radiative Forcing Model Intercomparison Project (RFMIP) endorsed by CMIP6 seeks to provide a foundation for answering the question through three related activities: (i) accurate characterization of the effective radiative forcing relative to a near-preindustrial baseline and careful diagnosis of the components of this forcing; (ii) assessment ofmore » the absolute accuracy of clear-sky radiative transfer parameterizations against reference models on the global scales relevant for climate modeling; and (iii) identification of robust model responses to tightly specified aerosol radiative forcing from 1850 to present. Complete characterization of effective radiative forcing can be accomplished with 180 years (Tier 1) of atmosphere-only simulation using a sea-surface temperature and sea ice concentration climatology derived from the host model's preindustrial control simulation. Assessment of parameterization error requires trivial amounts of computation but the development of small amounts of infrastructure: new, spectrally detailed diagnostic output requested as two snapshots at present-day and preindustrial conditions, and results from the model's radiation code applied to specified atmospheric conditions. In conclusion, the search for robust responses to aerosol changes relies on the CMIP6 specification of anthropogenic aerosol properties; models using this specification can contribute to RFMIP with no additional simulation, while those using a full aerosol model are requested to perform at least one and up to four 165-year coupled ocean–atmosphere simulations at Tier 1.« less

A New Paradigm for Diagnosing Contributions to Model Aerosol Forcing Error

NASA Astrophysics Data System (ADS)

Jones, A. L.; Feldman, D. R.; Freidenreich, S.; Paynter, D.; Ramaswamy, V.; Collins, W. D.; Pincus, R.

2017-12-01

A new paradigm in benchmark absorption-scattering radiative transfer is presented that enables both the globally averaged and spatially resolved testing of climate model radiation parameterizations in order to uncover persistent sources of biases in the aerosol instantaneous radiative effect (IRE). A proof of concept is demonstrated with the Geophysical Fluid Dynamics Laboratory AM4 and Community Earth System Model 1.2.2 climate models. Instead of prescribing atmospheric conditions and aerosols, as in prior intercomparisons, native snapshots of the atmospheric state and aerosol optical properties from the participating models are used as inputs to an accurate radiation solver to uncover model-relevant biases. These diagnostic results show that the models' aerosol IRE bias is of the same magnitude as the persistent range cited ( 1 W/m2) and also varies spatially and with intrinsic aerosol optical properties. The findings underscore the significance of native model error analysis and its dispositive ability to diagnose global biases, confirming its fundamental value for the Radiative Forcing Model Intercomparison Project.

Re-Evaluation of Dust Radiative Forcing Using Remote Measurements of Dust Absorption

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.; Tanre, Didier; Karnieli, Arnon; Remer, Lorraine A.

1998-01-01

Spectral remote observations of dust properties from space and from the ground creates a powerful tool for determination of dust absorption of solar radiation with an unprecedented accuracy. Absorption is a key component in understanding dust impact on climate. We use Landsat spaceborne measurements at 0.47 to 2.2 microns over Senegal with ground based sunphotometers to find that Saharan dust absorption of solar radiation is two to four times smaller than in models. Though dust absorbs in the blue, almost no absorption was found for wavelengths greater 0.6 microns. The new finding increases by 50% recent estimated solar radiative forcing by dust and decreases the estimated dust heating of the lower troposphere. Dust transported from Asia shows slightly higher absorption probably due to the presence of black carbon from populated regions. Large scale application of this method to satellite data from the Earth Observing System can reduce significantly the uncertainty in the dust radiative effects.

Understanding the Asian summer monsoon response to greenhouse warming: the relative roles of direct radiative forcing and sea surface temperature change

NASA Astrophysics Data System (ADS)

Li, Xiaoqiong; Ting, Mingfang

2017-10-01

Future hydroclimate projections from state-of-the-art climate models show large uncertainty and model spread, particularly in the tropics and over the monsoon regions. The precipitation and circulation responses to rising greenhouse gases involve a fast component associated with direct radiative forcing and a slow component associated with sea surface temperature (SST) warming; the relative importance of the two may contribute to model discrepancies. In this study, regional hydroclimate responses to greenhouse warming are assessed using output from coupled general circulation models in the Coupled Model Intercomparison Project-Phase 5 (CMIP5) and idealized atmospheric general circulation model experiments from the Atmosphere Model Intercomparison Project. The thermodynamic and dynamic mechanisms causing the rainfall changes are examined using moisture budget analysis. Results show that direct radiative forcing and SST change exert significantly different responses both over land and ocean. For most part of the Asian monsoon region, the summertime rainfall changes are dominated by the direct CO2 radiative effect through enhanced monsoon circulation. The response to SST warming shows a larger model spread compared to direct radiative forcing, possibly due to the cancellation between the thermodynamical and dynamical components. While the thermodynamical response of the Asian monsoon is robust across the models, there is a lack of consensus for the dynamical response among the models and weak multi-model mean responses in the CMIP5 ensemble, which may be related to the multiple physical processes evolving on different time scales.

[Radiative and hygienic certification in Armed Forces, problems of its implementation and ways of perfection].

PubMed

Rusakov, V N; Cherkashin, A V; Shishkanov, A P; Ian'shin, L A; Gracheva, T N

2010-12-01

Radiative and hygienic passportization is one of the most actual pattern of socio and hygienic monitoring in Armed Forces. Radiative and hygienic passport is the main document which characterizes the safety control in military unit and uses the sources of ionizing radiation. Sanitary and epidemiologic institutions were imputed to control the formation of radiative and hygienic passports, analysis and generalization of its data, formation of conclusions about the condition of radiation security in the military units. According to radiative and hygienic passportization, which took place in 2009, the radiation security in the Armed Forces and organizations is satisfactory, but there are some problems of providing of radiation security of personnel under the professional and medical radiation. The salvation of its problems requires the effective work of official functionary of radiac object and institutions of state sanitary and epidemiological supervision in Armed Forces of Russian Federation.

New directions: Mineral dust and ozone - Heterogeneous chemistry

NASA Astrophysics Data System (ADS)

Ramachandran, S.

2015-04-01

Aerosols, the tiny solid or liquid particles suspended in air and produced from natural sources and anthropogenic activities, continue to contribute the largest uncertainty to radiative forcing (IPCC, 2013). Aerosol particles give rise to radiative forcing directly through scattering and absorption of solar and infrared radiation in the atmosphere. Aerosols also give rise to indirect radiative forcing by modifying the cloud optical properties and lifetimes. Among the aerosol species mineral dust and black carbon cause a warming (positive forcing) while sulphate and sea salt cause a cooling (negative forcing) of the Earth-atmosphere system. In tropics and sub-tropics mineral dust is a major contributor to aerosol loading and optical thickness. The global source strength of dust aerosol varies significantly on spatial and temporal scales. The source regions of dust are mainly deserts, dry lake beds, and semi-arid regions, in addition to drier regions where vegetation has been reduced or soil surfaces that are disturbed by man made activities. Anthropogenic activities mainly related to agriculture such as harvesting, ploughing, overgrazing, and cement production and transport also produce mineral dust. An estimated 2500 terragram (Tg, 1012 g) of mineral dust is emitted into the atmosphere per year, and dominates the aerosol mass over continental regions in south Asia and China accounting for ∼35% of the total aerosol mass (IPCC, 2013). In India, dust is prevalent throughout the north and western India during the year and peaks during premonsoon season.

Postfire influences of snag attrition on albedo and radiative forcing

NASA Astrophysics Data System (ADS)

O'Halloran, Thomas L.; Acker, Steven A.; Joerger, Verena M.; Kertis, Jane; Law, Beverly E.

2014-12-01

This paper examines albedo perturbation and radiative forcing after a high-severity fire in a mature forest in the Oregon Cascade Range. Correlations between postfire albedo and seedling, sapling, and snag (standing dead tree) density were investigated across fire severity classes and seasons for years 4-15 after fire. Albedo perturbation was 14 times larger in winter compared to summer and increased with fire severity class for the first several years. Albedo perturbation increased linearly with time over the study period. Correlations between albedo perturbations and the vegetation densities were strongest with snags, and significant in all fire classes in both summer and winter (R < -0.92, p < 0.01). The resulting annual radiative forcing at the top of the atmosphere became more negative linearly at a rate of -0.86 W m-2 yr-1, reaching -15 W m-2 in year 15 after fire. This suggests that snags can be the dominant controller of postfire albedo on decadal time scales.

Roles of production, consumption and trade in global and regional aerosol radiative forcing

NASA Astrophysics Data System (ADS)

Lin, J.; Tong, D.; Davis, S. J.; Ni, R.; Tan, X.; Pan, D.; Zhao, H.; Lu, Z.; Streets, D. G.; Feng, T.; Zhang, Q.; Yan, Y.; Hu, Y.; Li, J.; Liu, Z.; Jiang, X.; Geng, G.; He, K.; Huang, Y.; Guan, D.

2016-12-01

Anthropogenic aerosols exert strong radiative forcing on the climate system. Prevailing view regards aerosol radiative forcing as a result of emissions from regions' economic production, with China and other developing regions having the largest contributions to radiative forcing at present. However, economic production is driven by global demand for computation, and international trade allows for separation of regions consuming goods and services from regions where goods and related aerosol pollution are produced. It has recently been recognized that regions' consumption and trade have profoundly altered the spatial distribution of aerosol emissions and pollution. Building upon our previous work, this study quantifies for the first time the roles of trade and consumption in aerosol climate forcing attributed to different regions. We contrast the direct radiative forcing of aerosols related to regions' consumption of goods and services against the forcing due to emissions produced in each region. Aerosols assessed include black carbon, primary organic aerosol, and secondary inorganic aerosols including sulfate, nitrate and ammonium. We find that global aerosol radiative forcing due to emissions produced in East Asia is much stronger than the forcing related to goods and services ultimately consumed in that region because of its large net export of emissions-intensive goods. The opposite is true for net importers like Western Europe and North America: global radiative forcing related to consumption is much greater than the forcing due to emissions produced in these regions. Overall, trade is associated with a shift of radiative forcing from net importing to net exporting regions. Compared to greenhouse gases such as carbon dioxide, the short atmospheric lifetimes of aerosols cause large localized differences in radiative forcing. International efforts to reduce emissions in the exporting countries will help alleviate trade-related climate and health impacts of aerosols while lowering global emissions associated with global consumption. Ref: Lin et al., China's international trade and air pollution in the United States, PNAS, 2014 Lin et al., Global climate forcing of aerosols embodied in international trade, Nature Geoscience, 2016

Transport of Aerosols from Asia and Their Radiative Effects Over the Western Pacific: A 3-D Model Study for ACE-Asia Experiment During Spring 2001

NASA Technical Reports Server (NTRS)

Chin, Mian; Ginoux, Paul; Flatau, Piotr; Anderson, Tad; Masonis, Sarah; Russell, Phil; Schmid, Beat; Livingston, John; Redemann, Jens; Kahn, Ralph;

Intercomparison of Models Representing Direct Shortwave Radiative Forcing by Sulfate Aerosols

NASA Technical Reports Server (NTRS)

Boucher, O.; Schwartz, S. E.; Ackerman, T. P.; Anderson, T. L.; Bergstrom, B.; Bonnel, B.; Dahlback, A.; Fouquart, Y.; Chylek, P.; Fu, Q.;

Acoustic Radiation Force of a Quasi-Gaussian Beam on an Elastic Sphere in a Fluid.

PubMed

Nikolaeva, A V; Sapozhnikov, O A; Bailey, M R

2016-09-01

Acoustic radiation force has many applications. One of the related technologies is the ability to noninvasively expel stones from the kidney. To optimize the procedure it is important to develop theoretical approaches that can provide rapid calculations of the radiation force depending in stone size and elastic properties, together with ultrasound beam diameter, intensity, and frequency. We hypothesize that the radiation force nonmonotonically depends on the ratio between the acoustic beam width and stone diameter because of coupling between the acoustic wave in the fluid and shear waves in the stone. Testing this hypothesis by considering a spherical stone and a quasi-Gaussian beam was performed in the current work. The calculation of the radiation force was conducted for elastic spheres of two types. Dependence of the magnitude of the radiation force on the beam diameter at various fixed values of stone diameters was modeled. In addition to using real material properties, speed of shear wave in the stone was varied to reveal the importance of shear waves in the stone. It was found that the radiation force reaches its maximum at the beamwidth comparable to the stone diameter; the gain in the force magnitude can reach 40% in comparison with the case of a narrow beam.

Climate Response of Direct Radiative Forcing of Anthropogenic Black Carbon

NASA Technical Reports Server (NTRS)

Chung, Serena H.; Seinfeld,John H.

2008-01-01

The equilibrium climate effect of direct radiative forcing of anthropogenic black carbon (BC) is examined by 100-year simulations in the Goddard Institute for Space Studies General Circulation Model II-prime coupled to a mixed-layer ocean model. Anthropogenic BC is predicted to raise globally and annually averaged equilibrium surface air temperature by 0.20 K if BC is assumed to be externally mixed. The predicted increase is significantly greater in the Northern Hemisphere (0.29 K) than in the Southern Hemisphere (0.11 K). If BC is assumed to be internally mixed with the present day level of sulfate aerosol, the predicted annual mean surface temperature increase rises to 0.37 K globally, 0.54 K for the Northern Hemisphere, and 0.20 K for the Southern Hemisphere. The climate sensitivity of BC direct radiative forcing is calculated to be 0.6 K W (sup -1) square meters, which is about 70% of that of CO2, independent of the assumption of BC mixing state. The largest surface temperature response occurs over the northern high latitudes during winter and early spring. In the tropics and midlatitudes, the largest temperature increase is predicted to occur in the upper troposphere. Direct radiative forcing of anthropogenic BC is also predicted to lead to a change of precipitation patterns in the tropics; precipitation is predicted to increase between 0 and 20 N and decrease between 0 and 20 S, shifting the intertropical convergence zone northward. If BC is assumed to be internally mixed with sulfate instead of externally mixed, the change in precipitation pattern is enhanced. The change in precipitation pattern is not predicted to alter the global burden of BC significantly because the change occurs predominantly in regions removed from BC sources.

Radiative Forcing of the Pinatubo Aerosol as a Function of Latitude and Time

NASA Technical Reports Server (NTRS)

Bergstrom, R. W.; Kinne, S.; Russell, P. B.; Bauman, J. J.; Minnis, P.

1996-01-01

We present calculations of the radiative forcing of the Mt. Pinatubo aerosols as a function of latitude and time after the eruption and compare the results with GOES satellite data. The results from the model indicate that the net effect of the aerosol was to cool the earth-atmosphere system with the most significant radiative effect in the tropics (corresponding to the location of the tropical stratospheric reservoir) and at latitudes greater than 60 deg. The high-latitude maximum is a combined effect of the high-latitude peak in optical depth (Trepte et al 1994) and the large solar zenith angles. The comparison of the predicted and measured net flux shows relatively good agreement, with the model consistently under predicting the cooling effect of the aerosol.

Radiative Forcing of the Pinatubo Aerosol as a Function of Latitude and Time

NASA Technical Reports Server (NTRS)

Bergstrom, Robert W.; Kinne, S.; Russell, P. B.; Bauman, J. J.; Minnis, P.

2000-01-01

We present calculations of the radiative forcing of the Mt. Pinatubo aerosols as a function of latitude and time after the eruption and compare the results with GOES satellite data. The results from the model indicate that the net effect of the aerosol was to cool the earth-atmosphere system with the most significant radiative effect in the tropics (corresponding to the location of the tropical stratospheric reservoir) and at latitudes greater than 60 degrees. The high-latitude maximum is a combined effect of the high-latitude peak in optical depth (Trepte et al 1994) and the large solar zenith angles. The comparison of the predicted and measured net flux shows relatively good agreement, with the model consistently under predicting the cooling effect of the aerosol.

Black carbon radiative forcing at TOA decreased during aging.

PubMed

Wu, Yu; Cheng, Tianhai; Zheng, Lijuan; Chen, Hao

2016-12-05

During aging processing, black carbon (also called soot) particles may tend to be mixed with other aerosols, and highly influence their radiative forcing. In this study, freshly emitted soot particles were simulated as fractal aggregates composed of small spherical primary monomers. After aging in the atmosphere, soot monomers were coated by a thinly layer of sulfate as thinly coated soot particles. These soot particles were entirely embedded into large sulfate particle by further aging, and becoming heavily coated soot particles. In clear-sky conditions, black carbon radiative forcing with different aging states were investigated for the bottom and top of atmosphere (BOA and TOA). The simulations showed that black carbon radiative forcing increased at BOA and decreased at TOA after their aging processes. Thinly and heavily coated states increased up to ~12% and ~35% black carbon radiative forcing at BOA, and black carbon radiative forcing at TOA can reach to ~20% and ~100% smaller for thinly and heavily coated states than those of freshly emitted states, respectively. The effect of aging states of black carbon radiative forcing was varied with surface albedo, aerosol optical depth and solar zenith angles. These findings would be helpful for the assessments of climate change.

Profile of heating rate due to aerosols using lidar and skyradiometer in SKYNET Hefei site

NASA Astrophysics Data System (ADS)

Wang, Z.; Liu, D.; Xie, C.

2015-12-01

Atmospheric aerosols have a significant impact on climate due to their important role in modifying atmosphere energy budget. On global scale, the direct radiative forcing is estimated to be in the range of -0.9 to -0.1 Wm-2 for aerosols [1]. Yet, these estimates are subject to very large uncertainties because of uncertainties in spatial and temporal variations of aerosols. At local scales, as aerosol properties can vary spatially and temporally, radiative forcing due to aerosols can be also very different and it can exceed the global value by an order of magnitude. Hence, it is very important to investigate aerosol loading, properties, and radiative forcing due to them in detail on local regions of climate significance. Haze and dust events in Hefei, China are explored by Lidar and Skyradiometer. Aerosol optical properties including the AOD, SSA, AAE and size distribution are analysed by using the SKYRAD.PACK [2] and presented in this paper. Furthermore, the radiative forcing due to aerosols and the heating rate in the ATM are also calculated using SBDART model [3]. The results are shown that the vertical heating rate is tightly related to aerosol profile. References: 1. IPCC. 2007. Climate Change 2007: The Physical Science Basic. Contribution of Working Group I Contribution to the Intergovernmental Panel on Climate Change Fourth Assessment Report. Solomon S, Qing D H, Manning M, et al. eds., Cambridge University Press, Cambridge, United Kingdom and New York, N Y, USA. 2. Nakajima, T., G. Tonna, R. Rao, Y. Kaufman, and B. Holben, 1996: Use of sky brightness measurements from ground for remote sensing of particulate poly dispersions, Appl. Opt., 35, 2672-2686. 3. Ricchiazzi et al 1998. SBDART: a research and teaching software tool for plane-parallel radiative transfer in the Earth's atmosphere,Bulletin of the American Meteorological Society,79,2101-2114.

Intercomparison of shortwave radiative transfer schemes in global aerosol modeling: results from the AeroCom Radiative Transfer Experiment

NASA Astrophysics Data System (ADS)

Randles, C. A.; Kinne, S.; Myhre, G.; Schulz, M.; Stier, P.; Fischer, J.; Doppler, L.; Highwood, E.; Ryder, C.; Harris, B.; Huttunen, J.; Ma, Y.; Pinker, R. T.; Mayer, B.; Neubauer, D.; Hitzenberger, R.; Oreopoulos, L.; Lee, D.; Pitari, G.; Di Genova, G.; Quaas, J.; Rose, Fred G.; Kato, S.; Rumbold, S. T.; Vardavas, I.; Hatzianastassiou, N.; Matsoukas, C.; Yu, H.; Zhang, F.; Zhang, H.; Lu, P.

2012-12-01

In this study we examine the performance of 31 global model radiative transfer schemes in cloud-free conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scattering-only aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multi-angular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly -10 to 20%, with over- and underestimates of radiative cooling at higher and lower sun elevation, respectively. Inter-model diversity (relative standard deviation) increases from ~10 to 15% as sun elevation increases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

Intercomparison of shortwave radiative transfer schemes in global aerosol modeling: results from the AeroCom Radiative Transfer Experiment

NASA Astrophysics Data System (ADS)

Randles, C. A.; Kinne, S.; Myhre, G.; Schulz, M.; Stier, P.; Fischer, J.; Doppler, L.; Highwood, E.; Ryder, C.; Harris, B.; Huttunen, J.; Ma, Y.; Pinker, R. T.; Mayer, B.; Neubauer, D.; Hitzenberger, R.; Oreopoulos, L.; Lee, D.; Pitari, G.; Di Genova, G.; Quaas, J.; Rose, F. G.; Kato, S.; Rumbold, S. T.; Vardavas, I.; Hatzianastassiou, N.; Matsoukas, C.; Yu, H.; Zhang, F.; Zhang, H.; Lu, P.

2013-03-01

In this study we examine the performance of 31 global model radiative transfer schemes in cloud-free conditions with prescribed gaseous absorbers and no aerosols (Rayleigh atmosphere), with prescribed scattering-only aerosols, and with more absorbing aerosols. Results are compared to benchmark results from high-resolution, multi-angular line-by-line radiation models. For purely scattering aerosols, model bias relative to the line-by-line models in the top-of-the atmosphere aerosol radiative forcing ranges from roughly -10 to 20%, with over- and underestimates of radiative cooling at lower and higher solar zenith angle, respectively. Inter-model diversity (relative standard deviation) increases from ~10 to 15% as solar zenith angle decreases. Inter-model diversity in atmospheric and surface forcing decreases with increased aerosol absorption, indicating that the treatment of multiple-scattering is more variable than aerosol absorption in the models considered. Aerosol radiative forcing results from multi-stream models are generally in better agreement with the line-by-line results than the simpler two-stream schemes. Considering radiative fluxes, model performance is generally the same or slightly better than results from previous radiation scheme intercomparisons. However, the inter-model diversity in aerosol radiative forcing remains large, primarily as a result of the treatment of multiple-scattering. Results indicate that global models that estimate aerosol radiative forcing with two-stream radiation schemes may be subject to persistent biases introduced by these schemes, particularly for regional aerosol forcing.

Key drivers of ozone change and its radiative forcing over the 21st century

NASA Astrophysics Data System (ADS)

Iglesias-Suarez, Fernando; Kinnison, Douglas E.; Rap, Alexandru; Maycock, Amanda C.; Wild, Oliver; Young, Paul J.

2018-05-01

Over the 21st century changes in both tropospheric and stratospheric ozone are likely to have important consequences for the Earth's radiative balance. In this study, we investigate the radiative forcing from future ozone changes using the Community Earth System Model (CESM1), with the Whole Atmosphere Community Climate Model (WACCM), and including fully coupled radiation and chemistry schemes. Using year 2100 conditions from the Representative Concentration Pathway 8.5 (RCP8.5) scenario, we quantify the individual contributions to ozone radiative forcing of (1) climate change, (2) reduced concentrations of ozone depleting substances (ODSs), and (3) methane increases. We calculate future ozone radiative forcings and their standard error (SE; associated with inter-annual variability of ozone) relative to year 2000 of (1) 33 ± 104 m Wm-2, (2) 163 ± 109 m Wm-2, and (3) 238 ± 113 m Wm-2 due to climate change, ODSs, and methane, respectively. Our best estimate of net ozone forcing in this set of simulations is 430 ± 130 m Wm-2 relative to year 2000 and 760 ± 230 m Wm-2 relative to year 1750, with the 95 % confidence interval given by ±30 %. We find that the overall long-term tropospheric ozone forcing from methane chemistry-climate feedbacks related to OH and methane lifetime is relatively small (46 m Wm-2). Ozone radiative forcing associated with climate change and stratospheric ozone recovery are robust with regard to background climate conditions, even though the ozone response is sensitive to both changes in atmospheric composition and climate. Changes in stratospheric-produced ozone account for ˜ 50 % of the overall radiative forcing for the 2000-2100 period in this set of simulations, highlighting the key role of the stratosphere in determining future ozone radiative forcing.

Negative radiation forces and the asymmetry of scattered radiation: spheres in Bessel beams

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Zhang, Likun

2011-11-01

The discovery that acoustical and optical, radiation forces computed on spheres placed on the axis of acoustical and optical Bessel beams may be opposite the direction of beam propagation makes it appropriate to reexamine the relationship between radiation forces and the asymmetry of the scattered radiation. For all of the previously identified acoustical cases in which the force was negative and the scattering pattern was also computed, it was found that the backscattering was suppressed and the forward scattering relatively enhanced (see e.g.). In the present research the acoustic radiation force on an arbitrary isotropic sphere is related to the asymmetry in the scattering and the extinction introduced by the sphere for the case of a helical Bessel beam of arbitrary order. The analysis confirms that conditions are more favorable for generating negative forces when the asymmetry is such that the backscattering is suppressed relative to the forward scattering. It is also found, however, that absorption of power by the sphere gives rise to a positive force contribution, a term which has been neglected in the corresponding optical analysis.

Degradation of the Adhesive Properties of MD-944 Diode Tape by Simulated Low Earth Orbit Environmental Factors

NASA Technical Reports Server (NTRS)

Albyn, K.; Finckenor, M.

2006-01-01

The International Space Station (ISS) solar arrays utilize MD-944 diode tape with silicone pressure-sensitive adhesive to protect the underlying diodes and also provide a high-emittance surface. On-orbit, the silicone adhesive will be exposed and ultimately convert to a glass-like silicate due to atomic oxygen (AO). The current operational plan is to retract ISS solar array P6 and leave it stored under load for a long duration (6 mo or more). The exposed silicone adhesive must not cause the solar array to stick to itself or cause the solar array to fail during redeployment. The Environmental Effects Branch at Marshall Space Flight Center, under direction from the ISS Program Office Environments Team, performed simulated space environment exposures with 5-eV AO, near ultraviolet radiation and ionizing radiation. The exposed diode tape samples were put under preload and then the resulting blocking force was measured using a tensile test machine. Test results indicate that high-energy AO, ultraviolet radiation, and electron ionizing radiation exposure all reduce the blocking force for a silicone-to-silicone bond. AO exposure produces the most significant reduction in blocking force

Simulations of Cloud-Radiation Interaction Using Large-Scale Forcing Derived from the CINDY/DYNAMO Northern Sounding Array

NASA Technical Reports Server (NTRS)

Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; Feng, Zhe; Comstock, Jennifer M.; Minnis, Patrick; Nordeen, Michele L.

2015-01-01

The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large-scale forcing data set derived from the DYNAMO northern sounding array observations, and carried out in a doubly periodic domain using the Weather Research and Forecasting (WRF) model. Simulated cloud properties and radiative fluxes are compared to those derived from the S-PolKa radar and satellite observations. To accommodate the uncertainty in simulated cloud microphysics, a number of single-moment (1M) and double-moment (2M) microphysical schemes in the WRF model are tested. The 1M schemes tend to underestimate radiative flux anomalies in the active phases of the MJO events, while the 2M schemes perform better, but can overestimate radiative flux anomalies. All the tested microphysics schemes exhibit biases in the shapes of the histograms of radiative fluxes and radar reflectivity. Histograms of radiative fluxes and brightness temperature indicate that radiative biases are not evenly distributed; the most significant bias occurs in rainy areas with OLR less than 150 W/ cu sq in the 2M schemes. Analysis of simulated radar reflectivities indicates that this radiative flux uncertainty is closely related to the simulated stratiform cloud coverage. Single-moment schemes underestimate stratiform cloudiness by a factor of 2, whereas 2M schemes simulate much more stratiform cloud.

Regional aerosol radiative and hydrological effects over the mid-Atlantic corridor

NASA Astrophysics Data System (ADS)

Creekmore, Torreon N.

A thorough assessment of direct, indirect, and semi-direct influences of aerosols on Earth's energy budget is required to better understand climate and estimate how it may change in the future. Clear-sky surface broadband (measured and modeled) irradiance, spectral aerosol optical depth, heating rate profiles, and non-radiative flux measurements were conducted at a state-of-the-art site, developed by the NOAA-Howard University Center for Atmospheric Sciences (NCAS) program, providing a best estimate of aerosol radiative atmosphere-surface interactions. Methods developed by the Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Program were applied to: (1) temporally quantify regional aerosol forcing, (2) to derive an empirical equation describing a relationship between aerosol optical depth and normalized diffuse ratio, (3) evaluate aerosol impacts on atmospheric heating, and (4) evaluate how aerosol forcing impacts may possibly reduce latent and sensible fluxes. Measurements were obtained during the period of May--September for the years of 2005, 2006, and 2007. Atmospheric aerosols are among the key uncertainties affecting the Earth's climate and atmospheric radiative processes. Present-day increases in aerosol concentrations directly, indirectly, and semi-directly impact the Earth's energy budget (i.e., cooling the surface and heating the atmosphere), thereby contributing to climate change. The Howard University Beltsville Site (HUBS) has experienced a greater loss in mean normalized aerosol radiative forcing with time, as observations show a decrease from --0.9 in 2005 to --3.1 and --3.4 W/m2 for 2006 and 2007 respectively, in mean net surface irradiance. The mean normalized aerosol radiative forcing estimated for the period considered was --2.5 W/m2. The reduction in surface solar insolation is due to increased scattering and absorption related to increased aerosol burdens v for the period, promoting surface cooling and atmospheric heating. Calculation of radiative flux and heating rates profiles, which are constrained by HUBS observations, were performed by the 1-D Fu-Liou radiative transfer model to investigate the effect of polluted and pristine aerosol conditions on the surface energy budget and hydrological cycle. For HUBS the surface forcing (--14.2 W/m2) and atmospheric forcing (9.9 W/m2) were significantly larger than the TOA (--4.3 W/m2) radiative forcing. Associated aerosol heating, as well as reduced surface insolation, may lead to increasing near surface static stability, and reduced vertical transport of moisture into the atmospheric boundary layer, and over time, a possible spin-down of the hydrological cycle. It is shown that HUBS provides an ideal opportunity for improving measurements and datasets, thus allowing for both the study and understanding of aerosol impacts on the climate system. Further, results show that in order to provide reference quality data and constrain aerosol radiative effects over land, ground-based research sites must conform to HUBS standards of: (1) instrumentation (e.g. passive and active sensors); (2) operational protocols (e.g. calibration and routine cleaning); (3) rigorous cloud screening protocols; and (4) incorporation of ARM QC and modified FFA algorithms. HUBS surface measurements provides the reference quality data necessary and capability required to help enhance measurements and constrain current uncertainties in estimates of aerosol direct effects over land. Incorporating a combined technique of both active and passive instruments reduced the direct radiative forcing estimates by ˜82 W/m2. The analysis of aerosol effects over HUBS helps continue in bridging the gap of applying measurements for improvement of climate simulations by generating observational products, which describes aerosol and radiation field characteristics in detail.

Variability of aerosol optical depth and aerosol radiative forcing over Northwest Himalayan region

NASA Astrophysics Data System (ADS)

Saheb, Shaik Darga; Kant, Yogesh; Mitra, D.

2016-05-01

In recent years, the aerosol loading in India is increasing that has significant impact on the weather/climatic conditions. The present study discusses the analysis of temporal (monthly and seasonal) variation of aerosol optical depth(AOD) by the ground based observations from sun photometer and estimate the aerosol radiative forcing and heating rate over selected station Dehradun in North western Himalayas, India during 2015. The in-situ measurements data illustrate that the maximum seasonal average AOD observed during summer season AOD at 500nm ≍ 0.59+/-0.27 with an average angstrom exponent, α ≍0.86 while minimum during winter season AOD at 500nm ≍ 0.33+/-0.10 with angstrom exponent, α ≍1.18. The MODIS and MISR derived AOD was also compared with the ground measured values and are good to be in good agreement. Analysis of air mass back trajectories using HYSPLIT model reveal that the transportation of desert dust during summer months. The Optical Properties of Aerosols and clouds (OPAC) model was used to compute the aerosol optical properties like single scattering albedo (SSA), Angstrom coefficient (α) and Asymmetry(g) parameter for each day of measurement and they are incorporated in a Discrete Ordinate Radiative Transfer model, i.e Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) to estimate the direct short-wave (0.25 to 4 μm) Aerosol Radiative forcing at the Surface (SUR), the top-of-atmosphere (TOA) and Atmosphere (ATM). The maximum Aerosol Radiative Forcing (ARF) was observed during summer months at SUR ≍ -56.42 w/m2, at TOA ≍-21.62 w/m2 whereas in ATM ≍+34.79 w/m2 with corresponding to heating rate 1.24°C/day with in lower atmosphere.

Impact of mountain pine beetle outbreaks on forest albedo and radiative forcing, as derived from Moderate Resolution Imaging Spectroradiometer, Rocky Mountains, USA

NASA Astrophysics Data System (ADS)

Vanderhoof, M.; Williams, C. A.; Ghimire, B.; Rogan, J.

2013-12-01

pine beetle (Dendroctonus ponderosae) outbreaks in North America are widespread and have potentially large-scale impacts on albedo and associated radiative forcing. Mountain pine beetle outbreaks in Colorado and southern Wyoming have resulted in persistent and significant increases in both winter albedo (change peaked 10 years post outbreak at 0.06 ± 0.01 and 0.05 ± 0.01, in lodgepole pine (Pinus contorta) and ponderosa pine (Pinus ponderosa) stands, respectively) and spring albedo (change peaked 10 years post outbreak at 0.06 ± 0.01 and 0.04 ± 0.01, in lodgepole pine and ponderosa pine stands, respectively). Instantaneous top-of-atmosphere radiative forcing peaked for both lodgepole pine and ponderosa pine stands in winter at 10 years post outbreak at -1.7 ± 0.2 W m-2 and -1.4 ± 0.2 W m-2, respectively. The persistent increase in albedo with time since mountain pine beetle disturbance combined with the continued progression of the attack across the landscape from 1994-2011 resulted in an exponential increase in winter and annual radiative cooling (MW) over time. In 2011 the rate of radiative forcing within the study area reached -982.7 ± 139.0 MW, -269.8 ± 38.2 MW, -31.1 ± 4.4 MW, and -147.8 ± 20.9 MW in winter, spring, summer, and fall, respectively. An increase in radiative cooling has the potential to decrease sensible and/or latent heat flux by reducing available energy. Such changes could affect current mountain pine beetle outbreaks which are influenced by climatic conditions.

Strong enhancement of dispersion forces from microwave radiation

NASA Astrophysics Data System (ADS)

Sernelius, B. E.

2002-11-01

We have studied non-thermal effects of microwave radiation on the forces between objects. This is the first step in a study of possible effects of microwave radiation from cellular phones on biological tissue. We have used a simplified model for human blood cells in blood. We find for the normal radiation level of cellular phones an enhancement of the attractive force with ten orders of magnitude as compared to the corresponding effect at thermal radiation.

The influence of hepatic steatosis on the evaluation of fibrosis with non-alcoholic fatty liver disease by acoustic radiation force impulse.

PubMed

Yanrong Guo; Haoming Lin; Xinyu Zhang; Huiying Wen; Siping Chen; Xin Chen

2017-07-01

Acoustic radiation force impulse (ARFI) elastography is a non-invasive method for the assessment of liver by measuring liver stiffness. The aim of this study is to evaluate the accuracy of ARFI for the diagnosis of liver fibrosis and to assess impact of steatosis on liver fibrosis stiffness measurement, in rats model of non-alcoholic fatty liver disease (NAFLD). The rat models were conducted in 59 rats. The right liver lobe was processed and embedded in a fabricated gelatin solution. Liver mechanics were measured using shear wave velocity (SWV) induced by acoustic radiation force. In rats with NAFLD, the diagnostic performance of ARFI elastography in predicting severe fibrosis (F ≥ 3) and cirrhosis (F ≥ 4) had the areas under the receiver operating characteristic curves (AUROC) of 0.993 and 0.985. Among rats mean SWV values were significantly higher in rats with severe steatosis by histology compared to those mild or without steatosis for F0-F2 fibrosis stages (3.07 versus 2.51 m/s, P = 0.01). ARFI elastography is a promising method for staging hepatic fibrosis with NAFLD in rat models. The presence of severe steatosis is a significant factor for assessing the lower stage of fibrosis.

Long-term Satellite Observations of Cloud and Aerosol Radiative Effects Using the (A)ATSR Satellite Data Record

NASA Astrophysics Data System (ADS)

Christensen, M.; McGarragh, G.; Thomas, G.; Povey, A.; Proud, S.; Poulsen, C. A.; Grainger, R. G.

2016-12-01

Radiative forcing by clouds, aerosols, and their interactions constitute some of the largest sources of uncertainties in the climate system (Chapter 7 IPCC, 2013). It is essential to understand the past through examination of long-term satellite observation records to provide insight into the uncertainty characteristics of these radiative forcers. As part of the ESA CCI (Climate Change Initiative) we have recently implemented a broadband radiative flux algorithm (known as BUGSrad) into the Optimal Retrieval for Aerosol and Cloud (ORAC) scheme. ORAC achieves radiative consistency of its aerosol and cloud products through an optimal estimation scheme and is highly versatile, enabling retrievals for numerous satellite sensors: ATSR, MODIS, VIIRS, AVHRR, SLSTR, SEVIRI, and AHI. An analysis of the 17-year well-calibrated Along Track Scanning Radiometer (ATSR) data is used to quantify trends in cloud and aerosol radiative effects over a wide range of spatiotemporal scales. The El Niño Southern Oscillation stands out as the largest contributing mode of variability to the radiative energy balance (long wave and shortwave fluxes) at the top of the atmosphere. Furthermore, trends in planetary albedo show substantial decreases across the Arctic Ocean (likely due to the melting of sea ice and snow) and modest increases in regions dominated by stratocumulus (e.g., off the coast of California) through notable increases in cloud fraction and liquid water path. Finally, changes in volcanic activity and biomass burning aerosol over this period show sizeable radiative forcing impacts at local-scales. We will demonstrate that radiative forcing from aerosols and clouds have played a significant role in the identified key climate processes using 17 years of satellite observational data.

First Estimates of the Radiative Forcing of Aerosols Generated from Biomass Burning using Satellite Data

NASA Technical Reports Server (NTRS)

Chistopher, Sundar A.; Kliche, Donna V.; Chou, Joyce; Welch, Ronald M.

1996-01-01

Collocated measurements from the Advanced Very High Resolution Radiometer (AVHRR) and the Earth Radiation Budget Experiment (ERBE) scanner are used to examine the radiative forcing of atmospheric aerosols generated from biomass burning for 13 images in South America. Using the AVHRR, Local Area Coverage (LAC) data, a new technique based on a combination of spectral and textural measures is developed for detecting these aerosols. Then, the instantaneous shortwave, longwave, and net radiative forcing values are computed from the ERBE instantaneous scanner data. Results for the selected samples from 13 images show that the mean instantaneous net radiative forcing for areas with heavy aerosol loading is about -36 W/sq m and that for the optically thin aerosols are about -16 W/sq m. These results, although preliminary, provide the first estimates of radiative forcing of atmospheric aerosols from biomass burning using satellite data.

First Estimates of the Radiative Forcing of Aerosols Generated from Biomass Burning Using Satellite Data

NASA Technical Reports Server (NTRS)

Christopher, Sundar A.; Kliche, Donna A.; Chou, Joyce; Welch, Ronald M.

1996-01-01

Collocated measurements from the Advanced Very High Resolution Radiometer (AVHRR) and the Earth Radiation Budget Experiment (ERBE) scanner are used to examine the radiative forcing of atmospheric aerosols generated from biomass burning for 13 images in South America. Using the AVHRR, Local Area Coverage (LAC) data, a new technique based on a combination of spectral and textural measures is developed for detecting these aerosols. Then, the instantaneous shortwave, longwave, and net radiative forcing values are computed from the ERBE instantaneous scanner data. Results for the selected samples from 13 images show that the mean instantaneous net radiative forcing for areas with heavy aerosol loading is about -36 W/sq m and that for the optically thin aerosols are about -16 W/sq m. These results, although preliminary, provide the first estimates of radiative forcing of atmospheric aerosols from biomass burning using satellite data.

Variation in Rising Limb of Colorado River Snowmelt Runoff Hydrograph Controlled by Dust Radiative Forcing in Snow

NASA Astrophysics Data System (ADS)

Painter, Thomas H.; Skiles, S. McKenzie; Deems, Jeffrey S.; Brandt, W. Tyler; Dozier, Jeff

2018-01-01

Common practice and conventional wisdom hold that fluctuations in air temperature control interannual variability in snowmelt and subsequent river runoff. However, recent observations in the Upper Colorado River Basin confirm that net solar radiation and by extension radiative forcing by dust deposited on snow cover exerts the primary forcing on snowmelt. We show that the variation in the shape of the rising limb of the annual hydrograph is controlled by variability in dust radiative forcing and surprisingly is independent of variations in winter and spring air temperatures. These observations suggest that hydroclimatic modeling must be improved to account for aerosol forcings of the water cycle. Anthropogenic climate change will likely reduce total snow accumulations and cause snowmelt runoff to occur earlier. However, dust radiative forcing of snowmelt is likely consuming important adaptive capacity that would allow human and natural systems to be more resilient to changing hydroclimatic conditions.

Direct Aerosol Radiative Forcing: Calculations and Measurements from the Tropospheric

NASA Technical Reports Server (NTRS)

Russell, P. B.; Hignett, P.; Stowe, L. L.; Livingston, J. M.; Kinne, S.; Wong, J.; Chan, K. Roland (Technical Monitor)

1997-01-01

Radiative forcing is defined as the change in the net (downwelling minus upwelling) radiative flux at a given level in the atmosphere. This net flux is the radiative power density available to drive climatic processes in the earth-atmosphere system below that level. Recent research shows that radiative forcing by aerosol particles is a major source of uncertainty in climate predictions. To reduce those uncertainties, TARFOX was designed to determine direct (cloud-free) radiative forcing by the aerosols in one of the world's major industrial pollution plumes--that flowing from the east coast of the US over the Atlantic Ocean. TARFOX measured a variety of aerosol radiative effects (including direct forcing) while simultaneously measuring the chemical, physical, and optical properties of the aerosol particles causing those effects. The resulting data sets permit a wide variety of tests of the consistency, or closure, among the measurements and the models that link them. Because climate predictions use the same or similar model components, closure tests help to assess and reduce prediction uncertainties. In this work we use the TARFOX-determined aerosol, gas, and surface properties to compute radiative forcing for a variety of aerosol episodes, with inadvisable optical depths ranging from 0.07 to 0.6. We calculate forcing by several techniques with varying degrees of sophistication, in part to test the range of applicability of simplified techniques--which are often the only ones feasible in climate predictions by general circulation models (GCMs). We then compare computed forcing to that determined from: (1) Upwelling and downwelling fluxes (0.3-0.7 mm and 0.7-3.0 mm) measured by radiometers on the UK MRF C-130. and (2) Daily average cloud-free absorbed solar and emitted thermal radiative flux at the top of the atmosphere derived from the AVHRR radiometer on the NOAA- 14 satellite. The calculations and measurements all yield aerosol direct radiative forcing in the range -50 to -190 W sq m per unit inadvisable optical depth. The magnitudes are about 15 to 100 times larger than the global-average direct forcing expected for the global-average sulfate aerosol optical depth of 0.04. The reasons for the larger forcing in TARFOX include the relatively large optical depths and the focus on cloud-free, daytime conditions over the dark ocean surface. These are the conditions that produce the actual major radiative forcing events that contribute to any global-average climate effect. Detailed comparisons of calculated and measured forcings for specific events are used for more refined tests of closure.

Methodologies in the modeling of combined chemo-radiation treatments

NASA Astrophysics Data System (ADS)

Grassberger, C.; Paganetti, H.

2016-11-01

The variety of treatment options for cancer patients has increased significantly in recent years. Not only do we combine radiation with surgery and chemotherapy, new therapeutic approaches such as immunotherapy and targeted therapies are starting to play a bigger role. Physics has made significant contributions to radiation therapy treatment planning and delivery. In particular, treatment plan optimization using inverse planning techniques has improved dose conformity considerably. Furthermore, medical physics is often the driving force behind tumor control and normal tissue complication modeling. While treatment optimization and outcome modeling does focus mainly on the effects of radiation, treatment modalities such as chemotherapy are treated independently or are even neglected entirely. This review summarizes the published efforts to model combined modality treatments combining radiation and chemotherapy. These models will play an increasing role in optimizing cancer therapy not only from a radiation and drug dosage standpoint, but also in terms of spatial and temporal optimization of treatment schedules.

Active noise control using noise source having adaptive resonant frequency tuning through stiffness variation

NASA Technical Reports Server (NTRS)

Rajiyah, Harindra (Inventor); Hedeen, Robert A. (Inventor); Pla, Frederic G. (Inventor); Renshaw, Anthony A. (Inventor)

1995-01-01

A noise source for an aircraft engine active noise cancellation system in which the resonant frequency of a noise radiating element is tuned to permit noise cancellation over a wide range of frequencies. The resonant frequency of the noise radiating element is tuned by a plurality of force transmitting mechanisms which contact the noise radiating element. Each one of the force transmitting mechanisms includes an expandable element and a spring in contact with the noise radiating element so that excitation of the element varies the spring force applied to the noise radiating element. The elements are actuated by a controller which receives input of a signal proportional to displacement of the noise radiating element and a signal corresponding to the blade passage frequency of the engine's fan. In response, the controller determines a control signal which is sent to the elements and causes the spring force applied to the noise radiating element to be varied. The force transmitting mechanisms can be arranged to either produce bending or linear stiffness variations in the noise radiating element.

Radiation Forces and Torques without Stress (Tensors)

ERIC Educational Resources Information Center

Bohren, Craig F.

2011-01-01

To understand radiation forces and torques or to calculate them does not require invoking photon or electromagnetic field momentum transfer or stress tensors. According to continuum electromagnetic theory, forces and torques exerted by radiation are a consequence of electric and magnetic fields acting on charges and currents that the fields induce…

Spectral shifting strongly constrains molecular cloud disruption by radiation pressure on dust

NASA Astrophysics Data System (ADS)

Reissl, Stefan; Klessen, Ralf S.; Mac Low, Mordecai-Mark; Pellegrini, Eric W.

2018-03-01

Aim. We aim to test the hypothesis that radiation pressure from young star clusters acting on dust is the dominant feedback agent disrupting the largest star-forming molecular clouds and thus regulating the star-formation process. Methods: We performed multi-frequency, 3D, radiative transfer calculations including both scattering and absorption and re-emission to longer wavelengths for model clouds with masses of 104-107 M⊙, containing embedded clusters with star formation efficiencies of 0.009-91%, and varying maximum grain sizes up to 200 μm. We calculated the ratio between radiative and gravitational forces to determine whether radiation pressure can disrupt clouds. Results: We find that radiation pressure acting on dust almost never disrupts star-forming clouds. Ultraviolet and optical photons from young stars to which the cloud is optically thick do not scatter much. Instead, they quickly get absorbed and re-emitted by the dust at thermal wavelengths. As the cloud is typically optically thin to far-infrared radiation, it promptly escapes, depositing little momentum in the cloud. The resulting spectrum is more narrowly peaked than the corresponding Planck function, and exhibits an extended tail at longer wavelengths. As the opacity drops significantly across the sub-mm and mm wavelength regime, the resulting radiative force is even smaller than for the corresponding single-temperature blackbody. We find that the force from radiation pressure falls below the strength of gravitational attraction by an order of magnitude or more for either Milky Way or moderate starbust conditions. Only for unrealistically large maximum grain sizes, and star formation efficiencies far exceeding 50% do we find that the strength of radiation pressure can exceed gravity. Conclusions: We conclude that radiation pressure acting on dust does not disrupt star-forming molecular clouds in any Local Group galaxies. Radiation pressure thus appears unlikely to regulate the star-formation process on either local or global scales.

Radiative forcing over the conterminous United States due to contemporary land cover land use albedo change

USGS Publications Warehouse

Barnes, Christopher; Roy, David P.

2008-01-01

Recently available satellite land cover land use (LCLU) and albedo data are used to study the impact of LCLU change from 1973 to 2000 on surface albedo and radiative forcing for 36 ecoregions covering 43% of the conterminous United States (CONUS). Moderate Resolution Imaging Spectroradiometer (MODIS) snow-free broadband albedo values are derived from Landsat LCLU classification maps located using a stratified random sampling methodology to estimate ecoregion estimates of LCLU induced albedo change and surface radiative forcing. The results illustrate that radiative forcing due to LCLU change may be disguised when spatially and temporally explicit data sets are not used. The radiative forcing due to contemporary LCLU albedo change varies geographically in sign and magnitude, with the most positive forcings (up to 0.284 Wm−2) due to conversion of agriculture to other LCLU types, and the most negative forcings (as low as −0.247 Wm−2) due to forest loss. For the 36 ecoregions considered a small net positive forcing (i.e., warming) of 0.012 Wm−2 is estimated.

The Aerosol Coarse Mode Initiative

NASA Astrophysics Data System (ADS)

Arnott, W. P.; Adhikari, N.; Air, D.; Kassianov, E.; Barnard, J.

2014-12-01

Many areas of the world show an aerosol volume distribution with a significant coarse mode and sometimes a dominant coarse mode. The large coarse mode is usually due to dust, but sea salt aerosol can also play an important role. However, in many field campaigns, the coarse mode tends to be ignored, because it is difficult to measure. This lack of measurements leads directly to a concomitant "lack of analysis" of this mode. Because, coarse mode aerosols can have significant effects on radiative forcing, both in the shortwave and longwave spectrum, the coarse mode -- and these forcings -- should be accounted for in atmospheric models. Forcings based only on fine mode aerosols have the potential to be misleading. In this paper we describe examples of large coarse modes that occur in areas of large aerosol loading (Mexico City, Barnard et al., 2010) as well as small loadings (Sacramento, CA; Kassianov et al., 2012; and Reno, NV). We then demonstrate that: (1) the coarse mode can contribute significantly to radiative forcing, relative to the fine mode, and (2) neglecting the coarse mode may result in poor comparisons between measurements and models. Next we describe -- in general terms -- the limitations of instrumentation to measure the coarse mode. Finally, we suggest a new initiative aimed at examining coarse mode aerosol generation mechanisms; transport and deposition; chemical composition; visible and thermal IR refractive indices; morphology; microphysical behavior when deposited on snow and ice; and specific instrumentation needs. Barnard, J. C., J. D. Fast, G. Paredes-Miranda, W. P. Arnott, and A. Laskin, 2010: Technical Note: Evaluation of the WRF-Chem "Aerosol Chemical to Aerosol Optical Properties" Module using data from the MILAGRO campaign, Atmospheric Chemistry and Physics, 10, 7325-7340. Kassianov, E. I., M. S. Pekour, and J. C. Barnard, 2012: Aerosols in Central California: Unexpectedly large contribution of coarse mode to aerosol radiative forcing, Geophys. Res. Lett., 39, L20806, doi:10.1029/2012GL053469.

Satellite-derived aerosol radiative forcing from the 2004 British Columbia wildfires

USGS Publications Warehouse

Guo, Song; Leighton, H.

2008-01-01

The British Columbia wildfires of 2004 was one of the largest wildfire events in the last ten years in Canada. Both the shortwave and longwave smoke aerosol radiative forcing at the top-of-atmosphere (TOA) are investigated using data from the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Clouds and the Earth's Radiant Energy System (CERES) instruments. Relationships between the radiative forcing fluxes (??F) and wildfire aerosol optical thickness (AOT) at 0.55 ??m (??0.55) are deduced for both noontime instantaneous forcing and diurnally averaged forcing. The noontime averaged instantaneous shortwave and longwave smoke aerosol radiative forcing at the TOA are 45.8??27.5 W m-2 and -12.6??6.9 W m-2, respectively for a selected study area between 62??N and 68??N in latitude and 125??W and 145??W in longitude over three mainly clear-sky days (23-25 June). The derived diurnally averaged smoke aerosol shortwave radiative forcing is 19.9??12.1 W m-2 for a mean ??0.55 of 1.88??0.71 over the same time period. The derived ??F-?? relationship can be implemented in the radiation scheme used in regional climate models to assess the effect of wildfire aerosols.

Sensitivity of the radiative forcing by stratospheric sulfur geoengineering to the amount and strategy of the SO2injection studied with the LMDZ-S3A model

NASA Astrophysics Data System (ADS)

Kleinschmitt, Christoph; Boucher, Olivier; Platt, Ulrich

2018-02-01

The enhancement of the stratospheric sulfate aerosol layer has been proposed as a method of geoengineering to abate global warming. Previous modelling studies found that stratospheric aerosol geoengineering (SAG) could effectively compensate for the warming by greenhouse gases on the global scale, but also that the achievable cooling effect per sulfur mass unit, i.e. the forcing efficiency, decreases with increasing injection rate. In this study we use the atmospheric general circulation model LMDZ with the sectional aerosol module S3A to determine how the forcing efficiency depends on the injected amount of SO2, the injection height, and the spatio-temporal pattern of injection. We find that the forcing efficiency may decrease more drastically for larger SO2 injections than previously estimated. As a result, the net instantaneous radiative forcing does not exceed the limit of -2 W m-2 for continuous equatorial SO2 injections and it decreases (in absolute value) for injection rates larger than 20 Tg S yr-1. In contrast to other studies, the net radiative forcing in our experiments is fairly constant with injection height (in a range 17 to 23 km) for a given amount of SO2 injected. Also, spreading the SO2 injections between 30° S and 30° N or injecting only seasonally from varying latitudes does not result in a significantly larger (i.e. more negative) radiative forcing. Other key characteristics of our simulations include a consequent stratospheric heating, caused by the absorption of solar and infrared radiation by the aerosol, and changes in stratospheric dynamics, with a collapse of the quasi-biennial oscillation at larger injection rates, which has impacts on the resulting spatial aerosol distribution, size, and optical properties. But it has to be noted that the complexity and uncertainty of stratospheric processes cause considerable disagreement among different modelling studies of stratospheric aerosol geoengineering. This may be addressed through detailed model intercomparison activities, as observations to constrain the simulations of stratospheric aerosol geoengineering are not available and analogues (such as volcanic eruptions) are imperfect.

Second harmonic generation efficiency affected by radiation force of a high-energy laser beam through stress within a mounted potassium dihydrogen phosphate crystal

NASA Astrophysics Data System (ADS)

Su, Ruifeng; Zhu, Mingzhi; Huang, Zhan; Wang, Baoxu; Wu, Wenkai

2018-01-01

Influence of radiation force of a high-energy laser beam on the second harmonic generation (SHG) efficiency through stress within a mounted potassium dihydrogen phosphate (KDP) crystal is studied, as well as an active method of improving the SHG efficiency by controlling the stress is proposed. At first, the model for studying the influence of the radiation force on the SHG efficiency is established, where the radiation force is theoretically analyzed, the stress caused by the radiation force is theoretically analyzed and numerically calculated using the finite-element method, and the influence of the stress on the SHG efficiency is theoretically analyzed. Then, a method of improving the SHG efficiency by controlling the stress through adjusting the structural parameters of the mounting set of the KDP crystal is examined. It demonstrates that the radiation force causes stress within the KDP crystal and further militates against the SHG efficiency; however, the SHG efficiency could be improved by controlling the stress through adjusting the structural parameters of the mounting set of the KDP crystal.

Negative radiation forces on spheres illuminated by acoustic Bessel beams.

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Thiessen, David B.

2007-11-01

An analytical solution for the scattering of an acoustic Bessel beam by a sphere centered on the beam has made it possible to explore the way the acoustic radiation force on elastic and fluid spheres depends on beam and material parameters. Situations have been previously noted where, even in the absence of absorption, the radiation force of the beam on the sphere is opposite the direction of beam propagation [1]. In extensions of that work, conditions have been identified for such a force reversal on solid spheres and elastic shells. Negative radiation forces may be useful for manipulation of objects in reduced gravity and of biological cells (with single beam acoustic tweezers). The finite element method (FEM) has been used to evaluate the total acoustic field in the region near the sphere. This makes it possible to evaluate the radiation force from numerical integration of an appropriate projection of the Brillouin radiation stress tensor. FEM and analytical results agree for plane wave and Bessel beam illumination. 1. P. L. Marston, J. Acoust. Soc. Am. 120, 3518-3524 (2006).

Observationally constrained estimates of carbonaceous aerosol radiative forcing.

PubMed

Chung, Chul E; Ramanathan, V; Decremer, Damien

2012-07-17

Carbonaceous aerosols (CA) emitted by fossil and biomass fuels consist of black carbon (BC), a strong absorber of solar radiation, and organic matter (OM). OM scatters as well as absorbs solar radiation. The absorbing component of OM, which is ignored in most climate models, is referred to as brown carbon (BrC). Model estimates of the global CA radiative forcing range from 0 to 0.7 Wm(-2), to be compared with the Intergovernmental Panel on Climate Change's estimate for the pre-Industrial to the present net radiative forcing of about 1.6 Wm(-2). This study provides a model-independent, observationally based estimate of the CA direct radiative forcing. Ground-based aerosol network data is integrated with field data and satellite-based aerosol observations to provide a decadal (2001 through 2009) global view of the CA optical properties and direct radiative forcing. The estimated global CA direct radiative effect is about 0.75 Wm(-2) (0.5 to 1.0). This study identifies the global importance of BrC, which is shown to contribute about 20% to 550-nm CA solar absorption globally. Because of the inclusion of BrC, the net effect of OM is close to zero and the CA forcing is nearly equal to that of BC. The CA direct radiative forcing is estimated to be about 0.65 (0.5 to about 0.8) Wm(-2), thus comparable to or exceeding that by methane. Caused in part by BrC absorption, CAs have a net warming effect even over open biomass-burning regions in Africa and the Amazon.

Observationally constrained estimates of carbonaceous aerosol radiative forcing

PubMed Central

Chung, Chul E.; Ramanathan, V.; Decremer, Damien

2012-01-01

Carbonaceous aerosols (CA) emitted by fossil and biomass fuels consist of black carbon (BC), a strong absorber of solar radiation, and organic matter (OM). OM scatters as well as absorbs solar radiation. The absorbing component of OM, which is ignored in most climate models, is referred to as brown carbon (BrC). Model estimates of the global CA radiative forcing range from 0 to 0.7 Wm-2, to be compared with the Intergovernmental Panel on Climate Change’s estimate for the pre-Industrial to the present net radiative forcing of about 1.6 Wm-2. This study provides a model-independent, observationally based estimate of the CA direct radiative forcing. Ground-based aerosol network data is integrated with field data and satellite-based aerosol observations to provide a decadal (2001 through 2009) global view of the CA optical properties and direct radiative forcing. The estimated global CA direct radiative effect is about 0.75 Wm-2 (0.5 to 1.0). This study identifies the global importance of BrC, which is shown to contribute about 20% to 550-nm CA solar absorption globally. Because of the inclusion of BrC, the net effect of OM is close to zero and the CA forcing is nearly equal to that of BC. The CA direct radiative forcing is estimated to be about 0.65 (0.5 to about 0.8) Wm-2, thus comparable to or exceeding that by methane. Caused in part by BrC absorption, CAs have a net warming effect even over open biomass-burning regions in Africa and the Amazon. PMID:22753522

Effect of cloud cover and surface type on earth's radiation budget derived from the first year of ERBE data

NASA Technical Reports Server (NTRS)

Gibson, G. G.; Denn, F. M.; Young, D. F.; Harrison, E. F.; Minnis, P.; Barkstrom, B. R.

1990-01-01

One year of ERBE data is analyzed for variations in outgoing LW and absorbed solar flux. Differences in land and ocean radiation budgets as well as differences between clear-sky and total scenes, including clouds, are studied. The variation of monthly average radiative parameters is examined for February 1985 through January 1986 for selected study regions and on zonal and global scales. ERBE results show significant seasonal variations in both outgoing LW and absorbed SW flux, and a pronounced difference between oceanic and continental surfaces. The main factors determining cloud radiative forcing in a given region are solar insolation, cloud amount, cloud type, and surface properties. The strongest effects of clouds are found in the midlatitude storm tracks over the oceans. Over much of the globe, LW warming is balanced by SW cooling. The annual-global average net cloud forcing shows that clouds have a net cooling effect on the earth for the year.

Simulations of cloud-radiation interaction using large-scale forcing derived from the CINDY/DYNAMO northern sounding array

DOE PAGES

Wang, Shuguang; Sobel, Adam H.; Fridlind, Ann; ...

2015-09-25

The recently completed CINDY/DYNAMO field campaign observed two Madden-Julian oscillation (MJO) events in the equatorial Indian Ocean from October to December 2011. Prior work has indicated that the moist static energy anomalies in these events grew and were sustained to a significant extent by radiative feedbacks. We present here a study of radiative fluxes and clouds in a set of cloud-resolving simulations of these MJO events. The simulations are driven by the large scale forcing dataset derived from the DYNAMO northern sounding array observations, and carried out in a doubly-periodic domain using the Weather Research and Forecasting (WRF) model. simulatedmore » cloud properties and radiative fluxes are compared to those derived from the S-Polka radar and satellite observations. Furthermore, to accommodate the uncertainty in simulated cloud microphysics, a number of single moment (1M) and double moment (2M) microphysical schemes in the WRF model are tested.« less

Aerosol Direct Radiative Effects and Heating in the New Era of Active Satellite Observations

NASA Astrophysics Data System (ADS)

Matus, Alexander V.

Atmospheric aerosols impact the global energy budget by scattering and absorbing solar radiation. Despite their impacts, aerosols remain a significant source of uncertainty in our ability to predict future climate. Multi-sensor observations from the A-Train satellite constellation provide valuable observational constraints necessary to reduce uncertainties in model simulations of aerosol direct effects. This study will discuss recent efforts to quantify aerosol direct effects globally and regionally using CloudSat's radiative fluxes and heating rates product. Improving upon previous techniques, this approach leverages the capability of CloudSat and CALIPSO to retrieve vertically resolved estimates of cloud and aerosol properties critical for accurately evaluating the radiative impacts of aerosols. We estimate the global annual mean aerosol direct effect to be -1.9 +/- 0.6 W/m2, which is in better agreement with previously published estimates from global models than previous satellite-based estimates. Detailed comparisons against a fully coupled simulation of the Community Earth System Model, however, reveal that this agreement on the global annual mean masks large regional discrepancies between modeled and observed estimates of aerosol direct effects related to model biases in cloud cover. A low bias in stratocumulus cloud cover over the southeastern Pacific Ocean, for example, leads to an overestimate of the radiative effects of marine aerosols. Stratocumulus clouds over the southeastern Atlantic Ocean can enhance aerosol absorption by 50% allowing aerosol layers to remain self-lofted in an area of subsidence. Aerosol heating is found to peak at 0.6 +/- 0.3 K/day an altitude of 4 km in September when biomass burning reaches a maximum. Finally, the contributions of observed aerosols components are evaluated to estimate the direct radiative forcing of anthropogenic aerosols. Aerosol forcing is computed using satellite-based radiative kernels that describe the sensitivity of shortwave fluxes in response to aerosol optical depth. The direct radiative forcing is estimated to be -0.21 W/m2 with the largest contributions from pollution that is partially offset by a positive forcing from smoke aerosols. The results from these analyses provide new benchmarks on the global radiative effects of aerosols and offer new insights for improving future assessments.

Global warming and ocean stratification: A potential result of large extraterrestrial impacts

NASA Astrophysics Data System (ADS)

Joshi, Manoj; von Glasow, Roland; Smith, Robin S.; Paxton, Charles G. M.; Maycock, Amanda C.; Lunt, Daniel J.; Loptson, Claire; Markwick, Paul

2017-04-01

The prevailing paradigm for the climatic effects of large asteroid or comet impacts is a reduction in sunlight and significant short-term cooling caused by atmospheric aerosol loading. Here we show, using global climate model experiments, that the large increases in stratospheric water vapor that can occur upon impact with the ocean cause radiative forcings of over +20 W m-2 in the case of 10 km sized bolides. The result of such a positive forcing is rapid climatic warming, increased upper ocean stratification, and potentially disruption of upper ocean ecosystems. Since two thirds of the world's surface is ocean, we suggest that some bolide impacts may actually warm climate overall. For impacts producing both stratospheric water vapor and aerosol loading, radiative forcing by water vapor can reduce or even cancel out aerosol-induced cooling, potentially causing 1-2 decades of increased temperatures in both the upper ocean and on the land surface. Such a response, which depends on the ratio of aerosol to water vapor radiative forcing, is distinct from many previous scenarios for the climatic effects of large bolide impacts, which mostly account for cooling from aerosol loading. Finally, we discuss how water vapor forcing from bolide impacts may have contributed to two well-known phenomena: extinction across the Cretaceous/Paleogene boundary and the deglaciation of the Neoproterozoic snowball Earth.

Annotated Bibliography: Polymers in Concrete.

DTIC Science & Technology

1982-10-01

under the general supervision of Mr. Bryant Mather, Chief, SL, and Mr. John Scanlon, Chief, Concrete Technology Division , SL, and under the direct...Foreign Technology Division , Wright-Patterson Air Force Base, Ohio. The shrinkage effect on concrete is a significant factor in solving the problem of using...Infrared Radiation," p 13, Jun 1974, Foreign Technology Division , Wright-Patterson Air Force Base, Ohio. Infrared irradiation is an effective means of

Accurate Satellite-Derived Estimates of Tropospheric Ozone Radiative Forcing

NASA Technical Reports Server (NTRS)

Joiner, Joanna; Schoeberl, Mark R.; Vasilkov, Alexander P.; Oreopoulos, Lazaros; Platnick, Steven; Livesey, Nathaniel J.; Levelt, Pieternel F.

2008-01-01

Estimates of the radiative forcing due to anthropogenically-produced tropospheric O3 are derived primarily from models. Here, we use tropospheric ozone and cloud data from several instruments in the A-train constellation of satellites as well as information from the GEOS-5 Data Assimilation System to accurately estimate the instantaneous radiative forcing from tropospheric O3 for January and July 2005. We improve upon previous estimates of tropospheric ozone mixing ratios from a residual approach using the NASA Earth Observing System (EOS) Aura Ozone Monitoring Instrument (OMI) and Microwave Limb Sounder (MLS) by incorporating cloud pressure information from OMI. Since we cannot distinguish between natural and anthropogenic sources with the satellite data, our estimates reflect the total forcing due to tropospheric O3. We focus specifically on the magnitude and spatial structure of the cloud effect on both the shortand long-wave radiative forcing. The estimates presented here can be used to validate present day O3 radiative forcing produced by models.

Long-Term Climate Implications of Persistent Loss of Tropical Peat Carbon Following Land Use Conversion

NASA Astrophysics Data System (ADS)

Frolking, S. E.; Dommain, R.; Glaser, P. H.; Joos, F.; Jeltsch-Thommes, A.

2016-12-01

The climate mitigation potential of tropical peatlands has gained increased attention as Southeast Asian tropical peat swamp forests are being deforested, drained and burned at very high rates, causing globally significant carbon dioxide (CO2) emissions to the atmosphere. We used a simple force-restore model to represent the perturbation to the atmospheric CO2 and CH4 burdens, and net radiative forcing, resulting from long-term conversion of tropical peat swamp forests to oil palm or acacia plantations. Drainage ditches are installed in land-use conversion to both oil palm and acacia, leading to a persistent change in the system greenhouse gas balance with the atmosphere. Drainage causes the net CO2 exchange to switch from a weak sink (removal from the atmosphere) in the accumulating peat of a swamp forest to a relatively strong source as the peat is oxidized. CH4 emissions increase due to relatively high emissions from the ditches themselves. For these systems, persistent CO2 fluxes have a much stronger impact on atmospheric radiative forcing than do the CH4 fluxes. Prior to conversion, slow peat accumulation (net CO2 uptake) over millennia establishes a slowly increasing net radiative cooling perturbation to the atmosphere. Upon conversion, CO2 loss rates are 16-32 times higher than pre-conversion CO2 uptake rates. Rapid loss rates cause the net radiative forcing perturbation to quickly (decades) become a net warming, which can persist for many centuries after the peat has all been oxidized.

Acoustic radiation force on an air bubble and soft fluid spheres in ideal liquids: example of a high-order Bessel beam of quasi-standing waves.

PubMed

Mitri, F G

2009-04-01

The partial wave series for the scattering of a high-order Bessel beam (HOBB) of acoustic quasi-standing waves by an air bubble and fluid spheres immersed in water and centered on the axis of the beam is applied to the calculation of the acoustic radiation force. A HOBB refers to a type of beam having an axial amplitude null and an azimuthal phase gradient. Radiation force examples obtained through numerical evaluation of the radiation force function are computed for an air bubble, a hexane, a red blood and mercury fluid spheres in water. The examples were selected to illustrate conditions having progressive, standing and quasi-standing waves with appropriate selection of the waves' amplitude ratio. An especially noteworthy result is the lack of a specific vibrational mode contribution to the radiation force determined by appropriate selection of the HOBB parameters.

Acoustic radiation force of a Bessel beam on a porous sphere.

PubMed

Azarpeyvand, Mahdi

2012-06-01

The possibility of using acoustic Bessel beams to produce an axial pulling force on porous particles is examined in an exact manner. The mathematical model utilizes the appropriate partial-wave expansion method in spherical coordinates, while Biot's model is used to describe the wave motion within the poroelastic medium. Of particular interest here is to examine the feasibility of using Bessel beams for (a) acoustic manipulation of fine porous particles and (b) suppression of particle resonances. To verify the viability of the technique, the radiation force and scattering form-function are calculated for aluminum and silica foams at various porosities. Inspection of the results has shown that acoustic manipulation of low porosity (<0.3) spheres is similar to that of solid elastic spheres, but this behavior significantly changes at higher porosities. Results have also shown a strong correlation between the backscattered form-function and the regions of negative radiation force. It has also been observed that the high-order resonances of the particle can be effectively suppressed by choosing the beam conical angle such that the acoustic contribution from that particular mode vanishes. This investigation may be helpful in the development of acoustic tweezers for manipulation of micro-porous drug delivery carrier and contrast agents.

Investigation of Carbonaceous Aerosol Optical Properties to Understand Impacts on Air Quality and Composition

NASA Astrophysics Data System (ADS)

Olson, Michael R.

The optical properties of carbonaceous aerosols were investigated to understand the impact source emissions and ambient particulate matter (PM) have on atmospheric radiative forcing. Black carbon (BC) is a strong absorber of visible light and contributes highly to atmospheric radiative forcing, therefore it is important to link BC properties to combustion emission sources. Brown carbon (BrC) is poorly understood and may be an important contributor to both positive and negative radiative forcing. The research investigates these primary knowledge gaps. The optical properties of carbonaceous aerosols were investigated to understand the impact source emissions and ambient particulate matter (PM) have on atmospheric radiative forcing. Black carbon (BC) is a strong absorber of visible light and contributes highly to atmospheric radiative forcing, therefore it is important to link BC properties to combustion emission sources. Brown carbon (BrC) is poorly understood and may be an important contributor to both positive and negative radiative forcing. The research investigates these primary knowledge gaps. Multiple methods were developed and applied to quantify the mass absorption cross-section (MAC) at multiple wavelengths of source and ambient samples. The MAC of BC was determined to be approximately 7.5 m2g-1 at 520nm. However, the MAC was highly variable with OC fraction and wavelength. The BrC MAC was similar for all sources, with the highest absorption in the UV at 370nm; the MAC quickly decreases at larger wavelengths. In the UV, the light absorption by BrC could exceed BC contribution by over 100 times, but only when the OC fraction is large (>90%) as compared to the total carbon. BrC was investigated by measuring the light absorption of solvent extracted fractions in water, dichloromethane, and methanol. Source emissions exhibited greater light absorption in methanol extractions as compared to water and DCM extracts. The BrC MAC was 2.4 to 3.7 m2g-1 at 370nm in methanol. Ambient samples showed similar MACs for the water and methanol extracts. Dichloromethane extracts did not have a significant light absorption characteristics for ambient samples. BrC and BC were measured in Beijing, China. Both were reduced significantly when restrictive air pollution controls were put in place. The industrial regions south and east of Beijing were the highest contributors to ambient BrC and BC. The controls reduced BrC more than BC as compared to observations during the regions heating period. Using the color characteristics of ambient PM, a model was developed to estimate elemental and organic carbon (EC/OC). The method will allow fast and cost effective quantification of PM composition in combination with large climate and health studies, especially in the developing world.

The Dependence of Cloud-SST Feedback on Circulation Regime and Timescale

NASA Astrophysics Data System (ADS)

Middlemas, E.; Clement, A. C.; Medeiros, B.

2017-12-01

Studies suggest cloud radiative feedback amplifies internal variability of Pacific sea surface temperature (SST) on interannual-and-longer timescales, though only a few modeling studies have tested the quantitative importance of this feedback (Bellomo et al. 2014b, Brown et al. 2016, Radel et al. 2016 Burgman et al. 2017). We prescribe clouds from a previous control run in the radiation module in Community Atmospheric Model (CAM5-slab), a method called "cloud-locking". By comparing this run to a control run, in which cloud radiative forcing can feedback on the climate system, we isolate the effect of cloud radiative forcing on SST variability. Cloud-locking prevents clouds from radiatively interacting with atmospheric circulation, water vapor, and SST, while maintaining a similar mean state to the control. On all timescales, cloud radiative forcing's influence on SST variance is modulated by the circulation regime. Cloud radiative forcing amplifies SST variance in subsiding regimes and dampens SST variance in convecting regimes. In this particular model, a tug of war between latent heat flux and cloud radiative forcing determines the variance of SST, and the winner depends on the timescale. On decadal-and-longer timescales, cloud radiative forcing plays a relatively larger role than on interannual-and-shorter timescales, while latent heat flux plays a smaller role. On longer timescales, the absence of cloud radiative feedback changes SST variance in a zonally asymmetric pattern in the Pacific Ocean that resembles an IPO-like pattern. We also present an analysis of cloud feedback's role on Pacific SST variability among preindustrial control CMIP5 models to test the model robustness of our results. Our results suggest that circulation plays a crucial role in cloud-SST feedbacks across the globe and cloud radiative feedbacks cannot be ignored when studying SST variability on decadal-and-longer timescales.

On the contribution of circumferential resonance modes in acoustic radiation force experienced by cylindrical shells

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Behzad, Mehdi

2014-10-01

A body insonified by a constant (time-varying) intensity sound field is known to experience a steady (oscillatory) force that is called the steady-state (dynamic) acoustic radiation force. Using the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of a resonance field and a background (non-resonance) component, we show that the radiation force acting on a cylindrical shell may be synthesized as a composition of three components: background part, resonance part and their interaction. The background component reveals the pure geometrical reflection effects and illustrates a regular behavior with respect to frequency, while the others demonstrate a singular behavior near the resonance frequencies. The results illustrate that the resonance effects associated to partial waves can be isolated by the subtraction of the background component from the total (steady-state or dynamic) radiation force function (i.e., residue component). In the case of steady-state radiation force, the components are exerted on the body as static forces. For the case of oscillatory amplitude excitation, the components are exerted at the modulation frequency with frequency-dependant phase shifts. The results demonstrate the dominant contribution of the non-resonance component of dynamic radiation force at high frequencies with respect to the residue component, which offers the potential application of ultrasound stimulated vibro-acoustic spectroscopy technique in low frequency resonance spectroscopy purposes. Furthermore, the proposed formulation may be useful essentially due to its intrinsic value in physical acoustics. In addition, it may unveil the contribution of resonance modes in the dynamic radiation force experienced by the cylindrical objects and its underlying physics.

Effects of increasing aerosol on regional climate change in China: Observation and modeling

NASA Astrophysics Data System (ADS)

Qian, Y.; Leung, L.; Ghan, S. J.

2002-12-01

We present regional simulations of climate, aerosol properties, and direct radiative forcing and climatic effects of aerosol and analyze the pollutant emissions and observed climatic data during the latter decades of last century in China. The regional model generally captures the spatial distributions and seasonal pattern of temperature and precipitation. Aerosol extinction coefficient and aerosol optical depth are generally well simulated in both magnitude and spatial distribution, which provides a reliable foundation for estimating the radiative forcing and climatic effects of aerosol. The radiative forcing of aerosol is in the range of -1 to -14 W m-2 in autumn and summer and -1 to -9 W m-2 in spring and winter, with substantial spatial variability at the sub-regional scale. A strong maximum in negative radiative forcing corresponding to the maximum optical depth is found over the Sichuan Basin, where emission as well as relative humidity are high, and stagnant atmospheric conditions inhibit pollutants dispersion. Negative radiative forcing of aerosol induces a surface cooling, which is stronger in the range of -0.6 to -1.2oC in autumn and winter than in spring (-0.3 to -0.6oC) and summer (0.0 to -0.9oC) over the Sichuan Basin and East China due to more significant effects of cloud and precipitation in the summer and spring. Aerosol-induced cooling is mainly contributed by cooling in the daytime temperature. The cooling reaches a maximum and is statistically significant in the Sichuan Basin. The effect of aerosol on precipitation is not evident in our simulations. The temporal and spatial patterns of temperature trends observed in the second half of the twentieth century, including the asymmetric daily maximum and minimum temperature trends, are at least qualitatively consistent with the simulated aerosol-induced cooling over the Sichuan Basin and East China. It supports the hypothesis that the observed temperature trends during the latter decades of the twentieth century, especially the cooling trends over the Sichuan Basin and some parts of East China, which are exceptions to the large scale warming trend in the northern hemisphere, are at least partly related to the cooling induced by atmospheric aerosol loading that has been increasing since the middle of the last century.

Unbinding of targeted ultrasound contrast agent microbubbles by secondary acoustic forces.

PubMed

Garbin, Valeria; Overvelde, Marlies; Dollet, Benjamin; de Jong, Nico; Lohse, Detlef; Versluis, Michel

2011-10-07

Targeted molecular imaging with ultrasound contrast agent microbubbles is achieved by incorporating targeting ligands on the bubble coating and allows for specific imaging of tissues affected by diseases. Improved understanding of the interplay between the acoustic forces acting on the bubbles during insonation with ultrasound and other forces (e.g. shear due to blood flow, binding of targeting ligands to receptors on cell membranes) can help improve the efficacy of this technique. This work focuses on the effects of the secondary acoustic radiation force, which causes bubbles to attract each other and may affect the adhesion of targeted bubbles. First, we examine the translational dynamics of ultrasound contrast agent microbubbles in contact with (but not adherent to) a semi-rigid membrane due to the secondary acoustic radiation force. An equation of motion that effectively accounts for the proximity of the membrane is developed, and the predictions of the model are compared with experimental data extracted from optical recordings at 15 million frames per second. A time-averaged model is also proposed and validated. In the second part of the paper, initial results on the translation due to the secondary acoustic radiation force of targeted, adherent bubbles are presented. Adherent bubbles are also found to move due to secondary acoustic radiation force, and a restoring force is observed that brings them back to their initial positions. For increasing magnitude of the secondary acoustic radiation force, a threshold is reached above which the adhesion of targeted microbubbles is disrupted. This points to the fact that secondary acoustic radiation forces can cause adherent bubbles to detach and alter the spatial distribution of targeted contrast agents bound to tissues during activation with ultrasound. While the details of the rupture of intermolecular bonds remain elusive, this work motivates the use of the secondary acoustic radiation force to measure the strength of adhesion of targeted microbubbles.

Black carbon vertical profiles strongly affect its radiative forcing uncertainty

NASA Astrophysics Data System (ADS)

Samset, B. H.; Myhre, G.; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, T. K.; Bian, H.; Bellouin, N.; Diehl, T.; Easter, R. C.; Ghan, S. J.; Iversen, T.; Kinne, S.; Kirkevåg, A.; Lamarque, J.-F.; Lin, G.; Liu, X.; Penner, J.; Seland, Ø.; Skeie, R. B.; Stier, P.; Takemura, T.; Tsigaridis, K.; Zhang, K.

2012-11-01

The impact of black carbon (BC) aerosols on the global radiation balance is not well constrained. Here twelve global aerosol models are used to show that at least 20% of the present uncertainty in modeled BC direct radiative forcing (RF) is due to diversity in the simulated vertical profile of BC mass. Results are from phases 1 and 2 of the global aerosol model intercomparison project (AeroCom). Additionally, a significant fraction of the variability is shown to come from high altitudes, as, globally, more than 40% of the total BC RF is exerted above 5 km. BC emission regions and areas with transported BC are found to have differing characteristics. These insights into the importance of the vertical profile of BC lead us to suggest that observational studies are needed to better characterize the global distribution of BC, including in the upper troposphere.

Black carbon vertical profiles strongly affect its radiative forcing uncertainty

NASA Astrophysics Data System (ADS)

Samset, B. H.; Myhre, G.; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, T. K.; Bian, H.; Bellouin, N.; Diehl, T.; Easter, R. C.; Ghan, S. J.; Iversen, T.; Kinne, S.; Kirkevåg, A.; Lamarque, J.-F.; Lin, G.; Liu, X.; Penner, J. E.; Seland, Ø.; Skeie, R. B.; Stier, P.; Takemura, T.; Tsigaridis, K.; Zhang, K.

2013-03-01

The impact of black carbon (BC) aerosols on the global radiation balance is not well constrained. Here twelve global aerosol models are used to show that at least 20% of the present uncertainty in modeled BC direct radiative forcing (RF) is due to diversity in the simulated vertical profile of BC mass. Results are from phases 1 and 2 of the global aerosol model intercomparison project (AeroCom). Additionally, a significant fraction of the variability is shown to come from high altitudes, as, globally, more than 40% of the total BC RF is exerted above 5 km. BC emission regions and areas with transported BC are found to have differing characteristics. These insights into the importance of the vertical profile of BC lead us to suggest that observational studies are needed to better characterize the global distribution of BC, including in the upper troposphere.

Black Carbon Vertical Profiles Strongly Affect Its Radiative Forcing Uncertainty

NASA Technical Reports Server (NTRS)

Samset, B. H.; Myhre, G.; Schulz, M.; Balkanski, Y.; Bauer, S.; Berntsen, T. K.; Bian, H.; Bellouin, N.; Diehl, T.; Easter, R. C.;

The effect of radiation pressure on spatial distribution of dust inside H II regions

NASA Astrophysics Data System (ADS)

Ishiki, Shohei; Okamoto, Takashi; Inoue, Akio K.

2018-02-01

We investigate the impact of radiation pressure on spatial dust distribution inside H II regions using one-dimensional radiation hydrodynamic simulations, which include absorption and re-emission of photons by dust. In order to investigate grain-size effects as well, we introduce two additional fluid components describing large and small dust grains in the simulations. Relative velocity between dust and gas strongly depends on the drag force. We include collisional drag force and coulomb drag force. We find that, in a compact H II region, a dust cavity region is formed by radiation pressure. Resulting dust cavity sizes (˜0.2 pc) agree with observational estimates reasonably well. Since dust inside an H II region is strongly charged, relative velocity between dust and gas is mainly determined by the coulomb drag force. Strength of the coulomb drag force is about 2 order of magnitude larger than that of the collisional drag force. In addition, in a cloud of mass 105 M⊙, we find that the radiation pressure changes the grain-size distribution inside H II regions. Since large (0.1 μm) dust grains are accelerated more efficiently than small (0.01 μm) grains, the large-to-small grain mass ratio becomes smaller by an order of magnitude compared with the initial one. Resulting dust-size distributions depend on the luminosity of the radiation source. The large and small grain segregation becomes weaker when we assume stronger radiation source, since dust grain charges become larger under stronger radiation and hence coulomb drag force becomes stronger.

Radiative Forcing Due to Enhancements in Tropospheric Ozone and Carbonaceous Aerosols Caused by Asian Fires During Spring 2008

NASA Technical Reports Server (NTRS)

Natarajan, Murali; Pierce, R. Bradley; Lenzen, Allen J.; Al-Saadi, Jassim A.; Soja, Amber J.; Charlock, Thomas P.; Rose, Fred G.; Winker, David M.; Worden, John R.

2012-01-01

Simulations of tropospheric ozone and carbonaceous aerosol distributions, conducted with the Real-time Air Quality Modeling System (RAQMS), are used to study the effects of major outbreaks of fires that occurred in three regions of Asia, namely Thailand, Kazakhstan, and Siberia, during spring 2008. RAQMS is a global scale meteorological and chemical modeling system. Results from these simulations, averaged over April 2008, indicate that tropospheric ozone column increases by more than 10 Dobson units (DU) near the Thailand region, and by lesser amounts in the other regions due to the fires. Widespread increases in the optical depths of organic and black carbon aerosols are also noted. We have used an off-line radiative transfer model to evaluate the direct radiative forcing due to the fire-induced changes in atmospheric composition. For clear sky, the monthly averaged radiative forcing at the top of the atmosphere (TOA) is mostly negative with peak values less than -12 W/sq m occurring near the fire regions. The negative forcing represents the increased outgoing shortwave radiation caused by scattering due to carbonaceous aerosols. At high latitudes, the radiative forcing is positive due to the presence of absorbing aerosols over regions of high surface albedo. Regions of positive forcing at TOA are more pronounced under total sky conditions. The monthly averaged radiative forcing at the surface is mostly negative, and peak values of less than -30 W/sq m occur near the fire regions. Persistently large negative forcing at the surface could alter the surface energy budget and potentially weaken the hydrological cycle.

Uncertainties in Carbon Dioxide Radiative Forcing in Atmospheric General Circulation Models

NASA Technical Reports Server (NTRS)

Cess, R. D.; Zhang, M.-H.; Potter, G. L.; Gates, W. L.; Taylor, K. E.; Barker, H. W.; Colman, R. A.; Fraser, J. R.; McAvaney, B. J.; Dazlich, D. A.;

Smoke over haze: Comparative analysis of satellite, surface radiometer, and airborne in situ measurements of aerosol optical properties and radiative forcing over the eastern United States

NASA Astrophysics Data System (ADS)

Vant-Hull, Brian; Li, Zhanqing; Taubman, Brett F.; Levy, Robert; Marufu, Lackson; Chang, Fu-Lung; Doddridge, Bruce G.; Dickerson, Russell R.

2005-05-01

In July 2002 Canadian forest fires produced a major smoke episode that blanketed the east coast of the United States. Properties of the smoke aerosol were measured in situ from aircraft, complementing operational Aerosol Robotic Network (AERONET), and Moderate Resolution Imaging Spectroradiometer (MODIS) remotely sensed aerosol retrievals. This study compares single scattering albedo and phase function derived from the in situ measurements and AERONET retrievals in order to evaluate their consistency for application to satellite retrievals of optical depth and radiative forcing. These optical properties were combined with MODIS reflectance observations to calculate optical depth. The use of AERONET optical properties yielded optical depths 2-16% lower than those directly measured by AERONET. The use of in situ-derived optical properties resulted in optical depths 22-43% higher than AERONET measurements. These higher optical depths are attributed primarily to the higher absorption measured in situ, which is roughly twice that retrieved by AERONET. The resulting satellite retrieved optical depths were in turn used to calculate integrated radiative forcing at both the surface and top of atmosphere. Comparisons to surface (Surface Radiation Budget Network (SURFRAD) and ISIS) and to satellite (Clouds and Earth Radiant Energy System CERES) broadband radiometer measurements demonstrate that the use of optical properties derived from the aircraft measurements provided a better broadband forcing estimate (21% error) than those derived from AERONET (33% error). Thus AERONET-derived optical properties produced better fits to optical depth measurements, while in situ properties resulted in better fits to forcing measurements. These apparent inconsistencies underline the significant challenges facing the aerosol community in achieving column closure between narrow and broadband measurements and calculations.

Multidecadal trends in aerosol radiative forcing over the Arctic: Contribution of changes in anthropogenic aerosol to Arctic warming since 1980

NASA Astrophysics Data System (ADS)

Breider, Thomas J.; Mickley, Loretta J.; Jacob, Daniel J.; Ge, Cui; Wang, Jun; Payer Sulprizio, Melissa; Croft, Betty; Ridley, David A.; McConnell, Joseph R.; Sharma, Sangeeta; Husain, Liaquat; Dutkiewicz, Vincent A.; Eleftheriadis, Konstantinos; Skov, Henrik; Hopke, Phillip K.

2017-03-01

Arctic observations show large decreases in the concentrations of sulfate and black carbon (BC) aerosols since the early 1980s. These near-term climate-forcing pollutants perturb the radiative balance of the atmosphere and may have played an important role in recent Arctic warming. We use the GEOS-Chem global chemical transport model to construct a 3-D representation of Arctic aerosols that is generally consistent with observations and their trends from 1980 to 2010. Observations at Arctic surface sites show significant decreases in sulfate and BC mass concentrations of 2-3% per year. We find that anthropogenic aerosols yield a negative forcing over the Arctic, with an average 2005-2010 Arctic shortwave radiative forcing (RF) of -0.19 ± 0.05 W m-2 at the top of atmosphere (TOA). Anthropogenic sulfate in our study yields more strongly negative forcings over the Arctic troposphere in spring (-1.17 ± 0.10 W m-2) than previously reported. From 1980 to 2010, TOA negative RF by Arctic aerosol declined, from -0.67 ± 0.06 W m-2 to -0.19 ± 0.05 W m-2, yielding a net TOA RF of +0.48 ± 0.06 W m-2. The net positive RF is due almost entirely to decreases in anthropogenic sulfate loading over the Arctic. We estimate that 1980-2010 trends in aerosol-radiation interactions over the Arctic and Northern Hemisphere midlatitudes have contributed a net warming at the Arctic surface of +0.27 ± 0.04 K, roughly one quarter of the observed warming. Our study does not consider BC emissions from gas flaring nor the regional climate response to aerosol-cloud interactions or BC deposition on snow.

Greenhouse gas policy influences climate via direct effects of land-use change

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jones, Andrew D.; Collins, William D.; Edmonds, James A.

2013-06-01

Proposed climate mitigation measures do not account for direct biophysical climate impacts of land-use change (LUC), nor do the stabilization targets modeled for the 5th Climate Model Intercomparison Project (CMIP5) Representative Concentration Pathways (RCPs). To examine the significance of such effects on global and regional patterns of climate change, a baseline and alternative scenario of future anthropogenic activity are simulated within the Integrated Earth System Model, which couples the Global Change Assessment Model, Global Land-use Model, and Community Earth System Model. The alternative scenario has high biofuel utilization and approximately 50% less global forest cover compared to the baseline, standardmore » RCP4.5 scenario. Both scenarios stabilize radiative forcing from atmospheric constituents at 4.5 W/m2 by 2100. Thus, differences between their climate predictions quantify the biophysical effects of LUC. Offline radiative transfer and land model simulations are also utilized to identify forcing and feedback mechanisms driving the coupled response. Boreal deforestation is found to strongly influence climate due to increased albedo coupled with a regional-scale water vapor feedback. Globally, the alternative scenario yields a 21st century warming trend that is 0.5 °C cooler than baseline, driven by a 1 W/m2 mean decrease in radiative forcing that is distributed unevenly around the globe. Some regions are cooler in the alternative scenario than in 2005. These results demonstrate that neither climate change nor actual radiative forcing are uniquely related to atmospheric forcing targets such as those found in the RCP’s, but rather depend on particulars of the socioeconomic pathways followed to meet each target.« less

Measuring the radiation force of megahertz ultrasound acting on a solid spherical scatterer

NASA Astrophysics Data System (ADS)

Nikolaeva, A. V.; Tsysar, S. A.; Sapozhnikov, O. A.

2016-01-01

The paper considers the problem of precise measurement of the acoustic radiation force of an ultrasonic beam on targets in the form of solid spherical scatterers. Using known analytic relations, a numerical model is developed to perform calculations for different sizes of spherical scatterers and arbitrary frequencies of the incident acoustic wave. A novel method is proposed for measuring the radiation force, which is based on the principle of acoustic echolocation. The radiation force is measured experimentally in a wide range of incident wave intensities using two chosen methods differing in the way the location of the target is controlled.

Radiative Forcing by Contrails

NASA Technical Reports Server (NTRS)

Meerkoetter, R.; Schumann, U.; Doelling, D. R.; Nakajima, T.; Tsushima, Y.

1999-01-01

A parametric study of the instantaneous radiative impact of contrails is presented using three different radiative transfer models for a series of model atmospheres and cloud parameters. Contrails are treated as geometrically and optically thin plane parallel homogeneous cirrus layers in a static atmospheres The ice water content is varied as a function of ambient temperature. The model atmospheres include tropical, mid-latitude, and subarctic summer and winter atmospheres Optically thin contrails cause a positive net forcing at top of the atmosphere. At the surface the radiative forcing is negative during daytime. The forcing increases with the optical depth and the amount of contrail cover. At the top of the atmosphere a mean contrail cover of 0.1% with average optical depth of 0.2 to 0.5 causes about 0.01 to 0.03 W/m(exp 2)a daily mean instantaneous radiative forcing. Contrails cool the surface during the day and heat the surface during the night, and hence reduce the daily temperature amplitude The net effect depends strongly on the daily variation of contrail cloud cover. The indirect radiative forcing due to particle changes in natural cirrus clouds may be of the same magnitude as the direct one due to additional cover.

Sensible heat has significantly affected the global hydrological cycle over the historical period.

PubMed

Myhre, G; Samset, B H; Hodnebrog, Ø; Andrews, T; Boucher, O; Faluvegi, G; Fläschner, D; Forster, P M; Kasoar, M; Kharin, V; Kirkevåg, A; Lamarque, J-F; Olivié, D; Richardson, T B; Shawki, D; Shindell, D; Shine, K P; Stjern, C W; Takemura, T; Voulgarakis, A

2018-05-15

Globally, latent heating associated with a change in precipitation is balanced by changes to atmospheric radiative cooling and sensible heat fluxes. Both components can be altered by climate forcing mechanisms and through climate feedbacks, but the impacts of climate forcing and feedbacks on sensible heat fluxes have received much less attention. Here we show, using a range of climate modelling results, that changes in sensible heat are the dominant contributor to the present global-mean precipitation change since preindustrial time, because the radiative impact of forcings and feedbacks approximately compensate. The model results show a dissimilar influence on sensible heat and precipitation from various drivers of climate change. Due to its strong atmospheric absorption, black carbon is found to influence the sensible heat very differently compared to other aerosols and greenhouse gases. Our results indicate that this is likely caused by differences in the impact on the lower tropospheric stability.

Climate implications of including albedo effects in terrestrial carbon policy

NASA Astrophysics Data System (ADS)

Jones, A. D.; Collins, W.; Torn, M. S.; Calvin, K. V.

2012-12-01

Proposed strategies for managing terrestrial carbon in order to mitigate anthropogenic climate change, such as financial incentives for afforestation, soil carbon sequestration, or biofuel production, largely ignore the direct effects of land use change on climate via biophysical processes that alter surface energy and water budgets. Subsequent influences on temperature, hydrology, and atmospheric circulation at regional and global scales could potentially help or hinder climate stabilization efforts. Because these policies often rely on payments or credits expressed in units of CO2-equivalents, accounting for biophysical effects would require a metric for comparing the strength of biophysical climate perturbation from land use change to that of emitting CO2. One such candidate metric that has been suggested in the literature on land use impacts is radiative forcing, which underlies the global warming potential metric used to compare the climate effects of various greenhouse gases with one another. Expressing land use change in units of radiative forcing is possible because albedo change results in a net top-of-atmosphere radiative flux change. However, this approach has also been critiqued on theoretical grounds because not all climatic changes associated with land use change are principally radiative in nature, e.g. changes in hydrology or the vertical distribution of heat within the atmosphere, and because the spatial scale of land use change forcing differs from that of well-mixed greenhouse gases. To explore the potential magnitude of this discrepancy in the context of plausible scenarios of future land use change, we conduct three simulations with the Community Climate System Model 4 (CCSM4) utilizing a slab ocean model. Each simulation examines the effect of a stepwise change in forcing relative to a pre-industrial control simulation: 1) widespread conversion of forest land to crops resulting in approximately 1 W/m2 global-mean radiative forcing from albedo change, 2) an increase in CO2 concentrations that exactly balances the forcing from land use change at the global level, and 3) a simulation combining the first two effects, resulting in net zero global-mean forcing as would occur in an idealized carbon cap-and-trade scheme that accounts for the albedo effect of land use change. The pattern of land use change that we examine is derived from an integrated assessment model that accounts for population, demographic, technological, and policy changes over the 21st century. We find significant differences in the pattern of climate change associated with each of these forcing scenarios, demonstrating the non-additivity of radiative forcing from land-use change and greenhouse gases in the context of a hypothetical scenario of future land use change. These results have implications for the development of land use and climate policies.

Regional Attribution of Ozone Production and Associated Radiative Forcing: a Step to Crediting NOx Emission Reductions

NASA Astrophysics Data System (ADS)

Naik, V.; Mauzerall, D. L.; Horowitz, L.; Schwarzkopf, D.; Ramaswamy, V.; Oppenheimer, M.

2004-12-01

The global distribution of tropospheric ozone (O3) depends on the location of emissions of its precursors in addition to chemical and dynamical factors. The global picture of O3 forcing is, therefore, a sum of regional forcings arising from emissions of precursors from different sources. The Kyoto Protocol does not include ozone as a greenhouse gas, and emission reductions of ozone precursors made under Kyoto or any similar agreement would presently receive no credit. In this study, we quantitatively estimate the contribution of emissions of nitrogen oxides (NOx), the primary limiting O3 precursor in the non-urban atmosphere, from specific countries and regions of the world to global O3 concentration distributions. We then estimate radiative forcing resulting from the regional perturbations of NOx emissions. This analysis is intended as an early step towards incorporating O3 into the Kyoto Protocol or any successor agreement. Under such a system countries could obtain credit for improvements in local air quality that result in reductions of O3 concentrations because of the associated reductions in radiative forcing. We use the global chemistry transport model, MOZART-2, to simulate the global O3 distribution for base year 1990 and perturbations to this distribution caused by a 10% percent reduction in the base emissions of NOx from the United States, Europe, East Asia, India, South America, and Africa. We calculate the radiative forcing for the simulated base and perturbed O3 distributions using the GFDL radiative transfer model. The difference between the radiative forcing from O3 for the base and perturbed distributions provides an estimate of the marginal radiative forcing from a region's emissions of NOx. We will present a quantitative analysis of the magnitude, spatial, and temporal distribution of radiative forcing resulting from marginal changes in the NOx emissions from each region.

A new radiation infrastructure for the Modular Earth Submodel System (MESSy, based on version 2.51)

NASA Astrophysics Data System (ADS)

Dietmüller, Simone; Jöckel, Patrick; Tost, Holger; Kunze, Markus; Gellhorn, Catrin; Brinkop, Sabine; Frömming, Christine; Ponater, Michael; Steil, Benedikt; Lauer, Axel; Hendricks, Johannes

2016-06-01

The Modular Earth Submodel System (MESSy) provides an interface to couple submodels to a base model via a highly flexible data management facility (Jöckel et al., 2010). In the present paper we present the four new radiation related submodels RAD, AEROPT, CLOUDOPT, and ORBIT. The submodel RAD (including the shortwave radiation scheme RAD_FUBRAD) simulates the radiative transfer, the submodel AEROPT calculates the aerosol optical properties, the submodel CLOUDOPT calculates the cloud optical properties, and the submodel ORBIT is responsible for Earth orbit calculations. These submodels are coupled via the standard MESSy infrastructure and are largely based on the original radiation scheme of the general circulation model ECHAM5, however, expanded with additional features. These features comprise, among others, user-friendly and flexibly controllable (by namelists) online radiative forcing calculations by multiple diagnostic calls of the radiation routines. With this, it is now possible to calculate radiative forcing (instantaneous as well as stratosphere adjusted) of various greenhouse gases simultaneously in only one simulation, as well as the radiative forcing of cloud perturbations. Examples of online radiative forcing calculations in the ECHAM/MESSy Atmospheric Chemistry (EMAC) model are presented.

Micromechanical Resonator Driven by Radiation Pressure Force.

PubMed

Boales, Joseph A; Mateen, Farrukh; Mohanty, Pritiraj

2017-11-22

Radiation pressure exerted by light on any surface is the pressure generated by the momentum of impinging photons. The associated force - fundamentally, a quantum mechanical aspect of light - is usually too small to be useful, except in large-scale problems in astronomy and astrodynamics. In atomic and molecular optics, radiation pressure can be used to trap or cool atoms and ions. Use of radiation pressure on larger objects such as micromechanical resonators has been so far limited to its coupling to an acoustic mode, sideband cooling, or levitation of microscopic objects. In this Letter, we demonstrate direct actuation of a radio-frequency micromechanical plate-type resonator by the radiation pressure force generated by a standard laser diode at room temperature. Using two independent methods, the magnitude of the resonator's response to forcing by radiation pressure is found to be proportional to the intensity of the incident light.

Simulation of seasonal cloud forcing anomalies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Randall, D.A.

1990-08-01

One useful way to classify clouds is according to the processes that generate them. There are three main cloud-formation agencies: deep convection; surface evaporation; large-scale lifting in the absence of conditional instability. Although traditionally clouds have been viewed as influencing the atmospheric general circulation primarily through the release of latent heat, the atmospheric science literature contains abundant evidence that, in reality, clouds influence the general circulation through four more or less equally important effects: interactions with the solar and terrestrial radiation fields; condensation and evaporation; precipitation; small-scale circulations within the atmosphere. The most advanced of the current generation of GCMsmore » include parameterizations of all four effects. Until recently there has been lingering skepticism, in the general circulation modeling community, that the radiative effects of clouds significantly influence the atmospheric general circulation. GCMs have provided the proof that the radiative effects of clouds are important for the general circulation of the atmosphere. An important concept in analysis of the effects of clouds on climate is the cloud radiative forcing (CRF), which is defined as the difference between the radiative flux which actually occurs in the presence of clouds, and that which would occur if the clouds were removed but the atmospheric state were otherwise unchanged. We also use the term CRF to denote warming or cooling tendencies due to cloud-radiation interactions. Cloud feedback is the change in CRF that accompanies a climate change. The present study concentrates on the planetary CRF and its response to external forcing, i.e. seasonal change.« less

Snow driven Radiative Forcing in High Latitude Areas of Disturbance Using Higher Resolution Albedo Products from Landsat and Sentinel-2

NASA Astrophysics Data System (ADS)

Erb, A.; Li, Z.; Schaaf, C.; Wang, Z.; Rogers, B. M.

2017-12-01

Land surface albedo plays an important role in the surface energy budget and radiative forcing by determining the proportion of absorbed incoming solar radiation available to drive photosynthesis and surface heating. In Arctic regions, albedo is particularly sensitive to land cover and land use change (LCLUC) and modeling efforts have shown it to be the primary driver of effective radiative forcing from the biogeophysical effects of LCLUC. In boreal forests, the effects of these changes are complicated during snow covered periods when newly exposed, highly reflective snow can serve as the primary driver of radiative forcing. In Arctic biomes disturbance scars from fire, pest and harvest can remain in the landscape for long periods of time. As such, understanding the magnitude and persistence of these disturbances, especially in the shoulder seasons, is critical. The Landsat and Sentinel-2 Albedo Products couple 30m and 20m surface reflectances with concurrent 500m BRDF Products from the MODerate resolution Imaging Spectroradiometer (MODIS). The 12 bit radiometric fidelity of Sentinel-2 and Landsat-8 allow for the inclusion of high-quality, unsaturated albedo calculations over snow covered surfaces at scales more compatible with fragmented landscapes. Recent work on the early spring albedo of fire scars has illustrated significant post-fire spatial heterogeneity of burn severity at the landscape scale and highlights the need for a finer spatial resolution albedo record. The increased temporal resolution provided by multiple satellite instruments also allows for a better understanding of albedo dynamics during the dynamic shoulder seasons and in historically difficult high latitude locations where persistent cloud cover limits high quality retrievals. Here we present how changes in the early spring albedo of recent boreal forest disturbance in Alaska and central Canada affects landscape-scale radiative forcing. We take advantage of the long historical Landsat record to examine pre-disturbance albedo trends and to link historical land cover and disturbance history to post-disturbance early spring albedo values. We examine the impact of landscape heterogeneity on albedo in the growing and dormant seasons and quantify the effects of snow exposure changes from over-story canopy loss.

Case Studies of the Vertical Structure of the Direct Shortwave Aerosol Radiative Forcing During TARFOX

NASA Technical Reports Server (NTRS)

Redemann, J.; Turco, R. P.; Liou, K. N.; Hobbs, P. V.; Hartley, W. S.; Bergstrom, R. W.; Browell, E. V.; Russell, P. B.

2000-01-01

The vertical structure of aerosol-induced radiative flux changes in the Earth's troposphere affects local heating rates and thereby convective processes, the formation and lifetime of clouds, and hence the distribution of chemical constituents. We present observationally based estimates of the vertical structure of direct shortwave aerosol radiative forcing for two case studies from the Tropospheric Aerosol Radiative Forcing Observational Experiment (TARFOX) which took place on the U.S. east coast in July 1996. The aerosol radiative forcings are computed using the Fu-Liou broadband radiative transfer model. The aerosol optical properties used in the radiative transfer simulations are calculated from independent vertically resolved estimates of the complex aerosol indices of refraction in two to three distinct vertical layers, using profiles of in situ particle size distributions measured aboard the University of Washington research aircraft. Aerosol single-scattering albedos at 450 nm thus determined range from 0.9 to 0.985, while the asymmetry factor varies from 0.6 to 0.8. The instantaneous shortwave aerosol radiative forcings derived from the optical properties of the aerosols are of the order of -36 Wm(exp -2) at the top of the atmosphere and about -56 Wm(exp -2) at the surface for both case studies.

A synergetic approach for estimating the local direct aerosol forcing: Application to an urban zone during the Expérience sur Site pour Contraindre les Modèles de Pollution et de Transport d'Emission (ESCOMPTE) experiment

NASA Astrophysics Data System (ADS)

Roger, J. C.; Mallet, M.; Dubuisson, P.; Cachier, H.; Vermote, E.; Dubovik, O.; Despiau, S.

2006-07-01

A method dedicated to the investigation of direct radiative forcing of the main anthropogenic aerosol species (ammonium sulfate, black carbon, particulate organic matter) is presented. We computed the direct radiative aerosol forcing at the top of atmosphere (TOA), at the bottom of atmosphere (BOA), and into the atmospheric layer (ATM). The methodology is based on chemical, photometric, and satellite measurements. We first determined the optical properties of the main aerosol species and then computed their direct radiative impact at local scale. The method was applied to a periurban zone during the Expérience sur Site pour Contraindre les Modèles de Pollution et de Transport d'Emission experiment. Optical computations indicate that the single scattering albedo, for the total aerosol population in the external mixture, is equal to 0.83 ± 0.04 at 550 nm, indicative of a strong absorption of the solar radiation. At the same time the mean asymmetry parameter is equal to 0.59 ± 0.04, and the mean aerosol optical thickness is equal to 0.30 ± 0.02, at 550 nm. The anthropogenic urban aerosol layer reduces significantly the daily surface illumination (-24 W m-2 > ΔFBOA > -47.5 W m-2) by reflection to space (-6 W m-2 > ΔFTOA > -9 W m-2) and by absorption of the solar radiation into the atmosphere (17 W m-2 < ΔFATM < 39 W m-2). The available resulting energy in the atmospheric column heats the lowermost part of the atmosphere from 1.1°K d-1 to 2.8°K d-1. Our study shows that the black carbon particles have a large contribution to the BOA forcing (almost 50% of the total daily forcing), whereas the ammonium sulfate particles contribute only to about 10%. Conversely, the TOA daily forcing is mostly driven by the ammonium sulfate aerosol (around 50%).

Effect of Ex Vivo Ionizing Radiation on Static and Fatigue Properties of Mouse Vertebral Bodies

NASA Technical Reports Server (NTRS)

Emerzian, Shannon R.; Pendleton, Megan M.; Li, Alfred; Liu, Jennifer W.; Alwood, Joshua S.; O’Connell, Grace D.; Keaveny, Tony M.

2018-01-01

For a variety of medical and scientific reasons, human bones can be exposed to a wide range of ionizing radiation levels. In vivo radiation therapy (0.05 kGy) is used in cancer treatment, and ex vivo irradiation (25-35 kGy) is used to sterilize bone allografts. Ionizing radiation in these applications has been shown to increase risk of fracture, decrease bone quality and degrade collagen integrity. Past studies have investigated the deleterious effects of radiation on cortical or trabecular bone specimens individually, but to date no studies have examined whole bones containing both cortical and trabecular tissue. Furthermore, a clear relationship between the dose and the mechanical and biochemical response of bone's extracellular matrix has yet to be established for doses ranging from cancer therapy to allograft sterilization (0.05-35 kGy). To gain insight into these issues, we conducted an ex vivo radiation study to investigate non-cellular (i.e. matrix) effects of ionizing radiation dose on vertebral whole bone mechanical properties, over a range of radiation doses (0.05-35 kGy), with a focus on any radiation-induced changes in collagen. With underlying mechanisms of action in mind, we hypothesized that any induced reductions in mechanical properties would be associated with changes in collagen integrity. METHODS: 20-week old female mice were euthanized and the lumbar spine was dissected using IACUC approved protocols. The lumbar vertebrae (L1- S1) were extracted from the spine via cuts through adjacent intervertebral discs, and the endplates, posterior processes, surrounding musculature, and soft tissues were removed (approx. 1.5mm diameter, approx. 2mm height). Specimens were randomly assigned to one of five groups for ex vivo radiation exposure: x-ray irradiation at 0.05, 1, 17, or 35 kGy, or a 0 kGy control. Following irradiation, the vertebrae were imaged using microcomputed tomography (micro-CT) and then subjected to either monotonic compressive loading to failure or uniform cyclic compressive loading. During cyclic testing, samples were loaded in force control to a force level that corresponded to a strain of 0.46%, as determined in advance by a linearly elastic micro-CT-based finite element analysis for each specimen. Tests were stopped at imminent fracture, defined as a rapid increase in strain. The main outcome for the monotonic test was the strength (maximum force); for cyclic testing it was the fatigue life (log of the number of cycles of loading at imminent failure). A fluorometric assay was used on the S1 vertebrae to measure the number of non-enzymatic collagen crosslinks[4]. A one-way ANOVA was performed on mechanical properties and collagen crosslinks; means were compared with controls using Dunnett's method, with a Tukey-Kramer post-hoc analysis when significance was found (p < or = 0.05). RESULTS: Compared to the unirradiated control group, the concentration of non-enzymatic collagen crosslinks was significantly increased for all irradiated groups (p < 0.0001), and being higher by at least 50% (Figure 1a). By contrast, the radiation effects on the collagen were only evident at the higher doses. For irradiation exposures of 17 kGy or more, strength decreased substantially as the radiation level was increased, but no effect was evident below 17 kGy (Figure 1b). There was no significant change in the stiffness or maximum displacement for any radiation dose (p>0.05). The finite element analysis prescribed force level for cyclic loading exceeded the measured (monotonic) strength of the 17 and 35 kGy irradiated groups (mean +/- SD, 20.6 +/- 5.6 N; 13.2 +/- 3.7 N, respectively) and therefore these groups were eliminated from the fatigue study. The fatigue life for the 0.05 and 1 kGy groups were similar to each other and were not statistically significantly different from the control group (Figure 1c).

Experimental measurement of interparticle acoustic radiation force in the Rayleigh limit

NASA Astrophysics Data System (ADS)

Mohapatra, Abhishek Ray; Sepehrirahnama, Shahrokh; Lim, Kian-Meng

2018-05-01

Acoustophoresis is a form of contact-free particle manipulation in microfluidic devices. The precision of manipulation can be enhanced with better understanding of the acoustic radiation force. In this paper we present the measurements of interparticle radiation force between a pair of polystyrene beads in the Rayleigh limit. The study is conducted for three different sizes of beads and the experimental results are of the same order of magnitude when compared with theoretical predictions. However, the experimental values are larger than the theoretical values. The trend of a decrease in the magnitude of the interparticle radiation force with decreasing particle size and increasing center-to-center distance between the particles is also observed experimentally. The experiments are conducted in the specific scenario where the pair of beads are in close proximity, but not in contact with each other, and the beads are approaching the pressure nodal plane with the center-to-center line aligned perpendicular to the incident wave. This scenario minimizes the presence of the primary radiation force, allowing accurate measurement of the interparticle force. The attractive nature of the interparticle force is observed, consistent with theoretical predictions.

Evaluation of multiple forcing data sets for precipitation and shortwave radiation over major land areas of China

NASA Astrophysics Data System (ADS)

Yang, Fan; Lu, Hui; Yang, Kun; He, Jie; Wang, Wei; Wright, Jonathon S.; Li, Chengwei; Han, Menglei; Li, Yishan

2017-11-01

Precipitation and shortwave radiation play important roles in climatic, hydrological and biogeochemical cycles. Several global and regional forcing data sets currently provide historical estimates of these two variables over China, including the Global Land Data Assimilation System (GLDAS), the China Meteorological Administration (CMA) Land Data Assimilation System (CLDAS) and the China Meteorological Forcing Dataset (CMFD). The CN05.1 precipitation data set, a gridded analysis based on CMA gauge observations, also provides high-resolution historical precipitation data for China. In this study, we present an intercomparison of precipitation and shortwave radiation data from CN05.1, CMFD, CLDAS and GLDAS during 2008-2014. We also validate all four data sets against independent ground station observations. All four forcing data sets capture the spatial distribution of precipitation over major land areas of China, although CLDAS indicates smaller annual-mean precipitation amounts than CN05.1, CMFD or GLDAS. Time series of precipitation anomalies are largely consistent among the data sets, except for a sudden decrease in CMFD after August 2014. All forcing data indicate greater temporal variations relative to the mean in dry regions than in wet regions. Validation against independent precipitation observations provided by the Ministry of Water Resources (MWR) in the middle and lower reaches of the Yangtze River indicates that CLDAS provides the most realistic estimates of spatiotemporal variability in precipitation in this region. CMFD also performs well with respect to annual mean precipitation, while GLDAS fails to accurately capture much of the spatiotemporal variability and CN05.1 contains significant high biases relative to the MWR observations. Estimates of shortwave radiation from CMFD are largely consistent with station observations, while CLDAS and GLDAS greatly overestimate shortwave radiation. All three forcing data sets capture the key features of the spatial distribution, but estimates from CLDAS and GLDAS are systematically higher than those from CMFD over most of mainland China. Based on our evaluation metrics, CLDAS slightly outperforms GLDAS. CLDAS is also closer than GLDAS to CMFD with respect to temporal variations in shortwave radiation anomalies, with substantial differences among the time series. Differences in temporal variations are especially pronounced south of 34° N. Our findings provide valuable guidance for a variety of stakeholders, including land-surface modelers and data providers.

Spatially Refined Aerosol Direct Radiative Forcing Efficiencies

EPA Science Inventory

Global aerosol direct radiative forcing (DRF) is an important metric for assessing potential climate impacts of future emissions changes. However, the radiative consequences of emissions perturbations are not readily quantified nor well understood at the level of detail necessary...

Radiative flux and forcing parameterization error in aerosol-free clear skies.

PubMed

Pincus, Robert; Mlawer, Eli J; Oreopoulos, Lazaros; Ackerman, Andrew S; Baek, Sunghye; Brath, Manfred; Buehler, Stefan A; Cady-Pereira, Karen E; Cole, Jason N S; Dufresne, Jean-Louis; Kelley, Maxwell; Li, Jiangnan; Manners, James; Paynter, David J; Roehrig, Romain; Sekiguchi, Miho; Schwarzkopf, Daniel M

2015-07-16

Radiation parameterizations in GCMs are more accurate than their predecessorsErrors in estimates of 4 ×CO 2 forcing are large, especially for solar radiationErrors depend on atmospheric state, so global mean error is unknown.

Modelling the effects of the radiation reaction force on the interaction of thin foils with ultra-intense laser fields

NASA Astrophysics Data System (ADS)

Duff, M. J.; Capdessus, R.; Del Sorbo, D.; Ridgers, C. P.; King, M.; McKenna, P.

2018-06-01

The effects of the radiation reaction (RR) force on thin foils undergoing radiation pressure acceleration (RPA) are investigated. Using QED-particle-in-cell simulations, the influence of the RR force on the collective electron dynamics within the target can be examined. The magnitude of the RR force is found to be strongly dependent on the target thickness, leading to effects which can be observed on a macroscopic scale, such as changes to the distribution of the emitted radiation and the target dynamics. This suggests that such parameters may be controlled in experiments at multi-PW laser facilities. In addition, the effects of the RR force are characterized in terms of an average radiation emission angle. We present an analytical model which, for the first time, describes the effect of the RR force on the collective electron dynamics within the ‘light-sail’ regime of RPA. The predictions of this model can be tested in future experiments with ultra-high intensity lasers interacting with solid targets.

Climatic Effects of 1950-2050 Changes in US Anthropogenic Aerosols. Part 1; Aerosol Trends and Radiative Forcing

NASA Technical Reports Server (NTRS)

Leibensperger, E. M.; Mickley, L. J.; Jacob, D. J.; Chen, W.-T.; Seinfeld, J. H.; Nenes, A.; Adams, P. J.; Streets, D. G.; Kumar, N.; Rind, D.

2012-01-01

We calculate decadal aerosol direct and indirect (warm cloud) radiative forcings from US anthropogenic sources over the 1950-2050 period. Past and future aerosol distributions are constructed using GEOS-Chem and historical emission inventories and future projections from the IPCC A1B scenario. Aerosol simulations are evaluated with observed spatial distributions and 1980-2010 trends of aerosol concentrations and wet deposition in the contiguous US. Direct and indirect radiative forcing is calculated using the GISS general circulation model and monthly mean aerosol distributions from GEOS-Chem. The radiative forcing from US anthropogenic aerosols is strongly localized over the eastern US. We find that its magnitude peaked in 1970-1990, with values over the eastern US (east of 100 deg W) of -2.0Wm(exp-2 for direct forcing including contributions from sulfate (-2.0Wm-2), nitrate (-0.2Wm(exp-2), organic carbon (-0.2Wm(exp-2), and black carbon (+0.4Wm(exp-2). The uncertainties in radiative forcing due to aerosol radiative properties are estimated to be about 50 %. The aerosol indirect effect is estimated to be of comparable magnitude to the direct forcing. We find that the magnitude of the forcing declined sharply from 1990 to 2010 (by 0.8Wm(exp-2) direct and 1.0Wm(exp-2 indirect), mainly reflecting decreases in SO2 emissions, and project that it will continue declining post-2010 but at a much slower rate since US SO2 emissions have already declined by almost 60% from their peak. This suggests that much of the warming effect of reducing US anthropogenic aerosol sources has already been realized. The small positive radiative forcing from US BC emissions (+0.3Wm(exp-2 over the eastern US in 2010; 5% of the global forcing from anthropogenic BC emissions worldwide) suggests that a US emission control strategy focused on BC would have only limited climate benefit.

Radiative Forcing Over Ocean by Ship Wakes

NASA Technical Reports Server (NTRS)

Gatebe, Charles K.; Wilcox, E.; Poudyal, R.; Wang, J.

2011-01-01

Changes in surface albedo represent one of the main forcing agents that can counteract, to some extent, the positive forcing from increasing greenhouse gas concentrations. Here, we report on enhanced ocean reflectance from ship wakes over the Pacific Ocean near the California coast, where we determined, based on airborne radiation measurements that ship wakes can increase reflected sunlight by more than 100%. We assessed the importance of this increase to climate forcing, where we estimated the global radiative forcing of ship wakes to be -0.00014 plus or minus 53% Watts per square meter assuming a global distribution of 32331 ships of size of greater than or equal to 100000 gross tonnage. The forcing is smaller than the forcing of aircraft contrails (-0.007 to +0.02 Watts per square meter), but considering that the global shipping fleet has rapidly grown in the last five decades and this trend is likely to continue because of the need of more inter-continental transportation as a result of economic globalization, we argue that the radiative forcing of wakes is expected to be increasingly important especially in harbors and coastal regions.

The contribution of China’s emissions to global climate forcing

NASA Astrophysics Data System (ADS)

Li, Bengang; Gasser, Thomas; Ciais, Philippe; Piao, Shilong; Tao, Shu; Balkanski, Yves; Hauglustaine, Didier; Boisier, Juan-Pablo; Chen, Zhuo; Huang, Mengtian; Li, Laurent Zhaoxin; Li, Yue; Liu, Hongyan; Liu, Junfeng; Peng, Shushi; Shen, Zehao; Sun, Zhenzhong; Wang, Rong; Wang, Tao; Yin, Guodong; Yin, Yi; Zeng, Hui; Zeng, Zhenzhong; Zhou, Feng

2016-03-01

Knowledge of the contribution that individual countries have made to global radiative forcing is important to the implementation of the agreement on “common but differentiated responsibilities” reached by the United Nations Framework Convention on Climate Change. Over the past three decades, China has experienced rapid economic development, accompanied by increased emission of greenhouse gases, ozone precursors and aerosols, but the magnitude of the associated radiative forcing has remained unclear. Here we use a global coupled biogeochemistry-climate model and a chemistry and transport model to quantify China’s present-day contribution to global radiative forcing due to well-mixed greenhouse gases, short-lived atmospheric climate forcers and land-use-induced regional surface albedo changes. We find that China contributes 10% ± 4% of the current global radiative forcing. China’s relative contribution to the positive (warming) component of global radiative forcing, mainly induced by well-mixed greenhouse gases and black carbon aerosols, is 12% ± 2%. Its relative contribution to the negative (cooling) component is 15% ± 6%, dominated by the effect of sulfate and nitrate aerosols. China’s strongest contributions are 0.16 ± 0.02 watts per square metre for CO2 from fossil fuel burning, 0.13 ± 0.05 watts per square metre for CH4, -0.11 ± 0.05 watts per square metre for sulfate aerosols, and 0.09 ± 0.06 watts per square metre for black carbon aerosols. China’s eventual goal of improving air quality will result in changes in radiative forcing in the coming years: a reduction of sulfur dioxide emissions would drive a faster future warming, unless offset by larger reductions of radiative forcing from well-mixed greenhouse gases and black carbon.

The contribution of China's emissions to global climate forcing.

PubMed

Li, Bengang; Gasser, Thomas; Ciais, Philippe; Piao, Shilong; Tao, Shu; Balkanski, Yves; Hauglustaine, Didier; Boisier, Juan-Pablo; Chen, Zhuo; Huang, Mengtian; Li, Laurent Zhaoxin; Li, Yue; Liu, Hongyan; Liu, Junfeng; Peng, Shushi; Shen, Zehao; Sun, Zhenzhong; Wang, Rong; Wang, Tao; Yin, Guodong; Yin, Yi; Zeng, Hui; Zeng, Zhenzhong; Zhou, Feng

2016-03-17

Knowledge of the contribution that individual countries have made to global radiative forcing is important to the implementation of the agreement on "common but differentiated responsibilities" reached by the United Nations Framework Convention on Climate Change. Over the past three decades, China has experienced rapid economic development, accompanied by increased emission of greenhouse gases, ozone precursors and aerosols, but the magnitude of the associated radiative forcing has remained unclear. Here we use a global coupled biogeochemistry-climate model and a chemistry and transport model to quantify China's present-day contribution to global radiative forcing due to well-mixed greenhouse gases, short-lived atmospheric climate forcers and land-use-induced regional surface albedo changes. We find that China contributes 10% ± 4% of the current global radiative forcing. China's relative contribution to the positive (warming) component of global radiative forcing, mainly induced by well-mixed greenhouse gases and black carbon aerosols, is 12% ± 2%. Its relative contribution to the negative (cooling) component is 15% ± 6%, dominated by the effect of sulfate and nitrate aerosols. China's strongest contributions are 0.16 ± 0.02 watts per square metre for CO2 from fossil fuel burning, 0.13 ± 0.05 watts per square metre for CH4, -0.11 ± 0.05 watts per square metre for sulfate aerosols, and 0.09 ± 0.06 watts per square metre for black carbon aerosols. China's eventual goal of improving air quality will result in changes in radiative forcing in the coming years: a reduction of sulfur dioxide emissions would drive a faster future warming, unless offset by larger reductions of radiative forcing from well-mixed greenhouse gases and black carbon.

Absorption, scattering, and radiation force efficiencies in the longitudinal wave scattering by a small viscoelastic particle in an isotropic solid.

PubMed

Lopes, J H; Leão-Neto, J P; Silva, G T

2017-11-01

Analytical expressions of the absorption, scattering, and elastic radiation force efficiency factors are derived for the longitudinal plane wave scattering by a small viscoelastic particle in a lossless solid matrix. The particle is assumed to be much smaller than the incident wavelength, i.e., the so-called long-wavelength (Rayleigh) approximation. The efficiencies are dimensionless quantities that represent the absorbed and scattering powers and the elastic radiation force on the particle. In the quadrupole approximation, they are expressed in terms of contrast functions (bulk and shear moduli, and density) between the particle and solid matrix. The results for a high-density polyethylene particle embedded in an aluminum matrix agree with those obtained with the partial wave expansion method. Additionally, the connection between the elastic radiation force and forward scattering function is established through the optical theorem. The present results should be useful for ultrasound characterization of particulate composites, and the development of implanted devices activated by radiation force.

Low Reynolds Number Droplet Combustion In CO2 Enriched Atmospheres In Microgravity

NASA Technical Reports Server (NTRS)

Hicks, M. C.

2003-01-01

The effect of radiative feedback from the gas phase in micro-gravity combustion processes has been of increasing concern because of the implications in the selection and evaluation of appropriate fire suppressants. The use of CO2, an optically thick gas in the infrared region of the electromagnetic spectrum, has garnered widespread acceptance as an effective fire suppressant for most ground based applications. Since buoyant forces often dominate the flow field in 1-g environments the temperature field between the flame front and the fuel surface is not significantly affected by gas phase radiative absorption and re-emission as these hot gases are quickly swept downstream. However, in reduced gravity environments where buoyant-driven convective flows are negligible and where low-speed forced convective flows may be present at levels where gas phase radiation becomes important, then changes in environment that enhance gas phase radiative effects need to be better understood. This is particularly true in assessments of flammability limits and selection of appropriate fire suppressants for future space applications. In recognition of this, a ground-based investigation has been established that uses a droplet combustion configuration to systematically study the effects of enhanced gas phase radiation on droplet burn rates, flame structure, and radiative output from the flame zone.

Does temperature nudging overwhelm aerosol radiative effects in regional integrated climate models?

NASA Astrophysics Data System (ADS)

He, Jian; Glotfelty, Timothy; Yahya, Khairunnisa; Alapaty, Kiran; Yu, Shaocai

2017-04-01

Nudging (data assimilation) is used in many regional integrated meteorology-air quality models to reduce biases in simulated climatology. However, in such modeling systems, temperature changes due to nudging could compete with temperature changes induced by radiatively active and hygroscopic short-lived tracers leading to two interesting dilemmas: when nudging is continuously applied, what are the relative sizes of these two radiative forces at regional and local scales? How do these two forces present in the free atmosphere differ from those present at the surface? This work studies these two issues by converting temperature changes due to nudging into pseudo radiative effects (PRE) at the surface (PRE_sfc), in troposphere (PRE_atm), and at the top of atmosphere (PRE_toa), and comparing PRE with the reported aerosol radiative effects (ARE). Results show that the domain-averaged PRE_sfc is smaller than ARE_sfc estimated in previous studies and this work, but could be significantly larger than ARE_sfc at local scales. PRE_atm is also much smaller than ARE_atm. These results indicate that appropriate nudging methodology could be applied to the integrated models to study aerosol radiative effects at continental/regional scales, but it should be treated with caution for local scale applications.

Acoustic Radiation Force Impulse Quantification in the Evaluation of Renal Parenchyma Elasticity in Pediatric Patients With Chronic Kidney Disease: Preliminary Results.

PubMed

Bilgici, Meltem Ceyhan; Bekci, Tumay; Genc, Gurkan; Tekcan, Demet; Tomak, Leman

2017-08-01

To evaluate renal parenchymal elasticity with acoustic radiation force impulse imaging in pediatric patients with chronic kidney disease (CKD) and compare with healthy volunteers. Thirty-eight healthy volunteers and 30 pediatric CKD patients were enrolled in this prospective study. The shear wave velocity (SW) values of both kidneys in CKD patients and healthy volunteers were evaluated. The mean SW in healthy volunteers was 2.21 ± 0.34 m/s, whereas the same value was 1.81 ± 0.49, 1.72 ± 0.63, 1.66 ± 0.29, 1.48 ± 0.37, and 1.23 ± 0.27 for stages 1, 2, 3, 4, and 5 in CKD patients, respectively. The SW was significantly lower for each stage in the CKD patients compared with healthy volunteers. Acoustic radiation force impulse could not predict the different stages of CKD, with the exception of stage 5. The cut-off value for predicting CKD was 1.81 m/s; at this threshold, sensitivity was 76.5% and specificity was 92.1% (area under the curve = 0.870 [95% confidence interval: 0.750-0.990]; P < .001). Interobserver agreement expressed as intraclass coefficient correlation was 0.65 (95% confidence interval: 0.34 to 0.83; P < .001). Acoustic radiation force impulse may be a potentially useful tool in detecting CKD in pediatric patients. © 2017 by the American Institute of Ultrasound in Medicine.

Atmospheric response and feedback to radiative forcing from biomass burning in tropical South America

Treesearch

Yongqiang Liu

2005-01-01

Simulations are performed to understand the importance of smoke from biomass burning in tropical South America to regional radiation and climate. The National Center for Atmospheric Research (NCAR) regional climate model coupled with the NCAR column radiative model is used to estimate smoke direct radiative forcing and consequent atmospheric perturbations during a...

Simulation of Dust Radiative Impact on the Red Sea Using Coupled Regional Ocean/Atmosphere Modeling System

NASA Astrophysics Data System (ADS)

Stenchikov, G. L.; Osipov, S.

2016-12-01

This study focuses on the Middle East regional climate response to the dust aerosol radiative forcing. MODIS and SEVIRI satellite observations show extremely high (exceeding 1) dust optical depths over the southern Red Sea during the summer season. The significant north-to-south gradient of the dust optical depth over the Red Sea persists throughout the entire year. The radiative forcing of dust at the sea surface exceeds 120 Wm-2. The effect of this forcing to the Red Sea thermal regime and circulations is not well quantified yet. Therefore here we employ the Regional Ocean Modeling system (ROMS) fully coupled with the Weather Research and Forecasting (WRF) model to study the impact of dust on the Red Sea. The WRF was modified to interactively account for the radiative effect of dust. Daily spectral optical properties of dust are computed using Mie, T-matrix and geometric optics approaches, and are based on the SEVIRI climatological optical depth. The WRF model parent and nested domains are configured over the Middle East and North Africa (MENA) region and over the Red Sea with 30 and 10 km resolution, respectively. The ROMS model over the Red Sea has 2 km grid spacing. The simulations show that, in the equilibrium response, dust causes 0.5-0.7K cooling of the Red Sea surface waters, and weakens the overturning circulation in the Red Sea. The salinity distribution, fresh water and heat budgets are significantly perturbed. This indicates that dust plays an important role in formation of the Red Sea energy balance and circulation regimes, and has to be thoroughly accounted for in the future modeling studies.

Scattering and Absorption of E&M radiation by small particles-applications to study impact of biomass aerosols on climate

NASA Astrophysics Data System (ADS)

Bililign, Solomon; Singh, Sujeeta; Fiddler, Marc; Smith, Damon

2015-03-01

The phenomena of scattering, absorption, and emission of light and other electromagnetic radiation by small particles are central to many science and engineering disciplines. Absorption of solar radiation by black carbon aerosols has a significant impact on the atmospheric energy distribution and hydrologic processes. By intercepting incoming solar radiation before it reaches the surface, aerosols heat the atmosphere and, in turn, cool the surface. The magnitude of the atmospheric forcing induced by anthropogenic absorbing aerosols, mainly black carbon (BC) emitted from biomass burning and combustion processes has been suggested to be comparable to the atmospheric forcing by all greenhouse gases (GHGs). Despite the global abundance of biomass burning for cooking, forests clearing for agriculture and wild fires, the optical properties of these aerosols have not been characterized at wide range of wavelengths. Our laboratory uses a combination of Cavity ring down spectroscopy and integrating nephelometry to measure optical properties of (extinction, absorption and scattering coefficients) of biomass aerosols. Preliminary results will be presented. Supported by the Department of Defense under Grant #W911NF-11-1-0188.

Theoretical and Experimental Investigation of Particle Trapping via Acoustic Bubbles

NASA Astrophysics Data System (ADS)

Chen, Yun; Fang, Zecong; Merritt, Brett; Saadat-Moghaddam, Darius; Strack, Dillon; Xu, Jie; Lee, Sungyon

2014-11-01

One important application of lab-on-a-chip devices is the trapping and sorting of micro-objects, with acoustic bubbles emerging as an effective, non-contact method. Acoustically actuated bubbles are known to exert a secondary radiation force on micro-particles and trap them, when this radiation force exceeds the drag force that acts to keep the particles in motion. In this study, we theoretically evaluate the magnitudes of these two forces for varying actuation frequencies and voltages. In particular, the secondary radiation force is calculated directly from bubble oscillation shapes that have been experimentally measured for varying acoustic parameters. Finally, based on the force estimates, we predict the threshold voltage and frequency for trapping and compare them to the experimental results.

Aerosol properties computed from aircraft-based observations during the ACE- Asia campaign. 2; A case study of lidar ratio closure and aerosol radiative effects

NASA Technical Reports Server (NTRS)

Kuzmanoski, Maja; Box, M. A.; Schmid, B.; Box, G. P.; Wang, J.; Russell, P. B.; Bates, D.; Jonsson, H. H.; Welton, Ellsworth J.; Flagan, R. C.

2005-01-01

For a vertical profile with three distinct layers (marine boundary, pollution and dust), observed during the ACE-Asia campaign, we carried out a comparison between the modeled lidar ratio vertical profile and that obtained from collocated airborne NASA AATS-14 sunphotometer and shipborne Micro-Pulse Lidar (MPL) measurements. Vertically resolved lidar ratio was calculated from two size distribution vertical profiles - one obtained by inversion of sunphotometer-derived extinction spectra, and one measured in-situ - combined with the same refractive index model based on aerosol chemical composition. The aerosol model implies single scattering albedos of 0.78 - 0.81 and 0.93 - 0.96 at 0.523 microns (the wavelength of the lidar measurements), in the pollution and dust layers, respectively. The lidar ratios calculated from the two size distribution profiles have close values in the dust layer; they are however, significantly lower than the lidar ratios derived from combined lidar and sunphotometer measurements, most probably due to the use of a simple nonspherical model with a single particle shape in our calculations. In the pollution layer, the two size distribution profiles yield generally different lidar ratios. The retrieved size distributions yield a lidar ratio which is in better agreement with that derived from lidar/sunphotometer measurements in this layer, with still large differences at certain altitudes (the largest relative difference was 46%). We explain these differences by non-uniqueness of the result of the size distribution retrieval and lack of information on vertical variability of particle refractive index. Radiative transfer calculations for this profile showed significant atmospheric radiative forcing, which occurred mainly in the pollution layer. We demonstrate that if the extinction profile is known then information on the vertical structure of absorption and asymmetry parameter is not significant for estimating forcing at TOA and the surface, while it is of importance for estimating vertical profiles of radiative forcing and heating rates.

Radiative Susceptibility of Cloudy Atmospheres to Droplet Number Perturbations: 2. Global analysis from MODIS

NASA Technical Reports Server (NTRS)

Oreopoulos, Lazaros; Platnick, Steven

2008-01-01

Global distributions of albedo susceptibility for areas covered by liquid clouds are presented for 4 months in 2005. The susceptibility estimates are based on expanded definitions presented in a companion paper and include relative cloud droplet number concentration (CDNC) changes, perturbations in cloud droplet asymmetry parameter and single-scattering albedo, atmospheric/surface effects, and incorporation of the full solar spectrum. The cloud properties (optical thickness and effective radius) used as input in the susceptibility calculations come from MODIS Terra and Aqua Collection 5 gridded data. Geographical distributions of susceptibility corresponding to absolute ( absolute cloud susceptibility ) and relative ( relative cloud susceptibility ) CDNC changes are markedly different indicating that the detailed nature of the cloud microphysical perturbation is important for determining the radiative forcing associated with the first indirect aerosol effect. However, both types of susceptibility exhibit common characteristics such as significant reductions when perturbations in single-scattering properties are omitted, significant increases when atmospheric absorption and surface albedo effects are ignored, and the tendency to decrease with latitude, to be higher over ocean than over land, and to be statistically similar between the morning and afternoon MODIS overpasses. The satellite-based susceptibility analysis helps elucidate the role of present-day cloud and land surface properties in indirect aerosol forcing responses. Our realistic yet moderate CDNC perturbations yield forcings on the order of 1-2 W/sq m for cloud optical property distributions and land surface spectral albedos observed by MODIS. Since susceptibilities can potentially be computed from model fields, these results have practical application in assessing the reasonableness of model-generated estimates of the aerosol indirect radiative forcing.

Evaluation of Rapid Adjustments to Radiative Forcing for Five Climate Forcing Agents in the Precipitation Driver Response Model Intercomparison Project (PDRMIP)

NASA Astrophysics Data System (ADS)

Smith, C. J.; Forster, P.; Richardson, T.; Myhre, G.

2016-12-01

Effective radiative forcing (ERF), rather than "traditional" radiative forcing (RF), has become an increasingly popular metric in recent years, as it more closely links the difference in the earth's top-of-atmosphere (TOA) energy budget to equilibrium near-surface temperature rise. One method to diagnose ERF is to take the difference of TOA radiative fluxes from two climate model runs (a perturbation and a control) with prescribed sea-surface temperatures and sea-ice coverage. ERF can be thought of as the sum of a direct forcing, which is the pure radiative effect of a forcing agent, plus rapid adjustments, which are changes in climate state triggered by the forcing agent that themselves affect the TOA energy budget and are unrelated to surface temperature changes.In addition to the classic experiment of doubling of CO2 (2xCO2), we analyse rapid adjustments to a tripling of methane (3xCH4), a quintupling of sulphate aerosol (5xSul), a ten times increase in black carbon (10xBC) and a 2% increase in the solar constant (2%Sol). We use CMIP-style climate model diagnostics from six participating models of the Precipitation Driver Response Model Intercomparison Project (PDRMIP).Assuming approximately linear contributions to the TOA flux differences, the rapid adjustments from changes in atmospheric temperature, surface temperature, surface albedo and water vapour can be cleanly and simply separated from the direct forcing by radiative kernels. The rapid adjustments are in turn decomposed into stratospheric and tropospheric components. We introduce kernels based on the HadGEM2 climate model and find similar results to those based on other models. Cloud adjustments are evaluated as a residual of the TOA radiative fluxes between all-sky and clear-sky runs once direct forcing and rapid adjustments have been subtracted. The cloud adjustments are also calculated online within the HadGEM2 model using the ISCCP simulator. For aerosol forcing experiments, rapid adjustments vary substantially between models. Much of the contribution to this model spread is in the cloud adjustments. We also notice a spread in the model calculations of direct forcing for greenhouse gases, which suggest differences in the radiative transfer parameterisations used by each model.

A novel nanometric DNA thin film as a sensor for alpha radiation

PubMed Central

Kulkarni, Atul; Kim, Byeonghoon; Dugasani, Sreekantha Reddy; Joshirao, Pranav; Kim, Jang Ah; Vyas, Chirag; Manchanda, Vijay; Kim, Taesung; Park, Sung Ha

2013-01-01

The unexpected nuclear accidents have provided a challenge for scientists and engineers to develop sensitive detectors, especially for alpha radiation. Due to the high linear energy transfer value, sensors designed to detect such radiation require placement in close proximity to the radiation source. Here we report the morphological changes and optical responses of artificially designed DNA thin films in response to exposure to alpha radiation as observed by an atomic force microscope, a Raman and a reflectance spectroscopes. In addition, we discuss the feasibility of a DNA thin film as a radiation sensing material. The effect of alpha radiation exposure on the DNA thin film was evaluated as a function of distance from an 241Am source and exposure time. Significant reflected intensity changes of the exposed DNA thin film suggest that a thin film made of biomolecules can be one of promising candidates for the development of online radiation sensors. PMID:23792924

Forcings and feedbacks by land ecosystem changes on climate change

NASA Astrophysics Data System (ADS)

Betts, R. A.

2006-12-01

Vegetation change is involved in climate change through both forcing and feedback processes. Emissions of CO{2} from past net deforestation are estimated to have contributed approximately 0.22 0.51 Wm - 2 to the overall 1.46 Wm - 2 radiative forcing by anthropogenic increases in CO{2} up to the year 2000. Deforestation-induced increases in global mean surface albedo are estimated to exert a radiative forcing of 0 to -0.2 Wm - 2, and dust emissions from land use may exert a radiative forcing of between approximately +0.1 and -0.2 Wm - 2. Changes in the fluxes of latent and sensible heat due to tropical deforestation are simulated to have exerted other local warming effects which cannot be quantified in terms of a Wm - 2 radiative forcing, with the potential for remote effects through changes in atmospheric circulation. With tropical deforestation continuing rapidly, radiative forcing by surface albedo change may become less useful as a measure of the forcing of climate change by changes in the physical properties of the land surface. Although net global deforestation is continuing, future scenarios used for climate change prediction suggest that fossil fuel emissions of CO{2} may continue to increase at a greater rate than land use emissions and therefore continue to increase in dominance as the main radiative forcing. The CO{2} rise may be accelerated by up to 66% by feedbacks arising from global soil carbon loss and forest dieback in Amazonia as a consequence of climate change, and Amazon forest dieback may also exert feedbacks through changes in the local water cycle and increases in dust emissions.

Estimating radiative feedbacks from stochastic fluctuations in surface temperature and energy imbalance

NASA Astrophysics Data System (ADS)

Proistosescu, C.; Donohoe, A.; Armour, K.; Roe, G.; Stuecker, M. F.; Bitz, C. M.

2017-12-01

Joint observations of global surface temperature and energy imbalance provide for a unique opportunity to empirically constrain radiative feedbacks. However, the satellite record of Earth's radiative imbalance is relatively short and dominated by stochastic fluctuations. Estimates of radiative feedbacks obtained by regressing energy imbalance against surface temperature depend strongly on sampling choices and on assumptions about whether the stochastic fluctuations are primarily forced by atmospheric or oceanic variability (e.g. Murphy and Forster 2010, Dessler 2011, Spencer and Braswell 2011, Forster 2016). We develop a framework around a stochastic energy balance model that allows us to parse the different contributions of atmospheric and oceanic forcing based on their differing impacts on the covariance structure - or lagged regression - of temperature and radiative imbalance. We validate the framework in a hierarchy of general circulation models: the impact of atmospheric forcing is examined in unforced control simulations of fixed sea-surface temperature and slab ocean model versions; the impact of oceanic forcing is examined in coupled simulations with prescribed ENSO variability. With the impact of atmospheric and oceanic forcing constrained, we are able to predict the relationship between temperature and radiative imbalance in a fully coupled control simulation, finding that both forcing sources are needed to explain the structure of the lagged-regression. We further model the dependence of feedback estimates on sampling interval by considering the effects of a finite equilibration time for the atmosphere, and issues of smoothing and aliasing. Finally, we develop a method to fit the stochastic model to the short timeseries of temperature and radiative imbalance by performing a Bayesian inference based on a modified version of the spectral Whittle likelihood. We are thus able to place realistic joint uncertainty estimates on both stochastic forcing and radiative feedbacks derived from observational records. We find that these records are, as of yet, too short to be useful in constraining radiative feedbacks, and we provide estimates of how the uncertainty narrows as a function of record length.

Quantifying organic aerosol single scattering albedo over tropical biomass burning regions using ground-based observation

NASA Astrophysics Data System (ADS)

Chu, J. E.

2016-12-01

Despite growing evidence of light-absorbing organic aerosols (OAs), OA light absorption has been poorly understood due to difficulties in aerosol light absorption measurements. In this study, we developed an empirical method to quantify OA single scattering albedo (SSA), the ratio of light scattering to extinction, using ground-based Aerosol Robotic Network (AERONET) observation. Our method includes partitioning fine-mode aerosol optical depth (fAOD) to individual aerosol's optical depth (AOD), separating black carbon and OA absorption aerosol optical depths, and finally binding OA SSA and sulfate+nitrate AOD. Our best estimate of OA SSA over tropical biomass burning region is 0.91 at 550nm with a range of 0.82-0.93. It implies the common OA SSA values of 0.96-1.0 in aerosol CTMs and GCMs significantly underrepresent OA light absorption. Model experiments with prescribed OA SSA showed that the enhanced absorption of solar radiation due to light absorbing OA yields global mean radiative forcing is +0.09 Wm-2 at the TOA, +0.21 Wm-2 at the atmosphere, and -0.12 Wm-2 at the surface. Compared to the previous assessment of OA radiative forcing reported in AeroCom II project, our result indicate that OA light absorption causes TOA radiative forcing by OA to change from negative (i.e., cooling effect) to positive (warming effect).

Advances in Mineral Dust Source Composition Measurement with Imaging Spectroscopy at the Salton Sea, CA

NASA Astrophysics Data System (ADS)

Green, R. O.; Realmuto, V. J.; Thompson, D. R.; Mahowald, N. M.; Pérez García-Pando, C.; Miller, R. L.; Clark, R. N.; Swayze, G. A.; Okin, G. S.

2015-12-01

Mineral dust emitted from the Earth's surface is a principal contributor to direct radiative forcing over the arid regions, where shifts in climate have a significant impact on agriculture, precipitation, and desert encroachment around the globe. Dust particles contribute to both positive and negative forcing, depending on the composition of the particles. Particle composition is a function of the surface mineralogy of dust source regions, but poor knowledge of surface mineralogy on regional to global scales limits the skill of Earth System models to predict shifts in regional climate around the globe. Earth System models include the source, emission, transport and deposition phases of the dust cycle. In addition to direct radiative forcing contributions, mineral dust impacts include indirect radiative forcing, modification of the albedo and melting rates of snow and ice, kinetics of tropospheric photochemistry, formation and deposition of acidic aerosols, supply of nutrients to aquatic and terrestrial ecosystems, and impact on human health and safety. We demonstrate the ability to map mineral dust source composition in the Salton Sea dust source region with imaging spectroscopy measurements acquired as part of the NASA HyspIRI preparatory airborne campaign. These new spectroscopically derived compositional measurements provide a six orders of magnitude improvement over current atlases for this dust source region and provide a pathfinder example for a remote measurement approach to address this critical dust composition gap for global Earth System models.

Longwave Radiative Forcing of Saharan Dust Aerosols Estimated from MODIS, MISR and CERES Observations on Terra

NASA Technical Reports Server (NTRS)

Zhang, Jiang-Long; Christopher, Sundar A.

2003-01-01

Using observations from the Multi-angle Imaging Spectroradiometer (MISR), the Moderate Resolution Imaging Spectroradiometer (MODIS), and the Clouds and the Earth's Radiant Energy System (CERES) instruments onboard the Terra satellite; we present a new technique for studying longwave (LW) radiative forcing of dust aerosols over the Saharan desert for cloud-free conditions. The monthly-mean LW forcing for September 2000 is 7 W/sq m and the LW forcing efficiency' (LW(sub eff)) is 15 W/sq m. Using radiative transfer calculations, we also show that the vertical distribution of aerosols and water vapor are critical to the understanding of dust aerosol forcing. Using well calibrated, spatially and temporally collocated data sets, we have combined the strengths of three sensors from the same satellite to quantify the LW radiative forcing, and show that dust aerosols have a "warming" effect over the Saharan desert that will counteract the shortwave "cooling effect" of aerosols.

Reduction of vibration forces transmitted from a radiator cooling fan to a vehicle body

NASA Astrophysics Data System (ADS)

Lim, Jonghyuk; Sim, Woojeong; Yun, Seen; Lee, Dongkon; Chung, Jintai

2018-04-01

This article presents methods for reducing transmitted vibration forces caused by mass unbalance of the radiator cooling fan during vehicle idling. To identify the effects of mass unbalance upon the vibration characteristics, vibration signals of the fan blades were experimentally measured both with and without an added mass. For analyzing the vibration forces transmitted to the vehicle body, a dynamic simulation model was established that reflected the vibration characteristics of the actual system. This process included a method described herein for calculating the equivalent stiffness and the equivalent damping of the shroud stators and rubber mountings. The dynamic simulation model was verified by comparing its results with experimental results of the radiator cooling fan. The dynamic simulation model was used to analyze the transmitted vibration forces at the rubber mountings. Also, a measure was established to evaluate the effects of varying the design parameters upon the transmitted vibration forces. We present design guidelines based on these analyses to reduce the transmitted vibration forces of the radiator cooling fan.

Forcing and Responses of the Surface Energy Budget at Summit, Greenland

NASA Astrophysics Data System (ADS)

Miller, Nathaniel B.

Energy exchange at the Greenland Ice Sheet surface governs surface temperature variability, a factor critical for representing increasing surface melt extent, which portends a rise in global sea level. A comprehensive set of cloud, tropospheric, near-surface and sub-surface measurements at Summit Station is utilized to determine the driving forces and subsequent responses of the surface energy budget (SEB). This budget includes radiative, turbulent, and ground heat fluxes, and ultimately controls the evolution of surface temperature. At Summit Station, clouds radiatively warm the surface in all months with an annual average cloud radiative forcing value of 33 W m -2, largely driven by the occurrence of liquid-bearing clouds. The magnitude of the surface temperature response is dependent on how turbulent and ground heat fluxes modulate changes to radiative forcing. Relationships between forcing terms and responding surface fluxes show that changes in the upwelling longwave radiation compensate for 65-85% (50- 60%) of the total change in radiative forcing in the winter (summer). The ground heat flux is the second largest response term (16% annually), especially during winter. Throughout the annual cycle, the sensible heat flux response is comparatively constant (9%) and latent heat flux response is only 1.5%, becoming more of a factor in modulating surface temperature responses during the summer. Combining annual cycles of these responses with cloud radiative forcing results, clouds warm the surface by an estimated 7.8°C annually. A reanalysis product (ERA-I), operational model (CFSv2), and climate model (CESM) are evaluated utilizing the comprehensive set of SEB observations and process-based relationships. Annually, surface temperatures in each model are warmer than observed with overall poor representation of the coldest surface temperatures. Process-based relationships between different SEB flux terms offer insight into how well a modeling framework represents physical processes and the ability to distinguish errors in forcing versus those in physical representation. Such relationships convey that all three models underestimate the response of surface temperatures to changes in radiative forcing. These results provide a method to expose model deficiencies and indicate the importance of representing surface, sub-surface and boundary-layer processes when portraying cloud impacts on surface temperature variability.

Relative importance of thermal versus carbon dioxide induced warming from fossil-fuel combustion

NASA Astrophysics Data System (ADS)

Zhang, X.; Caldeira, K.

2015-12-01

The Earth is heated both when reduced carbon is oxidized to carbon dioxide and when outgoing longwave radiation is trapped by carbon dioxide in the atmosphere (CO2 greenhouse effect). The purpose of this study is to improve our understanding of time scales and relative magnitudes of climate forcing increase over time from pulse, continuous, and historical CO2 and thermal emissions. To estimate the amount of global warming that would be produced by thermal and CO2 emissions from fossil fuel combustion, we calculate thermal emissions with thermal contents of fossil fuels and estimate CO2 emissions with emission factors from Intergovernmental Panel on Climate Change (IPCC) AR5. We then use a schematic climate model mimicking Coupled Model Intercomparison Project Phase 5 to investigate the climate forcing and the time-integrated climate forcing. We show that, considered globally, direct thermal forcing from fossil fuel combustion is about 1.71% the radiative forcing from CO2 that has accumulated in the atmosphere from past fossil fuel combustion. When a new power plant comes on line, the radiative forcing from the accumulation of released CO2 exceeds the thermal emissions from the power plant in less than half a year (and about 3 months for coal plants). Due to the long lifetime of CO2 in the atmosphere, CO2 radiative forcing greatly overwhelms direct thermal forcing on longer time scales. Ultimately, the cumulative radiative forcing from the CO2 exceeds the direct thermal forcing by a factor of ~100,000.

Impact of Dust Radiative Forcing upon Climate. Chapter 13

NASA Technical Reports Server (NTRS)

Miller, Ronald L.; Knippertz, Peter; Perez Garcia-Pando, Carlos; Perlwitz, Jan P.; Tegan, Ina

2014-01-01

Dust aerosols perturb the atmospheric radiative flux at both solar and thermal wavelengths, altering the energy and water cycles. The climate adjusts by redistributing energy and moisture, so that local temperature perturbations, for example, depend upon the forcing over the entire extent of the perturbed circulation. Within regions frequently mixed by deep convection, including the deep tropics, dust particles perturb the surface air temperature primarily through radiative forcing at the top of the atmosphere (TOA). Many models predict that dust reduces global precipitation. This reduction is typically attributed to the decrease of surface evaporation in response to dimming of the surface. A counterexample is presented, where greater shortwave absorption by dust increases evaporation and precipitation despite greater dimming of the surface. This is attributed to the dependence of surface evaporation upon TOA forcing through its influence upon surface temperature and humidity. Perturbations by dust to the surface wind speed and vegetation (through precipitation anomalies) feed back upon the dust aerosol concentration. The current uncertainty of radiative forcing attributed to dust and the resulting range of climate perturbations calculated by models remain a useful test of our understanding of the mechanisms relating dust radiative forcing to the climate response.

Trends and projections of Southern Hemisphere baroclinicity: the role of external forcing and impact on Australian rainfall

NASA Astrophysics Data System (ADS)

Frederiksen, Carsten S.; Frederiksen, Jorgen S.; Sisson, Janice M.; Osbrough, Stacey L.

2017-05-01

Changes in the characteristics of Southern Hemisphere (SH) storms, in all seasons, during the second half of the twentieth century, have been related to changes in the annual cycle of SH baroclinic instability. In particular, significant negative trends in baroclinic instability, as measured by the Phillips Criterion, have been found in the region of the climatological storm tracks; a zonal band of significant positive trends occur further poleward. Corresponding to this decrease/increase in baroclinic instability there is a decrease/increase in the growth rate of storm formation at these latitudes over this period, and in some cases a preference for storm formation further poleward than normal. Based on model output from a multi-model ensemble (MME) of coupled atmosphere-ocean general circulation models, it is shown that these trends are the result of external radiative forcing, including anthropogenic greenhouse gases, ozone, aerosols and land-use change. The MME is used in an analysis of variance method to separate the internal (natural) variability in the Phillips Criterion from influences associated with anomalous external radiative forcing. In all seasons, the leading externally forced mode has a significant trend and a loading pattern highly correlated with the pattern of trends in the Phillips Criterion. The covariance between the externally forced component of SH rainfall and the leading external mode strongly resembles the MME pattern of SH rainfall trends. A comparison between similar analyses of MME simulations using the second half of the twenty-first century of the Representative Concentration Pathways (RCP) RCP8.5 and RCP4.5 scenarios show that trends in the Phillips Criterion and rainfall are projected to continue and intensify under increasing anthropogenic greenhouse gas concentrations.

Evaluation of ACCMIP Outgoing Longwave Radiation from Tropospheric Ozone Using TES Satellite Observations.

NASA Technical Reports Server (NTRS)

Bowman, Kevin W.; Shindell, Drew Todd; Worden, H. M.; Lamarque, J. F.; Young, P. J.; Stevenson, D. S.; Qu, Z.; delaTorre, M.; Bergmann, D.; Cameron-Smith, P. J.;

Climate Implications of the Heterogeneity of Anthropogenic Aerosol Forcing

NASA Astrophysics Data System (ADS)

Persad, Geeta Gayatri

Short-lived anthropogenic aerosols are concentrated in regions of high human activity, where they interact with radiation and clouds, causing horizontally heterogeneous radiative forcing between polluted and unpolluted regions. Aerosols can absorb shortwave energy in the atmosphere, but deplete it at the surface, producing opposite radiative perturbations between the surface and atmosphere. This thesis investigates climate and policy implications of this horizontal and vertical heterogeneity of anthropogenic aerosol forcing, employing the Geophysical Fluid Dynamics Laboratory's AM2.1 and AM3 models, both at a global scale and using East Asia as a regional case study. The degree of difference between spatial patterns of climate change due to heterogeneous aerosol forcing versus homogeneous greenhouse gas forcing deeply impacts the detection, attribution, and prediction of regional climate change. This dissertation addresses a gap in current understanding of these two forcings' response pattern development, using AM2.1 historical forcing simulations. The results indicate that fast atmospheric and land-surface processes alone substantially homogenize the global pattern of surface energy flux response to heterogeneous aerosol forcing. Aerosols' vertical redistribution of energy significantly impacts regional climate, but is incompletely understood. It is newly identified here, via observations and historical and idealized forcing simulations, that increased aerosol-driven atmospheric absorption may explain half of East Asia's recent surface insolation decline. Further, aerosols' surface and atmospheric effects counteract each other regionally---atmospheric heating enhances summer monsoon circulation, while surface dimming suppresses it---but absorbing aerosols' combined effects reduce summer monsoon rainfall. This thesis constitutes the first vertical decomposition of aerosols' impacts in this high-emissions region and elucidates the monsoonal response to aerosols' surface versus atmospheric forcing. Future aerosol emissions patterns will affect the distribution of regional climate impacts. This dissertation interrogates how international trade affects existing assumptions about East Asia's future black carbon aerosol emissions, using integrated assessment modeling, emissions and economic data, and AM3 simulations. Exports emerge as a uniquely large and potentially growing source of Chinese black carbon emissions that could impede projected regional emissions reductions, with substantial climate and health consequences. The findings encourage greater emissions projection sophistication and illustrate how societal decisions may influence future aerosol forcing heterogeneity.

Relationship of scattering phase shifts to special radiation force conditions for spheres in axisymmetric wave-fields.

PubMed

Marston, Philip L; Zhang, Likun

2017-05-01

When investigating the radiation forces on spheres in complicated wave-fields, the interpretation of analytical results can be simplified by retaining the s-function notation and associated phase shifts imported into acoustics from quantum scattering theory. For situations in which dissipation is negligible, as taken to be the case in the present investigation, there is an additional simplification in that partial-wave phase shifts become real numbers that vanish when the partial-wave index becomes large and when the wave-number-sphere-radius product vanishes. By restricting attention to monopole and dipole phase shifts, transitions in the axial radiation force for axisymmetric wave-fields are found to be related to wave-field parameters for traveling and standing Bessel wave-fields by considering the ratio of the phase shifts. For traveling waves, the special force conditions concern negative forces while for standing waves, the special force conditions concern vanishing radiation forces. An intermediate step involves considering the functional dependence on phase shifts. An appendix gives an approximation for zero-force plane standing wave conditions. Connections with early investigations of acoustic levitation are mentioned and some complications associated with viscosity are briefly noted.

Aerosol influence on energy balance of the middle atmosphere of Jupiter.

PubMed

Zhang, Xi; West, Robert A; Irwin, Patrick G J; Nixon, Conor A; Yung, Yuk L

2015-12-22

Aerosols are ubiquitous in planetary atmospheres in the Solar System. However, radiative forcing on Jupiter has traditionally been attributed to solar heating and infrared cooling of gaseous constituents only, while the significance of aerosol radiative effects has been a long-standing controversy. Here we show, based on observations from the NASA spacecraft Voyager and Cassini, that gases alone cannot maintain the global energy balance in the middle atmosphere of Jupiter. Instead, a thick aerosol layer consisting of fluffy, fractal aggregate particles produced by photochemistry and auroral chemistry dominates the stratospheric radiative heating at middle and high latitudes, exceeding the local gas heating rate by a factor of 5-10. On a global average, aerosol heating is comparable to the gas contribution and aerosol cooling is more important than previously thought. We argue that fractal aggregate particles may also have a significant role in controlling the atmospheric radiative energy balance on other planets, as on Jupiter.

LINKING REGIONAL AEROSOL EMISSION CHANGES WITH MULTIPLE IMPACT MEASURES THROUGH DIRECT AND CLOUD-RELATED FORCING ESTIMATES

EPA Science Inventory

Outputs expected from this project include improved confidence in direct radiative forcing and cloud radiative forcing, particularly over the United States and with regard to United States emissions publicly available, documented data sets including emission inventories of siz...

Annual Cycle of Cloud Forcing of Surface Radiation Budget

NASA Technical Reports Server (NTRS)

Wilber, Anne C.; Smith, G. Louis; Stackhouse, Paul W., Jr.; Gupta, Shashi K.

2006-01-01

The climate of the Earth is determined by its balance of radiation. The incoming and outgoing radiation fluxes are strongly modulated by clouds, which are not well understood. The Earth Radiation Budget Experiment (Barkstrom and Smith, 1986) provided data from which the effects of clouds on radiation at the top of the atmosphere (TOA) could be computed (Ramanathan, 1987). At TOA, clouds increase the reflected solar radiation, tending to cool the planet, and decrease the OLR, causing the planet to retain its heat (Ramanathan et al., 1989; Harrison et al., 1990). The effects of clouds on radiation fluxes are denoted cloud forcing. These shortwave and longwave forcings counter each other to various degrees, so that in the tropics the result is a near balance. Over mid and polar latitude oceans, cloud forcing at TOA results in large net loss of radiation. Here, there are large areas of stratus clouds and cloud systems associated with storms. These systems are sensitive to surface temperatures and vary strongly with the annual cycle. During winter, anticyclones form over the continents and move to the oceans during summer. This movement of major cloud systems causes large changes of surface radiation, which in turn drives the surface temperature and sensible and latent heat released to the atmosphere.

On radiation forces acting on a transparent nanoparticle in the field of a focused laser beam

DOE Office of Scientific and Technical Information (OSTI.GOV)

Afanas'ev, A A; Rubinov, A N; Gaida, L S

2015-10-31

Radiation forces acting on a transparent spherical nanoparticle in the field of a focused Gaussian laser beam are studied theoretically in the Rayleigh scattering regime. Expressions are derived for the scattering force and Cartesian components of the gradient force. The resultant force acting on a nanoparticle located in the centre of a laser beam is found. The parameters of the focused beam and optical properties of the nanoparticle for which the longitudinal component of the gradient force exceeds the scattering force are determined. Characteristics of the transverse gradient force are discussed. (nanophotonics)

Global Climate Forcing from Albedo Change Caused by Large-scale Deforestation and Reforestation: Quantification and Attribution of Geographic Variation

NASA Technical Reports Server (NTRS)

Gao, Feng; Ghimire, Bardan; Jiao, Tong; Williams, Christopher A.; Masek, Jeffrey; Schaaf, Crystal

2017-01-01

Large-scale deforestation and reforestation have contributed substantially to historical and contemporary global climate change in part through albedo-induced radiative forcing, with meaningful implications for forest management aiming to mitigate climate change. Associated warming or cooling varies widely across the globe due to a range of factors including forest type, snow cover, and insolation, but resulting geographic variation remain spoorly described and has been largely based on model assessments. This study provides an observation-based approach to quantify local and global radiative forcings from large-scale deforestation and reforestation and further examines mechanisms that result in the spatial heterogeneity of radiative forcing. We incorporate a new spatially and temporally explicit land cover-specific albedo product derived from Moderate Resolution Imaging Spectroradiometer with a historical land use data set (Land Use Harmonization product). Spatial variation in radiative forcing was attributed to four mechanisms, including the change in snow-covered albedo, change in snow-free albedo, snow cover fraction, and incoming solar radiation. We find an albedo-only radiative forcing (RF) of -0.819 W m(exp -2) if year 2000 forests were completely deforested and converted to croplands. Albedo RF from global reforestation of present-day croplands to recover year 1700 forests is estimated to be 0.161 W m)exp -2). Snow-cover fraction is identified as the primary factor in determining the spatial variation of radiative forcing in winter, while the magnitude of the change in snow-free albedo is the primary factor determining variations in summertime RF. Findings reinforce the notion that, for conifers at the snowier high latitudes, albedo RF diminishes the warming from forest loss and the cooling from forest gain more so than for other forest types, latitudes, and climate settings.

A global modeling study on carbonaceous aerosol microphysical characteristics and radiative forcing

NASA Astrophysics Data System (ADS)

Bauer, S. E.; Menon, S.; Koch, D.; Bond, T. C.; Tsigaridis, K.

2010-02-01

Recently, attention has been drawn towards black carbon aerosols as a short-term climate warming mitigation candidate. However the global and regional impacts of the direct, cloud-indirect and semi-direct forcing effects are highly uncertain, due to the complex nature of aerosol evolution and the way that mixed, aged aerosols interact with clouds and radiation. A detailed aerosol microphysical scheme, MATRIX, embedded within the GISS climate model is used in this study to present a quantitative assessment of the impact of microphysical processes involving black carbon, such as emission size distributions and optical properties on aerosol cloud activation and radiative forcing. Our best estimate for net direct and indirect aerosol radiative forcing between 1750 and 2000 is -0.56 W/m2. However, the direct and indirect aerosol effects are quite sensitive to the black and organic carbon size distribution and consequential mixing state. The net radiative forcing can vary between -0.32 to -0.75 W/m2 depending on these carbonaceous particle properties at emission. Assuming that sulfates, nitrates and secondary organics form a coating around a black carbon core, rather than forming a uniformly mixed particle, changes the overall net aerosol radiative forcing from negative to positive. Taking into account internally mixed black carbon particles let us simulate correct aerosol absorption. Black carbon absorption is amplified by sulfate and nitrate coatings, but even more strongly by organic coatings. Black carbon mitigation scenarios generally showed reduced radiative forcing when sources with a large proportion of black carbon, such as diesel, are reduced; however reducing sources with a larger organic carbon component as well, such as bio-fuels, does not necessarily lead to climate benefits.

Radiation Pressure Measurements on Micron Size Individual Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Craven, P.D.; Spann, J. F.; Tankosic, D.; Witherow, W. K.; LeClair, A.; West, E.; Sheldon, R.; Gallagher, D. L.; Adrian, M. L.

2003-01-01

Measurements of electromagnetic radiation pressure have been made on individual silica (SiO2) particles levitated in an electrodynamic balance. These measurements were made by inserting single charged particles of known diameter in the 0.2 micron to 6.82 micron range and irradiating them from above with laser radiation focused to beam-widths of approx. 175-400 micron, at ambient pressures approx. 10(exp -3) to 10(exp -4) torr. The downward displacement of the particle due to the radiation force is balanced by the electrostatic force indicated by the compensating dc potential applied to the balance electrodes, providing a direct measure of the radiation force on the levitated particle. Theoretical calculations of the radiation pressure with a least-squares fit to the measured data yield the radiation pressure efficiencies of the particles, and comparisons with Mie scattering theory calculations provide the imaginary part of the refractive index of silica and the corresponding extinction and scattering efficiencies.

Radiation Pressure Measurements on Micron-Size Individual Dust Grains

NASA Technical Reports Server (NTRS)

Abbas, M. M.; Craven, P. D.; Spann, J. F.; Witherow, W. K.; West, E. A.; Gallagher, D. L.; Adrian, M. L.; Fishman, G. J.; Tankosic, D.; LeClair, A.

2003-01-01

Measurements of electromagnetic radiation pressure have been made on individual silica (SiO2) particles levitated in an electrodynamic balance. These measurements were made by inserting single charged particles of known diameter in the 0.2- to 6.82-micron range and irradiating them from above with laser radiation focused to beam widths of approximately 175- 400 microns at ambient pressures particle due to the radiation force is balanced by the electrostatic force indicated by the compensating dc potential applied to the balance electrodes, providing a direct measure of the radiation force on the levitated particle. Theoretical calculations of the radiation pressure with a least-squares fit to the measured data yield the radiation pressure efficiencies of the particles, and comparisons with Mie scattering theory calculations provide the imaginary part of the refractive index of SiO2 and the corresponding extinction and scattering efficiencies.

Acoustic manipulation of oscillating spherical bodies: Emergence of axial negative acoustic radiation force

NASA Astrophysics Data System (ADS)

Rajabi, Majid; Mojahed, Alireza

2016-11-01

In this paper, emergence of negative axial acoustic radiation force on a rigid oscillating spherical body is investigated for acoustic manipulation purposes. The problem of plane acoustic wave scattering from an oscillating spherical body submerged in an ideal acoustic fluid medium is solved. For the case of oscillating direction collinear with the wave propagation wave number vector (desired path), it has been shown that the acoustic radiation force, as a result of nonlinear acoustic wave interaction with bodies can be expressed as a linear function of incident wave field and the oscillation properties of the oscillator (i.e., amplitude and phase of oscillation). The negative (i.e., pulling effects) and positive (i.e., pushing effects) radiation force situations are divided in oscillation complex plane with a specific frequency-dependant straight line. This characteristic line defines the radiation force cancellation state. In order to investigate the stability of the mentioned manipulation strategy, the case of misaligned oscillation of sphere with the wave propagation direction is studied. The proposed methodology may suggest a novel concept of single-beam acoustic handling techniques based on smart carriers.

Calculation of the acoustic radiation force on coated spherical shells in progressive and standing plane waves.

PubMed

Mitri, F G

2006-07-01

In this paper, analytical equations are derived for the time-averaged radiation force induced by progressive and standing acoustic waves incident on elastic spherical shells covered with a layer of viscoelastic and sound-absorbing material. The fluid surrounding the shells is considered compressible and nonviscous. The incident field is assumed to be moderate so that the scattered field from the shells is taken to linear approximation. The analytical results are illustrated by means of a numerical example in which the radiation force function curves are displayed, with particular emphasis on the coating thickness and the content of the hollow region of the shells. The fluid-loading on the radiation force function curves is analysed as well. This study attempts to generalize the various treatments of radiation force due to both progressive and standing waves on spherically-shaped structures immersed in ideal fluids. The results show that various ways can be effectively used for damping resonance peaks, such as by changing the fluid in the interior hollow region of the shells or by changing the coating thickness.

First observation-based estimates of cloud-free aerosol radiative forcing across China

Treesearch

Zhanqing Li; Kwon-Ho Lee; Yuesi Wang; Jinyuan Xin; Wei-Min Hao

2010-01-01

Heavy loading of aerosols in China is widely known, but little is known about their impact on regional radiation budgets, which is often expressed as aerosol radiative forcing (ARF). Cloud‐free direct ARF has either been estimated by models across the region or determined at a handful of locations with aerosol and/or radiation measurements. In this study, ARF...

Identification of impact force acting on composite laminated plates using the radiated sound measured with microphones

NASA Astrophysics Data System (ADS)

Atobe, Satoshi; Nonami, Shunsuke; Hu, Ning; Fukunaga, Hisao

2017-09-01

Foreign object impact events are serious threats to composite laminates because impact damage leads to significant degradation of the mechanical properties of the structure. Identification of the location and force history of the impact that was applied to the structure can provide useful information for assessing the structural integrity. This study proposes a method for identifying impact forces acting on CFRP (carbon fiber reinforced plastic) laminated plates on the basis of the sound radiated from the impacted structure. Identification of the impact location and force history is performed using the sound pressure measured with microphones. To devise a method for identifying the impact location from the difference in the arrival times of the sound wave detected with the microphones, the propagation path of the sound wave from the impacted point to the sensor is examined. For the identification of the force history, an experimentally constructed transfer matrix is employed to relate the force history to the corresponding sound pressure. To verify the validity of the proposed method, impact tests are conducted by using a CFRP cross-ply laminate as the specimen, and an impulse hammer as the impactor. The experimental results confirm the validity of the present method for identifying the impact location from the arrival time of the sound wave detected with the microphones. Moreover, the results of force history identification show the feasibility of identifying the force history accurately from the measured sound pressure using the experimental transfer matrix.

A Biomimetic Propulsor for Active Noise Control. Part 2: Theory

NASA Astrophysics Data System (ADS)

Annaswamy Krol, A., Jr.; Bandyopadhyay, P. R.

2000-11-01

The alteration of radiated noise in underwater propulsors using biomimetic active control is considered. Wake momentum filling is carried out by introducing artificial muscles at the trailing edge of a stator blade of an upstream stator propulsor, and articulating them like a fish tail (see companion abstract Part 1). Using a systems framework, we derive a methodology for the articulation of the muscles with active control. The unsteady force produced on the rotor because of velocity perturbations due to actuator displacements, wake deficits caused by stator boundary layers, and blade rotation is modeled. Linear and adaptive nonlinear control strategies are described for articulating the tail using unsteady force measurements. This active control procedure can be viewed as the realization of “virtual” blades with different sweep and noise characteristics and can affect the noise spectrum due to direct radiation significantly. The work provides an understanding of the effect of nonuniform wakes on radiated noise and can lead to a general approach by which wakes can be altered.

PHOTOPHORESIS IN A DILUTE, OPTICALLY THICK MEDIUM AND DUST MOTION IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

McNally, Colin P.; Hubbard, Alexander, E-mail: cmcnally@nbi.dk, E-mail: ahubbard@amnh.org

2015-11-20

We derive expressions for the photophoretic force on opaque spherical particles in a dilute gas in the optically thick regime where the radiation field is in local thermal equilibrium. Under those conditions, the radiation field has a simple form, leading to well defined analytical approximations for the photophoretic force that also consider both the internal thermal conduction within the particle, and the effects of heat conduction and radiation to the surrounding gas. We derive these results for homogeneous spherical particles; and for the double layered spheres appropriate for modeling solid grains with porous aggregate mantles. Then, as a specific astrophysicalmore » application of these general physical results, we explore the parameter space relevant to the photophoresis driven drift of dust in protoplanetary disks. We show that highly porous silicate grains have sufficiently low thermal conductivities that photophoretic effects, such as significant relative velocities between particles with differing porosity or levitation above the midplane, are expected to occur.« less

Electromagnetic forces in negative-refractive-index metamaterials: A first-principles study

NASA Astrophysics Data System (ADS)

Yannopapas, Vassilios; Galiatsatos, Pavlos G.

2008-04-01

According to the theory of Veselago, when a particle immersed within a metamaterial with negative refractive index is illuminated by plane wave, it experiences a reversed radiation force due to the antiparallel directions of the phase velocity and energy flow. By employing an ab initio method, we show that, in the limit of zero losses, the effect of reversed radiation pressure is generally true only for the specular beam. Waves generated by diffraction of the incident light at the surface of the slab of the metamaterial can produce a total force which is parallel to the radiation flow. However, when the actual losses of the materials are taken into account, the phenomenon of reversed radiation force is evident within the whole range of a negative refractive index band.

Acoustic radiation force acting on elastic and viscoelastic spherical shells placed in a plane standing wave field.

PubMed

Mitri, F G

2005-08-01

The theory of the acoustic radiation force acting on elastic spherical shells suspended in a plane standing wave field is developed in relation to their thickness and the content of their hollow regions. The theory is modified to include the effect of a hysteresis type of absorption of compressional and shear waves in the material. The fluid-loading effect on the acoustic radiation force function Y(st) is analyzed as well. Results of numerical calculations are presented for a number of elastic and viscoelastic materials, with the hollow region filled with water or air. These results show how the damping due to absorption, the change of the interior fluid inside the shells' hollow regions, and the exterior fluid surrounding their structures, affect the acoustic radiation force.

Smoke Over Haze: Comparative Analysis of Satellite, Surface Radiometer and Airborne In-Situ Measurements of Aerosol Optical Properties and Radiative Forcing Over the Eastern US

NASA Astrophysics Data System (ADS)

vant-Hull, B.; Li, Z.; Taubman, B.; Marufu, L.; Levy, R.; Chang, F.; Doddridge, B.; Dickerson, R.

2004-12-01

In July 2002 Canadian forest fires produced a major smoke episode that blanketed the U.S. East Coast. Properties of the smoke aerosol were measured in-situ from aircraft, complementing operational AERONET and MODIS remote sensed aerosol retrievals. This study compares single scattering albedo and phase function derived from the in-situ measurements and AERONET retrievals in order to evaluate their consistency for application to satellite retrievals of optical depth and radiative forcing. These optical properties were combined with MODIS reflectance observations to calculate optical depth. The use of AERONET optical properties yielded optical depths 2% to 16% lower than those directly measured by AERONET. The use of in-situ derived optical properties resulted in optical depths 22% to 43% higher than AERONET measurements. These higher optical depths are attributed primarily to the higher absorption measured in-situ, which is roughly twice that retrieved by AERONET. The resulting satellite retrieved optical depths were in turn used to calculate integrated radiative forcing at both the surface and TOA. Comparisons to surface (SurfRad and ISIS) and to satellite (CERES) broadband radiometer measurements demonstrate that the use of optical properties derived from the aircraft measurements provided a better broadband forcing estimate (21% error) than those derived from AERONET (33% error). Thus AERONET derived optical properties produced better fits to optical depth measurements, while in-situ properties resulted in better fits to forcing measurements. These apparent inconsistencies underline the significant challenges facing the aerosol community in achieving column closure between narrow and broadband measurements and calculations.

Radiation Dose Assessments for Shore-Based Individuals in Operation Tomodachi

DTIC Science & Technology

2012-09-30

force (lbs avoirdupois) pound-force inch pound-force/inch pound-force/foot2 pound-force/inch2 (psi) pound- mass (lbm avoirdupois) pound- mass ...foot2 (moment of inertia) pound- mass /foot3 rad (radiation dose absorbed) roentgen shake slug torr (mm Hg, 00 C) 1.000 000 x E -10 1.013 25 x E...who provided technical consultation and critical reviews of environmental monitoring data. • Mr. Brian Sanchez of ARA, Inc., who designed and

Satellite Estimates of the Direct Radiative Forcing of Biomass Burning Aerosols Over South America and Africa

NASA Technical Reports Server (NTRS)

Christopher, Sundar A.; Wang, Min; Kliche, Donna V.; Berendes, Todd; Welch, Ronald M.; Yang, S.K.

1997-01-01

Atmospheric aerosol particles, both natural and anthropogenic are important to the earth's radiative balance. Therefore it is important to provide adequate validation information on the spatial, temporal and radiative properties of aerosols. This will enable us to predict realistic global estimates of aerosol radiative effects more confidently. The current study utilizes 66 AVHRR LAC (Local Area Coverage) and coincident Earth Radiation Budget Experiment (ERBE) images to characterize the fires, smoke and radiative forcings of biomass burning aerosols over four major ecosystems of South America.

Do radiative feedbacks depend on the structure and type of climate forcing, or only on the spatial pattern of surface temperature change?

NASA Astrophysics Data System (ADS)

Haugstad, A.; Battisti, D. S.; Armour, K.

2016-12-01

Earth's climate sensitivity depends critically on the strength of radiative feedbacks linking surface warming to changes in top-of-atmosphere (TOA) radiation. Many studies use a simplistic idea of radiative feedbacks, either by treating them as global mean quantities, or by assuming they can be defined uniquely by geographic location and thus that TOA radiative response depends only on local surface warming. For example, a uniform increase in sea-surface temperature has been widely used as a surrogate for global warming (e.g., Cess et al 1990 and the CMIP 'aqua4k' simulations), with the assumption that this produces the same radiative feedbacks as those arising from a doubling of carbon dioxide - even though the spatial patterns of warming differ. However, evidence suggests that these assumptions are not valid, and local feedbacks may be integrally dependent on the structure of warming or type of climate forcing applied (Rose et al 2014). This study thus investigates the following questions: to what extent do local feedbacks depend on the structure and type of forcing applied? And, to what extent do they depend on the pattern of surface temperature change induced by that forcing? Using an idealized framework of an aquaplanet atmosphere-only model, we show that radiative feedbacks are indeed dependent on the large scale structure of warming and type of forcing applied. For example, the climate responds very differently to two forcings of equal global magnitude but applied in different global regions; the pattern of local feedbacks arising from uniform warming are not the same as that arising from polar amplified warming; and the same local feedbacks can be induced by distinct forcing patterns, provided that they produce the same pattern of surface temperature change. These findings suggest that the so-called `efficacies' of climate forcings can be understood simply in terms of how local feedbacks depend on the temperature patterns they induce.

An exploration in acoustic radiation force experienced by cylindrical shells via resonance scattering theory.

PubMed

Rajabi, Majid; Behzad, Mehdi

2014-04-01

In nonlinear acoustic regime, a body insonified by a sound field is known to experience a steady force that is called the acoustic radiation force (RF). This force is a second-order quantity of the velocity potential function of the ambient medium. Exploiting the sufficiency of linear solution representation of potential function in RF formulation, and following the classical resonance scattering theorem (RST) which suggests the scattered field as a superposition of the resonant field and a background (non-resonant) component, we will show that the radiation force is a composition of three components: background part, resonant part and their interaction. Due to the nonlinearity effects, each part contains the contribution of pure partial waves in addition to their mutual interaction. The numerical results propose the residue component (i.e., subtraction of the background component from the RF) as a good indicator of the contribution of circumferential surface waves in RF. Defining the modal series of radiation force function and its components, it will be shown that within each partial wave, the resonance contribution can be synthesized as the Breit-Wigner form for adequately none-close resonant frequencies. The proposed formulation may be helpful essentially due to its inherent value as a canonical subject in physical acoustics. Furthermore, it may make a tunnel through the circumferential resonance reducing effects on radiation forces. Copyright © 2013 Elsevier B.V. All rights reserved.

Mathematical model of the solar radiation force and torques acting on the components of a spacecraft

NASA Technical Reports Server (NTRS)

Georgevic, R. M.

1971-01-01

General expressions for the solar radiation force and torques are derived in the vectorial form for any given reflecting surface, provided that the reflecting characteristics of the surface, as well as the value of the solar constant, are known. An appropriate choice of a spacecraft-fixed frame of reference leads to relatively simple expressions for the solar radiation forces and torques in terms of the functions of the sun-spacecraft-earth angle.

Tunable optical lens array using viscoelastic material and acoustic radiation force

DOE Office of Scientific and Technical Information (OSTI.GOV)

Koyama, Daisuke, E-mail: dkoyama@mail.doshisha.ac.jp; Kashihara, Yuta; Matsukawa, Mami

2015-10-28

A movable optical lens array that uses acoustic radiation force was investigated. The lens array consists of a glass plate, two piezoelectric bimorph transducers, and a transparent viscoelastic gel film. A cylindrical lens array with a lens pitch of 4.6 mm was fabricated using the acoustic radiation force generated by the flexural vibration of the glass plate. The focal point and the positioning of the lenses can be changed using the input voltage and the driving phase difference between the two transducers, respectively.

Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue

DOE Office of Scientific and Technical Information (OSTI.GOV)

Treweek, Benjamin C., E-mail: btreweek@utexas.edu; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.

Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitudemore » and direction, which may enable more accurate noninvasive determination of tissue properties.« less

Acoustic radiation force due to arbitrary incident fields on spherical particles in soft tissue

NASA Astrophysics Data System (ADS)

Treweek, Benjamin C.; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.; Hamilton, Mark F.

2015-10-01

Acoustic radiation force is of interest in a wide variety of biomedical applications ranging from tissue characterization (e.g. elastography) to tissue treatment (e.g. high intensity focused ultrasound, kidney stone fragment removal). As tissue mechanical properties are reliable indicators of tissue health, the former is the focus of the present contribution. This is accomplished through an investigation of the acoustic radiation force on a spherical scatterer embedded in tissue. Properties of both the scatterer and the surrounding tissue are important in determining the magnitude and the direction of the force. As these properties vary, the force computation shows changes in magnitude and direction, which may enable more accurate noninvasive determination of tissue properties.

Mechanisms controlling the dependence of surface warming on cumulative carbon emissions over the next century in a suite of Earth system models

NASA Astrophysics Data System (ADS)

Williams, Richard; Roussenov, Vassil; Goodwin, Philip; Resplandy, Laure; Bopp, Laurent

2017-04-01

Insight into how to avoid dangerous climate may be obtained from Earth system model projections, which reveal a near-linear dependence of global-mean surface warming on cumulative carbon emissions. This dependence of surface warming on carbon emissions is interpreted in terms of a product of three terms: the dependence of surface warming on radiative forcing, the fractional radiative forcing contribution from atmospheric CO2 and the dependence of radiative forcing from atmospheric CO2 on cumulative carbon emissions. Mechanistically each of these dependences varies, respectively, with ocean heat uptake, the CO2 and non-CO2 radiative forcing, and the ocean and terrestrial uptake of carbon. An ensemble of 9 Earth System models forced by up to 4 Representative Concentration Pathways are diagnosed. In all cases, the dependence of surface warming on carbon emissions evolves primarily due to competing effects of heat and carbon uptake over the upper ocean: there is a reduced effect of radiative forcing from CO2 due to ocean carbon uptake, which is partly compensated by enhanced surface warming due to a reduced effect of ocean heat uptake. There is a wide spread in the dependence of surface warming on carbon emissions, undermining the ability to identify the maximum permitted carbon emission to avoid dangerous climate. Our framework reveals how uncertainty in the future warming trend is high over the next few decades due to relatively high uncertainties in ocean heat uptake, non-CO2 radiative forcing and the undersaturation of carbon in the ocean.

Estimates of cloud radiative forcing in contrail clusters using GOES imagery

NASA Astrophysics Data System (ADS)

Duda, David P.; Minnis, Patrick; Nguyen, Louis

2001-03-01

Using data from the Geostationary Operational Environmental Satellite (GOES), the evolution of solar and longwave radiative forcing in contrail clusters is presented in several case studies. The first study examines contrails developing over the midwestern United States in a region of upper tropospheric moisture enhanced by the remnants of Hurricane Nora on September 26, 1997. Two other cases involve contrail clusters that formed over the Chesapeake Bay and the Atlantic Ocean on February 11 and March 5, 1999, respectively. The last study includes contrails forming over the tropical Pacific near Hawaii. Observations of tropical contrails near Hawaii show that the contrail optical properties are similar to those measured from satellite in the midlatitudes, with visible optical depths between 0.3 and 0.5 and particle sizes between 30 and 60 μm as the contrails mature into diffuse cloudiness. Radiative transfer model simulations of the tropical contrail case suggest that ice crystal shape may have an important effect on radiative forcing in contrails. The magnitudes of the observed solar and longwave radiative forcings were 5.6 and 3.2 W m-2 less than those from the corresponding model simulations, and these differences are attributed to the subpixel scale low clouds and uncertainties in the anisotropic reflectance and limb-darkening models used to estimate the observed forcing. Since the broadband radiative forcing in contrails often changes rapidly, contrail forcing estimates based only on the polar orbiting advanced very high resolution radiometer (AVHRR) data could be inaccurate due to the lack of sufficient temporal sampling.

A multilinear regression methodology to analyze the effect of atmospheric and surface forcing on Arctic clouds

NASA Astrophysics Data System (ADS)

Boeke, R.; Taylor, P. C.; Li, Y.

2017-12-01

Arctic cloud amount as simulated in CMIP5 models displays large intermodel spread- models disagree on the processes important for cloud formation as well as the radiative impact of clouds. The radiative response to cloud forcing can be better assessed when the drivers of Arctic cloud formation are known. Arctic cloud amount (CA) is a function of both atmospheric and surface conditions, and it is crucial to separate the influences of unique processes to understand why the models are different. This study uses a multilinear regression methodology to determine cloud changes using 3 variables as predictors: lower tropospheric stability (LTS), 500-hPa vertical velocity (ω500), and sea ice concentration (SIC). These three explanatory variables were chosen because their effects on clouds can be attributed to unique climate processes: LTS is a thermodynamic indicator of the relationship between clouds and atmospheric stability, SIC determines the interaction between clouds and the surface, and ω500 is a metric for dynamical change. Vertical, seasonal profiles of necessary variables are obtained from the Coupled Model Intercomparison Project 5 (CMIP5) historical simulation, an ocean-atmosphere couple model forced with the best-estimate natural and anthropogenic radiative forcing from 1850-2005, and statistical significance tests are used to confirm the regression equation. A unique heuristic model will be constructed for each climate model and for observations, and models will be tested by their ability to capture the observed cloud amount and behavior. Lastly, the intermodel spread in Arctic cloud amount will be attributed to individual processes, ranking the relative contributions of each factor to shed light on emergent constraints in the Arctic cloud radiative effect.

Host Model Uncertainty in Aerosol Radiative Effects: the AeroCom Prescribed Experiment and Beyond

NASA Astrophysics Data System (ADS)

Stier, Philip; Schutgens, Nick; Bian, Huisheng; Boucher, Olivier; Chin, Mian; Ghan, Steven; Huneeus, Nicolas; Kinne, Stefan; Lin, Guangxing; Myhre, Gunnar; Penner, Joyce; Randles, Cynthia; Samset, Bjorn; Schulz, Michael; Yu, Hongbin; Zhou, Cheng; Bellouin, Nicolas; Ma, Xiaoyan; Yu, Fangqun; Takemura, Toshihiko

2013-04-01

Anthropogenic and natural aerosol radiative effects are recognized to affect global and regional climate. Multi-model "diversity" in estimates of the aerosol radiative effect is often perceived as a measure of the uncertainty in modelling aerosol itself. However, current aerosol models vary considerably in model components relevant for the calculation of aerosol radiative forcings and feedbacks and the associated "host-model uncertainties" are generally convoluted with the actual uncertainty in aerosol modelling. In the AeroCom Prescribed intercomparison study we systematically isolate and quantify host model uncertainties on aerosol forcing experiments through prescription of identical aerosol radiative properties in eleven participating models. Host model errors in aerosol radiative forcing are largest in regions of uncertain host model components, such as stratocumulus cloud decks or areas with poorly constrained surface albedos, such as sea ice. Our results demonstrate that host model uncertainties are an important component of aerosol forcing uncertainty that require further attention. However, uncertainties in aerosol radiative effects also include short-term and long-term feedback processes that will be systematically explored in future intercomparison studies. Here we will present an overview of the proposals for discussion and results from early scoping studies.

The NSA/SHEBA Cloud & Radiation Comparison Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janet M. Intrieri; Matthew D. Shupe

2004-08-23

Cloud and radiation data from two distinctly different Arctic areas are analyzed to study the differences between coastal Alaskan and open Arctic Ocean region clouds and their respective influence on the surface radiation budget. The cloud and radiation datasets were obtained from 1) the DOE North Slope of Alaska (NSA) facility in the coastal town of Barrow, Alaska, and 2) the SHEBA field program, which was conducted from an icebreaker frozen in, and drifting with, the sea-ice for one year in the Western Arctic Ocean. Radar, lidar, radiometer, and sounding measurements from both locations were used to produce annual cyclesmore » of cloud occurrence and height, atmospheric temperature and humidity, surface longwave and shortwave broadband fluxes, surface albedo, and cloud radiative forcing. In general, both regions revealed a similar annual trend of cloud occurrence fraction with minimum values in winter (60-75%) and maximum values during spring, summer and fall (80-90%). However, the annual average cloud occurrence fraction for SHEBA (76%) was lower than the 6-year average cloud occurrence at NSA (92%). Both Arctic areas also showed similar annual cycle trends of cloud forcing with clouds warming the surface through most of the year and a period of surface cooling during the summer, when cloud shading effects overwhelm cloud greenhouse effects. The greatest difference between the two regions was observed in the magnitude of the cloud cooling effect (i.e., shortwave cloud forcing), which was significantly stronger at NSA and lasted for a longer period of time than at SHEBA. This is predominantly due to the longer and stronger melt season at NSA (i.e., albedo values that are much lower coupled with Sun angles that are somewhat higher) than the melt season observed over the ice pack at SHEBA. Longwave cloud forcing values were comparable between the two sites indicating a general similarity in cloudiness and atmospheric temperature and humidity structure between the two regions.« less

Nondestructive Inspection (NDI) Facility Radiation Protection Survey for Homestead AFB, FL

DTIC Science & Technology

2012-10-31

worker radiation dosimetry records, Bioenvironmental Engineering’s occupational safety records, NDI’s operating procedures/instructions, radiation...Nondestructive Inspection Methods (2) Air Force Manual 48-125, Personnel Ionizing Radiation Dosimetry (3) Air Force Occupational Safety and Health Standard...radiography 3. TLDs properly stored (AFMAN 48-125; T.O. 33B-1-1, 6.8.5.4.4) 4. TLDs returned to storage rack at the end

Climate Response to Negative Greenhouse Gas Radiative Forcing in Polar Winter

NASA Astrophysics Data System (ADS)

Flanner, M. G.; Huang, X.; Chen, X.; Krinner, G.

2018-02-01

Greenhouse gas (GHG) additions to Earth's atmosphere initially reduce global outgoing longwave radiation, thereby warming the planet. In select environments with temperature inversions, however, increased GHG concentrations can actually increase local outgoing longwave radiation. Negative top of atmosphere and effective radiative forcing (ERF) from this situation give the impression that local surface temperatures could cool in response to GHG increases. Here we consider an extreme scenario in which GHG concentrations are increased only within the warmest layers of winter near-surface inversions of the Arctic and Antarctic. We find, using a fully coupled Earth system model, that the underlying surface warms despite the GHG addition exerting negative ERF and cooling the troposphere in the vicinity of the GHG increase. This unique radiative forcing and thermal response is facilitated by the high stability of the polar winter atmosphere, which inhibit thermal mixing and amplify the impact of surface radiative forcing on surface temperature. These findings also suggest that strategies to exploit negative ERF via injections of short-lived GHGs into inversion layers would likely be unsuccessful in cooling the planetary surface.

Development of a wave-induced forcing threshold for nearshore impact of Wave Energy Converter arrays

NASA Astrophysics Data System (ADS)

O'Dea, A.; Haller, M. C.; Ozkan-Haller, H. T.

2016-02-01

Wave-induced forcing is a function of spatial gradients in the wave radiation stresses and is the main driver of alongshore currents, rip currents, and nearshore sediment transport. The installation of nearshore Wave Energy Converter (WEC) arrays may cause significant changes in the surf zone radiation stresses and could therefore impact nearshore littoral processes. In the first part of this study, a new threshold for nearshore hydrodynamic impact due to the presence of WEC devices is established based on changes in the alongshore radiation stress gradients shoreward of WEC arrays. The threshold is defined based on the relationship between nearshore radiation stresses and alongshore currents as observed in field data. Next, we perform a parametric study of the nearshore impact of WEC arrays using the SWAN wave model. Trials are conducted on an idealized, alongshore-uniform beach with a range of WEC array configurations, locations, and incident wave conditions, and conditions that generate radiation stress gradients above the impact threshold are identified. Finally, the same methodology is applied to two wave energy test sites off the coast of Newport, OR with more complicated bathymetries. Although the trends at the field sites are similar to those seen in the parametric study, the location and extent of the changes in the alongshore radiation stress gradients appear to be heavily influenced by the local bathymetry.

Black carbon radiative forcing over the Tibetan Plateau

NASA Astrophysics Data System (ADS)

He, Cenlin; Li, Qinbin; Liou, Kuo-Nan; Takano, Yoshi; Gu, Yu; Qi, Ling; Mao, Yuhao; Leung, L. Ruby

2014-11-01

We estimate the snow albedo forcing and direct radiative forcing (DRF) of black carbon (BC) in the Tibetan Plateau using a global chemical transport model in conjunction with a stochastic snow model and a radiative transfer model. The annual mean BC snow albedo forcing is 2.9 W m-2 averaged over snow-covered plateau regions, which is a factor of 3 larger than the value over global land snowpack. BC-snow internal mixing increases the albedo forcing by 40-60% compared with external mixing, and coated BC increases the forcing by 30-50% compared with uncoated BC aggregates, whereas Koch snowflakes reduce the forcing by 20-40% relative to spherical snow grains. The annual BC DRF at the top of the atmosphere is 2.3 W m-2 with uncertainties of -70-85% in the plateau after scaling the modeled BC absorption optical depth to Aerosol Robotic Network observations. The BC forcings are attributed to emissions from different regions.

Radiative Forcing Due to Major Aerosol Emitting Sectors in China and India

NASA Technical Reports Server (NTRS)

Streets, David G.; Shindell, Drew Todd; Lu, Zifeng; Faluvegi, Greg

2013-01-01

Understanding the radiative forcing caused by anthropogenic aerosol sources is essential for making effective emission control decisions to mitigate climate change. We examined the net direct plus indirect radiative forcing caused by carbonaceous aerosol and sulfur emissions in key sectors of China and India using the GISS-E2 chemistry-climate model. Diesel trucks and buses (67 mW/ sq. m) and residential biofuel combustion (52 mW/ sq. m) in India have the largest global mean, annual average forcings due mainly to the direct and indirect effects of BC. Emissions from these two sectors in China have near-zero net global forcings. Coal-fired power plants in both countries exert a negative forcing of about -30 mW/ sq. m from production of sulfate. Aerosol forcings are largest locally, with direct forcings due to residential biofuel combustion of 580 mW/ sq. m over India and 416 mW/ sq. m over China, but they extend as far as North America, Europe, and the Arctic

Contributions of radiative factors to enhanced dryland warming over East Asia

NASA Astrophysics Data System (ADS)

Zhang, Yanting; Guan, Xiaodan; Yu, Haipeng; Xie, Yongkun; Jin, Hongchun

2017-08-01

Enhanced near-surface atmospheric warming has occurred over East Asia in recent decades, especially in drylands. Although local factors have been confirmed to provide considerable contributions to this warming, such factors have not been sufficiently analyzed. In this study, we extracted the radiatively forced temperature (RFT) associated with the built-up greenhouse gases, aerosol emission, and various other radiative forcing over East Asia and found a close relationship between RFT and CO2. In addition, using climate model experiments, we explored the responses of temperature changes to black carbon (BC), CO2, and SO4 and found that the enhanced dryland warming induced by CO2 had the largest magnitude and was strengthened by the warming effect of BC. Moreover, the sensitivity of daily maximum and minimum temperature changes to BC, CO2, and SO4 was examined. It showed asymmetric responses of daily maximum and minimum temperature to radiative factors, which led to an obvious change of diurnal temperature range (DTR), especially in drylands. The DTR's response to CO2 is the most significant. Therefore, CO2 not only plays a dominant role in enhanced warming but also greatly affects the decrease of DTR in drylands. However, the mechanisms of these radiative factors' effects in the process of DTR change are not clear and require more investigation.

Radiative effect of anthropogenic dust ageing

NASA Astrophysics Data System (ADS)

Klingmueller, K.; Lelieveld, J.; Karydis, V.; Stenchikov, G. L.

2017-12-01

The chemical ageing of mineral dust mixing due to the uptake of air pollution affects the optical and hygroscopical properties of the dust particles and their atmospheric residence time. This results in an anthropogenic radiative forcing associated with mineral dust despite the natural origin of most dust particles. Using the atmospheric chemistry-climate model EMAC with a detailed parametrisation of chemical ageing and an emission scheme accounting for the chemical composition of desert soils, we study the direct radiative forcing globally and regionally. Preliminary results indicate large positive and negative forcings, depending on the region. The predominantly negative top of atmosphere forcing over large parts of the dust belt, from West Africa to East Asia, reaches about -2 W / m2 south of the Sahel, in contrast to positive forcings over India and the western Atlantic. Globally averaged, these forcings partially counterbalance, resulting in a negative forcing of -0.04 to -0.05 W / m2, nevertheless representing a considerable fraction of the total dust forcing.

The roles of vertical mixing, solar radiation, and wind stress in a model simulation of the sea surface temperature seasonal cycle in the tropical Pacfic Ocean

NASA Technical Reports Server (NTRS)

Chen, Dake; Busalacchi, Antonio J.; Rothstein, Lewis M.

1994-01-01

The climatological seasonal cycle of sea surface temperature (SST) in the tropical Pacific is simulated using a newly developed upper ocean model. The roles of vertical mixing, solar radiation, and wind stress are investigated in a hierarchy of numerical experiments with various combinations of vertical mixing algorithms and surface-forcing products. It is found that the large SST annual cycle in the eastern equatorial Pacific is, to a large extent, controlled by the annually varying mixed layer depth which, in turn, is mainly determined by the competing effects of solar radiation and wind forcing. With the application of our hybrid vertical mixing scheme the model-simulated SST annual cycle is much improved in both amplitude and phase as compared to the case of a constant mixed layer depth. Beside the strong effects on vertical mixing, solar radiation is the primary heating term in the surface layer heat budget, and wind forcing influences SST by driving oceanic advective processes that redistribute heat in the upper ocean. For example, the SST seasonal cycle in the western Pacific basically follows the semiannual variation of solar heating, and the cycle in the central equatorial region is significantly affected by the zonal advective heat flux associated with the seasonally reversing South Equatorial Current. It has been shown in our experiments that the amount of heat flux modification needed to eliminate the annual mean SST errors in the model is, on average, no larger than the annual mean uncertainties among the various surface flux products used in this study. Whereas a bias correction is needed to account for remaining uncertainties in the annual mean heat flux, this study demonstrates that with proper treatment of mixed layer physics and realistic forcing functions the seasonal variability of SST is capable of being simulated successfully in response to external forcing without relying on a relaxation or damping formulation for the dominant surface heat flux contributions.

Mechanism of the quasi-zero axial acoustic radiation force experienced by elastic and viscoelastic spheres in the field of a quasi-Gaussian beam and particle tweezing.

PubMed

Mitri, F G; Fellah, Z E A

2014-01-01

The present analysis investigates the (axial) acoustic radiation force induced by a quasi-Gaussian beam centered on an elastic and a viscoelastic (polymer-type) sphere in a nonviscous fluid. The quasi-Gaussian beam is an exact solution of the source free Helmholtz wave equation and is characterized by an arbitrary waist w₀ and a diffraction convergence length known as the Rayleigh range z(R). Examples are found where the radiation force unexpectedly approaches closely to zero at some of the elastic sphere's resonance frequencies for kw₀≤1 (where this range is of particular interest in describing strongly focused or divergent beams), which may produce particle immobilization along the axial direction. Moreover, the (quasi)vanishing behavior of the radiation force is found to be correlated with conditions giving extinction of the backscattering by the quasi-Gaussian beam. Furthermore, the mechanism for the quasi-zero force is studied theoretically by analyzing the contributions of the kinetic, potential and momentum flux energy densities and their density functions. It is found that all the components vanish simultaneously at the selected ka values for the nulls. However, for a viscoelastic sphere, acoustic absorption degrades the quasi-zero radiation force. Copyright © 2013 Elsevier B.V. All rights reserved.

A New Method of Comparing Forcing Agents in Climate Models

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kravitz, Benjamin S.; MacMartin, Douglas; Rasch, Philip J.

We describe a new method of comparing different climate forcing agents (e.g., CO2, CH4, and solar irradiance) that avoids many of the ambiguities introduced by temperature-related climate feedbacks. This is achieved by introducing an explicit feedback loop external to the climate model that adjusts one forcing agent to balance another while keeping global mean surface temperature constant. Compared to current approaches, this method has two main advantages: (i) the need to define radiative forcing is bypassed and (ii) by maintaining roughly constant global mean temperature, the effects of state dependence on internal feedback strengths are minimized. We demonstrate this approachmore » for several different forcing agents and derive the relationships between these forcing agents in two climate models; comparisons between forcing agents are highly linear in concordance with predicted functional forms. Transitivity of the relationships between the forcing agents appears to hold within a wide range of forcing. The relationships between the forcing agents obtained from this method are consistent across both models but differ from relationships that would be obtained from calculations of radiative forcing, highlighting the importance of controlling for surface temperature feedback effects when separating radiative forcing and climate response.« less

Radiation force on drops and bubbles in acoustic Bessel beams modeled using finite elements

NASA Astrophysics Data System (ADS)

Marston, Philip L.; Thiessen, David B.; Zhang, Likun

2009-11-01

Analysis of the scattering of sound by spheres centered on ordinary and helicoidal (higher-order) Bessel beams makes it possible to evaluate the acoustic radiation force on idealized drops and bubbles centered on the beam [1]. For potential applications it would be necessary to know if a small transverse displacement of the sphere from the beam's axis causes a radiation force that pushes the sphere toward (or away from) the axis of the beam. We applied 3D-finite elements to that problem. To trust FEM calculations of the radiation force with helicoidal beams it was first necessary to verify that analytical values for the axial force are recovered in the on-axis helicoidal case since only the zero-order beam had been previously studied with FEM. Cases have been identified where the force pushes a slightly off-set drop or bubble toward the axis. For some cases the effective potential method of Gorkov may be used to predict the transverse stability of small spheres.[4pt] [1] P. L. Marston, J. Acoust. Soc. Am. 125, 3539-3545 (2009).

Nonlinear effects in the radiation force generated by amplitude-modulated focused beams

NASA Astrophysics Data System (ADS)

González, Nuria; Jiménez, Noé; Redondo, Javier; Roig, Bernardino; Picó, Rubén; Sánchez-Morcillo, Víctor; Konofagou, Elisa E.; Camarena, Francisco

2012-10-01

Harmonic Motion Imaging (HMI) uses an amplitude-modulated (AM) beam to induce an oscillatory radiation force before, during and after ablation. In this paper, the findings from a numerical analysis of the effects related with the nonlinear propagation of AM focused ultrasonic beams in water on the radiation force and the location of its maxima will be presented. The numerical modeling is performed using the KZK nonlinear parabolic equation. The radiation force is generated by a focused transducer with a gain of 18, a carrier frequency of 1 MHz and a modulation frequency of 25 kHz. The modulated excitation generates a spatially-invariant force proportional to the intensity. Regarding the nonlinear wave propagation, the force is no longer proportional to the intensity, reaching a factor of eight between the nonlinear and linear estimations. Also, a 9 mm shift in the on-axis force peak occurs when the initial pressure increased from 1 to 300 kPa. This spatial shift, due to the nonlinear effects, becomes dynamic in AM focused beams, as the different signal periods have different amplitudes. This study shows that both the value and the spatial position of the force peak are affected by the nonlinear propagation of the ultrasonic waves.

Acoustic attraction, repulsion and radiation force cancellation on a pair of rigid particles with arbitrary cross-sections in 2D: Circular cylinders example

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2017-11-01

The acoustic radiation forces arising on a pair of sound impenetrable cylindrical particles of arbitrary cross-sections are derived. Plane progressive, standing or quasi-standing waves with an arbitrary incidence angle are considered. Multiple scattering effects are described using the multipole expansion formalism and the addition theorem of cylindrical wave functions. An effective incident acoustic field on a particular object is determined, and used with the scattered field to derive closed-form analytical expressions for the radiation force vector components. The mathematical expressions for the radiation force components are exact, and have been formulated in partial-wave series expansions in cylindrical coordinates involving the angle of incidence, the reflection coefficient forming the progressive or the (quasi)standing wave field, the addition theorem, and the expansion coefficients. Numerical examples illustrate the analysis for two rigid circular cross-sections immersed in a non-viscous fluid. Computations for the dimensionless radiation force functions are performed with emphasis on varying the angle of incidence, the interparticle distance, the sizes of the particles as well as the characteristics of the incident field. Depending on the interparticle distance and angle of incidence, one of the particles yields neutrality; it experiences no force and becomes unresponsive (i.e., ;invisible;) to the linear momentum transfer of the effective incident field due to multiple scattering cancellation effects. Moreover, attractive or repulsive forces between the two particles may arise depending on the interparticle distance, the angle of incidence and size parameters of the particles. This study provides a complete analytical method and computations for the axial and transverse radiation force components in multiple acoustic scattering encompassing the cases of plane progressive, standing or quasi-standing waves of arbitrary incidence by a pair of scatterers. Potential applications concern the prediction of the forces used in acoustically-engineered metamaterials with reconfigurable periodicities, cloaking devices, and liquid crystals to name a few examples.

Acoustophoretic separation of airborne millimeter-size particles by a Fresnel lens.

PubMed

Cicek, Ahmet; Korozlu, Nurettin; Adem Kaya, Olgun; Ulug, Bulent

2017-03-02

We numerically demonstrate acoustophoretic separation of spherical solid particles in air by means of an acoustic Fresnel lens. Beside gravitational and drag forces, freely-falling millimeter-size particles experience large acoustic radiation forces around the focus of the lens, where interplay of forces lead to differentiation of particle trajectories with respect to either size or material properties. Due to the strong acoustic field at the focus, radiation force can divert particles with source intensities significantly smaller than those required for acoustic levitation in a standing field. When the lens is designed to have a focal length of 100 mm at 25 kHz, finite-element method simulations reveal a sharp focus with a full-width at half-maximum of 0.5 wavelenghts and a field enhancement of 18 dB. Through numerical calculation of forces and simulation of particle trajectories, we demonstrate size-based separation of acrylic particles at a source sound pressure level of 153 dB such that particles with diameters larger than 0.5 mm are admitted into the central hole, whereas smaller particles are rejected. Besides, efficient separation of particles with similar acoustic properties such as polyethylene, polystyrene and acrylic particles of the same size is also demonstrated.

Acoustophoretic separation of airborne millimeter-size particles by a Fresnel lens

NASA Astrophysics Data System (ADS)

Cicek, Ahmet; Korozlu, Nurettin; Adem Kaya, Olgun; Ulug, Bulent

2017-03-01

We numerically demonstrate acoustophoretic separation of spherical solid particles in air by means of an acoustic Fresnel lens. Beside gravitational and drag forces, freely-falling millimeter-size particles experience large acoustic radiation forces around the focus of the lens, where interplay of forces lead to differentiation of particle trajectories with respect to either size or material properties. Due to the strong acoustic field at the focus, radiation force can divert particles with source intensities significantly smaller than those required for acoustic levitation in a standing field. When the lens is designed to have a focal length of 100 mm at 25 kHz, finite-element method simulations reveal a sharp focus with a full-width at half-maximum of 0.5 wavelenghts and a field enhancement of 18 dB. Through numerical calculation of forces and simulation of particle trajectories, we demonstrate size-based separation of acrylic particles at a source sound pressure level of 153 dB such that particles with diameters larger than 0.5 mm are admitted into the central hole, whereas smaller particles are rejected. Besides, efficient separation of particles with similar acoustic properties such as polyethylene, polystyrene and acrylic particles of the same size is also demonstrated.

Acoustophoretic separation of airborne millimeter-size particles by a Fresnel lens

PubMed Central

Cicek, Ahmet; Korozlu, Nurettin; Adem Kaya, Olgun; Ulug, Bulent

2017-01-01

We numerically demonstrate acoustophoretic separation of spherical solid particles in air by means of an acoustic Fresnel lens. Beside gravitational and drag forces, freely-falling millimeter-size particles experience large acoustic radiation forces around the focus of the lens, where interplay of forces lead to differentiation of particle trajectories with respect to either size or material properties. Due to the strong acoustic field at the focus, radiation force can divert particles with source intensities significantly smaller than those required for acoustic levitation in a standing field. When the lens is designed to have a focal length of 100 mm at 25 kHz, finite-element method simulations reveal a sharp focus with a full-width at half-maximum of 0.5 wavelenghts and a field enhancement of 18 dB. Through numerical calculation of forces and simulation of particle trajectories, we demonstrate size-based separation of acrylic particles at a source sound pressure level of 153 dB such that particles with diameters larger than 0.5 mm are admitted into the central hole, whereas smaller particles are rejected. Besides, efficient separation of particles with similar acoustic properties such as polyethylene, polystyrene and acrylic particles of the same size is also demonstrated. PMID:28252033

Black carbon radiative forcing derived from AERONET measurements and models over an urban location in the southeastern Iberian Peninsula

NASA Astrophysics Data System (ADS)

Valenzuela, A.; Arola, A.; Antón, M.; Quirantes, A.; Alados-Arboledas, L.

2017-07-01

This paper provides an account of observed variations in Black carbon (BC) aerosol concentrations and their induced radiative forcing for the first time over Granada a measurement site in Southeastern Iberian Peninsula. Column-integrated BC concentrations were retrieved for the period 2005-2012. Monthly averages of BC concentrations (± one standard deviation) ranged from higher values in January and December with 4.0 ± 2.5 and 4 ± 3 mg/m2, respectively, to lower values in July and August with 1.6 ± 1.2 and 2.0 ± 0.5 mg/m2, respectively. This reduction is not only observed in the average values, but also in the median, third and first quartiles. The average BC concentration in winter (3.8 ± 0.6 mg/m2) was substantially higher than in summer (1.9 ± 0.3 mg/m2), being the eight-year average of 2.9 ± 0.9 mg/m2. The reduction in the use of fossil fuels during the economic crisis contributed significantly to reduced atmospheric loadings of BC. According to our analysis this situation persisted until 2010. BC concentration values were analyzed in terms of air mass influence using cluster analysis. BC concentrations for cluster 1 (local and regional areas) showed high correlations with air masses frequency in winter and autumn. In these seasons BC sources were related to the intense road traffic and increased BC emissions from domestic heating. High BC concentrations were found in autumn just when air mass frequencies for cluster 3 (Mediterranean region) were more elevated, suggesting that air masses coming from that area transport biomass burning particles towards Granada. BC aerosol optical properties were retrieved from BC fraction using aerosol AERONET size volume distribution and Mie theory. A radiative transfer model (SBDART) was used to estimate the aerosol radiative forcing separately for composite aerosol (total aerosols) and exclusively for BC aerosols. The mean radiative forcing for composite aerosol was + 23 ± 6 W/m2 (heating rate of + 0.21 ± 0.06 K/day) and + 15 ± 6 W/m2 for BC aerosol (heating rate of + 0.15 ± 0.06 K/day). These values of radiative forcing and heating rate for BC aerosol represent about 70% of their values for composite aerosol, which highlights the crucial role that BC aerosols play in modifying the radiation budget and climate.

Frequency dependence of the acoustic radiation force acting on absorbing cylindrical shells.

PubMed

Mitri, Farid G

2005-02-01

The frequency dependence of the radiation force function Y(p) for absorbing cylindrical shells suspended in an inviscid fluid in a plane incident sound field is analysed, in relation to the thickness and the content of their interior hollow region. The theory is modified to include the effect of hysteresis type absorption of compressional and shear waves in the material. The results of numerical calculations are presented for two viscoelastic (lucite and phenolic polymer) materials, with the hollow region filled with water or air indicating how damping and change of the interior fluid inside the shell's hollow region affect the acoustic radiation force. The acoustic radiation force acting on cylindrical lucite shells immersed in a high density fluid (in this case mercury) and filled with water in their hollow region, is also studied.

Acoustic forcing of a liquid drop

NASA Technical Reports Server (NTRS)

Lyell, M. J.

1992-01-01

The development of systems such as acoustic levitation chambers will allow for the positioning and manipulation of material samples (drops) in a microgravity environment. This provides the capability for fundamental studies in droplet dynamics as well as containerless processing work. Such systems use acoustic radiation pressure forces to position or to further manipulate (e.g., oscillate) the sample. The primary objective was to determine the effect of a viscous acoustic field/tangential radiation pressure forcing on drop oscillations. To this end, the viscous acoustic field is determined. Modified (forced) hydrodynamic field equations which result from a consistent perturbation expansion scheme are solved. This is done in the separate cases of an unmodulated and a modulated acoustic field. The effect of the tangential radiation stress on the hydrodynamic field (drop oscillations) is found to manifest as a correction to the velocity field in a sublayer region near the drop/host interface. Moreover, the forcing due to the radiation pressure vector at the interface is modified by inclusion of tangential stresses.

Radiative flux and forcing parameterization error in aerosol-free clear skies

DOE PAGES

Pincus, Robert; Mlawer, Eli J.; Oreopoulos, Lazaros; ...

2015-07-03

This article reports on the accuracy in aerosol- and cloud-free conditions of the radiation parameterizations used in climate models. Accuracy is assessed relative to observationally validated reference models for fluxes under present-day conditions and forcing (flux changes) from quadrupled concentrations of carbon dioxide. Agreement among reference models is typically within 1 W/m 2, while parameterized calculations are roughly half as accurate in the longwave and even less accurate, and more variable, in the shortwave. Absorption of shortwave radiation is underestimated by most parameterizations in the present day and has relatively large errors in forcing. Error in present-day conditions is essentiallymore » unrelated to error in forcing calculations. Recent revisions to parameterizations have reduced error in most cases. As a result, a dependence on atmospheric conditions, including integrated water vapor, means that global estimates of parameterization error relevant for the radiative forcing of climate change will require much more ambitious calculations.« less

About the feasibilities of controlling the properties of thermoelectric energy converters using optical radiation

NASA Astrophysics Data System (ADS)

Kshevetsky, Oleg S.

2018-01-01

We represent evaluating analysis of the feasibilities for controlling the properties of thermoelectric energy converters using EM radiation in the regimes of cooling, heating, electromotive force generation, or electric current generation. Thus we investigate the influence of optical radiation both on electric conductivity and thermo-electromotive force coefficient of thermoelectric materials. We also discuss promising applications for controlling the properties of thermoelectric energy converters using EM radiation. We represent the results of experimental study of positionsensitive energy converters in the regimes of electromotive force generation and the electric current generation (in part, photo-thermoelectric position-sensitive temperature detectors), position-sensitive photo-thermoelectric energy converters in the regimes of cooling, heating, parallel photoelectric and thermoelectric conversion of sun-light optical radiation into electric power.

Radiation reaction effect on laser driven auto-resonant particle acceleration

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sagar, Vikram; Sengupta, Sudip; Kaw, P. K.

2015-12-15

The effects of radiation reaction force on laser driven auto-resonant particle acceleration scheme are studied using Landau-Lifshitz equation of motion. These studies are carried out for both linear and circularly polarized laser fields in the presence of static axial magnetic field. From the parametric study, a radiation reaction dominated region has been identified in which the particle dynamics is greatly effected by this force. In the radiation reaction dominated region, the two significant effects on particle dynamics are seen, viz., (1) saturation in energy gain by the initially resonant particle and (2) net energy gain by an initially non-resonant particlemore » which is caused due to resonance broadening. It has been further shown that with the relaxation of resonance condition and with optimum choice of parameters, this scheme may become competitive with the other present-day laser driven particle acceleration schemes. The quantum corrections to the Landau-Lifshitz equation of motion have also been taken into account. The difference in the energy gain estimates of the particle by the quantum corrected and classical Landau-Lifshitz equation is found to be insignificant for the present day as well as upcoming laser facilities.« less

Radiation forces on small particles in the solar system

NASA Technical Reports Server (NTRS)

Burns, J. A.; Lamy, P. L.; Soter, S.

1979-01-01

Solar radiation forces on small particles in the solar system are examined, and the resulting orbital evolution of interplanetary and circumplanetary dust is considered. An expression is derived for the effects of radiation pressure and Poynting-Robertson drag on small, spherical particles using the energy and momentum transformation laws of special relativity, and numerical examples are presented to illustrate that radiation pressure and Poynting-Robertson drag are only important for particles within a narrow size range. The orbital consequences of these radiation forces are considered both for heliocentric and planetocentric orbiting particles, and the coupling between particle sizes and dynamics is discussed. A qualitative derivation is presented for the differential Doppler effect, which is due to the differential Doppler shifting of radiation from approaching and receding solar hemispheres, and the Yarkovsky effect, which is important for rotating meter-to kilometer-sized particles, is briefly described.

Atmospheric Response And Feedback To Smoke Radiative Forcing From Wildland Fires

Treesearch

Yongqiang Liu

2003-01-01

Smoke from wildland fires is one of the sources of atmospheric anthropogenic aerosols. it can dramatically affect regional and global radiative balance. Ross et al. (1998) estimated a direct radiative forcing of nearly -20 Wm-2 for the 1995 Amazonian smoke season (August and September). Penner et al. (1992) indicated that the magnitude of the...

Radiation pressure excitation of Low Temperature Atomic Force & Magnetic Force Microscope (LT-AFM/MFM) for Imaging

NASA Astrophysics Data System (ADS)

Karci, Ozgur; Celik, Umit; Oral, Ahmet; NanoMagnetics Instruments Ltd. Team; Middle East Tech Univ Team

2015-03-01

We describe a novel method for excitation of Atomic Force Microscope (AFM) cantilevers by means of radiation pressure for imaging in an AFM for the first time. Piezo excitation is the most common method for cantilever excitation, but it may cause spurious resonance peaks. A fiber optic interferometer with 1310 nm laser was used both to measure the deflection of cantilever and apply a force to the cantilever in a LT-AFM/MFM from NanoMagnetics Instruments. The laser power was modulated at the cantilever`s resonance frequency by a digital Phase Lock Loop (PLL). The force exerted by the radiation pressure on a perfectly reflecting surface by a laser beam of power P is F = 2P/c. We typically modulate the laser beam by ~ 800 μW and obtain 10nm oscillation amplitude with Q ~ 8,000 at 2.5x10-4 mbar. The cantilever's stiffness can be accurately calibrated by using the radiation pressure. We have demonstrated performance of the radiation pressure excitation in AFM/MFM by imaging a hard disk sample between 4-300K and Abrikosov vortex lattice in BSCCO single crystal at 4K to for the first time.

Active electromagnetic invisibility cloaking and radiation force cancellation

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2018-03-01

This investigation shows that an active emitting electromagnetic (EM) Dirichlet source (i.e., with axial polarization of the electric field) in a homogeneous non-dissipative/non-absorptive medium placed near a perfectly conducting boundary can render total invisibility (i.e. zero extinction cross-section or efficiency) in addition to a radiation force cancellation on its surface. Based upon the Poynting theorem, the mathematical expression for the extinction, radiation and amplification cross-sections (or efficiencies) are derived using the partial-wave series expansion method in cylindrical coordinates. Moreover, the analysis is extended to compute the self-induced EM radiation force on the active source, resulting from the waves reflected by the boundary. The numerical results predict the generation of a zero extinction efficiency, achieving total invisibility, in addition to a radiation force cancellation which depend on the source size, the distance from the boundary and the associated EM mode order of the active source. Furthermore, an attractive EM pushing force on the active source directed toward the boundary or a repulsive pulling one pointing away from it can arise accordingly. The numerical predictions and computational results find potential applications in the design and development of EM cloaking devices, invisibility and stealth technologies.

Aerosol and ozone changes as forcing for climate evolution between 1850 and 2100

NASA Astrophysics Data System (ADS)

Szopa, Sophie; Balkanski, Y.; Schulz, M.; Bekki, S.; Cugnet, D.; Fortems-Cheiney, A.; Turquety, S.; Cozic, A.; Déandreis, C.; Hauglustaine, D.; Idelkadi, A.; Lathière, J.; Lefevre, F.; Marchand, M.; Vuolo, R.; Yan, N.; Dufresne, J.-L.

2013-05-01

Global aerosol and ozone distributions and their associated radiative forcings were simulated between 1850 and 2100 following a recent historical emission dataset and under the representative concentration pathways (RCP) for the future. These simulations were used in an Earth System Model to account for the changes in both radiatively and chemically active compounds, when simulating the climate evolution. The past negative stratospheric ozone trends result in a negative climate forcing culminating at -0.15 W m-2 in the 1990s. In the meantime, the tropospheric ozone burden increase generates a positive climate forcing peaking at 0.41 W m-2. The future evolution of ozone strongly depends on the RCP scenario considered. In RCP4.5 and RCP6.0, the evolution of both stratospheric and tropospheric ozone generate relatively weak radiative forcing changes until 2060-2070 followed by a relative 30 % decrease in radiative forcing by 2100. In contrast, RCP8.5 and RCP2.6 model projections exhibit strongly different ozone radiative forcing trajectories. In the RCP2.6 scenario, both effects (stratospheric ozone, a negative forcing, and tropospheric ozone, a positive forcing) decline towards 1950s values while they both get stronger in the RCP8.5 scenario. Over the twentieth century, the evolution of the total aerosol burden is characterized by a strong increase after World War II until the middle of the 1980s followed by a stabilization during the last decade due to the strong decrease in sulfates in OECD countries since the 1970s. The cooling effects reach their maximal values in 1980, with -0.34 and -0.28 W m-2 respectively for direct and indirect total radiative forcings. According to the RCP scenarios, the aerosol content, after peaking around 2010, is projected to decline strongly and monotonically during the twenty-first century for the RCP8.5, 4.5 and 2.6 scenarios. While for RCP6.0 the decline occurs later, after peaking around 2050. As a consequence the relative importance of the total cooling effect of aerosols becomes weaker throughout the twenty-first century compared with the positive forcing of greenhouse gases. Nevertheless, both surface ozone and aerosol content show very different regional features depending on the future scenario considered. Hence, in 2050, surface ozone changes vary between -12 and +12 ppbv over Asia depending on the RCP projection, whereas the regional direct aerosol radiative forcing can locally exceed -3 W m-2.

The Use of Remote Sensing to Resolve the Aerosol Radiative Forcing

NASA Technical Reports Server (NTRS)

Kaufman, Y. J.; Tanre, D.; Remer, Lorraine

1999-01-01

Satellites are used for remote sensing of aerosol optical thickness and optical properties in order to derive the aerosol direct and indirect radiative forcing of climate. Accuracy of the derived aerosol optical thickness is used as a measure of the accuracy in deriving the aerosol radiative forcing. Several questions can be asked to challenge this concept. Is the accuracy of the satellite-derived aerosol direct forcing limited to the accuracy of the measured optical thickness? What are the spectral bands needed to derive the total aerosol forcing? Does most of the direct or indirect aerosol forcing of climate originate from regions with aerosol concentrations that are high enough to be detected from space? What should be the synergism ground-based and space-borne remote sensing to solve the problem? We shall try to answer some of these questions, using AVIRIS airborne measurements and simulations.

Aerosol-Induced Changes of Convective Cloud Anvils Produce Strong Climate Warming

NASA Technical Reports Server (NTRS)

Koren, I.; Remer, L. A.; Altaratz, O.; Martins, J. V.; Davidi, A.

2010-01-01

The effect of aerosol on clouds poses one of the largest uncertainties in estimating the anthropogenic contribution to climate change. Small human-induced perturbations to cloud characteristics via aerosol pathways can create a change in the top-of-atmosphere radiative forcing of hundreds of Wm(exp-2) . Here we focus on links between aerosol and deep convective clouds of the Atlantic and Pacific Intertropical Convergence Zones, noting that the aerosol environment in each region is entirely different. The tops of these vertically developed clouds consisting of mostly ice can reach high levels of the atmosphere, overshooting the lower stratosphere and reaching altitudes greater than 16 km. We show a link between aerosol, clouds and the free atmosphere wind profile that can change the magnitude and sign of the overall climate radiative forcing. We find that increased aerosol loading is associated with taller cloud towers and anvils. The taller clouds reach levels of enhanced wind speeds that act to spread and thin the anvi1 clouds, increasing areal coverage and decreasing cloud optical depth. The radiative effect of this transition is to create a positive radiative forcing (warming) at top-of-atmosphere. Furthermore we introduce the cloud optical depth (r), cloud height (Z) forcing space and show that underestimation of radiative forcing is likely to occur in cases of non homogenous clouds. Specifically, the mean radiative forcing of towers and anvils in the same scene can be several times greater than simply calculating the forcing from the mean cloud optical depth in the scene. Limitations of the method are discussed, alternative sources of aerosol loading are tested and meteorological variance is restricted, but the trend of taller clouds; increased and thinner anvils associated with increased aerosol loading remains robust through all the different tests and perturbations.

Radiative Forcings from Albedo and Carbon Dynamics after Disturbance in Massachusetts Forests

NASA Astrophysics Data System (ADS)

MacLean, R. G.; Williams, C. A.

2014-12-01

Recent efforts have sought to compare and contrast the radiative forcings excited by forest disturbances due to both biogeochemical and biogeophysical mechanisms (Bonan et al., 2008) using either in situ measurements (e.g. Randerson et al., 2005; Randerson et al., 2006) or modeling (e.g. Brovkin et al., 2004). Study of boreal forest disturbances led to the important finding that the albedo increase from snow exposure after a canopy destroying fire offsets the warming from carbon emissions (Randerson et al. 2005). Similar study is lacking for temperate forests, leading to uncertainty about the net effect of albedo and carbon forcings following their disturbance. This work quantifies the gross and net radiative forcings from albedo and carbon mechanisms at two clear cut sites in Harvard Forest, Massachusetts, one a Norway spruce plantation clear cut in 2008 and the other a red pine plantation cleared in 1990. Carbon fluxes are estimated from detailed biomass inventories at both sites, as well as additional measurement with eddy covariance at the 2008 clearing. Associated radiative forcing is estimated with conventional methods estimating the perturbation to CO2 in the atmosphere and its lifetime considering ocean uptake (pulse response) and vegetation regrowth. Albedo change is assessed with Landsat derived albedo for both sites, as well as in situ measurements at the 2008 clearing. Associated radiative forcing is estimated with the model-derived radiative kernels provided by Shell et al (2008). From these extensive records we offer an in depth characterization of albedo and carbon forcings immediately following disturbance through to canopy closure and stem exclusion stages of forest growth in a mid-latitude temperate forest region.

Radiative forcing from aircraft NOx emissions: Mechanisms and seasonal dependence

NASA Astrophysics Data System (ADS)

Stevenson, David S.; Doherty, Ruth M.; Sanderson, Michael G.; Collins, William J.; Johnson, Colin E.; Derwent, Richard G.

2004-09-01

A chemistry-climate model has been applied to study the radiative forcings generated by aircraft NOx emissions through changes in ozone and methane. Four numerical experiments, where an extra pulse of aircraft NOx was emitted into the model atmosphere for a single month (January, April, July, or October), were compared to a control experiment, allowing the aircraft impact to be isolated. The extra NOx produces a short-lived (few months) pulse of ozone that generates a positive radiative forcing. However, the NOx and O3 both generate OH, which leads to a reduction in CH4. A detailed analysis of the OH budget reveals the spatial structure and chemical reactions responsible for the generation of the OH perturbation. Methane's long lifetime means that the CH4 anomaly decays slowly (perturbation lifetime of 11.1 years). The negative CH4 anomaly also has an associated negative O3 anomaly, and both of these introduce a negative radiative forcing. There are important seasonal differences in the response of O3 and CH4 to aircraft NOx, related to the annual cycle in photochemistry; the O3 radiative forcing calculations also have a seasonal dependence. The long-term globally integrated annual mean net forcing calculated here is approximately zero, although earlier work suggests a small net positive forcing. The model design (e.g., upper tropospheric chemistry, convection parameterization) and experimental setup (pulse magnitude and duration) may somewhat influence the results: further work with a range of models is required to confirm these results quantitatively.

Strong radiative heating due to the mixing state of black carbon in atmospheric aerosols.

PubMed

Jacobson, M Z

2001-02-08

Aerosols affect the Earth's temperature and climate by altering the radiative properties of the atmosphere. A large positive component of this radiative forcing from aerosols is due to black carbon--soot--that is released from the burning of fossil fuel and biomass, and, to a lesser extent, natural fires, but the exact forcing is affected by how black carbon is mixed with other aerosol constituents. From studies of aerosol radiative forcing, it is known that black carbon can exist in one of several possible mixing states; distinct from other aerosol particles (externally mixed) or incorporated within them (internally mixed), or a black-carbon core could be surrounded by a well mixed shell. But so far it has been assumed that aerosols exist predominantly as an external mixture. Here I simulate the evolution of the chemical composition of aerosols, finding that the mixing state and direct forcing of the black-carbon component approach those of an internal mixture, largely due to coagulation and growth of aerosol particles. This finding implies a higher positive forcing from black carbon than previously thought, suggesting that the warming effect from black carbon may nearly balance the net cooling effect of other anthropogenic aerosol constituents. The magnitude of the direct radiative forcing from black carbon itself exceeds that due to CH4, suggesting that black carbon may be the second most important component of global warming after CO2 in terms of direct forcing.

Radiation testing of GaAs on CRRES and LIPS experiment

NASA Technical Reports Server (NTRS)

Trumble, T. M.; Masloski, K.

1984-01-01

The radiation damage of solar cells has become a prime concern to the U.S. Air Force due to longer satellite lifetime requirements. Flight experiments were undertaken on the Navy Living Plume Shield (LPS) satellite and the NASA/Air Force Combined Release and Radiation Effects Satellite (CRRES) to complement existing radiation testing. Each experiment, the rationale behind it, and its approach and status are presented. The effect of space radiation on gallium arsenide (GaAs) solar cells was the central parameter investigated. Specifications of the GaAs solar cells are given.

Dealing with a Nuclear Iran: Applying Historical Lessons in Deterrence

DTIC Science & Technology

2012-02-15

is not copyrighted, but is the property of the United States government. Biography Colonel Mark Doria is a U.S. Air Force fighter pilot...contaminated with radiation, including two of the most significant. Located in Jerusalem , just 25 miles from Tel Aviv, they are the Dome of the Rock

Optical Verification of Microbubble Response to Acoustic Radiation Force in Large Vessels With In Vivo Results.

PubMed

Wang, Shiying; Wang, Claudia Y; Unnikrishnan, Sunil; Klibanov, Alexander L; Hossack, John A; Mauldin, F William

2015-11-01

The objective of this study was to optically verify the dynamic behaviors of adherent microbubbles in large blood vessel environments in response to a new ultrasound technique using modulated acoustic radiation force. Polydimethylsiloxane (PDMS) flow channels coated with streptavidin were used in targeted groups to mimic large blood vessels. The custom-modulated acoustic radiation force beam sequence was programmed on a Verasonics research scanner. In vitro experiments were performed by injecting a biotinylated lipid-perfluorobutane microbubble dispersion through flow channels. The dynamic response of adherent microbubbles was detected acoustically and simultaneously visualized using a video camera connected to a microscope. In vivo verification was performed in a large abdominal blood vessel of a murine model for inflammation with injection of biotinylated microbubbles conjugated with P-selectin antibody. Aggregates of adherent microbubbles were observed optically under the influence of acoustic radiation force. Large microbubble aggregates were observed solely in control groups without targeted adhesion. Additionally, the dispersion of microbubble aggregates were demonstrated to lead to a transient acoustic signal enhancement in control groups (a new phenomenon we refer to as "control peak"). In agreement with in vitro results, the control peak phenomenon was observed in vivo in a murine model. This study provides the first optical observation of microbubble-binding dynamics in large blood vessel environments with application of a modulated acoustic radiation force beam sequence. With targeted adhesion, secondary radiation forces were unable to produce large aggregates of adherent microbubbles. Additionally, the new phenomenon called control peak was observed both in vitro and in vivo in a murine model for the first time. The findings in this study provide us with a better understanding of microbubble behaviors in large blood vessel environments with application of acoustic radiation force and could potentially guide future beam sequence designs or signal processing routines for enhanced ultrasound molecular imaging.

Optical Verification of Microbubble Response to Acoustic Radiation Force in Large Vessels with In Vivo Results

PubMed Central

Wang, Shiying; Wang, Claudia Y.; Unnikrishnan, Sunil; Klibanov, Alexander L.; Hossack, John A.; Mauldin, F. William

2015-01-01

Objectives To optically verify the dynamic behaviors of adherent microbubbles in large blood vessel environments in response to a new ultrasound technique using modulated acoustic radiation force. Materials and Methods Polydimethylsiloxane (PDMS) flow channels coated with streptavidin were used in targeted groups to mimic large blood vessels. The custom modulated acoustic radiation force beam sequence was programmed on a Verasonics research scanner. In vitro experiments were performed by injecting a biotinylated lipid-perfluorobutane microbubble dispersion through flow channels. The dynamic response of adherent microbubbles was detected acoustically and simultaneously visualized using a video camera connected to a microscope. In vivo verification was performed in a large abdominal blood vessel of a murine model for inflammation with injection of biotinylated microbubbles conjugated with P-selectin antibody. Results Aggregates of adherent microbubbles were observed optically under the influence of acoustic radiation force. Large microbubble aggregates were observed solely in control groups without targeted adhesion. Additionally, the dispersion of microbubble aggregates were demonstrated to lead to a transient acoustic signal enhancement in control groups (a new phenomenon we refer to as “control peak”). In agreement with in vitro results, the “control peak” phenomenon was observed in vivo in a murine model. Conclusions This study provides the first optical observation of microbubble binding dynamics in large blood vessel environments with application of a modulated acoustic radiation force beam sequence. With targeted adhesion, secondary radiation forces were unable to produce large aggregates of adherent microbubbles. Additionally, the new phenomenon called “control peak” was observed both in vitro and in vivo in a murine model for the first time. The findings in this study provide us with a better understanding of microbubble behaviors in large blood vessel environments with application of acoustic radiation force, and could potentially guide future beam sequence designs or signal processing routines for enhanced ultrasound molecular imaging. PMID:26135018

Real-Time Monitoring Of Regional Tissue Elasticity During FUS Focused Ultrasound Therapy Using Harmonic Motion Imaging

NASA Astrophysics Data System (ADS)

Maleke, Caroline; Pernot, Mathieu; Konofagou, Elisa

2006-05-01

The feasibility of the Harmonic Motion Imaging (HMI) technique for simultaneous monitoring and generation of focused ultrasound therapy using two separate focused ultrasound transducer elements has previously been shown. In this study, a new HMI technique is described that images tissue displacement induced by a harmonic radiation force induced using a single focused ultrasound element. First, wave propagation simulation models were used to compare the use of a single Amplitude-Modulated (AM) focused beam versus two overlapping focused beams as previously implemented for HMI. Simulation results indicated that, unlike in the two-beam configuration, the AM beam produced a consistent, stable focus for the applied harmonic radiation force. The AM beam thus offered the unique advantage of sustaining the application of the spatially-invariant radiation force. Experiments were then performed on gelatin gel phantoms and tissue in vitro bovine liver. The radiation force was generated by a 4.68 MHz focused transducer using a low-frequency Amplitude-Modulated (AM) RF-signal. RF data were acquired at 7.5 MHz with a PRF of 6.5 kHz and displacements were estimated using a 1D cross-correlation algorithm on successive RF signals. Furthermore, taking advantage of the real-time capability of our method, the change in the elastic properties was monitored during focused ultrasound (FUS) ablation of tissue in vitro bovine liver. Based on the harmonic displacements, their temperature-dependence, and the calculated acoustic radiation force, the change in the relative, regional stiffness could be monitored during heating and ablation, both using the displacement amplitude and the resulting phase shift change of the displacement relative to the radiation force temporal profile. In conclusion, the feasibility of using an AM radiation force for HMI for simultaneous monitoring and treatment during ultrasound therapy was demonstrated in phantoms and tissues in vitro. Further study of this method will include, ex vivo and in vivo, stiffness and temperature.

Simulating Black Carbon and Dust and their Radiative Forcing in Seasonal Snow: A Case Study over North China with Field Campaign Measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, Chun; Hu, Zhiyuan; Qian, Yun

2014-10-30

A state-of-the-art regional model, WRF-Chem, is coupled with the SNICAR model that includes the sophisticated representation of snow metamorphism processes available for climate study. The coupled model is used to simulate the black carbon (BC) and dust concentrations and their radiative forcing in seasonal snow over North China in January-February of 2010, with extensive field measurements used to evaluate the model performance. In general, the model simulated spatial variability of BC and dust mass concentrations in the top snow layer (hereafter BCS and DSTS, respectively) are quantitatively or qualitatively consistent with observations. The model generally moderately underestimates BCS in themore » clean regions but significantly overestimates BCS in some polluted regions. Most model results fall into the uncertainty ranges of observations. The simulated BCS and DSTS are highest with >5000 ng g-1 and up to 5 mg g-1, respectively, over the source regions and reduce to <50 ng g-1 and <1 μg g-1, respectively, in the remote regions. BCS and DSTS introduce similar magnitude of radiative warming (~10 W m-2) in snowpack, which is comparable to the magnitude of surface radiative cooling due to BC and dust in the atmosphere. This study represents the first effort in using a regional modeling framework to simulate BC and dust and their direct radiative forcing in snow. Although a variety of observational datasets have been used to attribute model biases, some uncertainties in the results remain, which highlights the need for more observations, particularly concurrent measurements of atmospheric and snow aerosols and the deposition fluxes of aerosols, in future campaigns.« less

Confronting the Uncertainty in Aerosol Forcing Using Comprehensive Observational Data

NASA Astrophysics Data System (ADS)

Johnson, J. S.; Regayre, L. A.; Yoshioka, M.; Pringle, K.; Sexton, D.; Lee, L.; Carslaw, K. S.

2017-12-01

The effect of aerosols on cloud droplet concentrations and radiative properties is the largest uncertainty in the overall radiative forcing of climate over the industrial period. In this study, we take advantage of a large perturbed parameter ensemble of simulations from the UK Met Office HadGEM-UKCA model (the aerosol component of the UK Earth System Model) to comprehensively sample uncertainty in aerosol forcing. Uncertain aerosol and atmospheric parameters cause substantial aerosol forcing uncertainty in climatically important regions. As the aerosol radiative forcing itself is unobservable, we investigate the potential for observations of aerosol and radiative properties to act as constraints on the large forcing uncertainty. We test how eight different theoretically perfect aerosol and radiation observations can constrain the forcing uncertainty over Europe. We find that the achievable constraint is weak unless many diverse observations are used simultaneously. This is due to the complex relationships between model output responses and the multiple interacting parameter uncertainties: compensating model errors mean there are many ways to produce the same model output (known as model equifinality) which impacts on the achievable constraint. However, using all eight observable quantities together we show that the aerosol forcing uncertainty can potentially be reduced by around 50%. This reduction occurs as we reduce a large sample of model variants (over 1 million) that cover the full parametric uncertainty to around 1% that are observationally plausible.Constraining the forcing uncertainty using real observations is a more complex undertaking, in which we must account for multiple further uncertainties including measurement uncertainties, structural model uncertainties and the model discrepancy from reality. Here, we make a first attempt to determine the true potential constraint on the forcing uncertainty from our model that is achievable using a comprehensive set of real aerosol and radiation observations taken from ground stations, flight campaigns and satellite. This research has been supported by the UK-China Research & Innovation Partnership Fund through the Met Office Climate Science for Service Partnership (CSSP) China as part of the Newton Fund, and by the NERC funded GASSP project.

Acoustic Radiation Force Elasticity Imaging in Diagnostic Ultrasound

PubMed Central

Doherty, Joshua R.; Trahey, Gregg E.; Nightingale, Kathryn R.; Palmeri, Mark L.

2013-01-01

The development of ultrasound-based elasticity imaging methods has been the focus of intense research activity since the mid-1990s. In characterizing the mechanical properties of soft tissues, these techniques image an entirely new subset of tissue properties that cannot be derived with conventional ultrasound techniques. Clinically, tissue elasticity is known to be associated with pathological condition and with the ability to image these features in vivo, elasticity imaging methods may prove to be invaluable tools for the diagnosis and/or monitoring of disease. This review focuses on ultrasound-based elasticity imaging methods that generate an acoustic radiation force to induce tissue displacements. These methods can be performed non-invasively during routine exams to provide either qualitative or quantitative metrics of tissue elasticity. A brief overview of soft tissue mechanics relevant to elasticity imaging is provided, including a derivation of acoustic radiation force, and an overview of the various acoustic radiation force elasticity imaging methods. PMID:23549529

Acoustic radiation force elasticity imaging in diagnostic ultrasound.

PubMed

Doherty, Joshua R; Trahey, Gregg E; Nightingale, Kathryn R; Palmeri, Mark L

2013-04-01

The development of ultrasound-based elasticity imaging methods has been the focus of intense research activity since the mid-1990s. In characterizing the mechanical properties of soft tissues, these techniques image an entirely new subset of tissue properties that cannot be derived with conventional ultrasound techniques. Clinically, tissue elasticity is known to be associated with pathological condition and with the ability to image these features in vivo; elasticity imaging methods may prove to be invaluable tools for the diagnosis and/or monitoring of disease. This review focuses on ultrasound-based elasticity imaging methods that generate an acoustic radiation force to induce tissue displacements. These methods can be performed noninvasively during routine exams to provide either qualitative or quantitative metrics of tissue elasticity. A brief overview of soft tissue mechanics relevant to elasticity imaging is provided, including a derivation of acoustic radiation force, and an overview of the various acoustic radiation force elasticity imaging methods.

Moderate Imaging Resolution Spectroradiometer (MODIS) Aerosol Optical Depth Retrieval for Aerosol Radiative Forcing

NASA Astrophysics Data System (ADS)

Asmat, A.; Jalal, K. A.; Ahmad, N.

2018-02-01

The present study uses the Aerosol Optical Depth (AOD) retrieved from Moderate Imaging Resolution Spectroradiometer (MODIS) data for the period from January 2011 until December 2015 over an urban area in Kuching, Sarawak. The results show the minimum AOD value retrieved from MODIS is -0.06 and the maximum value is 6.0. High aerosol loading with high AOD value observed during dry seasons and low AOD monitored during wet seasons. Multi plane regression technique used to retrieve AOD from MODIS (AODMODIS) and different statistics parameter is proposed by using relative absolute error for accuracy assessment in spatial and temporal averaging approach. The AODMODIS then compared with AOD derived from Aerosol Robotic Network (AERONET) Sunphotometer (AODAERONET) and the results shows high correlation coefficient (R2) for AODMODIS and AODAERONET with 0.93. AODMODIS used as an input parameters into Santa Barbara Discrete Ordinate Radiative Transfer (SBDART) model to estimate urban radiative forcing at Kuching. The observed hourly averaged for urban radiative forcing is -0.12 Wm-2 for top of atmosphere (TOA), -2.13 Wm-2 at the surface and 2.00 Wm-2 in the atmosphere. There is a moderate relationship observed between urban radiative forcing calculated using SBDART and AERONET which are 0.75 at the surface, 0.65 at TOA and 0.56 in atmosphere. Overall, variation in AOD tends to cause large bias in the estimated urban radiative forcing.

A numerical study of microparticle acoustophoresis driven by acoustic radiation forces and streaming-induced drag forces.

PubMed

Muller, Peter Barkholt; Barnkob, Rune; Jensen, Mads Jakob Herring; Bruus, Henrik

2012-11-21

We present a numerical study of the transient acoustophoretic motion of microparticles suspended in a liquid-filled microchannel and driven by the acoustic forces arising from an imposed standing ultrasound wave: the acoustic radiation force from the scattering of sound waves on the particles and the Stokes drag force from the induced acoustic streaming flow. These forces are calculated numerically in two steps. First, the thermoacoustic equations are solved to first order in the imposed ultrasound field taking into account the micrometer-thin but crucial thermoviscous boundary layer near the rigid walls. Second, the products of the resulting first-order fields are used as source terms in the time-averaged second-order equations, from which the net acoustic forces acting on the particles are determined. The resulting acoustophoretic particle velocities are quantified for experimentally relevant parameters using a numerical particle-tracking scheme. The model shows the transition in the acoustophoretic particle motion from being dominated by streaming-induced drag to being dominated by radiation forces as a function of particle size, channel geometry, and material properties.

Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability.

PubMed

Ghan, Steven; Wang, Minghuai; Zhang, Shipeng; Ferrachat, Sylvaine; Gettelman, Andrew; Griesfeller, Jan; Kipling, Zak; Lohmann, Ulrike; Morrison, Hugh; Neubauer, David; Partridge, Daniel G; Stier, Philip; Takemura, Toshihiko; Wang, Hailong; Zhang, Kai

2016-05-24

A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing.

Challenges in constraining anthropogenic aerosol effects on cloud radiative forcing using present-day spatiotemporal variability

PubMed Central

Ghan, Steven; Wang, Minghuai; Zhang, Shipeng; Ferrachat, Sylvaine; Gettelman, Andrew; Griesfeller, Jan; Kipling, Zak; Lohmann, Ulrike; Morrison, Hugh; Neubauer, David; Partridge, Daniel G.; Stier, Philip; Takemura, Toshihiko; Wang, Hailong; Zhang, Kai

2016-01-01

A large number of processes are involved in the chain from emissions of aerosol precursor gases and primary particles to impacts on cloud radiative forcing. Those processes are manifest in a number of relationships that can be expressed as factors dlnX/dlnY driving aerosol effects on cloud radiative forcing. These factors include the relationships between cloud condensation nuclei (CCN) concentration and emissions, droplet number and CCN concentration, cloud fraction and droplet number, cloud optical depth and droplet number, and cloud radiative forcing and cloud optical depth. The relationship between cloud optical depth and droplet number can be further decomposed into the sum of two terms involving the relationship of droplet effective radius and cloud liquid water path with droplet number. These relationships can be constrained using observations of recent spatial and temporal variability of these quantities. However, we are most interested in the radiative forcing since the preindustrial era. Because few relevant measurements are available from that era, relationships from recent variability have been assumed to be applicable to the preindustrial to present-day change. Our analysis of Aerosol Comparisons between Observations and Models (AeroCom) model simulations suggests that estimates of relationships from recent variability are poor constraints on relationships from anthropogenic change for some terms, with even the sign of some relationships differing in many regions. Proxies connecting recent spatial/temporal variability to anthropogenic change, or sustained measurements in regions where emissions have changed, are needed to constrain estimates of anthropogenic aerosol impacts on cloud radiative forcing. PMID:26921324

Validation and application of MODIS-derived clean snow albedo and dust radiative forcing

NASA Astrophysics Data System (ADS)

Rittger, K. E.; Bryant, A. C.; Seidel, F. C.; Bair, E. H.; Skiles, M.; Goodale, C. E.; Ramirez, P.; Mattmann, C. A.; Dozier, J.; Painter, T.

2012-12-01

Snow albedo is an important control on snowmelt. Though albedo evolution of aging snow can be roughly modeled from grain growth, dust and other light absorbing impurities are extrinsic and therefore must be measured. Estimates of clean snow albedo and surface radiative forcing from impurities, which can be inferred from MODIS 500 m surface reflectance products, can provide this driving data for snowmelt models. Here we use MODSCAG (MODIS snow covered area and grain size) to estimate the clean snow albedo and MODDRFS (MODIS dust radiative forcing of snow) to estimate the additional absorbed solar radiation from dust and black carbon. With its finer spatial (20 m) and spectral (10 nm) resolutions, AVIRIS provides a way to estimate the accuracy of MODIS products and understand variability of snow albedo at a finer scale that we explore though a range of topography. The AVIRIS database includes images from late in the accumulation season through the melt season when we are most interested in changes in snow albedo. In addition to the spatial validation, we employ the best estimate of albedo from MODIS in an energy balance reconstruction model to estimate the maximum snow water equivalent. MODDRFS calculates radiative forcing only in pixels that are completely snow-covered, so we spatially interpolate the product to estimate the forcing in all pixels where MODSCAG has given us estimates of clean snow albedo. Comparisons with snow pillows and courses show better agreement when the radiative forcing from absorbing impurities is included in the energy balance reconstruction.

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2015-12-01

The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numerical simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.

Radiative Forcing and Temperature Response to Changes in Urban Albedos and Associated CO2 Offsets

NASA Technical Reports Server (NTRS)

Menon, Surabi; Akbari, Hashem; Mahanama, Sarith; Sednev, Igor; Levinson, Ronnen

2009-01-01

The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the response of the total outgoing (outgoing shortwave+longwave) radiation to urban albedo changes. Globally, the total outgoing radiation increased by 0.5 W/square m and temperature decreased by -0.008 K for an average 0.003 increase in albedo. For the U.S. the total outgoing total radiation increased by 2.3 W/square meter, and temperature decreased by approximately 0.03 K for an average 0.01 increase in albedo. These values are for the boreal summer (Tune-July-August). Based on these forcings, the expected emitted CO2 offset for a plausible 0.25 and 0.15 increase in albedos of roofs and pavements, respectively, for all global urban areas, was found to be approximately 57 Gt CO2 . A more meaningful evaluation of the impacts of urban albedo increases on climate and the expected CO2 offsets would require simulations which better characterizes urban surfaces and represents the full annual cycle.

Rates of change in natural and anthropogenic radiative forcing over the past 20,000 years

PubMed Central

Joos, Fortunat; Spahni, Renato

2008-01-01

The rate of change of climate codetermines the global warming impacts on natural and socioeconomic systems and their capabilities to adapt. Establishing past rates of climate change from temperature proxy data remains difficult given their limited spatiotemporal resolution. In contrast, past greenhouse gas radiative forcing, causing climate to change, is well known from ice cores. We compare rates of change of anthropogenic forcing with rates of natural greenhouse gas forcing since the Last Glacial Maximum and of solar and volcanic forcing of the last millennium. The smoothing of atmospheric variations by the enclosure process of air into ice is computed with a firn diffusion and enclosure model. The 20th century increase in CO2 and its radiative forcing occurred more than an order of magnitude faster than any sustained change during the past 22,000 years. The average rate of increase in the radiative forcing not just from CO2 but from the combination of CO2, CH4, and N2O is larger during the Industrial Era than during any comparable period of at least the past 16,000 years. In addition, the decadal-to-century scale rate of change in anthropogenic forcing is unusually high in the context of the natural forcing variations (solar and volcanoes) of the past millennium. Our analysis implies that global climate change, which is anthropogenic in origin, is progressing at a speed that is unprecedented at least during the last 22,000 years. PMID:18252830

Aerosol influence on energy balance of the middle atmosphere of Jupiter

PubMed Central

Zhang, Xi; West, Robert A.; Irwin, Patrick G. J.; Nixon, Conor A.; Yung, Yuk L.

2015-01-01

Aerosols are ubiquitous in planetary atmospheres in the Solar System. However, radiative forcing on Jupiter has traditionally been attributed to solar heating and infrared cooling of gaseous constituents only, while the significance of aerosol radiative effects has been a long-standing controversy. Here we show, based on observations from the NASA spacecraft Voyager and Cassini, that gases alone cannot maintain the global energy balance in the middle atmosphere of Jupiter. Instead, a thick aerosol layer consisting of fluffy, fractal aggregate particles produced by photochemistry and auroral chemistry dominates the stratospheric radiative heating at middle and high latitudes, exceeding the local gas heating rate by a factor of 5–10. On a global average, aerosol heating is comparable to the gas contribution and aerosol cooling is more important than previously thought. We argue that fractal aggregate particles may also have a significant role in controlling the atmospheric radiative energy balance on other planets, as on Jupiter. PMID:26694318

Effect of particle-particle interactions on the acoustic radiation force in an ultrasonic standing wave

NASA Astrophysics Data System (ADS)

Lipkens, Bart; Ilinskii, Yurii A.; Zabolotskaya, Evgenia A.

2015-10-01

Ultrasonic standing waves are widely used for separation applications. In MEMS applications, a half wavelength standing wave field is generated perpendicular to a laminar flow. The acoustic radiation force exerted on the particle drives the particle to the center of the MEMS channel, where concentrated particles are harvested. In macro-scale applications, the ultrasonic standing wave spans multiple wavelengths. Examples of such applications are oil/water emulsion splitting [1], and blood/lipid separation [2]. In macro-scale applications, particles are typically trapped in the standing wave, resulting in clumping or coalescence of particles/droplets. Subsequent gravitational settling results in separation of the secondary phase. An often used expression for the radiation force on a particle is that derived by Gorkov [3]. The assumptions are that the particle size is small relative to the wavelength, and therefore, only monopole and dipole scattering contributions are used to calculate the radiation force. This framework seems satisfactory for MEMS scale applications where each particle is treated separately by the standing wave, and concentrations are typically low. In macro-scale applications, particle concentration is high, and particle clumping or droplet coalescence results in particle sizes not necessarily small relative to the wavelength. Ilinskii et al. developed a framework for calculation of the acoustic radiation force valid for any size particle [4]. However, this model does not take into account particle to particle effects, which can become important as particle concentration increases. It is known that an acoustic radiation force on a particle or a droplet is determined by the local field. An acoustic radiation force expression is developed that includes the effect of particle to particle interaction. The case of two neighboring particles is considered. The approach is based on sound scattering by the particles. The acoustic field at the location of one particle then consists of two components, the incident sound wave and the scattered field generated by the neighboring particle. The radiation force calculation then includes the contributions of these two fields and incorporates the mutual particle influence. In this investigation the droplet/particle influence on each other has been analyzed theoretically by using the method developed by Gorkov and modified by Ilinskii et al.

Effect of particle-particle interactions on the acoustic radiation force in an ultrasonic standing wave

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lipkens, Bart, E-mail: blipkens@wne.edu; Ilinskii, Yurii A., E-mail: ilinskii@gmail.com; Zabolotskaya, Evgenia A., E-mail: zheniazabolotskaya@gmail.com

Ultrasonic standing waves are widely used for separation applications. In MEMS applications, a half wavelength standing wave field is generated perpendicular to a laminar flow. The acoustic radiation force exerted on the particle drives the particle to the center of the MEMS channel, where concentrated particles are harvested. In macro-scale applications, the ultrasonic standing wave spans multiple wavelengths. Examples of such applications are oil/water emulsion splitting [1], and blood/lipid separation [2]. In macro-scale applications, particles are typically trapped in the standing wave, resulting in clumping or coalescence of particles/droplets. Subsequent gravitational settling results in separation of the secondary phase. Anmore » often used expression for the radiation force on a particle is that derived by Gorkov [3]. The assumptions are that the particle size is small relative to the wavelength, and therefore, only monopole and dipole scattering contributions are used to calculate the radiation force. This framework seems satisfactory for MEMS scale applications where each particle is treated separately by the standing wave, and concentrations are typically low. In macro-scale applications, particle concentration is high, and particle clumping or droplet coalescence results in particle sizes not necessarily small relative to the wavelength. Ilinskii et al. developed a framework for calculation of the acoustic radiation force valid for any size particle [4]. However, this model does not take into account particle to particle effects, which can become important as particle concentration increases. It is known that an acoustic radiation force on a particle or a droplet is determined by the local field. An acoustic radiation force expression is developed that includes the effect of particle to particle interaction. The case of two neighboring particles is considered. The approach is based on sound scattering by the particles. The acoustic field at the location of one particle then consists of two components, the incident sound wave and the scattered field generated by the neighboring particle. The radiation force calculation then includes the contributions of these two fields and incorporates the mutual particle influence. In this investigation the droplet/particle influence on each other has been analyzed theoretically by using the method developed by Gorkov and modified by Ilinskii et al.« less

Combining model and satellite data to investigate the effect of light absorbing impurities on snow melt and discharge generation

NASA Astrophysics Data System (ADS)

Matt, F.; Burkhart, J. F.

2017-12-01

Light absorbing impurities in snow and ice (LAISI) originating from atmospheric deposition enhance snow melt by increasing the absorption of solar radiation. The consequences are a shortening of the snow cover duration due to increased snow melt and, with respect to hydrologic processes, a temporal shift in the discharge generation. However, the effects as simulated in numerical models have large uncertainties. These uncertainties originate mainly from uncertainties in the wet and dry deposition of light absorbing aerosols, limitations in the model representation of the snowpack, and the lack of observable variables required to estimate model parameters. This leads to high uncertainties in the additional energy absorbed by the snow due to the presence of LAISI (the so called radiative forcing of LAISI), a key variable in understanding snowpack energy-balance dynamics. In this study, we present an approach combining distributed model simulations on the catchment scale and remotely sensed radiative forcing from LAISI in order to evaluate and improve model predictions. In a case study, we assess the effect of LAISI on snow melt and discharge generation in a high mountain catchment located in the western Himalaya using the distributed hydrologic model, Shyft. The snow albedo is hereby calculated from a radiative transfer model for snow, taking the increased absorption of solar radiation by LAISI into account. LAISI mixing ratios in snow are determined from atmospheric aerosol deposition rates. To asses the quality of our simulations, we model the instantaneous clear sky radiative forcing at MODIS overpass times, and compare it to the MODIS Dust Radiative Forcing in Snow (MODDRFS) satellite product. By scaling the deposition input to the model, we can optimize the simulated radiative forcing towards the satellite observations.

Validation of the North American Land Data Assimilation System (NLDAS) retrospective forcing over the southern Great Plains

NASA Astrophysics Data System (ADS)

Luo, Lifeng; Robock, Alan; Mitchell, Kenneth E.; Houser, Paul R.; Wood, Eric F.; Schaake, John C.; Lohmann, Dag; Cosgrove, Brian; Wen, Fenghua; Sheffield, Justin; Duan, Qingyun; Higgins, R. Wayne; Pinker, Rachel T.; Tarpley, J. Dan

2003-11-01

Atmospheric forcing used by land surface models is a critical component of the North American Land Data Assimilation System (NLDAS) and its quality crucially affects the final product of NLDAS and our work on model improvement. A three-year (September 1996-September 1999) retrospective forcing data set was created from the Eta Data Assimilation System and observations and used to run the NLDAS land surface models for this period. We compared gridded NLDAS forcing with station observations obtained from networks including the Oklahoma Mesonet and Atmospheric Radiation Measurement/Cloud and Radiation Testbed at the southern Great Plains. Differences in all forcing variables except precipitation between the NLDAS forcing data set and station observations are small at all timescales. While precipitation data do not agree very well at an hourly timescale, they do agree better at longer timescales because of the way NLDAS precipitation forcing is generated. A small high bias in downward solar radiation and a low bias in downward longwave radiation exist in the retrospective forcing. To investigate the impact of these differences on land surface modeling we compared two sets of model simulations, one forced by the standard NLDAS product and one with station-observed meteorology. The differences in the resulting simulations of soil moisture and soil temperature for each model were small, much smaller than the differences between the models and between the models and observations. This indicates that NLDAS retrospective forcing provides an excellent state-of-the-art data set for land surface modeling, at least over the southern Great Plains region.

The role of non-ionizing radiation pressure in star formation: the stability of cores and filaments

NASA Astrophysics Data System (ADS)

Seo, Young Min; Youdin, Andrew N.

2016-09-01

Stars form when filaments and dense cores in molecular clouds fragment and collapse due to self-gravity. In the most basic analyses of gravitational stability, the competition between self-gravity and thermal pressure sets the critical (I.e. maximum stable) mass of spheres and the critical line density of cylinders. Previous work has considered additional support from magnetic fields and turbulence. Here, we consider the effects of non-ionizing radiation, specifically the inward radiation pressure force that acts on dense structures embedded in an isotropic radiation field. Using hydrostatic, isothermal models, we find that irradiation lowers the critical mass and line density for gravitational collapse, and can thus act as a trigger for star formation. For structures with moderate central densities, ˜103 cm-3, the interstellar radiation field in the Solar vicinity has an order unity effect on stability thresholds. For more evolved objects with higher central densities, a significant lowering of stability thresholds requires stronger irradiation, as can be found closer to the Galactic centre or near stellar associations. Even when strong sources of ionizing radiation are absent or extincted, our study shows that interstellar irradiation can significantly influence the star formation process.

Radiation force of an arbitrary acoustic beam on an elastic sphere in a fluid

PubMed Central

Sapozhnikov, Oleg A.; Bailey, Michael R.

2013-01-01

A theoretical approach is developed to calculate the radiation force of an arbitrary acoustic beam on an elastic sphere in a liquid or gas medium. First, the incident beam is described as a sum of plane waves by employing conventional angular spectrum decomposition. Then, the classical solution for the scattering of a plane wave from an elastic sphere is applied for each plane-wave component of the incident field. The net scattered field is expressed as a superposition of the scattered fields from all angular spectrum components of the incident beam. With this formulation, the incident and scattered waves are superposed in the far field to derive expressions for components of the radiation stress tensor. These expressions are then integrated over a spherical surface to analytically describe the radiation force on an elastic sphere. Limiting cases for particular types of incident beams are presented and are shown to agree with known results. Finally, the analytical expressions are used to calculate radiation forces associated with two specific focusing transducers. PMID:23363086

Axial acoustic radiation force on a sphere in Gaussian field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Rongrong; Liu, Xiaozhou, E-mail: xzliu@nju.edu.cn; Gong, Xiufen

2015-10-28

Based on the finite series method, the acoustical radiation force resulting from a Gaussian beam incident on a spherical object is investigated analytically. When the position of the particles deviating from the center of the beam, the Gaussian beam is expanded as a spherical function at the center of the particles and the expanded coefficients of the Gaussian beam is calculated. The analytical expression of the acoustic radiation force on spherical particles deviating from the Gaussian beam center is deduced. The acoustic radiation force affected by the acoustic frequency and the offset distance from the Gaussian beam center is investigated.more » Results have been presented for Gaussian beams with different wavelengths and it has been shown that the interaction of a Gaussian beam with a sphere can result in attractive axial force under specific operational conditions. Results indicate the capability of manipulating and separating spherical spheres based on their mechanical and acoustical properties, the results provided here may provide a theoretical basis for development of single-beam acoustical tweezers.« less

Design of a phased array for the generation of adaptive radiation force along a path surrounding a breast lesion for dynamic ultrasound elastography imaging.

PubMed

Ekeom, Didace; Hadj Henni, Anis; Cloutier, Guy

2013-03-01

This work demonstrates, with numerical simulations, the potential of an octagonal probe for the generation of radiation forces in a set of points following a path surrounding a breast lesion in the context of dynamic ultrasound elastography imaging. Because of the in-going wave adaptive focusing strategy, the proposed method is adapted to induce shear wave fronts to interact optimally with complex lesions. Transducer elements were based on 1-3 piezocomposite material. Three-dimensional simulations combining the finite element method and boundary element method with periodic boundary conditions in the elevation direction were used to predict acoustic wave radiation in a targeted region of interest. The coupling factor of the piezocomposite material and the radiated power of the transducer were optimized. The transducer's electrical impedance was targeted to 50 Ω. The probe was simulated by assembling the designed transducer elements to build an octagonal phased-array with 256 elements on each edge (for a total of 2048 elements). The central frequency is 4.54 MHz; simulated transducer elements are able to deliver enough power and can generate the radiation force with a relatively low level of voltage excitation. Using dynamic transmitter beamforming techniques, the radiation force along a path and resulting acoustic pattern in the breast were simulated assuming a linear isotropic medium. Magnitude and orientation of the acoustic intensity (radiation force) at any point of a generation path could be controlled for the case of an example representing a heterogeneous medium with an embedded soft mechanical inclusion.

The acoustic radiation force on a heated (or cooled) rigid sphere - Theory

NASA Technical Reports Server (NTRS)

Lee, C. P.; Wang, T. G.

1984-01-01

A finite amplitude sound wave can exert a radiation force on an object due to second-order effect of the wave field. The radiation force on a rigid small sphere (i.e., in the long wavelength limit), which has a temperature different from that of the environment, is presently studied. This investigation assumes no thermally induced convection and is relevant to material processing in the absence of gravity. Both isotropic and nonisotropic temperature profiles are considered. In this calculation, the acoustic effect and heat transfer process are essentially decoupled because of the long wavelength limit. The heat transfer information required for determining the force is contained in the parameters, which are integrals over the temperature distribution.

U.S. Air Force Radiation in Space experiment for Gemini 6 flight

NASA Image and Video Library

1965-12-10

S65-58941 (27 Aug. 1965) --- U.S. Air Force Weapons Laboratory D-8 (Radiation in Space) experiment for Gemini-6 spaceflight. Kennedy Space Center alternative photo number is 104-KSC-65C-5533. Photo credit: NASA

Direct Observations of Excess Solar Absorption by Clouds

NASA Technical Reports Server (NTRS)

Pilewskie, Peter; Valero, Francisco P. J.

1995-01-01

Aircraft measurements of solar flux in the cloudy tropical atmosphere reveal that solar absorption by clouds is anomalously large when compared to theoretical estimates. The ratio of cloud forcing at an altitude of 20 kilometers to that at the surface is 1.58 rather than 1.0 as predicted by models. These results were derived from a cloud radiation experiment in which identical instrumentation was deployed on coordinated stacked aircraft. These findings indicate a significant difference between measurements and theory and imply that the interaction between clouds and solar radiation is poorly understood.

Intravascular ultrasound catheter to enhance microbubble-based drug delivery via acoustic radiation force.

PubMed

Kilroy, Joseph P; Klibanov, Alexander L; Wamhoff, Brian R; Hossack, John A

2012-10-01

Previous research has demonstrated that acoustic radiation force enhances intravascular microbubble adhesion to blood vessels in the presence of flow for moleculartargeted ultrasound imaging and drug delivery. A prototype acoustic radiation force intravascular ultrasound (ARFIVUS) catheter was designed and fabricated to displace a microbubble contrast agent in flow representative of conditions encountered in the human carotid artery. The prototype ARFIVUS transducer was designed to match the resonance frequency of 1.4- to 2.6-μm-diameter microbubbles modeled by an experimentally verified 1-D microbubble acoustic radiation force translation model. The transducer element was an elongated Navy Type I (hard) lead zirconate titanate (PZT) ceramic designed to operate at 3 MHz. Fabricated devices operated with center frequencies of 3.3 and 3.6 MHz with -6-dB fractional bandwidths of 55% and 50%, respectively. Microbubble translation velocities as high as 0.86 m/s were measured using a high-speed streak camera when insonating with the ARFIVUS transducer. Finally, the prototype was used to displace microbubbles in a flow phantom while imaging with a commercial 45-MHz imaging IVUS transducer. A sustained increase of 31 dB in average video intensity was measured following insonation with the ARFIVUS, indicating microbubble accumulation resulting from the application of acoustic radiation force.

Experimental Characterization of Radiation Forcing due to Atmospheric Aerosols

NASA Astrophysics Data System (ADS)

Sreenivas, K. R.; Singh, D. K.; Ponnulakshmi, V. K.; Subramanian, G.

2011-11-01

Micro-meteorological processes in the nocturnal atmospheric boundary layer (NBL) including the formation of radiation-fog and the development of inversion layers are controlled by heat transfer and the vertical temperature distribution close to the ground. In a recent study, it has been shown that the temperature profile close to the ground in stably-stratified, NBL is controlled by the radiative forcing due to suspended aerosols. Estimating aerosol forcing is also important in geo-engineering applications to evaluate the use of aerosols to mitigate greenhouse effects. Modeling capability in the above scenarios is limited by our knowledge of this forcing. Here, the design of an experimental setup is presented which can be used for evaluating the IR-radiation forcing on aerosols under either Rayleigh-Benard condition or under conditions corresponding to the NBL. We present results indicating the effect of surface emissivities of the top and bottom boundaries and the aerosol concentration on the temperature profiles. In order to understand the observed enhancement of the convection-threshold, we have determined the conduction-radiation time constant of an aerosol laden air layer. Our results help to explain observed temperature profiles in the NBL, the apparent stability of such profiles and indicate the need to account for the effect of aerosols in climatic/weather models.

Ultrasonic Measurement of Strain Distribution Inside Object Cyclically Compressed by Dual Acoustic Radiation Force

NASA Astrophysics Data System (ADS)

Odagiri, Yoshitaka; Hasegawa, Hideyuki; Kanai, Hiroshi

2008-05-01

One possible way to evaluate acupuncture therapy quantitatively is to measure the change in the elastic property of muscle after application of the therapy. Many studies have been conducted to measure mechanical properties of tissues using ultrasound-induced acoustic radiation force. To assess mechanical properties, strain must be generated in an object. However, a single radiation force is not effective because it mainly generates translational motion when the object is much harder than the surrounding medium. In this study, two cyclic radiation forces are simultaneously applied to a muscle phantom from two opposite horizontal directions so that the object is cyclically compressed in the horizontal direction. By the horizontal compression, the object is expanded vertically based on its incompressibility. The resultant vertical displacement is measured using another ultrasound pulse. Two ultrasonic transducers for actuation were both driven by the sum of two continuous sinusoidal signals at two slightly different frequencies [1 MHz and (1 M + 5) Hz]. The displacement of several micrometers in amplitude, which fluctuated at 5 Hz, was measured by the ultrasonic phased tracking method. Increase in thickness inside the object was observed just when acoustic radiation forces increased. Such changes in thickness correspond to vertical expansion due to horizontal compression.

Downscaling Aerosols and the Impact of Neglected Subgrid Processes on Direct Aerosol Radiative Forcing for a Representative Global Climate Model Grid Spacing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gustafson, William I.; Qian, Yun; Fast, Jerome D.

2011-07-13

Recent improvements to many global climate models include detailed, prognostic aerosol calculations intended to better reproduce the observed climate. However, the trace gas and aerosol fields are treated at the grid-cell scale with no attempt to account for sub-grid impacts on the aerosol fields. This paper begins to quantify the error introduced by the neglected sub-grid variability for the shortwave aerosol radiative forcing for a representative climate model grid spacing of 75 km. An analysis of the value added in downscaling aerosol fields is also presented to give context to the WRF-Chem simulations used for the sub-grid analysis. We foundmore » that 1) the impact of neglected sub-grid variability on the aerosol radiative forcing is strongest in regions of complex topography and complicated flow patterns, and 2) scale-induced differences in emissions contribute strongly to the impact of neglected sub-grid processes on the aerosol radiative forcing. The two of these effects together, when simulated at 75 km vs. 3 km in WRF-Chem, result in an average daytime mean bias of over 30% error in top-of-atmosphere shortwave aerosol radiative forcing for a large percentage of central Mexico during the MILAGRO field campaign.« less

The radiative forcing potential of different climate geoengineering options

NASA Astrophysics Data System (ADS)

Lenton, T. M.; Vaughan, N. E.

2009-01-01

Climate geoengineering proposals seek to rectify the Earth's current radiative imbalance, either by reducing the absorption of incoming solar (shortwave) radiation, or by removing CO2 from the atmosphere and transferring it to long-lived reservoirs, thus increasing outgoing longwave radiation. A fundamental criterion for evaluating geoengineering options is their climate cooling effectiveness, which we quantify here in terms of radiative forcing potential. We use a simple analytical approach, based on the global energy balance and pulse response functions for the decay of CO2 perturbations. This aids transparency compared to calculations with complex numerical models, but is not intended to be definitive. Already it reveals some significant errors in existing calculations, and it allows us to compare the relative effectiveness of a range of proposals. By 2050, only stratospheric aerosol injections or sunshades in space have the potential to cool the climate back toward its pre-industrial state, but some land carbon cycle geoengineering options are of comparable magnitude to mitigation "wedges". Strong mitigation, i.e. large reductions in CO2 emissions, combined with global-scale air capture and storage, afforestation, and bio-char production, i.e. enhanced CO2 sinks, might be able to bring CO2 back to its pre-industrial level by 2100, thus removing the need for other geoengineering. Alternatively, strong mitigation stabilising CO2 at 500 ppm, combined with geoengineered increases in the albedo of marine stratiform clouds, grasslands, croplands and human settlements might achieve a patchy cancellation of radiative forcing. Ocean fertilisation options are only worthwhile if sustained on a millennial timescale and phosphorus addition probably has greater long-term potential than iron or nitrogen fertilisation. Enhancing ocean upwelling or downwelling have trivial effects on any meaningful timescale. Our approach provides a common framework for the evaluation of climate geoengineering proposals, and our results should help inform the prioritisation of further research into them.

3D General Circulation Model of the Middle Atmosphere of Jupiter

NASA Astrophysics Data System (ADS)

Zube, Nicholas Gerard; Zhang, Xi; Li, Cheng; Le, Tianhao

2017-10-01

The characteristics of Jupiter’s large-scale stratospheric circulation remain largely unknown. Detailed distributions of temperature and photochemical species have been provided by recent observations [1], but have not yet been accurately reproduced by middle atmosphere general circulation models (GCM). Jupiter’s stratosphere and upper troposphere are influenced by radiative forcing from solar insolation and infrared cooling from hydrogen and hydrocarbons, as well as waves propagating from the underlying troposphere [2]. The relative significance of radiative and mechanical forcing on stratospheric circulation is still being debated [3]. Here we present a 3D GCM of Jupiter’s atmosphere with a correlated-k radiative transfer scheme. The simulation results are compared with observations. We analyze the impact of model parameters on the stratospheric temperature distribution and dynamical features. Finally, we discuss future tracer transport and gravity wave parameterization schemes that may be able to accurately simulate the middle atmosphere dynamics of Jupiter and other giant planets.[1] Kunde et al. 2004, Science 305, 1582.[2] Zhang et al. 2013a, EGU General Assembly, EGU2013-5797-2.[3] Conrath 1990, Icarus, 83, 255-281.

Self-Shadowing of a Spacecraft in the Computation of Surface Forces. An Example in Planetary Geodesy

NASA Astrophysics Data System (ADS)

Balmino, G.; Marty, J. C.

2018-03-01

We describe in details the algorithms used in modelling the self-shadowing between spacecraft components, which appears when computing the surface forces as precisely as possible and especially when moving parts are involved. This becomes necessary in planetary geodesy inverse problems using more and more precise orbital information to derive fundamental parameters of geophysical interest. Examples are given with two Mars orbiters, which show significant improvement on drag and solar radiation pressure model multiplying factors, a prerequisite for improving in turn the determination of other global models.

Dust aerosol properties and radiative forcing observed in spring during 2001-2014 over urban Beijing, China.

PubMed

Yu, Xingna; Lü, Rui; Kumar, K Raghavendra; Ma, Jia; Zhang, Qiuju; Jiang, Yilun; Kang, Na; Yang, Suying; Wang, Jing; Li, Mei

2016-08-01

The ground-based characteristics (optical and radiative properties) of dust aerosols measured during the springtime between 2001 and 2014 were investigated over urban Beijing, China. The seasonal averaged aerosol optical depth (AOD) during spring of 2001-2014 was about 0.78 at 440 nm. During dust days, higher AOD occurred associated with lower Ångström exponent (AE). The mean AE440-870 in the springtime was about 1.0, indicating dominance of fine particles over the region. The back-trajectory analysis revealed that the dust was transported from the deserts of Inner Mongolia and Mongolia arid regions to Beijing. The aerosol volume size distribution showed a bimodal distribution pattern, with its highest peak observed in coarse mode for all episodes (especially for dust days with increased volume concentration). The single scattering albedo (SSA) increased with wavelength on dust days, indicating the presence of more scattering particles. Furthermore, the complex parts (real and imaginary) of refractive index showed distinct characteristics with lower imaginary values (also scattering) on dust days. The shortwave (SW; 0.2-4.0 μm) and longwave (LW; 4-100 μm) aerosol radiative forcing (ARF) values were computed from the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model both at the top of atmosphere (TOA) and the bottom of atmosphere (BOA) during dust and non-dust (dust free) days, and the corresponding heating rates and forcing efficiencies were also estimated. The SW (LW) ARF, therefore, produced significant cooling (warming) effects at both the TOA and the BOA over Beijing.

Optical trapping/modification of nano-(micro)particles by gradient and photorefractive forces during laser illumination

NASA Astrophysics Data System (ADS)

Kukhtarev, N.; Kukhtareva, T.; Okafor, F.

2010-08-01

In this paper we describe photo-induced trapping/redistribution of silver nano-(micro) particles near the surface of photorefractive crystal LiNbO3:Fe. This type of optical trapping is due to combined forces of direct gradient-force trapping and asymmetric photorefractive forces of electro-phoresis and dielectro-phoresis. The silver nanoparticles were produced through extracellular biosynthesis on exposure to the fungus, Fusarium oxysporum (FO) and to the plant extracts. Pulsed and CW visible laser radiation lead to significant modification of nanoparticle clusters. This study indicates that extracellular biosynthesis can constitute a possible viable alternative method for the production of nanoparticles. In addition, the theoretical modeling of asymmetric photorefractive electric field grating has been presented and compared with the experimental results.

Satellite observed impacts of wildfires on regional atmosphere composition and shortwave radiative forcing: multiple cases study

NASA Astrophysics Data System (ADS)

Fu, Y.; Li, R.; Huang, J.; Bergeron, Y.; Fu, Y.

2017-12-01

Emissions of aerosols and trace gases from wildfires and the direct shortwave radiative forcing were studied using multi-satellite/sensor observations from Aqua Moderate-Resolution Imaging Spectroradiometer (MODIS), Aqua Atmospheric Infrared Sounder (AIRS), Aura Ozone Monitoring Instrument (OMI), and Aqua Cloud's and the Earth's Radiant Energy System (CERES). The selected cases occurred in Northeast of China (NEC), Siberia of Russia, California of America have dominant fuel types of cropland, mixed forest and needleleaf forest, respectively. The Fire radiative power (FRP) based emission coefficients (Ce) of aerosol, NOx (NO2+NO), formaldehyde (HCHO), and carbon monoxide (CO) showed significant differences from case to case. 1) the FRP of the cropland case in NEC is strongest, however, the Ce of aerosol is the lowest (20.51 ± 2.55 g MJ-1). The highest Ce of aerosol is 71.34 ± 13.24 g MJ-1 in the needleleaf fire case in California. 2) For NOx, the highest Ce existed in the cropland case in NEC (2.76 ± 0.25 g MJ-1), which is more than three times of those in the forest fires in Siberia and California. 3) The Ce of CO is 70.21±10.97 and 88.38±46.16 g MJ-1 in the forest fires in Western Siberia and California, which are about four times of that in cropland fire. 4) The variation of Ce of HCHO are relatively small among cases. Strong spatial correlations are found among aerosol optical depth (AOD), NOx, HCHO, and CO. The ratios of NOx to AOD, HCHO, and CO in the cropland case in NEC show much higher values than those in other cases. Although huge differences of emissions and composition ratios exist among cases, the direct shortwave (SW) radiative forcing efficiency (SWARFE) of smoke at the top of the atmosphere (TOA) are in good agreement, with the shortwave radiative forcing efficiencies values of 20.09 to 22.93 per unit AOD. Results in this study reveal noteworthy variations of the FRP-based emissions coefficient and relative chemical composition in the smoke. Nitrogen content in the fuel and/or soil, the biomes type burned, the combustion states (flaming or smoldering) and/or the weather condition might be respond for those differences among cases. This study also prove remarkable and consistent cooling effect of shortwave radiation forcing at TOA from the wildfire emissions in all selected cases.

Experimental Demonstration of a Synthetic Lorentz Force by Using Radiation Pressure.

PubMed

Šantić, N; Dubček, T; Aumiler, D; Buljan, H; Ban, T

2015-09-02

Synthetic magnetism in cold atomic gases opened the doors to many exciting novel physical systems and phenomena. Ubiquitous are the methods used for the creation of synthetic magnetic fields. They include rapidly rotating Bose-Einstein condensates employing the analogy between the Coriolis and the Lorentz force, and laser-atom interactions employing the analogy between the Berry phase and the Aharonov-Bohm phase. Interestingly, radiation pressure - being one of the most common forces induced by light - has not yet been used for synthetic magnetism. We experimentally demonstrate a synthetic Lorentz force, based on the radiation pressure and the Doppler effect, by observing the centre-of-mass motion of a cold atomic cloud. The force is perpendicular to the velocity of the cold atomic cloud, and zero for the cloud at rest. Our novel concept is straightforward to implement in a large volume, for a broad range of velocities, and can be extended to different geometries.

Mechanism of SOA formation determines magnitude of radiative effects

NASA Astrophysics Data System (ADS)

Zhu, Jialei; Penner, Joyce E.; Lin, Guangxing; Zhou, Cheng; Xu, Li; Zhuang, Bingliang

2017-11-01

Secondary organic aerosol (SOA) nearly always exists as an internal mixture, and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing state based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66% of SOA is internally mixed with sulfate, while 34% is internally mixed with primary soot. Compared with using an external mixture, the direct effect of SOA is decreased due to the decrease in total aerosol surface area and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced, and this is responsible for a large decrease in the cloud albedo effect. Internal mixing decreases the radiative effect of SOA by a factor of >4 compared with treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of ‑0.05 W m‑2. When the combined effects of changes in climate, anthropogenic emissions, and land use are included, the SOA forcing is ‑0.07 W m‑2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing.

Direct Aerosol Forcing Uncertainty

DOE Data Explorer

Mccomiskey, Allison

2008-01-15

Understanding sources of uncertainty in aerosol direct radiative forcing (DRF), the difference in a given radiative flux component with and without aerosol, is essential to quantifying changes in Earth's radiation budget. We examine the uncertainty in DRF due to measurement uncertainty in the quantities on which it depends: aerosol optical depth, single scattering albedo, asymmetry parameter, solar geometry, and surface albedo. Direct radiative forcing at the top of the atmosphere and at the surface as well as sensitivities, the changes in DRF in response to unit changes in individual aerosol or surface properties, are calculated at three locations representing distinct aerosol types and radiative environments. The uncertainty in DRF associated with a given property is computed as the product of the sensitivity and typical measurement uncertainty in the respective aerosol or surface property. Sensitivity and uncertainty values permit estimation of total uncertainty in calculated DRF and identification of properties that most limit accuracy in estimating forcing. Total uncertainties in modeled local diurnally averaged forcing range from 0.2 to 1.3 W m-2 (42 to 20%) depending on location (from tropical to polar sites), solar zenith angle, surface reflectance, aerosol type, and aerosol optical depth. The largest contributor to total uncertainty in DRF is usually single scattering albedo; however decreasing measurement uncertainties for any property would increase accuracy in DRF. Comparison of two radiative transfer models suggests the contribution of modeling error is small compared to the total uncertainty although comparable to uncertainty arising from some individual properties.

Mechanism of SOA formation determines magnitude of radiative effects

DOE PAGES

Zhu, Jialei; Penner, Joyce E.; Lin, Guangxing; ...

2017-11-13

Secondary organic aerosol (SOA) nearly always exists as an internal mixture and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing states based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66 % of SOA is internally mixed with sulfate, while 34 % is internally mixed with primary soot. When compared with using an external mixture, the direct effect of SOA is decreased, due to the decrease of total aerosol surface areamore » and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced and this is responsible for a large decrease in the cloud albedo effect. In total, internal mixing suppresses the radiative effect of SOA by a factor of >4 compared to treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of -0.05 W m-2. When the combined effects of changes in climate, anthropogenic emissions and land use are included, the SOA forcing is -0.07 W m-2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing.« less

Mechanism of SOA formation determines magnitude of radiative effects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Jialei; Penner, Joyce E.; Lin, Guangxing

Secondary organic aerosol (SOA) nearly always exists as an internal mixture and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing states based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66 % of SOA is internally mixed with sulfate, while 34 % is internally mixed with primary soot. When compared with using an external mixture, the direct effect of SOA is decreased, due to the decrease of total aerosol surface areamore » and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced and this is responsible for a large decrease in the cloud albedo effect. In total, internal mixing suppresses the radiative effect of SOA by a factor of >4 compared to treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of -0.05 W m-2. When the combined effects of changes in climate, anthropogenic emissions and land use are included, the SOA forcing is -0.07 W m-2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing.« less

Mechanism of SOA Formation Determines Magnitude of Radiative Effects

NASA Astrophysics Data System (ADS)

Zhu, J.; Penner, J.; Lin, G.; Zhou, C.

2017-12-01

Secondary organic aerosol (SOA) nearly always exists as an internal mixture and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing states based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66 % of SOA is internally mixed with sulfate, while 34 % is internally mixed with primary soot. When compared with using an external mixture, the direct effect of SOA is decreased, due to the decrease of total aerosol surface area and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced and this is responsible for a large decrease in the cloud albedo effect. In total, internal mixing suppresses the radiative effect of SOA by a factor of >4 compared to treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of -0.05 W m-2. When the combined effects of changes in climate, anthropogenic emissions and land use are included, the SOA forcing is -0.07 W m-2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing.

Mechanism of SOA formation determines magnitude of radiative effects

PubMed Central

Penner, Joyce E.; Lin, Guangxing; Zhou, Cheng; Xu, Li; Zhuang, Bingliang

2017-01-01

Secondary organic aerosol (SOA) nearly always exists as an internal mixture, and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing state based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66% of SOA is internally mixed with sulfate, while 34% is internally mixed with primary soot. Compared with using an external mixture, the direct effect of SOA is decreased due to the decrease in total aerosol surface area and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced, and this is responsible for a large decrease in the cloud albedo effect. Internal mixing decreases the radiative effect of SOA by a factor of >4 compared with treating SOA as an external mixture. The future SOA burden increases by 24% due to CO2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of −0.05 W m−2. When the combined effects of changes in climate, anthropogenic emissions, and land use are included, the SOA forcing is −0.07 W m−2, even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing. PMID:29133426

Mechanism of SOA formation determines magnitude of radiative effects.

PubMed

Zhu, Jialei; Penner, Joyce E; Lin, Guangxing; Zhou, Cheng; Xu, Li; Zhuang, Bingliang

2017-11-28

Secondary organic aerosol (SOA) nearly always exists as an internal mixture, and the distribution of this mixture depends on the formation mechanism of SOA. A model is developed to examine the influence of using an internal mixing state based on the mechanism of formation and to estimate the radiative forcing of SOA in the future. For the present day, 66% of SOA is internally mixed with sulfate, while 34% is internally mixed with primary soot. Compared with using an external mixture, the direct effect of SOA is decreased due to the decrease in total aerosol surface area and the increase of absorption efficiency. Aerosol number concentrations are sharply reduced, and this is responsible for a large decrease in the cloud albedo effect. Internal mixing decreases the radiative effect of SOA by a factor of >4 compared with treating SOA as an external mixture. The future SOA burden increases by 24% due to CO 2 increases and climate change, leading to a total (direct plus cloud albedo) radiative forcing of -0.05 W m -2 When the combined effects of changes in climate, anthropogenic emissions, and land use are included, the SOA forcing is -0.07 W m -2 , even though the SOA burden only increases by 6.8%. This is caused by the substantial increase of SOA associated with sulfate in the Aitken mode. The Aitken mode increase contributes to the enhancement of first indirect radiative forcing, which dominates the total radiative forcing. Copyright © 2017 the Author(s). Published by PNAS.

In vivo quantification of liver stiffness in a rat model of hepatic fibrosis with acoustic radiation force.

PubMed

Wang, Michael H; Palmeri, Mark L; Guy, Cynthia D; Yang, Liu; Hedlund, Laurence W; Diehl, Anna Mae; Nightingale, Kathryn R

2009-10-01

Liver fibrosis is currently staged using needle biopsy, a highly invasive procedure with a number of disadvantages. Measurement of liver stiffness changes that accompany progression of the disease may provide a quantitative and noninvasive method to assess the health of the liver. The purpose of this study is to investigate the correlation between liver stiffness measured by radiation force induced shear waves and disease related changes in the liver. An additional aim is to present initial findings on the effects of liver viscosity on radiation force induced shear wave morphology. Liver fibrosis was induced in 10 rats using carbon tetrachloride (CCl(4)), while five rats acted as controls. Liver stiffness was measured in vivo in all rats after a treatment period of 8 weeks using a modified Siemens SONOLINE Antares scanner (Siemens Medical Solutions USA, Ultrasound Division, Issaquah, WA, USA). The spatial coherence of radiation force induced shear waves propagating in the viscoelastic rat liver decreased significantly with propagation distance, compared with shear waves in an elastic phantom and a finite element model of a purely elastic medium. Animals were sacrificed after imaging and liver samples were taken for histopathologic analysis and collagen quantification using picrosirius red staining and hydroxyproline assay. At the end of the treatment period, five rats had healthy livers (stage F0), while six had severe fibrosis (F3) and the rest had light to moderate fibrosis (F1 and F2). The measured liver stiffness for the F0 group was 1.5+/-0.1 kPa (mean+/-95% confidence interval) and for F3 livers was 1.8+/-0.2 kPa. In this study, liver stiffness was found to be linearly correlated with the amount of collagen in the liver measured by picrosirius red staining (r(2)=0.43, p=0.008). In addition, stiffness spatial heterogeneity was also linearly correlated with liver collagen content (r(2)=0.58, p=0.001) by picrosirius red staining. These results are consistent with those obtained by Salameh et al. (2007) and Yin et al. (2007b) using animal models of liver fibrosis and MR elastography. This suggests that stiffness measurement using acoustic radiation force can provide a quantitative assessment of the extent of fibrosis in the liver and can be potentially used for the diagnosis, management and study of liver fibrosis.

Extended optical theorem in isotropic solids and its application to the elastic radiation force

NASA Astrophysics Data System (ADS)

Leão-Neto, J. P.; Lopes, J. H.; Silva, G. T.

2017-04-01

In this article, we derive the extended optical theorem for the elastic-wave scattering by a spherical inclusion (with and without absorption) in a solid matrix. This theorem expresses the extinction cross-section, i.e., the time-averaged power extracted from the incoming beam per its intensity, regarding the partial-wave expansion coefficients of the incident and scattered waves. We also establish the connection between the optical theorem and the elastic radiation force by a plane wave in a linear and isotropic solid. We obtain the absorption, scattering, and extinction efficiencies (the corresponding power per characteristic incident intensity per sphere cross-section area) for a plane wave and a spherically focused beam. We discuss to which extent the radiation force theory for plane waves can be used to the focused beam case. Considering an iron sphere embedded in an aluminum matrix, we numerically compute the scattering and elastic radiation force efficiencies. The radiation force on a stainless steel sphere embedded in a tissue-like medium (soft solid) is also computed. In this case, resonances are observed in the force as a function of the sphere size parameter (the wavenumber times the sphere radius). Remarkably, the relative difference between our findings and previous lossless liquid models is about 100% in the long-wavelength limit. Regarding some applications, the obtained results have a direct impact on ultrasound-based elastography techniques and ultrasonic nondestructive testing, as well as implantable devices activated by ultrasound.

The impact of Chernobyl on health and labour market performance.

PubMed

Lehmann, Hartmut; Wadsworth, Jonathan

2011-09-01

Using longitudinal data from Ukraine we examine the extent of any long-lasting effects of exposure to the Chernobyl disaster on the health and labour market performance of the adult workforce. Variation in the local area level of radiation fallout from the Chernobyl accident is considered as a random exogenous shock with which to try to establish its causal impact on poor health, labour force participation, hours worked and wages. There appears to be a significant positive association between local area-level radiation dosage and perception of poor health, though much weaker associations between local area-level dosage and other specific self-reported health conditions. There is also some evidence to suggest that those who lived in areas more exposed to Chernobyl-induced radiation have significantly lower levels of labour market performance 20 years on. Copyright © 2011 Elsevier B.V. All rights reserved.

Lidar characterizations of atmospheric aerosols and clouds

NASA Astrophysics Data System (ADS)

Ferrare, R. A.; Hostetler, C. A.; Hair, J. W.; Burton, S. P.

2017-12-01

Knowledge of the vertical profile, composition, concentration, and size distribution of aerosols is required to quantify the impacts of aerosols on human health, global and regional climate, clouds and precipitation. In particular, radiative forcing due to anthropogenic aerosols is the most uncertain part of anthropogenic radiative forcing, with aerosol-cloud interactions (ACI) as the largest source of uncertainty in current estimates of global radiative forcing. Improving aerosol transport model predictions of the vertical profile of aerosol optical and microphysical characteristics is crucial for improving assessments of aerosol radiative forcing. Understanding how aerosols and clouds interact is essential for investigating the aerosol indirect effect and ACI. Through its ability to provide vertical profiles of aerosol and cloud distributions as well as important information regarding the optical and physical properties of aerosols and clouds, lidar is a crucial tool for addressing these science questions. This presentation describes how surface, airborne, and satellite lidar measurements have been used to address these questions, and in particular how High Spectral Resolution Lidar (HSRL) measurements provide profiles of aerosol properties (backscatter, extinction, depolarization, concentration, size) important for characterizing radiative forcing. By providing a direct measurement of aerosol extinction, HSRL provides more accurate aerosol measurement profiles and more accurate constraints for models than standard retrievals from elastic backscatter lidar, which loses accuracy and precision at lower altitudes due to attenuation from overlying layers. Information regarding particle size and abundance from advanced lidar retrievals provides better proxies for cloud-condensation-nuclei (CCN), which are required for assessing aerosol-cloud interactions. When combined with data from other sensors, advanced lidar measurements can provide information on aerosol and cloud properties for addressing both direct and indirect radiative forcing.

Acoustic radiation force on a rigid elliptical cylinder in plane (quasi)standing waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mitri, F. G., E-mail: F.G.Mitri@ieee.org

2015-12-07

The acoustic radiation force on a 2D elliptical (non-circular) cylinder centered on the axis of wave propagation of plane quasi-standing and standing waves is derived, based on the partial-wave series expansion (PWSE) method in cylindrical coordinates. A non-dimensional acoustic radiation force function, which is the radiation force per unit length, per characteristic energy density and per unit cross-sectional surface of the ellipse, is defined in terms of the scattering coefficients that are determined by applying the Neumann boundary condition for an immovable surface. A system of linear equations involving a single numerical integration procedure is solved by matrix inversion. Numericalmore » simulations showing the transition from the quasi-standing to the (equi-amplitude) standing wave behaviour are performed with particular emphasis on the aspect ratio a/b, where a and b are the ellipse semi-axes, as well as the dimensionless size parameter kb (where k is the wavenumber), without the restriction to a particular range of frequencies. It is found that at high kb values > 1, the radiation force per length with broadside incidence is larger, whereas the opposite situation occurs in the long-wavelength limit (i.e., kb < 1). The results are particularly relevant in acoustic levitation of elliptical cylinders, the acoustic stabilization of liquid columns in a host medium, acousto-fluidics devices, and other particle dynamics applications to name a few. Moreover, the formalism presented here may be effectively applied to compute the acoustic radiation force on other 2D surfaces of arbitrary shape such as super-ellipses, Chebyshev cylindrical particles, or other non-circular geometries.« less

Spatiotemporal variation of surface shortwave forcing from fire-induced albedo change in interior Alaska

USGS Publications Warehouse

Huang, Shengli; Dahal, Devendra; Liu, Heping; Jin, Suming; Young, Claudia J.; Liu, Shuang; Liu, Shu-Guang

2015-01-01

The albedo change caused by both fires and subsequent succession is spatially heterogeneous, leading to the need to assess the spatiotemporal variation of surface shortwave forcing (SSF) as a component to quantify the climate impacts of high-latitude fires. We used an image reconstruction approach to compare postfire albedo with the albedo assuming fires had not occurred. Combining the fire-caused albedo change from the 2001-2010 fires in interior Alaska and the monthly surface incoming solar radiation, we examined the spatiotemporal variation of SSF in the early successional stage of around 10 years. Our results showed that while postfire albedo generally increased in fall, winter, and spring, some burned areas could show an albedo decrease during these seasons. In summer, the albedo increased for several years and then declined again. The spring SSF distribution did not show a latitudinal decrease from south to north as previously reported. The results also indicated that although the SSF is usually largely negative in the early successional years, it may not be significant during the first postfire year. The annual 2005-2010 SSF for the 2004 fire scars was -1.30, -4.40, -3.31, -4.00, -3.42, and -2.47 Wm-2. The integrated annual SSF map showed significant spatial variation with a mean of -3.15 Wm-2 and a standard deviation of 3.26 Wm-2, 16% of burned areas having positive SSF. Our results suggest that boreal deciduous fires would be less positive for climate change than boreal evergreen fires. Future research is needed to comprehensively investigate the spatiotemporal radiative and non-radiative forcings to determine the effect of boreal fires on climate.

Ultrasound-modulated optical tomography with intense acoustic bursts.

PubMed

Zemp, Roger J; Kim, Chulhong; Wang, Lihong V

2007-04-01

Ultrasound-modulated optical tomography (UOT) detects ultrasonically modulated light to spatially localize multiply scattered photons in turbid media with the ultimate goal of imaging the optical properties in living subjects. A principal challenge of the technique is weak modulated signal strength. We discuss ways to push the limits of signal enhancement with intense acoustic bursts while conforming to optical and ultrasonic safety standards. A CCD-based speckle-contrast detection scheme is used to detect acoustically modulated light by measuring changes in speckle statistics between ultrasound-on and ultrasound-off states. The CCD image capture is synchronized with the ultrasound burst pulse sequence. Transient acoustic radiation force, a consequence of bursts, is seen to produce slight signal enhancement over pure ultrasonic-modulation mechanisms for bursts and CCD exposure times of the order of milliseconds. However, acoustic radiation-force-induced shear waves are launched away from the acoustic sample volume, which degrade UOT spatial resolution. By time gating the CCD camera to capture modulated light before radiation force has an opportunity to accumulate significant tissue displacement, we reduce the effects of shear-wave image degradation, while enabling very high signal-to-noise ratios. Additionally, we maintain high-resolution images representative of optical and not mechanical contrast. Signal-to-noise levels are sufficiently high so as to enable acquisition of 2D images of phantoms with one acoustic burst per pixel.

Global Radiative Forcing of Coupled Tropospheric Ozone and Aerosols in a Unified General Circulation Model

NASA Technical Reports Server (NTRS)

Liao, Hong; Seinfeld, John H.; Adams, Peter J.; Mickley, Loretta J.

2008-01-01

Global simulations of sea salt and mineral dust aerosols are integrated into a previously developed unified general circulation model (GCM), the Goddard Institute for Space Studies (GISS) GCM II', that simulates coupled tropospheric ozone-NOx-hydrocarbon chemistry and sulfate, nitrate, ammonium, black carbon, primary organic carbon, and secondary organic carbon aerosols. The fully coupled gas-aerosol unified GCM allows one to evaluate the extent to which global burdens, radiative forcing, and eventually climate feedbacks of ozone and aerosols are influenced by gas-aerosol chemical interactions. Estimated present-day global burdens of sea salt and mineral dust are 6.93 and 18.1 Tg with lifetimes of 0.4 and 3.9 days, respectively. The GCM is applied to estimate current top of atmosphere (TOA) and surface radiative forcing by tropospheric ozone and all natural and anthropogenic aerosol components. The global annual mean value of the radiative forcing by tropospheric ozone is estimated to be +0.53 W m(sup -2) at TOA and +0.07 W m(sup -2) at the Earth's surface. Global, annual average TOA and surface radiative forcing by all aerosols are estimated as -0.72 and -4.04 W m(sup -2), respectively. While the predicted highest aerosol cooling and heating at TOA are -10 and +12 W m(sup -2) respectively, surface forcing can reach values as high as -30 W m(sup -2), mainly caused by the absorption by black carbon, mineral dust, and OC. We also estimate the effects of chemistry-aerosol coupling on forcing estimates based on currently available understanding of heterogeneous reactions on aerosols. Through altering the burdens of sulfate, nitrate, and ozone, heterogeneous reactions are predicted to change the global mean TOA forcing of aerosols by 17% and influence global mean TOA forcing of tropospheric ozone by 15%.

Significant radiative impact of volcanic aerosol in the lowermost stratosphere

PubMed Central

Andersson, Sandra M.; Martinsson, Bengt G.; Vernier, Jean-Paul; Friberg, Johan; Brenninkmeijer, Carl A. M.; Hermann, Markus; van Velthoven, Peter F. J.; Zahn, Andreas

2015-01-01

Despite their potential to slow global warming, until recently, the radiative forcing associated with volcanic aerosols in the lowermost stratosphere (LMS) had not been considered. Here we study volcanic aerosol changes in the stratosphere using lidar measurements from the NASA CALIPSO satellite and aircraft measurements from the IAGOS-CARIBIC observatory. Between 2008 and 2012 volcanism frequently affected the Northern Hemisphere stratosphere aerosol loadings, whereas the Southern Hemisphere generally had loadings close to background conditions. We show that half of the global stratospheric aerosol optical depth following the Kasatochi, Sarychev and Nabro eruptions is attributable to LMS aerosol. On average, 30% of the global stratospheric aerosol optical depth originated in the LMS during the period 2008–2011. On the basis of the two independent, high-resolution measurement methods, we show that the LMS makes an important contribution to the overall volcanic forcing. PMID:26158244

The importance of the Montreal Protocol in protecting climate.

PubMed

Velders, Guus J M; Andersen, Stephen O; Daniel, John S; Fahey, David W; McFarland, Mack

2007-03-20

The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer is a landmark agreement that has successfully reduced the global production, consumption, and emissions of ozone-depleting substances (ODSs). ODSs are also greenhouse gases that contribute to the radiative forcing of climate change. Using historical ODSs emissions and scenarios of potential emissions, we show that the ODS contribution to radiative forcing most likely would have been much larger if the ODS link to stratospheric ozone depletion had not been recognized in 1974 and followed by a series of regulations. The climate protection already achieved by the Montreal Protocol alone is far larger than the reduction target of the first commitment period of the Kyoto Protocol. Additional climate benefits that are significant compared with the Kyoto Protocol reduction target could be achieved by actions under the Montreal Protocol, by managing the emissions of substitute fluorocarbon gases and/or implementing alternative gases with lower global warming potentials.

The importance of the Montreal Protocol in protecting climate

PubMed Central

Velders, Guus J. M.; Andersen, Stephen O.; Daniel, John S.; Fahey, David W.; McFarland, Mack

2007-01-01

The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer is a landmark agreement that has successfully reduced the global production, consumption, and emissions of ozone-depleting substances (ODSs). ODSs are also greenhouse gases that contribute to the radiative forcing of climate change. Using historical ODSs emissions and scenarios of potential emissions, we show that the ODS contribution to radiative forcing most likely would have been much larger if the ODS link to stratospheric ozone depletion had not been recognized in 1974 and followed by a series of regulations. The climate protection already achieved by the Montreal Protocol alone is far larger than the reduction target of the first commitment period of the Kyoto Protocol. Additional climate benefits that are significant compared with the Kyoto Protocol reduction target could be achieved by actions under the Montreal Protocol, by managing the emissions of substitute fluorocarbon gases and/or implementing alternative gases with lower global warming potentials. PMID:17360370

Measuring the greenhouse effect and radiative forcing through the atmosphere

NASA Astrophysics Data System (ADS)

Philipona, Rolf; Kräuchi, Andreas; Brocard, Emmanuel

2013-04-01

In spite of a large body of existing measurements of incoming shortwave solar radiation and outgoing longwave terrestrial radiation at the Earth's surface and at the top of the atmosphere, there are few observations documenting how radiation profiles change through the atmosphere - information that is necessary to fully quantify the greenhouse effect of the Earth's atmosphere. Using weather balloons and specific radiometer equipped radiosondes, we continuously measured shortwave and longwave radiation fluxes from the surface of the Earth up to altitudes of 35 kilometers in the upper stratosphere. Comparing radiation profiles from night measurements with different amounts of water vapor, we show evidence of large greenhouse forcing. We show, that under cloud free conditions, water vapor increases with Clausius-Clapeyron ( 7% / K), and longwave downward radiation at the surface increases by 8 Watts per square meter per Kelvin. The longwave net radiation however, shows a positive increase (downward) of 2.4 Watts per square meter and Kelvin at the surface, which decreases with height and shows a similar but negative increase (upward) at the tropopause. Hence, increased tropospheric water vapor increases longwave net radiation towards the ground and towards space, and produces a heating of 0.42 Kelvin per Watt per square meter at the surface. References: Philipona et al., 2012: Solar and thermal radiation profiles and radiative forcing measured through the atmosphere. Geophys. Res. Lett., 39, L13806, doi: 10.1029/2012GL052087.

Lorentz-Abraham-Dirac versus Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions).

PubMed

Bulanov, Sergei V; Esirkepov, Timur Zh; Kando, Masaki; Koga, James K; Bulanov, Stepan S

2011-11-01

When the parameters of electron-extreme power laser interaction enter the regime of dominated radiation reaction, the electron dynamics changes qualitatively. The adequate theoretical description of this regime becomes crucially important with the use of the radiation friction force either in the Lorentz-Abraham-Dirac form, which possesses unphysical runaway solutions, or in the Landau-Lifshitz form, which is a perturbation valid for relatively low electromagnetic wave amplitude. The goal of the present paper is to find the limits of the Landau-Lifshitz radiation force applicability in terms of the electromagnetic wave amplitude and frequency. For this, a class of the exact solutions to the nonlinear problems of charged particle motion in the time-varying electromagnetic field is used.

Lorentz-Abraham-Dirac versus Landau-Lifshitz radiation friction force in the ultrarelativistic electron interaction with electromagnetic wave (exact solutions)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bulanov, Sergei V.; Esirkepov, Timur Zh.; Kando, Masaki

2011-11-15

When the parameters of electron-extreme power laser interaction enter the regime of dominated radiation reaction, the electron dynamics changes qualitatively. The adequate theoretical description of this regime becomes crucially important with the use of the radiation friction force either in the Lorentz-Abraham-Dirac form, which possesses unphysical runaway solutions, or in the Landau-Lifshitz form, which is a perturbation valid for relatively low electromagnetic wave amplitude. The goal of the present paper is to find the limits of the Landau-Lifshitz radiation force applicability in terms of the electromagnetic wave amplitude and frequency. For this, a class of the exact solutions to themore » nonlinear problems of charged particle motion in the time-varying electromagnetic field is used.« less

In Situ Measurement of Aerosol Extinction

NASA Technical Reports Server (NTRS)

Strawa, Anthony W.; Castaneda, R.; Owano, T. G.; Bear, D.; Gore, Warren J. (Technical Monitor)

2001-01-01

Aerosols are important contributors to the radiative forcing in the atmosphere. Much of the uncertainty in our knowledge of climate forcing is due to uncertainties in the radiative forcing due to aerosols as illustrated in the IPCC reports of the last ten years. Improved measurement of aerosol optical properties, therefore, is critical to an improved understanding of atmospheric radiative forcing. Additionally, attempts to reconcile in situ and remote measurements of aerosol radiative properties have generally not been successful. This is due in part to the fact that it has been impossible to measure aerosol extinction in situ in the past. In this presentation we introduce a new instrument that employs the techniques used in cavity ringdown spectroscopy to measure the aerosol extinction and scattering coefficients in situ. A prototype instrument has been designed and tested in the lab and the field. It is capable of measuring aerosol extinction coefficient to 2x10(exp -6) per meter. This prototype instrument is described and results are presented.

Magnitude and pattern of Arctic warming governed by the seasonality of radiative forcing.

PubMed

Bintanja, R; Krikken, F

2016-12-02

Observed and projected climate warming is strongest in the Arctic regions, peaking in autumn/winter. Attempts to explain this feature have focused primarily on identifying the associated climate feedbacks, particularly the ice-albedo and lapse-rate feedbacks. Here we use a state-of-the-art global climate model in idealized seasonal forcing simulations to show that Arctic warming (especially in winter) and sea ice decline are particularly sensitive to radiative forcing in spring, during which the energy is effectively 'absorbed' by the ocean (through sea ice melt and ocean warming, amplified by the ice-albedo feedback) and consequently released to the lower atmosphere in autumn and winter, mainly along the sea ice periphery. In contrast, winter radiative forcing causes a more uniform response centered over the Arctic Ocean. This finding suggests that intermodel differences in simulated Arctic (winter) warming can to a considerable degree be attributed to model uncertainties in Arctic radiative fluxes, which peak in summer.

Equivalence of expressions for the radiation force on cylinders and application to elliptical cylinders

NASA Astrophysics Data System (ADS)

Wei, Wei; Marston, Philip L.

2005-09-01

Using an appropriate grouping of terms, a radiation force expression for cylinders in a standing wave based on far-field scattering [W. Wei, D. B. Thiessen, and P. L. Marston, J. Acoust. Soc. Am. 116, 202-208 (2004)] is transformed to an expression given elsewhere [F. G. Mitri, Eur. Phys. J. B 44, 71-78 (2005)]. Mitri's result is from a near-field derivation for the specific case of a circular cylinder. In the usual case, in an ideal lossless media the far-field derivation is not an approximation. The far-field derivation also applies to noncircular objects having mirror symmetry about the incident wave vector. Some general and historical aspects of far-field derivations of optical and acoustical radiation force (going back to 1909) will be noted. Our formulation yields a simple low-frequency approximation for the radiation force on elliptical cylinders by introducing approximations for the partial-wave scattering coefficients of elliptical cylinders first derived by Rayleigh. [Work supported by NASA.

Climate change and maize yield in southern Africa: what can farm management do?

PubMed

Rurinda, Jairos; van Wijk, Mark T; Mapfumo, Paul; Descheemaeker, Katrien; Supit, Iwan; Giller, Ken E

2015-12-01

There is concern that food insecurity will increase in southern Africa due to climate change. We quantified the response of maize yield to projected climate change and to three key management options - planting date, fertilizer use and cultivar choice - using the crop simulation model, agricultural production systems simulator (APSIM), at two contrasting sites in Zimbabwe. Three climate periods up to 2100 were selected to cover both near- and long-term climates. Future climate data under two radiative forcing scenarios were generated from five global circulation models. The temperature is projected to increase significantly in Zimbabwe by 2100 with no significant change in mean annual total rainfall. When planting before mid-December with a high fertilizer rate, the simulated average grain yield for all three maize cultivars declined by 13% for the periods 2010-2039 and 2040-2069 and by 20% for 2070-2099 compared with the baseline climate, under low radiative forcing. Larger declines in yield of up to 32% were predicted for 2070-2099 with high radiative forcing. Despite differences in annual rainfall, similar trends in yield changes were observed for the two sites studied, Hwedza and Makoni. The yield response to delay in planting was nonlinear. Fertilizer increased yield significantly under both baseline and future climates. The response of maize to mineral nitrogen decreased with progressing climate change, implying a decrease in the optimal fertilizer rate in the future. Our results suggest that in the near future, improved crop and soil fertility management will remain important for enhanced maize yield. Towards the end of the 21st century, however, none of the farm management options tested in the study can avoid large yield losses in southern Africa due to climate change. There is a need to transform the current cropping systems of southern Africa to offset the negative impacts of climate change. © 2015 John Wiley & Sons Ltd.

The Use of Acoustic Radiation Force Decorrelation-Weighted Pulse Inversion for Enhanced Ultrasound Contrast Imaging.

PubMed

Herbst, Elizabeth B; Unnikrishnan, Sunil; Wang, Shiying; Klibanov, Alexander L; Hossack, John A; Mauldin, Frank William

2017-02-01

The use of ultrasound imaging for cancer diagnosis and screening can be enhanced with the use of molecularly targeted microbubbles. Nonlinear imaging strategies such as pulse inversion (PI) and "contrast pulse sequences" (CPS) can be used to differentiate microbubble signal, but often fail to suppress highly echogenic tissue interfaces. This failure results in false-positive detection and potential misdiagnosis. In this study, a novel acoustic radiation force (ARF)-based approach was developed for superior microbubble signal detection. The feasibility of this technique, termed ARF decorrelation-weighted PI (ADW-PI), was demonstrated in vivo using a subcutaneous mouse tumor model. Tumors were implanted in the hindlimb of C57BL/6 mice by subcutaneous injection of MC38 cells. Lipid-shelled microbubbles were conjugated to anti-VEGFR2 antibody and administered via bolus injection. An image sequence using ARF pulses to generate microbubble motion was combined with PI imaging on a Verasonics Vantage programmable scanner. ADW-PI images were generated by combining PI images with interframe signal decorrelation data. For comparison, CPS images of the same mouse tumor were acquired using a Siemens Sequoia clinical scanner. Microbubble-bound regions in the tumor interior exhibited significantly higher signal decorrelation than static tissue (n = 9, P < 0.001). The application of ARF significantly increased microbubble signal decorrelation (n = 9, P < 0.01). Using these decorrelation measurements, ADW-PI imaging demonstrated significantly improved microbubble contrast-to-tissue ratio when compared with corresponding CPS or PI images (n = 9, P < 0.001). Contrast-to-tissue ratio improved with ADW-PI by approximately 3 dB compared with PI images and 2 dB compared with CPS images. Acoustic radiation force can be used to generate adherent microbubble signal decorrelation without microbubble bursting. When combined with PI, measurements of the resulting microbubble signal decorrelation can be used to reconstruct images that exhibit superior suppression of highly echogenic tissue interfaces when compared with PI or CPS alone.

Can feedback analysis be used to uncover the physical origin of climate sensitivity and efficacy differences?

NASA Astrophysics Data System (ADS)

Rieger, Vanessa S.; Dietmüller, Simone; Ponater, Michael

2017-10-01

Different strengths and types of radiative forcings cause variations in the climate sensitivities and efficacies. To relate these changes to their physical origin, this study tests whether a feedback analysis is a suitable approach. For this end, we apply the partial radiative perturbation method. Combining the forward and backward calculation turns out to be indispensable to ensure the additivity of feedbacks and to yield a closed forcing-feedback-balance at top of the atmosphere. For a set of CO2-forced simulations, the climate sensitivity changes with increasing forcing. The albedo, cloud and combined water vapour and lapse rate feedback are found to be responsible for the variations in the climate sensitivity. An O3-forced simulation (induced by enhanced NOx and CO surface emissions) causes a smaller efficacy than a CO2-forced simulation with a similar magnitude of forcing. We find that the Planck, albedo and most likely the cloud feedback are responsible for this effect. Reducing the radiative forcing impedes the statistical separability of feedbacks. We additionally discuss formal inconsistencies between the common ways of comparing climate sensitivities and feedbacks. Moreover, methodical recommendations for future work are given.

Quantifying the climate-change consequences of shifting land use between forest and agriculture.

PubMed

Kirschbaum, Miko U F; Saggar, Surinder; Tate, Kevin R; Thakur, Kailash P; Giltrap, Donna L

2013-11-01

Land-use change between forestry and agriculture can cause large net emissions of carbon dioxide (CO2), and the respective land uses associated with forest and pasture lead to different on-going emission rates of methane (CH4) and nitrous oxide (N2O) and different surface albedo. Here, we quantify the overall net radiative forcing and consequent temperature change from specified land-use changes. These different radiative agents cause radiative forcing of different magnitudes and with different time profiles. Carbon emission can be very high when forests are cleared. Upon reforestation, the former carbon stocks can be regained, but the rate of carbon sequestration is much slower than the rate of carbon loss from deforestation. A production forest may undergo repeated harvest and regrowth cycles, each involving periods of C emission and release. Agricultural land, especially grazed pastures, have much higher N2O emissions than forests because of their generally higher nitrogen status that can be further enhanced through intensification of the nitrogen cycle by animal excreta. Because of its longevity in the atmosphere, N2O concentrations build up nearly linearly over many decades. CH4 emissions can be very high from ruminant animals grazing on pastures. Because of its short atmospheric longevity, the CH4 concentration from a converted pasture accumulates for only a few decades before reaching a new equilibrium when emission of newly produced CH4 is balanced by the oxidation of previously emitted CH4. Albedo changes generally have the opposite radiative forcing from those of the GHGs and partly negate their radiative forcing. Overall and averaged over 100 years, CO2 is typically responsible for 50% of radiative forcing and CH4 and N2O for 25% each. Albedo changes can negate the radiative forcing by the three greenhouse gases by 20-25%. Copyright © 2013 Elsevier B.V. All rights reserved.

Diagnostic medical imaging radiation exposure and risk of development of solid and hematologic malignancy.

PubMed

Fabricant, Peter D; Berkes, Marschall B; Dy, Christopher J; Bogner, Eric A

2012-05-01

Limiting patients' exposure to ionizing radiation during diagnostic imaging is of concern to patients and clinicians. Large single-dose exposures and cumulative exposures to ionizing radiation have been associated with solid tumors and hematologic malignancy. Although these associations have been a driving force in minimizing patients' exposure, significant risks are found when diagnoses are missed and subsequent treatment is withheld. Therefore, based on epidemiologic data obtained after nuclear and occupational exposures, dose exposure limits have been estimated. A recent collaborative effort between the US Food and Drug Administration and the American College of Radiology has provided information and tools that patients and imaging professionals can use to avoid unnecessary ionizing radiation scans and ensure use of the lowest feasible radiation dose necessary for studies. Further collaboration, research, and development should focus on producing technological advances that minimize individual study exposures and duplicate studies. This article outlines the research used to govern safe radiation doses, defines recent initiatives in decreasing radiation exposure, and provides orthopedic surgeons with techniques that may help decrease radiation exposure in their daily practice. Copyright 2012, SLACK Incorporated.

Simulated Space Environment Effects on the Blocking Force of Silicone Adhesive

NASA Technical Reports Server (NTRS)

Boeder, Paul; Mikatarian, Ron; Koontz, Steve; Albyn, Keith; Finckenor, Miria

2005-01-01

The International Space Station (ISS) solar arrays utilize MD-944 diode tape to protect the underlying diodes in the solar array panel circuit and also provide thermal conditioning and mechanical support. The diode tape consists of silicone pressure sensitive adhesive (Dow Coming QC-7725) with a protective Kapton over-layer. On-orbit, the Kapton over-layer will erode under exposure to atomic oxygen (AO) and the underlying exposed silicone adhesive will ultimately convert, under additional AO exposure, to a glass like silicate. The current operational plan is to retract ISS solar array P6 and leave it stored under load for a long duration (6 months or more) during ISS assembly. With the Kapton over-layer eroded away, the exposed silicone adhesive must not cause the solar array to stick to itself or cause the solar array to fail during redeployment. Previous testing by Lockheed-Martin Space Systems (LMSS) characterized silicone blocking following exposure to low energy atomic oxygen (AO) in an asher facility, but this is believed to be conservative. An additional series of tests was performed by the Environmental Effects Group at MSFC under direction from the ISS Program Office Environments Team. This test series included high energy AO (5 eV), near ultraviolet (NUV) radiation and ionizing radiation, singly and in combination. Additional samples were exposed to thermal energy AO (<0.1 ev) for comparison to the LMSS tests. Diode tape samples were exposed to each environment constituent individually, put under preload for seven days and then the resulting blocking force was measured using a tensile machine. Additional samples were exposed to AO, NUV and electrons in series and then put under long term (three to ten months) preload to determine the effect of preload duration on the resulting blocking force of the silicone-to-silicone bond. Test results indicate that high energy AO, ultraviolet radiation and electron ionizing radiation exposure all reduce the blocking force for a silicone-to-silicone bond. AO exposure produces the most significant reduction in blocking force.

Modeling East Asian Dust and Its Radiative Feedbacks in CAM4-BAM

NASA Astrophysics Data System (ADS)

Xie, Xiaoning; Liu, Xiaodong; Che, Huizheng; Xie, Xiaoxun; Wang, Hongli; Li, Jiandong; Shi, Zhengguo; Liu, Yangang

2018-01-01

East Asian dust and its radiative feedbacks are analyzed by the use of the fourth version of the Community Atmosphere Model (CAM4) with a bulk aerosol model parameterization (BAM) for the dust size distribution (CAM4-BAM). Two numerical experiments are conducted and intercompared: one with (Active) and one without (Passive) the radiative effects of dust aerosols. This CAM4-BAM captures the main spatial distribution of the dust aerosol optical depth (AOD) and the dust surface concentrations over East Asia, with positive correlations with the local observational data on annual and seasonal means. A comparative analysis of the Active and Passive experiments reveals that consideration of the dust-radiation interaction can significantly reduce dust emissions, loading, transport, and dry and wet depositions over East Asia, which is opposite to the enhanced dust cycle over North Africa. Further analysis of the contrasting dust-radiation feedbacks between North Africa and East Asia shows that over North Africa, the dust radiative forcing significantly increases the surface temperature and 10 m wind speed, whereas it decreases the surface temperature and the surface wind speeds over East Asia. These contrasting radiative effects, in turn, result in distinct dust cycle changes over these two regions. Mechanistic analysis reveals that the radiative contrasts between East Asia and North Africa are mainly due to the differences in their regional surface albedo, dust vertical distribution, and size distribution.

Solar radiation pressure effects on the Helios spacecraft

NASA Technical Reports Server (NTRS)

Georgevic, R. M.

1976-01-01

A mathematical model of the solar radiation force and torques, developed for the Mariner 10 Venus/Mercury spacecraft mission, was used for a detailed analysis of the effects of solar light pressure on the Helios spacecraft. Due to the fact that the main body of the Helios spacecraft is a surface of enclosure, inside of which most of the reradiated thermal energy is lost, expressions for the portion of the solar radiation force, produced by the thermal reradiation, had to be given a different form. Hence the need for the derivation of a somewhat different theoretical model for the force acting on the main body of the spacecraft.

Confocal acoustic radiation force optical coherence elastography using a ring ultrasonic transducer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Qi, Wenjuan; Department of Chemical Engineering and Materials Science, University of California, Irvine, Irvine, California 92697; Li, Rui

2014-03-24

We designed and developed a confocal acoustic radiation force optical coherence elastography system. A ring ultrasound transducer was used to achieve reflection mode excitation and generate an oscillating acoustic radiation force in order to generate displacements within the tissue, which were detected using the phase-resolved optical coherence elastography method. Both phantom and human tissue tests indicate that this system is able to sense the stiffness difference of samples and quantitatively map the elastic property of materials. Our confocal setup promises a great potential for point by point elastic imaging in vivo and differentiation of diseased tissues from normal tissue.

Aerosol optical properties and radiative effects: Assessment of urban aerosols in central China using 10-year observations

NASA Astrophysics Data System (ADS)

Zhang, Ming; Ma, Yingying; Gong, Wei; Liu, Boming; Shi, Yifan; Chen, ZhongYong

2018-06-01

Poor air quality episodes are common in central China. Here, based on 10 years of ground-based sun-photometric observations, aerosol optical and radiative forcing characteristics were analyzed in Wuhan, the biggest metropolis in central China. Aerosol optical depth (AOD) in the last decade declined significantly, while the Ångström exponent (AE) showed slight growth. Single scattering albedo (SSA) at 440 nm reached the lowest value (0.87) in winter and highest value (0.93) in summer. Aerosol parameters derived from sun-photometric observations were used as input in a radiative transfer model to calculate aerosol radiative forcing (ARF) on the surface in ultraviolet (UV), visible (VIS), near-infrared (NIR), and shortwave (SW) spectra. ARFSW sustained decreases (the absolute values) over the last 10 years. In terms of seasonal variability, due to the increases in multiple scattering effects and attenuation of the transmitted radiation as AOD increased, ARF in summer displayed the largest value (-73.94 W/m2). After eliminating the influence of aerosol loading, the maximum aerosol radiative forcing efficiency in SW range (ARFESW) achieved a value of -64.5 W/m2/AOD in April. The ARFE change in each sub-interval spectrum was related to the change in SSA and effective radius of fine mode particles (Refff), that is, ARFE increased with the decreases in SSA and Refff. The smallest contribution of ARFENIR to ARFESW was 34.11% under strong absorbing and fine particle conditions, and opposite results were found for the VIS range, whose values were always over 51.82%. Finally, due to the serious air pollution and frequency of haze day, aerosol characteristics in haze and clear days were analyzed. The percentage of ARFENIR increased from 35.71% on clear-air days to 37.63% during haze periods, while both the percentage of ARFEUV and ARFENIR in ARFESW kept decreasing. The results of this paper should help us to better understand the effect of aerosols on solar spectral radiation and to develop improved the aerosol models over central China.

Radiative forcing and climate response due to the presence of black carbon in cloud droplets

NASA Astrophysics Data System (ADS)

Wang, Zhili; Zhang, Hua; Li, Jiangnan; Jing, Xianwen; Lu, Peng

2013-05-01

Optical properties of clouds containing black carbon (BC) particles in their water droplets are calculated by using the Maxwell Garnett mixing rule and Mie theory. The obtained cloud optical properties were then applied to an interactive system by coupling an aerosol model with a General Circulation Model. This system is used to investigate the radiative forcing and the equilibrium climate response due to BC in cloud droplets. The simulated global annual mean radiative forcing at the top of the atmosphere due to the BC in cloud droplets is found to be 0.086 W m-2. Positive radiative forcing can be seen in Africa, South America, East and South Asia, and West Europe, with a maximum value of 1.5 W m-2 being observed in these regions. The enhanced cloud absorption is shown to increase the global annual mean values of solar heating rate, water vapor, and temperature, but to decrease the global annual mean cloud fraction. Finally, the global annual mean surface temperature is shown to increase by +0.08 K. The local maximum changes are found to be as low as -1.5 K and as high as +0.6 K. We show there has been a significant difference in surface temperature change in the Southern and Northern Hemisphere (+0.19 K and -0.04 K, respectively). Our results show that this interhemispheric asymmetry in surface temperature change could cause a corresponding change in atmospheric dynamics and precipitation. It is also found that the northern trade winds are enhanced in the Intertropical Convergence Zone (ITCZ). This results in northerly surface wind anomalies which cross the equator to converge with the enhanced southern trade winds in the tropics of Southern Hemisphere. This is shown to lead to an increase (a decrease) of vertical ascending motion and precipitation on the south (north) side of the equator, which could induce a southward shift in the tropical rainfall maximum related to the ITCZ.

Radiative forcing and climate response due to the presence of black carbon in cloud droplets

NASA Astrophysics Data System (ADS)

Wang, Z.; Zhang, H.; Li, J.; Jing, X.; Lu, P.

2013-05-01

Optical properties of clouds containing black carbon (BC) particles in their water droplets are calculated by using the Maxwell Garnett mixing rule and Mie theory. The obtained cloud optical properties were then applied to an interactive system by coupling an aerosol model with a General Circulation Model. This system is used to investigate the radiative forcing and the equilibrium climate response due to BC in cloud droplets. The simulated global annual mean radiative forcing at the top of the atmosphere due to the BC in cloud droplets is found to be 0.086 W m-2. Positive radiative forcing can be seen in Africa, South America, East and South Asia and West Europe, with a maximum value of 1.5 W m-2 being observed in these regions. The enhanced cloud absorption is shown to increase the global annual mean values of solar heating rate, water vapor and temperature, but to decrease the global annual mean cloud fraction. Finally, the global annual mean surface temperature is shown to increase by +0.08 K. The local maximum changes are found to be as low as -1.5 K and as high as +0.6 K. We show there has been a significant difference in surface temperature change in the Southern and Northern Hemisphere (+0.19 K and -0.04 K, respectively). Our results show that this interhemispheric asymmetry in surface temperature change could cause a corresponding change in atmospheric dynamics and precipitation. It is also found that the northern trade winds are enhanced in the Intertropical Convergence Zone (ITCZ). This results in northerly surface wind anomalies which cross the equator to converge with the enhanced southern trade winds in the tropics of Southern Hemisphere. This is shown to lead to an increase (a decrease) of vertical ascending motion and precipitation on the south (north) side of the equator, which could induce a southward shift in the tropical rainfall maximum related to the ITCZ.

Active Dust Mitigation Technology for Thermal Radiators for Lunar Exploration

NASA Technical Reports Server (NTRS)

Calle, C. I.; Buhler, C. R.; Hogue, M. D.; Johansen, M. R.; Hopkins, J. W.; Holloway, N. M. H.; Connell, J. W.; Chen, A.; Irwin, S. A.; Case, S. O.;

Assessment of Southern Ocean water mass circulation and characteristics in CMIP5 models: Historical bias and forcing response

NASA Astrophysics Data System (ADS)

Sallée, J.-B.; Shuckburgh, E.; Bruneau, N.; Meijers, A. J. S.; Bracegirdle, T. J.; Wang, Z.; Roy, T.

2013-04-01

The ability of the models contributing to the fifth Coupled Models Intercomparison Project (CMIP5) to represent the Southern Ocean hydrological properties and its overturning is investigated in a water mass framework. Models have a consistent warm and light bias spread over the entire water column. The greatest bias occurs in the ventilated layers, which are volumetrically dominated by mode and intermediate layers. The ventilated layers have been observed to have a strong fingerprint of climate change and to impact climate by sequestrating a significant amount of heat and carbon dioxide. The mode water layer is poorly represented in the models and both mode and intermediate water have a significant fresh bias. Under increased radiative forcing, models simulate a warming and lightening of the entire water column, which is again greatest in the ventilated layers, highlighting the importance of these layers for propagating the climate signal into the deep ocean. While the intensity of the water mass overturning is relatively consistent between models, when compared to observation-based reconstructions, they exhibit a slightly larger rate of overturning at shallow to intermediate depths, and a slower rate of overturning deeper in the water column. Under increased radiative forcing, atmospheric fluxes increase the rate of simulated upper cell overturning, but this increase is counterbalanced by diapycnal fluxes, including mixed-layer horizontal mixing, and mostly vanishes.

RCP4.5: A Pathway for Stabilization of Radiative Forcing by 2100

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomson, Allison M.; Calvin, Katherine V.; Smith, Steven J.

2011-07-29

Representative Concentration Pathway (RCP) 4.5 is a scenario that stabilizes radiative forcing at 4.5 W m{sup -2} in the year 2100 without ever exceeding that value. Simulated with the Global Change Assessment Model (GCAM), RCP4.5 includes long-term, global emissions of greenhouse gases, short-lived species, and land-use-land-cover in a global economic framework. RCP4.5 was updated from earlier GCAM scenarios to incorporate historical emissions and land cover information common to the RCP process and follows a cost-minimizing pathway to reach the target radiative forcing. The imperative to limit emissions in order to reach this target drives changes in the energy system, includingmore » shifts to electricity, to lower emissions energy technologies and to the deployment of carbon capture and geologic storage technology. In addition, the RCP4.5 emissions price also applies to land use emissions; as a result, forest lands expand from their present day extent. The simulated future emissions and land use were downscaled from the regional simulation to a grid to facilitate transfer to climate models. While there are many alternative pathways to achieve a radiative forcing level of 4.5 W m{sup -2}, the application of the RCP4.5 provides a common platform for climate models to explore the climate system response to stabilizing the anthropogenic components of radiative forcing.« less

Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement.

PubMed

Wang, Caroline W; Perez, Matthew J; Helmke, Brian P; Viola, Francesco; Lawrence, Michael B

2015-01-01

Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

Revised model for the radiation force exerted by standing surface acoustic waves on a rigid cylinder

NASA Astrophysics Data System (ADS)

Liang, Shen; Chaohui, Wang

2018-03-01

In this paper, a model for the radiation force exerted by standing surface acoustic waves (SSAWs) on a rigid cylinder in inviscid fluids is extended to account for the dependence on the Rayleigh angle. The conventional model for the radiation force used in the SSAW-based applications is developed in plane standing waves, which fails to predict the movement of the cylinder in the SSAW. Our revised model reveals that, in the direction normal to the piezoelectric substrate on which the SSAW is generated, acoustic radiation force can be large enough to drive the cylinder even in the long-wavelength limit. Furthermore, the force in this direction can not only push the cylinder away, but also pull it back toward the substrate. In the direction parallel to the substrate, the equilibrium positions for particles can be actively tuned by changing Rayleigh angle. As an example considered in the paper, with the reduction of Rayleigh angle the equilibrium positions for steel cylinders in water change from pressure nodes to pressure antinodes. The model can thus be used in the design of SSAWs for particle manipulations.

Pushing, pulling and electromagnetic radiation force cloaking by a pair of conducting cylindrical particles

NASA Astrophysics Data System (ADS)

Mitri, F. G.

2018-02-01

The present analysis shows that two conducting cylindrical particles illuminated by an axially-polarized electric field of plane progressive waves at arbitrary incidence will attract, repel or become totally cloaked (i.e., invisible to the transfer of linear momentum carried by the incident waves), depending on their sizes, the interparticle distance as well as the angle of incidence of the incident field. Based on the rigorous multipole expansion method and the translational addition theorem of cylindrical wave functions, the electromagnetic (EM) radiation forces arising from multiple scattering effects between a pair of perfectly conducting cylindrical particles of circular cross-sections are derived and computed. An effective incident field on a particular particle is determined first, and used subsequently with its corresponding scattered field to derive the closed-form analytical expressions for the radiation force vector components. The mathematical expressions for the EM radiation force components (i.e. longitudinal and transverse) are exact, and have been formulated in partial-wave series expansions in cylindrical coordinates involving the angle of incidence, the interparticle distance and the expansion coefficients. Numerical examples illustrate the analysis for two perfectly conducting circular cylinders in a homogeneous nonmagnetic medium of wave propagation. The computations for the dimensionless radiation force functions are performed with particular emphasis on varying the angle of incidence, the interparticle distance, and the sizes of the particles. Depending on the interparticle distance and angle of incidence, the cylinders yield total neutrality (or invisibility); they experience no force and become unresponsive to the transfer of the EM linear momentum due to multiple scattering cancellation effects. Moreover, pushing or pulling EM forces between the two cylinders arise depending on the interparticle distance, the angle of incidence and their size parameters. This study provides a complete analytical method and computations for the longitudinal and transverse radiation force components in the multiple scattering of EM plane progressive waves with potential applications in particle manipulation, optically-engineered metamaterials with reconfigurable periodicities and cloaking devices to name a few examples.

Testing for the Possible Influence of Unknown Climate Forcings upon Global Temperature Increases from 1950-2000

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anderson, Bruce T.; Knight, Jeff R.; Ringer, Mark A.

2012-10-15

Global-scale variations in the climate system over the last half of the twentieth century, including long-term increases in global-mean near-surface temperatures, are consistent with concurrent human-induced emissions of radiatively active gases and aerosols. However, such consistency does not preclude the possible influence of other forcing agents, including internal modes of climate variability or unaccounted for aerosol effects. To test whether other unknown forcing agents may have contributed to multidecadal increases in global-mean near-surface temperatures from 1950 to 2000, data pertaining to observed changes in global-scale sea surface temperatures and observed changes in radiatively active atmospheric constituents are incorporated into numericalmore » global climate models. Results indicate that the radiative forcing needed to produce the observed long-term trends in sea surface temperatures—and global-mean near-surface temperatures—is provided predominantly by known changes in greenhouse gases and aerosols. Further, results indicate that less than 10% of the long-term historical increase in global-mean near-surface temperatures over the last half of the twentieth century could have been the result of internal climate variability. In addition, they indicate that less than 25%of the total radiative forcing needed to produce the observed long-term trend in global-mean near-surface temperatures could have been provided by changes in net radiative forcing from unknown sources (either positive or negative). These results, which are derived from simple energy balance requirements, emphasize the important role humans have played in modifying the global climate over the last half of the twentieth century.« less

Satellite Remote Sensing of Fires, Smoke and Regional Radiative Energy Budgets

NASA Technical Reports Server (NTRS)

Christopher, Sundar A.; Wang, Min; Barbieri, Kristine; Welch, Ronald M.; Yang, Shi-Keng

1997-01-01

Using satellite imagery, more than five million square kilometers of the forest and cerrado regions over South America are extensively studied to monitor fires and smoke during the 1985 and 1986 biomass burning season. The results are characterized for four major eco-systems, namely: (1) Tropical Rain Forest (TRF), (2) Tropical Broadleaf Seasonal (TBS), (3) Mild/Warm/Hot Grass/Shrub (MGS), and (4) Savanna/Grass and Seasonal Woods (SGW). Using collocated measurements from the instantaneous scanner Earth Radiation Budget Experiment [ERBE) data, the direct regional radiative forcing of biomass burning aerosols are computed. The results show that more than 70% of the fires occur in the MGS and SGW eco-systems due to agricultural practices. The smoke generated from biomass burning has negative net radiative forcing values for all four major ecosystems within South America. The smoke found directly over the fires have mean net radiative forcing values ranging between -25.6 to -33.9 W/sq m for 1985 and between -12.9 to -40.8 W/sq m for 1986. These results confirm that the regional net radiative impact of biomass burning is one of cooling.

The 1985 Biomass Burning Season in South America: Satellite Remote Sensing of Fires, Smoke, and Regional Radiative Energy Budgets

NASA Technical Reports Server (NTRS)

Christopher, Sundar A.; Wang, Min; Berendes, Todd A.; Welch, Ronald M.; Yang, Shi-Keng

1998-01-01

Using satellite imagery, more than five million square kilometers of the forest and cerrado regions over South America are extensively studied to monitor fires and smoke during the 1985 biomass burning season. The results are characterized for four major ecosystems, namely: (1) tropical rain forest, (2) tropical broadleaf seasonal, (3) savannah/grass and seasonal woods (SGW), and (4) mild/warm/hot grass/shrub (MGS). The spatial and temporal distribution of fires are examined from two different methods using the multispectral Advanced Very High Resolution Radiometer Local Area Coverage data. Using collocated measurements from the instantaneous scanner Earth Radiation Budget Experiment data, the direct regional radiative forcing of biomass burning aerosols is computed. The results show that more than 70% of the fires occur in the MGS and SGW ecosystems due to agricultural practices. The smoke generated from biomass burning has negative instantaneous net radiative forcing values for all four major ecosystems within South America. The smoke found directly over the fires has mean net radiative forcing values ranging from -25.6 to -33.9 W m(exp -2). These results confirm that the regional net radiative impact of biomass burning is one of cooling. The spectral and broadband properties for clear-sky and smoke regions are also presented that could be used as input and/or validation for other studies attempting to model the impact of aerosols on the earth-atmosphere system. These results have important applications for future instruments from the Earth Observing System (EOS) program. Specifically, the combination of the Visible Infrared Scanner and Clouds and the Earth's Radiant Energy System (CERES) instruments from the Tropical Rainfall Measuring Mission and the combination of Moderate Resolution Imaging Spectrometer and CERES instruments from the EOS morning crossing mission could provide reliable estimates of the direct radiative forcing of aerosols on a global scale, thereby reducing the uncertainties in current global aerosol radiative forcing values.

A Multidisciplinary Approach to Assessing the Causal Components of Climate Change

NASA Astrophysics Data System (ADS)

Gosnold, W. D.; Todhunter, P. E.; Dong, X.; Rundquist, B.; Majorowicz, J.; Blackwell, D. D.

2004-05-01

Separation of climate forcing by anthropogenic greenhouse gases from natural radiative climate forcing is difficult because the composite temperature signal in the meteorological and multi-proxy temperature records cannot be resolved directly into radiative forcing components. To address this problem, we have initiated a large-scale, multidisciplinary project to test coherence between ground surface temperatures (GST) reconstructed from borehole T-z profiles, surface air temperatures (SAT), soil temperatures, and solar radiation. Our hypothesis is that radiative heating and heat exchange between the ground and the air directly control the ground surface temperature. Consequently, borehole T-z measurements at multi-year intervals spanning time periods when solar radiation, soil and air temperatures have been recorded should enable comparison of the thermal energy stored in the ground to these quantities. If coherence between energy storage, solar radiation, GST, SAT and multi-proxy temperature data can be discerned for a one or two decade scale, synthesis of GST and multi-proxy data over the past several centuries may enable us to separately determine the anthropogenic and natural forcings of climate change. The data we are acquiring include: (1) New T-z measurements in boreholes previously used in paleoclimate and heat flow research in Canada and the United States from the 1970's to the present. (2) Meteorological data from the US Historical Climatology Network and the Automated Weather Data Network of the High Plains Regional Climate Center, and Environment Canada. (3) Direct and remotely sensed data on land use, environment, and soil properties at selected borehole and meteorological sites for the periods between borehole observations. The project addresses three related questions: What is the coherence between the GST, SAT, soil temperatures and solar radiation? Have microclimate changes at borehole sites and climate stations affected temperature trends? If good coherence is obtained, can the coherence between thermal energy stored in the ground and radiative forcing during the time between T-z measurements be extended several centuries into the past?

Comparison of fluorescent and high-pressure sodium lamps on growth of leaf lettuce

NASA Technical Reports Server (NTRS)

Koontz, H. V.; Prince, R. P.; Koontz, R. F.; Knott, W. M. (Principal Investigator)

1987-01-01

Radiation from high-pressure sodium (HPS) lamps provided more than a 50% increased yield (fresh and dry weight of tops) of loose-leaf lettuce cultivars Grand Rapids Forcing and RubyConn, compared to that obtained by radiation from cool-white fluorescent (CWF) lamps at equal photosynthetic photon flux; yet, input wattage was approximately 36% less. It was postulated that the considerable output of 700 to 850 nm radiation from the HPS lamp was a significant factor of the increased yield. Under HPS lamps, the leaves of both cultivars were slightly less green with very little red pigmentation ('RubyConn') and slightly elongated, compared to CWF, but plant productivity per unit electrical energy input was vastly superior with HPS.

Interannual variability of the global net radiation balance and its consequence on global energy transport

NASA Technical Reports Server (NTRS)

Smith, Eric A.; Sohn, B. J.

1990-01-01

Global cloudiness and radiation budget data from Nimbus 6 and 7 are used to investigate the role of cloud and surface radiative forcing and elements of the earth's general circulation. Although globally integrated cloud forcing is nearly zero, there are large regional imbalances and well regulated processes in the shortwave and longwave spectrum that control the meridional gradient structure of the net radiation balance and the factors modulating the east-west oriented North Africa-western Pacific energy transport dipole. The analysis demonstrates that clouds play a dual role in both the shortwave and longwave spectra in terms of tropical and midlatitude east-west gradients. The key result is that cloud forcing, although not always the principle regulator of interannual variability of the global climate, serves to reinforce the basic three-cell meridional circulation.

Self-organization of granular media in airborne ultrasonic fields

NASA Astrophysics Data System (ADS)

Bobrovskaya, A. I.; Stepanenko, D. A.; Minchenya, V. T.

2012-05-01

The article presents results of experimental and theoretical studies of behaviour of granular media (powder materials) in airborne ultrasonic field created by flexurally-vibrating ring-shaped waveguide with resonant frequency in the range 20-40 kHz. Experiments show that action of acoustic radiation forces results in formation of ordered structures in the form of ultrathin walls (monolayers) with number corresponding to the number of ring nodal points. Action of secondary radiation forces (König forces) results in formation of collateral (secondary) walls situated nearby primary walls. Experimental observations are compared with results of modelling of acoustic radiation force field inside the ring by means of COMSOL Multiphysics and MathCad software. Results of the studies can be used in development of devices for ultrasonic separation and concentration of particles as well as for formation of ordered monolayers from spherical particles.

Acoustic Radiation Force Impulse Elastography in Determining the Effects of Type 1 Diabetes on Pancreas and Kidney Elasticity in Children.

PubMed

Sağlam, Dilek; Bilgici, Meltem Ceyhan; Kara, Cengiz; Yılmaz, Gülay Can; Çamlıdağ, İlkay

2017-11-01

The aim of this study is to determine the effects of type 1 diabetes on pancreas and kidney elasticity in children, using acoustic radiation force impulse ultrasound elastography. Sixty autoantibody-positive patients with type 1 diabetes (45% girls; mean [± SD] age, 11.7 ± 4.4 years; range, 1.9-19.3 years) admitted to the pediatric endocrinology outpatient clinic and 32 healthy children (50% girls; mean age, 10.2 ± 3.8 years; range, 2.1-17.3 years) were included in the study. Acoustic radiation force impulse elastography measurements were performed of the kidneys and pancreas in both groups. Body mass index, duration of diabetes, HbA1c levels, and insulin dosage of patients with type 1 diabetes were recorded. The mean shear-wave velocities of the pancreas were 0.99 ± 0.25 m/s in patients with type 1 diabetes and 1.09 ± 0.22 m/s in healthy control subjects; the difference was not significant (p = 0.08). The median shear-wave velocities of the right and left kidneys in patients with type 1 diabetes were 2.43 ± 0.29 and 2.47 ± 0.25 m/s, respectively. There were no significant differences in the shear-wave velocities of the right and left kidneys between the patients with type 1 diabetes and the healthy control subjects (p = 0.91 and p = 0.73, respectively). Correlation analysis showed no correlation between the shear-wave velocities of the pancreas and kidney versus HbA1c level, duration of diabetes, insulin dosage, height, weight, and body mass index of the patients with type 1 diabetes. The current study showed no significant difference in the shear-wave velocity of kidneys in children with type 1 diabetes with normoalbuminuria compared with the healthy control subjects. We also observed that the shear-wave velocity of the pancreas in children with type 1 diabetes and healthy control subjects did not differ significantly.

Dark solitons in laser radiation build-up dynamics.

PubMed

Woodward, R I; Kelleher, E J R

2016-03-01

We reveal the existence of slowly decaying dark solitons in the radiation build-up dynamics of bright pulses in all-normal dispersion mode-locked fiber lasers, numerically modeled in the framework of a generalized nonlinear Schrödinger equation. The evolution of noise perturbations to quasistationary dark solitons is examined, and the significance of background shape and soliton-soliton collisions on the eventual soliton decay is established. We demonstrate the role of a restoring force in extending soliton interactions in conservative systems to include the effects of dissipation, as encountered in laser cavities, and generalize our observations to other nonlinear systems.

Observations of enhanced aerosol longwave radiative forcing over an urban environment

NASA Astrophysics Data System (ADS)

Panicker, A. S.; Pandithurai, G.; Safai, P. D.; Kewat, S.

2008-02-01

Collocated measurements of sun/sky radiance, aerosol chemical composition and radiative fluxes have been utilized to estimate longwave aerosol radiative forcing over Pune, an Indian urban site during dry winter [Dec2004 to Feb2005] by two methods. Hybrid method which uses observed downwelling and modeled upwelling longwave fluxes for different aerosol loadings yielded a surface forcing of 9.4 Wm-2. Model approach includes utilization of skyradiometer derived spectral aerosol optical properties in the visible and near infra-red wavelengths, modeled aerosol properties in 1.2-40 μm using observed soot and chemical composition data, MODIS water vapor and TOMS column ozone in a radiative transfer model. Estimates from model method showed longwave enhancement of 6.5 and 8.2 Wm-2 at the surface with tropical model atmosphere and temporally varying profiles of temperature and humidity, respectively. Study reveals that about 25% of the aerosol shortwave cooling is being compensated by increase in longwave radiation due to aerosol absorption.

Radiative and Thermal Impacts of Smoke Aerosol Longwave Absorption during Fires in the Moscow Region in Summer 2010

NASA Astrophysics Data System (ADS)

Gorchakova, I. A.; Mokhov, I. I.; Anikin, P. P.; Emilenko, A. S.

2018-03-01

The aerosol longwave radiative forcing of the atmosphere and heating rate of the near-surface aerosol layer are estimated for the extreme smoke conditions in the Moscow region in summer 2010. Thermal radiation fluxes in the atmosphere are determined using the integral transmission function and semiempirical aerosol model developed on the basis of standard aerosol models and measurements at the Zvenigorod Scientific Station, Obukhov Institute of Atmospheric Physics, Russian Academy of Sciences. The aerosol radiative forcing reached 33 W/m2 at the lower atmospheric boundary and ranged between-1.0 and 1.0 W/m2 at the upper atmospheric boundary. The heating rate of the 10-m atmospheric layer near surface was up to 0.2 K/h during the maximum smoke conditions on August 7-9. The sensitivity of the aerosol longwave radiative forcing to the changes in the aerosol absorption coefficient and aerosol optical thickness are estimated.

Direct Aerosol Radiative Forcing Based on Combined A-Train Observations: Towards All-sky Estimates and Attribution to Aerosol Type

NASA Technical Reports Server (NTRS)

Redemann, Jens; Shinozuka, Y.; Kacenelenbogen, M.; Russell, P.; Vaughan, M.; Ferrare, R.; Hostetler, C.; Rogers, R.; Burton, S.; Livingston, J.;

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jingbo; Department of Radiation Oncology, Cancer Hospital, Chinese Academic Medical Sciences and Peking Union Medical College, Beijing; Cao, Jianzhong

Purpose: Poor pulmonary function (PF) is often considered a contraindication to definitive radiation therapy for lung cancer. This study investigated whether baseline PF was associated with radiation-induced lung toxicity (RILT) in patients with non-small cell lung cancer (NSCLC) receiving conformal radiation therapy (CRT). Methods and Materials: NSCLC patients treated with CRT and tested for PF at baseline were eligible. Baseline predicted values of forced expiratory volume in 1 sec (FEV1), forced vital capacity (FVC), and diffusion capacity of lung for carbon monoxide (DLCO) were analyzed. Additional factors included age, gender, smoking status, Karnofsky performance status, coexisting chronic obstructive pulmonary diseasemore » (COPD), tumor location, histology, concurrent chemotherapy, radiation dose, and mean lung dose (MLD) were evaluated for RILT. The primary endpoint was symptomatic RILT (SRILT), including grade ≥2 radiation pneumonitis and fibrosis. Results: There was a total of 260 patients, and SRILT occurred in 58 (22.3%) of them. Mean FEV1 values for SRILT and non-SRILT patients were 71.7% and 65.9% (P=.077). Under univariate analysis, risk of SRILT increased with MLD (P=.008), the absence of COPD (P=.047), and FEV1 (P=.077). Age (65 split) and MLD were significantly associated with SRILT in multivariate analysis. The addition of FEV1 and age with the MLD-based model slightly improved the predictability of SRILT (area under curve from 0.63-0.70, P=.088). Conclusions: Poor baseline PF does not increase the risk of SRILT, and combining FEV1, age, and MLD may improve the predictive ability.« less

Large contribution of natural aerosols to uncertainty in indirect forcing

NASA Astrophysics Data System (ADS)

Carslaw, K. S.; Lee, L. A.; Reddington, C. L.; Pringle, K. J.; Rap, A.; Forster, P. M.; Mann, G. W.; Spracklen, D. V.; Woodhouse, M. T.; Regayre, L. A.; Pierce, J. R.

2013-11-01

The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.

Protective Effects of Hydrogen against Low-Dose Long-Term Radiation-Induced Damage to the Behavioral Performances, Hematopoietic System, Genital System, and Splenic Lymphocytes in Mice

PubMed Central

Lei, Xiao; Zhao, Hainan; Liu, Pengfei; Xu, Yang; Chen, Yuanyuan; Chuai, Yunhai

2016-01-01

Molecular hydrogen (H2) has been previously reported playing an important role in ameliorating damage caused by acute radiation. In this study, we investigated the effects of H2 on the alterations induced by low-dose long-term radiation (LDLTR). All the mice in hydrogen-treated or radiation-only groups received 0.1 Gy, 0.5 Gy, 1.0 Gy, and 2.0 Gy whole-body gamma radiation, respectively. After the last time of radiation exposure, all the mice were employed for the determination of the body mass (BM) observation, forced swim test (FST), the open field test (OFT), the chromosome aberration (CA), the peripheral blood cells parameters analysis, the sperm abnormality (SA), the lymphocyte transformation test (LTT), and the histopathological studies. And significant differences between the treatment group and the radiation-only groups were observed, showing that H2 could diminish the detriment induced by LDLTR and suggesting the protective efficacy of H2 in multiple systems in mice against LDLTR. PMID:27774116

Effects of radiator shapes on the bubble diving and dispersion of ultrasonic argon process.

PubMed

Liu, Xuan; Xue, Jilai; Zhao, Qiang; Le, Qichi; Zhang, Zhiqiang

2018-03-01

In this work, three ultrasonic radiators in different shapes have been designed in order to investigate the effects of radiator shapes on the argon bubble dispersion and diving as well as the degassing efficiency on magnesium melt. The radiator shape has a strong influence on the bubble diving and dispersion by ultrasound. A massive argon bubble slowly flows out from the radiator with the hemispherical cap, due to the covering hemispherical cap. Using a concave radiator can intensively crush the argon bubbles and drive them much deep into the water/melt, depending on the competition between the argon flow and opposite joint shear force from the concave surface. The evolution of wall bubbles involves the ultrasonic cavities carrying dissolved gas, migrating to the vessel wall, and escaping from the liquid. Hydrogen removal can be efficiently achieved using a concave radiator. The hydrogen content can be reduced from 22.3 μg/g down to 8.7 μg/g. Mechanical properties are significantly promoted, due to the structure refinement and efficient hydrogen removal. Copyright © 2017 Elsevier B.V. All rights reserved.

A finite element model of remote palpation of breast lesions using radiation force: factors affecting tissue displacement.

PubMed

Nightingale, K R; Nightingale, R W; Palmeri, M L; Trahey, G E

2000-01-01

The early detection of breast cancer reduces patient mortality. The most common method of breast cancer detection is palpation. However, lesions that lie deep within the breast are difficult to palpate when they are small. Thus, a method of remote palpation, which may allow the detection of small lesions lying deep within the breast, is currently under investigation. In this method, acoustic radiation force is used to apply localized forces within tissue (to tissue volumes on the order of 2 mm3) and the resulting tissue displacements are mapped using ultrasonic correlation based methods. A volume of tissue that is stiffer than the surrounding medium (i.e., a lesion) distributes the force throughout the tissue beneath it, resulting in larger regions of displacement, and smaller maximum displacements. The resulting displacement maps may be used to image tissue stiffness. A finite-element-model (FEM) of acoustic remote palpation is presented in this paper. Using this model, a parametric analysis of the affect of varying tissue and acoustic beam characteristics on radiation force induced tissue displacements is performed. The results are used to evaluate the potential of acoustic remote palpation to provide useful diagnostic information in a clinical setting. The potential for using a single diagnostic transducer to both generate radiation force and track the resulting displacements is investigated.

Seasonal variation of columnar aerosol optical properties and radiative forcing over Beijing, China

NASA Astrophysics Data System (ADS)

Yu, Xingna; Lü, Rui; Liu, Chao; Yuan, Liang; Shao, Yixing; Zhu, Bin; Lei, Lu

2017-10-01

Long-term seasonal characteristics of aerosol optical properties and radiative forcing at Beijing (during March 2001-March 2015) were investigated using a combination of ground-based Sun/sky radiometer retrievals from the AERONET and a radiative transfer model. Aerosol optical depth (AOD) showed a distinct seasonal variation with higher values in spring and summer, and relatively lower values in fall and winter. Average Angstrom exponent (AE) in spring was lower than other seasons, implying the significant impact of dust episodes on aerosol size distribution. AE mainly distributed between 1.0 and 1.4 with an obvious uni-peak pattern in each season. The observation data showed that high AODs (>1.0) were clustered in the fine mode growth wing and the coarse mode. Compared to AOD, seasonal variation in single scattering albedo (SSA) showed an opposite pattern with larger values in summer and spring, and smaller ones in winter and fall. The highest volume size distribution and median radius of fine mode particles occurred in summer, while those of coarse mode particles in spring. The averaged aerosol radiative forcing (ARF) at the top of the atmosphere (TOA) in spring, summer, fall and winter were -33 ± 22 W m-2, -35 ± 22 W m-2, -28 ± 20 W m-2, and -24 ± 23 W m-2 respectively, and these differences were mainly due to the SSA seasonal variation. The largest positive ARF within atmosphere occurred in spring, implying strong warming in the atmosphere. The low heating ratio in summer was caused by the increase in water vapor content, which enhanced light scattering capacity (i.e., increased SSA).

Multi-site characterization of tropical aerosols: Implications for regional radiative forcing

NASA Astrophysics Data System (ADS)

Sumit, Kumar; Devara, P. C. S.; Manoj, M. G.

2012-03-01

A land campaign, as a part of the Indian Space Research Organization-Geosphere Biosphere Program (ISRO-GBP), has been organized using a suit of instruments like AERONET (Aerosol Robotic Network) Sun/Sky sunphotometer, Microtops-II (MICROprocessor-controlled Total Ozone Portable Spectrometer), short-wave pyranometer from December 1, 2006 to April 30, 2007, over five locations (Ahmedabad, Pune, Sinhgad, Trivandrum and Gadanki) representing different environments. The dominance of different aerosol types such as biomass burning, urban/industrial pollution, marine origin and desert-dust particles is expected at these five sites. In all locations, significant day-to-day variability in AOD and Ångström exponent is observed. The Ångström exponent exhibits its lowest values over semi-arid region (Ahmedabad) 0.4-0.7, while it is around 1.8 at rural site (Gadanki). The retrieved volume size distributions for Pune, Ahmedabad and Trivandrum are found to be bimodal with varying concentration of each mode. Interesting feature of this observation is, very low coarse-mode volume concentration observed at Trivandrum even though observations were made about 300 m from the coast. The synergy of results from these complementary measurements is reflected in the computed regional aerosol radiative forcing and heating rates. We have used a radiative transfer model (SBDART) to examine the variations of aerosol direct radiative effect (ADRE) and heating rates to give an overall estimation of the effect on climate. The ADRE, over different measurement sites, at short wavelength is found to be negative at the surface in the range of - 18 to - 59 W m - 2 , and TOA forcing values varied from + 0.9 to - 8 W m - 2 .

Effect of radiation processing on meat tenderisation

NASA Astrophysics Data System (ADS)

Kanatt, Sweetie R.; Chawla, S. P.; Sharma, Arun

2015-06-01

The effect of radiation processing (0, 2.5, 5 and 10 kGy) on the tenderness of three types of popularly consumed meat in India namely chicken, lamb and buffalo was investigated. In irradiated meat samples dose dependant reduction in water holding capacity, cooking yield and shear force was observed. Reduction in shear force upon radiation processing was more pronounced in buffalo meat. Protein and collagen solubility as well as TCA soluble protein content increased on irradiation. Radiation processing of meat samples resulted in some change in colour of meat. Results suggested that irradiation leads to dose dependant tenderization of meat. Radiation processing of meat at a dose of 2.5 kGy improved its texture and had acceptable odour.

Synoptic Traveling Weather Systems on Mars: Effects of Radiatively-Active Water Ice Clouds

NASA Astrophysics Data System (ADS)

Hollingsworth, Jeffery L.; Kahre, Melinda A.; Haberle, Robert; Atsuki Urata, Richard

2016-10-01

Atmospheric aerosols on Mars are critical in determining the nature of its thermal structure, its large-scale circulation, and hence the overall climate of the planet. We conduct multi-annual simulations with the latest version of the NASA Ames Mars global climate model (GCM), gcm2.3+, that includes a modernized radiative-transfer package and complex water-ice cloud microphysics package which permit radiative effects and interactions of suspended atmospheric aerosols (e.g., water ice clouds, water vapor, dust, and mutual interactions) to influence the net diabatic heating. Results indicate that radiatively active water ice clouds profoundly affect the seasonal and annual mean climate. The mean thermal structure and balanced circulation patterns are strongly modified near the surface and aloft. Warming of the subtropical atmosphere at altitude and cooling of the high latitude atmosphere at low levels takes place, which increases the mean pole-to-equator temperature contrast (i.e., "baroclinicity"). With radiatively active water ice clouds (RAC) compared to radiatively inert water ice clouds (nonRAC), significant changes in the intensity of the mean state and forced stationary Rossby modes occur, both of which affect the vigor and intensity of traveling, synoptic period weather systems. Such weather systems not only act as key agents in the transport of heat and momentum beyond the extent of the Hadley circulation, but also the transport of trace species such as water vapor, water ice-clouds, dust and others. The northern hemisphere (NH) forced Rossby waves and resultant wave train are augmented in the RAC case: the modes are more intense and the wave train is shifted equatorward. Significant changes also occur within the subtropics and tropics. The Rossby wave train sets up, combined with the traveling synoptic-period weather systems (i.e., cyclones and anticyclones), the geographic extent of storm zones (or storm tracks) within the NH. A variety of circulation features will be presented which indicate contrasts between the RAC and nonRAC cases, and which highlight key effects radiatively-active clouds have on physical and dynamical processes active in the current climate of Mars.

Synoptic Traveling Weather Systems on Mars: Effects of Radiatively-Active Water Ice Clouds

NASA Technical Reports Server (NTRS)

Hollingsworth, Jeffery; Kahre, Melinda; Haberle, Robert; Urata, Richard

2017-01-01

Atmospheric aerosols on Mars are critical in determining the nature of its thermal structure, its large-scale circulation, and hence the overall climate of the planet. We conduct multi-annual simulations with the latest version of the NASA Ames Mars global climate model (GCM), gcm2.3+, that includes a modernized radiative-transfer package and complex water-ice cloud microphysics package which permit radiative effects and interactions of suspended atmospheric aerosols (e.g., water ice clouds, water vapor, dust, and mutual interactions) to influence the net diabatic heating. Results indicate that radiatively active water ice clouds profoundly affect the seasonal and annual mean climate. The mean thermal structure and balanced circulation patterns are strongly modified near the surface and aloft. Warming of the subtropical atmosphere at altitude and cooling of the high latitude atmosphere at low levels takes place, which increases the mean pole-to-equator temperature contrast (i.e., "baroclinicity"). With radiatively active water ice clouds (RAC) compared to radiatively inert water ice clouds (nonRAC), significant changes in the intensity of the mean state and forced stationary Rossby modes occur, both of which affect the vigor and intensity of traveling, synoptic period weather systems. Such weather systems not only act as key agents in the transport of heat and momentum beyond the extent of the Hadley circulation, but also the transport of trace species such as water vapor, water ice-clouds, dust and others. The northern hemisphere (NH) forced Rossby waves and resultant wave train are augmented in the RAC case: the modes are more intense and the wave train is shifted equatorward. Significant changes also occur within the subtropics and tropics. The Rossby wave train sets up, combined with the traveling synoptic period weather systems (i.e., cyclones and anticyclones), the geographic extent of storm zones (or storm tracks) within the NH. A variety of circulation features will be presented which indicate contrasts between the RAC and nonRAC cases, and which highlight key effects radiatively-active clouds have on physical and dynamical processes active in the current climate of Mars.

Synoptic Traveling Weather Systems on Mars: Effects of Radiatively-Active Water Ice Clouds

NASA Technical Reports Server (NTRS)

Hollingsworth, Jeffery; Kahre, Melinda; Haberle, Robert; Urata, Richard

2017-01-01

Atmospheric aerosols on Mars are critical in determining the nature of its thermal structure, its large-scale circulation, and hence the overall climate of the planet. We conduct multi-annual simulations with the latest version of the NASA Ames Mars global climate model (GCM), gcm2.3+, that includes a modernized radiative-transfer package and complex water-ice cloud microphysics package which permit radiative effects and interactions of suspended atmospheric aerosols (e.g., water ice clouds, water vapor, dust, and mutual interactions) to influence the net diabatic heating. Results indicate that radiatively active water ice clouds profoundly affect the seasonal and annual mean climate. The mean thermal structure and balanced circulation patterns are strongly modified near the surface and aloft. Warming of the subtropical atmosphere at altitude and cooling of the high latitude atmosphere at low levels takes place, which increases the mean pole-to-equator temperature contrast (i.e., "baroclinicity"). With radiatively active water ice clouds (RAC) compared to radiatively inert water ice clouds (nonRAC), significant changes in the intensity of the mean state and forced stationary Rossby modes occur, both of which affect the vigor and intensity of traveling, synoptic period weather systems.Such weather systems not only act as key agents in the transport of heat and momentum beyond the extent of the Hadley circulation, but also the transport of trace species such as water vapor, water ice-clouds, dust and others. The northern hemisphere (NH) forced Rossby waves and resultant wave train are augmented in the RAC case: the modes are more intense and the wave train is shifted equatorward. Significant changes also occur within the subtropics and tropics. The Rossby wave train sets up, combined with the traveling synoptic period weather systems (i.e., cyclones and anticyclones), the geographic extent of storm zones (or storm tracks) within the NH. A variety of circulation features will be presented which indicate contrasts between the RAC and nonRAC cases, and which highlight key effects radiatively-active clouds have on physical and dynamical processes active in the current climate of Mars.

MO-FG-BRB-02: Uniform Access to Radiation Therapy by 2035: Global Task Force on Radiotherapy for Cancer Control

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jaffray, D.

The global burden of cancer is growing rapidly with an estimated 15 million new cases per year worldwide in 2015, growing to 19 million by 2025 and 24 million by 2035. The largest component of this growth will occur in low-to-middle income countries (LMICs). About half of these cases will require radiation treatment. The gap for available cancer treatment, including radiation therapy, between high-income countries (HICs) and LMICs is enormous. Accurate data and quantitative models to project the needs and the benefits of cancer treatment are a critical first step in closing the large cancer divide between LMICs and HICs.more » In this context, the Union for International Cancer Control (UICC) has developed a Global Task Force on Radiotherapy for Cancer Control (GTFRCC) with a charge to answer the question as to what it will take to close the gap between what exists today and reasonable access to radiation therapy globally by 2035 and what the potential clinical and economic benefits are for doing this. The Task Force has determined the projections of cancer incidence and the infrastructure required to provide access to radiation therapy globally. Furthermore it has shown that appropriate investment not only yields improved clinical outcomes for millions of patients but that it also provides an overall economic gain throughout all the income settings where this investment is made. This symposium will summarize the facets associated with this global cancer challenge by reviewing the cancer burden, looking at the requirements for radiation therapy, reviewing the benefits of providing such therapy both from a clinical and economic perspective and finally by looking at what approaches can be used to aid in the alleviation of this global cancer challenge. The speakers are world renowned experts in global public health issues (R. Atun), medical physics (D. Jaffray) and radiation oncology (N. Coleman). Learning Objectives: To describe the global cancer challenge and the corresponding potential benefits of addressing this challenge. To describe what radiation therapy infrastructure, in terms of facilities, equipment and personnel, will be required to address this challenge. To describe models of addressing personnel and infrastructure mobilization and capacity building within regions where significant cancer treatment disparities exist.« less

Monthly and seasonal variations of aerosol optical properties and direct radiative forcing over Zanjan, Iran

NASA Astrophysics Data System (ADS)

Gharibzadeh, Maryam; Alam, Khan; Abedini, Yousefali; Bidokhti, Abbasali Aliakbari; Masoumi, Amir

2017-11-01

Aerosol optical properties and radiative forcing over Zanjan in northwest of Iran has been analyzed during 2010-2013. The aerosol optical and radiative properties are less studied over Zanjan, and therefore, require a careful and in depth analysis. The optical properties like Aerosol Optical Depth (AOD), Ångström Exponent (AE), ASYmmetry parameter (ASY), Single Scattering Albedo (SSA), and Aerosol Volume Size Distribution (AVSD) have been evaluated using the ground-based AErosol RObotic NETwork (AERONET) data. Higher AOD while relatively lower AE were observed in the spring and summer, which showed the presence of coarse mode particles in these seasons. An obvious increase of coarse mode particles in AVSD distribution, as well as a higher value of SSA represented considerable addition of coarse mode particles like dust into the atmosphere of Zanjan in these two seasons. Increase in AE, while a decrease in AOD was detected in the winter and fall. The presence of fine particles indicates the dominance of particles like urban-industrial aerosols from local sources especially in the winter. The Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model was utilized to calculate the Aerosol Radiative Forcing (ARF) at the Top of the Atmosphere (TOA), earth's surface and within the atmosphere. The annual averaged ARF values were -13.47 W m-2 and -36.1 W m-2 at the TOA and earth's surface, respectively, which indicate a significant cooling effect. Likewise, the ARF efficiencies at the TOA and earth's surface were -65.08 W m-2 and -158.43 W m-2, respectively. The annual mean atmospheric ARF and heating rate within the atmosphere were 22.63 W m-2 and 0.27 Kday-1 respectively, represented the warming effect within the atmosphere. Finally, a good agreement was found between AERONET retrieved ARF and SBDART simulated ARF.

Simulations of radiation pressure experiments narrow down the energy and momentum of light in matter

NASA Astrophysics Data System (ADS)

Bethune-Waddell, Max; Chau, Kenneth J.

2015-12-01

Consensus on a single electrodynamic theory has yet to be reached. Discord was seeded over a century ago when Abraham and Minkowski proposed different forms of electromagnetic momentum density and has since expanded in scope with the gradual introduction of other forms of momentum and force densities. Although degenerate sets of electrodynamic postulates can be fashioned to comply with global energy and momentum conservation, hope remains to isolate a single theory based on detailed comparison between force density predictions and radiation pressure experiments. This comparison is two-fold challenging because there are just a handful of quantitative radiation pressure measurements over the past century and the solutions developed from different postulates, which consist of approximate expressions and inferential deductions, are scattered throughout the literature. For these reasons, it is appropriate to conduct a consolidated and comprehensive re-analysis of past experiments under the assumption that the momentum and energy of light in matter are degenerate. We create a combined electrodynamic/fluid dynamic simulation testbed that uses five historically significant sets of electrodynamic postulates, including those by Abraham and Minkowski, to model radiation pressure under diverse configurations with minimal assumptions. This leads to new interpretations of landmark investigations of light momentum, including the Balazs thought experiment, the Jones-Richards and Jones-Leslie measurements of radiation pressure on submerged mirrors, observations of laser-deformed fluid surfaces, and experiments on optical trapping and tractor beaming of dielectric particles. We discuss the merits and demerits of each set of postulates when compared to available experimental evidence and fundamental conservation laws. Of the five sets of postulates, the Abraham and Einstein-Laub postulates provide the greatest consistency with observations and the most physically plausible descriptions of electrodynamic interactions. Force density predictions made by these two postulates are unique under many conditions and their experimental isolation is potentially within reach.

Impacts of Human Alteration of the Nitrogen Cycle in the U.S. on Radiative Forcing

EPA Science Inventory

Nitrogen cycling processes affect radiative forcing directly through emissions of nitrous oxide (N2O) and indirectly because emissions of nitrogen oxide (NO x ) and ammonia (NH3) affect atmospheric concentrations of methane (CH4), carbon dioxide (CO2), water vapor (H2O), ozone (O...

Optical Quantification of Harmonic Acoustic Radiation Force Excitation in a Tissue-Mimicking Phantom.

PubMed

Suomi, Visa; Edwards, David; Cleveland, Robin

2015-12-01

Optical tracking was used to characterize acoustic radiation force-induced displacements in a tissue-mimicking phantom. Amplitude-modulated 3.3-MHz ultrasound was used to induce acoustic radiation force in the phantom, which was embedded with 10-μm microspheres that were tracked using a microscope objective and high-speed camera. For sine and square amplitude modulation, the harmonic components of the fundamental and second and third harmonic frequencies were measured. The displacement amplitudes were found to increase linearly with acoustic radiation force up to 10 μm, with sine modulation having 19.5% lower peak-to-peak amplitude values than square modulation. Square modulation produced almost no second harmonic, but energy was present in the third harmonic. For the sine modulation, energy was present in the second harmonic and low energy in the third harmonic. A finite-element model was used to simulate the deformation and was both qualitatively and quantitatively in agreement with the measurements. Copyright © 2015 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

Jeans instability in collisional strongly coupled dusty plasma with radiative condensation and polarization force

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prajapati, R. P., E-mail: prajapati-iter@yahoo.co.in; Bhakta, S.; Chhajlani, R. K.

2016-05-15

The influence of dust-neutral collisions, polarization force, and electron radiative condensation is analysed on the Jeans (gravitational) instability of partially ionized strongly coupled dusty plasma (SCDP) using linear perturbation (normal mode) analysis. The Boltzmann distributed ions, dynamics of inertialess electrons, charged dust and neutral particles are considered. Using the plane wave solutions, a general dispersion relation is derived which is modified due to the presence of dust-neutral collisions, strong coupling effect, polarization force, electron radiative condensation, and Jeans dust/neutral frequencies. In the long wavelength perturbations, the Jeans instability criterion depends upon strong coupling effect, polarization interaction parameter, and thermal loss,more » but it is independent of dust-neutral collision frequency. The stability of the considered configuration is analysed using the Routh–Hurwitz criterion. The growth rates of Jeans instability are illustrated, and stabilizing influence of viscoelasticity and dust-neutral collision frequency while destabilizing effect of electron radiative condensation, polarization force, and Jeans dust-neutral frequency ratio is observed. This work is applied to understand the gravitational collapse of SCDP with dust-neutral collisions.« less

Harmonic motion detection in a vibrating scattering medium.

PubMed

Urban, Matthew W; Chen, Shigao; Greenleaf, James

2008-09-01

Elasticity imaging is an emerging medical imaging modality that seeks to map the spatial distribution of tissue stiffness. Ultrasound radiation force excitation and motion tracking using pulse-echo ultrasound have been used in numerous methods. Dynamic radiation force is used in vibrometry to cause an object or tissue to vibrate, and the vibration amplitude and phase can be measured with exceptional accuracy. This paper presents a model that simulates harmonic motion detection in a vibrating scattering medium incorporating 3-D beam shapes for radiation force excitation and motion tracking. A parameterized analysis using this model provides a platform to optimize motion detection for vibrometry applications in tissue. An experimental method that produces a multifrequency radiation force is also presented. Experimental harmonic motion detection of simultaneous multifrequency vibration is demonstrated using a single transducer. This method can accurately detect motion with displacement amplitude as low as 100 to 200 nm in bovine muscle. Vibration phase can be measured within 10 degrees or less. The experimental results validate the conclusions observed from the model and show multifrequency vibration induction and measurements can be performed simultaneously.

Harmonic Motion Detection in a Vibrating Scattering Medium

PubMed Central

Urban, Matthew W.; Chen, Shigao; Greenleaf, James F.

2008-01-01

Elasticity imaging is an emerging medical imaging modality that seeks to map the spatial distribution of tissue stiffness. Ultrasound radiation force excitation and motion tracking using pulse-echo ultrasound have been used in numerous methods. Dynamic radiation force is used in vibrometry to cause an object or tissue to vibrate, and the vibration amplitude and phase can be measured with exceptional accuracy. This paper presents a model that simulates harmonic motion detection in a vibrating scattering medium incorporating 3-D beam shapes for radiation force excitation and motion tracking. A parameterized analysis using this model provides a platform to optimize motion detection for vibrometry applications in tissue. An experimental method that produces a multifrequency radiation force is also presented. Experimental harmonic motion detection of simultaneous multifrequency vibration is demonstrated using a single transducer. This method can accurately detect motion with displacement amplitude as low as 100 to 200 nm in bovine muscle. Vibration phase can be measured within 10° or less. The experimental results validate the conclusions observed from the model and show multifrequency vibration induction and measurements can be performed simultaneously. PMID:18986892

Effect of land cover change on snow free surface albedo across the continental United States

USGS Publications Warehouse

Wickham, J.; Nash, M.S.; Barnes, Christopher A.

2016-01-01

Land cover changes (e.g., forest to grassland) affect albedo, and changes in albedo can influence radiative forcing (warming, cooling). We empirically tested albedo response to land cover change for 130 locations across the continental United States using high resolution (30 m-×-30 m) land cover change data and moderate resolution (~ 500 m-×-500 m) albedo data. The land cover change data spanned 10 years (2001 − 2011) and the albedo data included observations every eight days for 13 years (2001 − 2013). Empirical testing was based on autoregressive time series analysis of snow free albedo for verified locations of land cover change. Approximately one-third of the autoregressive analyses for woody to herbaceous or forest to shrub change classes were not significant, indicating that albedo did not change significantly as a result of land cover change at these locations. In addition, ~ 80% of mean differences in albedo arising from land cover change were less than ± 0.02, a nominal benchmark for precision of albedo measurements that is related to significant changes in radiative forcing. Under snow free conditions, we found that land cover change does not guarantee a significant albedo response, and that the differences in mean albedo response for the majority of land cover change locations were small.

Longitudinal monitoring of liver stiffness by acoustic radiation force impulse imaging in patients with chronic hepatitis B receiving entecavir.

PubMed

Wu, Sheng-Di; Ding, Hong; Liu, Li-Li; Zhuang, Yuan; Liu, Yun; Cheng, Li-Sha; Wang, Si-Qi; Tseng, Yu-Jen; Wang, Ji-Yao; Jiang, Wei

2018-06-01

Acoustic radiation force impulse (ARFI) imaging measures liver stiffness (LS), which significantly correlates with the stage of liver fibrosis in treatment-naive patients with chronic hepatitis B (CHB). We aimed to prospectively assess the clinical usefulness of ARFI during long-term antiviral therapy in CHB. Seventy-one CHB patients were consecutively recruited and paired liver biopsies were performed in 27 patients. LS was assessed by ARFI semiannually during entecavir therapy. LS gradually decreased with treatment and continued to decrease after normalization of alanine aminotransaminase. Overall, 97.2% patients achieved improvement of LS, whereas 19.7% patients had more than 30% reduction in LS values between baseline and week 104. Multivariate linear regression analysis showed that the degree of LS reduction significantly correlated with the baseline levels of LS value, platelet and cholinesterase. In the 27 patients who underwent paired liver biopsies, LS significantly correlated with stage of fibrosis and inflammatory grade at baseline. LS values decreased more significantly in patients with fibrosis regression than those with static histological fibrosis. In CHB patients, LS assessed by ARFI was gradually reduced during antiviral therapy. Longitudinal monitoring of LS may be a promising noninvasive assessment of fibrosis regression during long-term antiviral therapy in CHB. Further large sample studies are needed. Copyright © 2017 Elsevier Masson SAS. All rights reserved.

Integration of Acoustic Radiation Force and Optical Imaging for Blood Plasma Clot Stiffness Measurement

PubMed Central

Wang, Caroline W.; Perez, Matthew J.; Helmke, Brian P.; Viola, Francesco; Lawrence, Michael B.

2015-01-01

Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood’s transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties. PMID:26042775

Model-based optical coherence elastography using acoustic radiation force

NASA Astrophysics Data System (ADS)

Aglyamov, Salavat; Wang, Shang; Karpiouk, Andrei; Li, Jiasong; Emelianov, Stanislav; Larin, Kirill V.

2014-02-01

Acoustic Radiation Force (ARF) stimulation is actively used in ultrasound elastography to estimate mechanical properties of tissue. Compared with ultrasound imaging, OCT provides advantage in both spatial resolution and signal-to-noise ratio. Therefore, a combination of ARF and OCT technologies can provide a unique opportunity to measure viscoelastic properties of tissue, especially when the use of high intensity radiation pressure is limited for safety reasons. In this presentation we discuss a newly developed theoretical model of the deformation of a layered viscoelastic medium in response to an acoustic radiation force of short duration. An acoustic impulse was considered as an axisymmetric force generated on the upper surface of the medium. An analytical solution of this problem was obtained using the Hankel transform in frequency domain. It was demonstrated that layers at different depths introduce different frequency responses. To verify the developed model, experiments were performed using tissue-simulating, inhomogeneous phantoms of varying mechanical properties. The Young's modulus of the phantoms was varied from 5 to 50 kPa. A single-element focused ultrasound transducer (3.5 MHz) was used to apply the radiation force with various durations on the surface of phantoms. Displacements on the phantom surface were measured using a phase-sensitive OCT at 25 kHz repetition frequency. The experimental results were in good agreement with the modeling results. Therefore, the proposed theoretical model can be used to reconstruct the mechanical properties of tissue based on ARF/OCT measurements.

Are there interactive effects of physiological and radiative forcing produced by increased CO2 concentration on changes of land hydrological cycle?

NASA Astrophysics Data System (ADS)

Peng, Jing; Dan, Li; Dong, Wenjie

2014-01-01

Three coupled climate-carbon cycle models including CESM (Community Earth System Model), CanEsm (the Canadian Centre for Climate Modelling and Analysis Earth System Model) and BCC (Beijing Climate Center Climate System Model) were used to estimate whether changes in land hydrological cycle responded to the interactive effects of CO2-physiological forcing and CO2-radiative forcing. No signs could be indicated that the interactive effects of CO2-physiological forcing and CO2-radiative forcing on the hydrological variables (e.g. precipitation, evapotranspiration and runoff) were detected at global and regional scales. For each model, increases in precipitation, evapotranspiration and runoff (e.g. 0.37, 0.18 and 0.25 mm/year2) were simulated in response to CO2-radiative forcing (experiment M3). Decreases in precipitation and evapotranspiration (about - 0.02 and - 0.09 mm/year2) were captured if the CO2 physiological effect was only accounted for (experiment M2). In this experiment, a reverse sign in runoff (the increase of 0.08 mm/year2) in contrast to M3 is presented. All models simulated the same signs across Eastern Asia in response to the CO2 physiological forcing and radiative forcing: increases in precipitation and evapotranspiration only considering greenhouse effect; reductions in precipitation and evapotranspiration in response to CO2-physiological effect; and enhanced trends in runoff from all experiments. However, there was still a large uncertainty on the magnitude of the effect of transpiration on runoff (decreased transpiration accounting for 8% to 250% of the increased runoff) from the three models. Two models (CanEsm and BCC) attributed most of the increase in runoff to the decrease in transpiration if the CO2-physiological effect was only accounted for, whereas CESM exhibited that the decrease in transpiration could not totally explain the increase in runoff. The attribution of the CO2-physiological forcing to changes in stomatal conductance versus changes in vegetation structure (e.g. increased Leaf Area Index) is an issue to discuss, and among the three models, no agreement appeared.

The role of earth radiation budget studies in climate and general circulation research

NASA Technical Reports Server (NTRS)

Ramanathan, V.

1987-01-01

The use of earth radiation budget (ERB) data for climate and general circulation research is studied. ERB measurements obtained in the 1960's and 1970's have provided data on planetary brightness, planetary global energy balances, the greenhouse effect, solar insolation, meridional heat transport by oceans and atmospheres, regional forcing, climate feedback processes, and the computation of albedo values in low latitudes. The role of clouds in governing climate, in influencing the general circulation, and in determining the sensitivity of climate to external perturbations needs to be researched; a procedure for analyzing the ERB data, which will address these problems, is described. The approach involves estimating the clear-sky fluxes from the high spatial resolution scanner measurement and defining a cloud radiative forcing; the global average of the sum of the solar and long-wave cloud forcing yields the net radiative effect of clouds on the climate.

Radiative Impacts of Further Arctic Sea Ice Melt: Using past Observations to Inform Future Climate Impacts

NASA Technical Reports Server (NTRS)

Pistone, K.; Eisenman, I.; Ramanathan, V.

2017-01-01

The Arctic region has seen dramatic changes over the past several decades, from polar amplification of global temperature rise to ecosystem changes to the decline of the sea ice. While there has been much speculation as to when the world will see an ice-free Arctic, the radiative impacts of an eventual disappearance of the Arctic sea ice are likely to be significant regardless of the timing. Using CERES radiation and microwave satellite sea ice data, Pistone et al (2014) estimated the radiative forcing due to albedo changes associated with the Arctic sea ice retreat over the 30 years of the satellite data record. In this study, we found that the Arctic Ocean saw a decrease in all-sky albedo of 4% (from 52% to 48%), for an estimated increase in solar heating of 6.4 W/m(exp 2) between 1979 and 2011, or 0.21 W/m(exp 2) when averaged over the globe. This value is substantial--approximately 25% as large as the forcing due to the change in CO2 during the same period. Here we update and expand upon this previous work and use the CERES broadband shortwave observations to explore the radiative impacts of a transition to completely ice-free Arctic Ocean. We estimate the annually-averaged Arctic Ocean planetary albedo under ice-free and cloud-free conditions to be 14% over the region, or approximately 25% lower in absolute terms than the Arctic Ocean cloud-free albedo in 1979. However, the question of all-sky conditions (i.e. including the effects of clouds) introduces a new level of complexity. We explore several cloud scenarios and the resultant impact on albedo. In each of these cases, the estimated forcing is not uniformly distributed throughout the year. We describe the relative contributions of ice loss by month as well as the spatial distributions of the resulting changes in absorbed solar energy. The seasonal timing and location—in addition to magnitude—of the altered solar absorption may have significant implications for atmospheric and ocean dynamics in the Arctic and at lower latitudes; this observationally-based estimate of the large-scale characteristics of an ice-free Arctic thus provides a valuable tool to complement and validate model-based assessments of future climate.

The Asian-Bering-North American teleconnection: seasonality, maintenance, and climate impact on North America

NASA Astrophysics Data System (ADS)

Yu, Bin; Lin, H.; Wu, Z. W.; Merryfield, W. J.

2018-03-01

The Asian-Bering-North American (ABNA) teleconnection index is constructed from the normalized 500-hPa geopotential field by excluding the Pacific-North American pattern contribution. The ABNA pattern features a zonally elongated wavetrain originating from North Asia and flowing downstream across Bering Sea and Strait towards North America. The large-scale teleconnection is a year-round phenomenon that displays strong seasonality with the peak variability in winter. North American surface temperature and temperature extremes, including warm days and nights as well as cold days and nights, are significantly controlled by this teleconnection. The ABNA pattern has an equivalent barotropic structure in the troposphere and is supported by synoptic-scale eddy forcing in the upper troposphere. Its associated sea surface temperature anomalies exhibit a horseshoe-shaped structure in the North Pacific, most prominent in winter, which is driven by atmospheric circulation anomalies. The snow cover anomalies over the West Siberian plain and Central Siberian Plateau in autumn and spring and over southern Siberia in winter may act as a forcing influence on the ABNA pattern. The snow forcing influence in winter and spring can be traced back to the preceding season, which provides a predictability source for this teleconnection and for North American temperature variability. The ABNA associated energy budget is dominated by surface longwave radiation anomalies year-round, with the temperature anomalies supported by anomalous downward longwave radiation and damped by upward longwave radiation at the surface.

Acoustic backscattering and radiation force on a rigid elliptical cylinder in plane progressive waves.

PubMed

Mitri, F G

2016-03-01

This work proposes a formal analytical theory using the partial-wave series expansion (PWSE) method in cylindrical coordinates, to calculate the acoustic backscattering form function as well as the radiation force-per-length on an infinitely long elliptical (non-circular) cylinder in plane progressive waves. The major (or minor) semi-axis of the ellipse coincides with the direction of the incident waves. The scattering coefficients for the rigid elliptical cylinder are determined by imposing the Neumann boundary condition for an immovable surface and solving a resulting system of linear equations by matrix inversion. The present method, which utilizes standard cylindrical (Bessel and Hankel) wave functions, presents an advantage over the solution for the scattering that is ordinarily expressed in a basis of elliptical Mathieu functions (which are generally non-orthogonal). Furthermore, an integral equation showing the direct connection of the radiation force function with the square of the scattering form function in the far-field from the scatterer (applicable for plane waves only), is noted and discussed. An important application of this integral equation is the adequate evaluation of the radiation force function from a bistatic measurement (i.e., in the polar plane) of the far-field scattering from any 2D object of arbitrary shape. Numerical predictions are evaluated for the acoustic backscattering form function and the radiation force function, which is the radiation force per unit length, per characteristic energy density, and per unit cross-sectional surface of the ellipse, with particular emphasis on the aspect ratio a/b, where a and b are the semi-axes, as well as the dimensionless size parameter kb, without the restriction to a particular range of frequencies. The results are particularly relevant in acoustic levitation, acousto-fluidics and particle dynamics applications. Copyright © 2015 Elsevier B.V. All rights reserved.

Seasonal and Elevational Variations of Black Carbon and Dust in Snow and Ice in the Solu-Khumbu, Nepal and Estimated Radiative Forcings

NASA Astrophysics Data System (ADS)

Kaspari, S.; Painter, T. H.; Gysel, M.; Skiles, M.; Schwikowski, M.

2014-12-01

Black carbon (BC) and dust deposited on snow and glacier surfaces can reduce the surface albedo, accelerate melt, and trigger albedo feedback. Assessing BC and dust concentrations in snow and ice in the Himalaya is of interest because this region borders large BC and dust sources, and seasonal snow and glacier ice in this region are an important source of water resources. Snow and ice samples were collected from crevasse profiles and snowpits at elevations between 5400 and 6400 m asl from Mera glacier located in the Solu-Khumbu region of Nepal. The samples were measured for Fe concentrations (used as a dust proxy) via ICP-MS, total impurity content gravimetrically, and BC concentrations using a Single Particle Soot Photometer (SP2). BC and Fe concentrations are substantially higher at elevations < 6000 m due to post-depositional processes including melt and sublimation and greater loading in the lower troposphere. Because the largest areal extent of snow and ice resides at elevations < 6000 m, the higher BC and dust concentrations at these elevations can reduce the snow and glacier albedo over large areas, accelerating melt, affecting glacier mass-balance and water resources, and contributing to a positive climate forcing. Radiative transfer modeling constrained by measurements at 5400 m at Mera La indicates that BC concentrations in the winter-spring snow/ice horizons are sufficient to reduce albedo by 6-10% relative to clean snow, corresponding to localized instantaneous radiative forcings of 75-120 W m-2. The other bulk impurity concentrations, when treated separately as dust, reduce albedo by 40-42% relative to clean snow and give localized instantaneous radiative forcings of 488 to 525 W m-2. Adding the BC absorption to the other impurities results in additional radiative forcings of 3 W m-2. While these results suggest that the snow albedo and radiative forcing effect of dust is considerably greater than BC, there are several sources of uncertainty.

Determining the infrared radiative effects of Saharan dust: a radiative transfer modelling study based on vertically resolved measurements at Lampedusa

NASA Astrophysics Data System (ADS)

Meloni, Daniela; di Sarra, Alcide; Brogniez, Gérard; Denjean, Cyrielle; De Silvestri, Lorenzo; Di Iorio, Tatiana; Formenti, Paola; Gómez-Amo, José L.; Gröbner, Julian; Kouremeti, Natalia; Liuzzi, Giuliano; Mallet, Marc; Pace, Giandomenico; Sferlazzo, Damiano M.

2018-03-01

Detailed measurements of radiation, atmospheric and aerosol properties were carried out in summer 2013 during the Aerosol Direct Radiative Impact on the regional climate in the MEDiterranean region (ADRIMED) campaign in the framework of the Chemistry-Aerosol Mediterranean Experiment (ChArMEx) experiment. This study focusses on the characterization of infrared (IR) optical properties and direct radiative effects of mineral dust, based on three vertical profiles of atmospheric and aerosol properties and IR broadband and narrowband radiation from airborne measurements, made in conjunction with radiosonde and ground-based observations at Lampedusa, in the central Mediterranean. Satellite IR spectra from the Infrared Atmospheric Sounder Interferometer (IASI) are also included in the analysis. The atmospheric and aerosol properties are used as input to a radiative transfer model, and various IR radiation parameters (upward and downward irradiance, nadir and zenith brightness temperature at different altitudes) are calculated and compared with observations. The model calculations are made for different sets of dust particle size distribution (PSD) and refractive index (RI), derived from observations and from the literature. The main results of the analysis are that the IR dust radiative forcing is non-negligible and strongly depends on PSD and RI. When calculations are made using the in situ measured size distribution, it is possible to identify the refractive index that produces the best match with observed IR irradiances and brightness temperatures (BTs). The most appropriate refractive indices correspond to those determined from independent measurements of mineral dust aerosols from the source regions (Tunisia, Algeria, Morocco) of dust transported over Lampedusa, suggesting that differences in the source properties should be taken into account. With the in situ size distribution and the most appropriate refractive index the estimated dust IR radiative forcing efficiency is +23.7 W m-2 at the surface, -7.9 W m-2 within the atmosphere, and +15.8 W m-2 at the top of the atmosphere. The use of column-integrated dust PSD from AERONET may also produce a good agreement with measured irradiances and BTs, but with significantly different values of the RI. This implies large differences, up to a factor of 2.5 at surface, in the estimated dust radiative forcing, and in the IR heating rate. This study shows that spectrally resolved measurements of BTs are important to better constrain the dust IR optical properties, and to obtain a reliable estimate of its radiative effects. Efforts should be directed at obtaining an improved description of the dust size distribution and its vertical distribution, as well as at including regionally resolved optical properties.

Light Absorption of Black Carbon Aerosol and Its Radiative Forcing Effect in an Megacity Atmosphere in South China

NASA Astrophysics Data System (ADS)

Lan, Zijuan

2013-04-01

The effects of black carbon (BC) aerosol on climate warming have been the study focus in the recent decade, the regional effect of BC light absorption is more significant. The reduction of BC is now expected to have significant near-term climate change mitigation. Mass absorption efficient (MAE) was one of the important optical properties of BC aerosol for evaluating the BC on its radiative forcing effect, while BC mixing state is one main influencing factor for MAE. Models have estimated that BC radiative forcing can be increased by a factor of ~2 for internally versus externally mixed BC. On the other hand, some organic carbon had been found to significantly absorb light at UV or shorter wavelengths in the most recent studies, with strong spectral dependence. But large uncertainties still remain in determining the positive forcing effect of BC on global clime change due to the technical limitations. In this study, advanced instrumentation (a three-wavelength photoacoustic soot spectrometer (PASS-3) and a single particle soot photometer (SP2)) were used to measure black carbon aerosol and analyze its optical properties in a megacity in South China, Shenzhen, during the summer of 2011. It is in the southeast corner of the Pearl River Delta (PRD) region, neighboring Hong Kong to the south. During the campaign, the average BC mass concentration was 4.0±3.1 μg m-3, accounting for about 11% of PM2.5 mass concentration, which mainly came from fossil fuel combustion rather than biomass burning. The MAE of BC ranged from 5.0 to 8.5 m2 g-1, with an average value of 6.5±0.5 m2 g-1. The percentage of internally mixed BC was averagely 24.3±7.9% and positively correlated with the MAE. It is estimated that the internally mixed BC amplified MAE by about 7% during the campaign, suggesting that the BC absorption enhancement due to internal mixing in the real atmosphere is relatively low in comparison with the predictions by theoretical models, which stands in accordance with the new finding of a very recent Science magazine paper by Cappa.

Aerosol Absorption Measurements from LANDSAT and CIMEL

NASA Technical Reports Server (NTRS)

Kaufman, Y. J.; Tanre, D.; Karnieli, A.; Remer, L.; Holben, B.

1999-01-01

Spectral remote observations of dust properties from space and from the ground create a powerful tool for determination of dust absorption of solar radiation with an unprecedented accuracy. Absorption is a key component in understanding dust impact on climate. We use Landsat space-borne measurements at 0.47 to 2.2 micrometer over Senegal with ground-based sunphotometers to find that Saharan dust absorption of solar radiation is two to four times smaller than in models. Though dust absorbs in the blue, almost no absorption was found for wavelengths greater than 0.6 micrometer. The new finding increases by 50% recent estimated solar radiative forcing by dust and decreases the estimated dust heating of the lower troposphere. Dust transported from Asia shows slightly higher absorption probably due to the presence of black carbon from populated regions. Large-scale application of this method to satellite data from the Earth Observing System can reduce significantly the uncertainty in the dust radiative effects.

Shortwave radiative forcing, rapid adjustment, and feedback to the surface by sulfate geoengineering: analysis of the Geoengineering Model Intercomparison Project G4 scenario

DOE PAGES

Kashimura, Hiroki; Abe, Manabu; Watanabe, Shingo; ...

2017-03-08

This paper evaluates the forcing, rapid adjustment, and feedback of net shortwave radiation at the surface in the G4 experiment of the Geoengineering Model Intercomparison Project by analysing outputs from six participating models. G4 involves injection of 5 Tg yr -1 of SO 2, a sulfate aerosol precursor, into the lower stratosphere from year 2020 to 2069 against a background scenario of RCP4.5. A single-layer atmospheric model for shortwave radiative transfer is used to estimate the direct forcing of solar radiation management (SRM), and rapid adjustment and feedbacks from changes in the water vapour amount, cloud amount, and surface albedo (compared with RCP4.5). The analysismore » shows that the globally and temporally averaged SRM forcing ranges from -3.6 to -1.6 W m -2, depending on the model. The sum of the rapid adjustments and feedback effects due to changes in the water vapour and cloud amounts increase the downwelling shortwave radiation at the surface by approximately 0.4 to 1.5 W m -2 and hence weaken the effect of SRM by around 50 %. The surface albedo changes decrease the net shortwave radiation at the surface; it is locally strong (~-4 W m -2) in snow and sea ice melting regions, but minor for the global average. The analyses show that the results of the G4 experiment, which simulates sulfate geoengineering, include large inter-model variability both in the direct SRM forcing and the shortwave rapid adjustment from change in the cloud amount, and imply a high uncertainty in modelled processes of sulfate aerosols and clouds.« less

Modeling dust as component minerals in the Community Atmosphere Model: development of framework and impact on radiative forcing

DOE PAGES

Scanza, Rachel; Mahowald, N.; Ghan, Steven J.; ...

2015-01-01

The mineralogy of desert dust is important due to its effect on radiation, clouds and biogeochemical cycling of trace nutrients. This study presents the simulation of dust radiative forcing as a function of both mineral composition and size at the global scale, using mineral soil maps for estimating emissions. Externally mixed mineral aerosols in the bulk aerosol module in the Community Atmosphere Model version 4 (CAM4) and internally mixed mineral aerosols in the modal aerosol module in the Community Atmosphere Model version 5.1 (CAM5) embedded in the Community Earth System Model version 1.0.5 (CESM) are speciated into common mineral componentsmore » in place of total dust. The simulations with mineralogy are compared to available observations of mineral atmospheric distribution and deposition along with observations of clear-sky radiative forcing efficiency. Based on these simulations, we estimate the all-sky direct radiative forcing at the top of the atmosphere as + 0.05 Wm⁻² for both CAM4 and CAM5 simulations with mineralogy. We compare this to the radiative forcing from simulations of dust in release versions of CAM4 and CAM5 (+0.08 and +0.17 Wm⁻²) and of dust with optimized optical properties, wet scavenging and particle size distribution in CAM4 and CAM5, -0.05 and -0.17 Wm⁻², respectively. The ability to correctly include the mineralogy of dust in climate models is hindered by its spatial and temporal variability as well as insufficient global in situ observations, incomplete and uncertain source mineralogies and the uncertainties associated with data retrieved from remote sensing methods.« less

The acoustic radiation force on a small thermoviscous or thermoelastic particle suspended in a viscous and heat-conducting fluid

NASA Astrophysics Data System (ADS)

Karlsen, Jonas; Bruus, Henrik

2015-11-01

We present a theoretical analysis (arxiv.org/abs/1507.01043) of the acoustic radiation force on a single small particle, either a thermoviscous fluid droplet or a thermoelastic solid particle, suspended in a viscous and heat-conducting fluid. Our analysis places no restrictions on the viscous and thermal boundary layer thicknesses relative to the particle radius, but it assumes the particle to be small in comparison to the acoustic wavelength. This is the limit relevant to scattering of ultrasound waves from sub-micrometer particles. For particle sizes smaller than the boundary layer widths, our theory leads to profound consequences for the acoustic radiation force. For example, for liquid droplets and solid particles suspended in gasses we predict forces orders of magnitude larger than expected from ideal-fluid theory. Moreover, for certain relevant choices of materials, we find a sign change in the acoustic radiation force on different-sized but otherwise identical particles. These findings lead to the concept of a particle-size-dependent acoustophoretic contrast factor, highly relevant to applications in acoustic levitation or separation of micro-particles in gases, as well as to handling of μm- and nm-sized particles such as bacteria and vira in lab-on-a-chip systems.

Assessment of the first indirect radiative effect of ammonium-sulfate-nitrate aerosols in East Asia

NASA Astrophysics Data System (ADS)

Han, Xiao; Zhang, Meigen; Skorokhod, Andrei

2017-11-01

A physically based cloud nucleation parameterization was introduced into an optical properties/radiative transfer module incorporated with the off-line air quality modeling system Regional Atmospheric Modeling System (RAMS)-Models-3 Community Multi Scale Air Quality (CMAQ) to investigate the distribution features of the first indirect radiative effects of sulfate, nitrate, and ammonium-sulfate-nitrate (ASN) over East Asia for the years of 2005, 2010, and 2013. The relationship between aerosol particles and cloud droplet number concentration could be properly described by this parameterization because the simulated cloud fraction and cloud liquid water path were generally reliable compared with Moderate Resolution Imaging Spectroradiometer (MODIS) retrieved data. Simulation results showed that the strong effect of indirect forcing was mainly concentrated in Southeast China, the East China Sea, the Yellow Sea, and the Sea of Japan. The highest indirect radiative forcing of ASN reached -3.47 W m-2 over Southeast China and was obviously larger than the global mean of the indirect forcing of all anthropogenic aerosols. In addition, sulfate provided about half of the contribution to the ASN indirect forcing effect. However, the effect caused by nitrate was weak because the mass burden of nitrate was very low during summer, whereas the cloud fraction was the highest. The analysis indicated that even though the interannual variation of indirect forcing magnitude generally followed the trend of aerosol mass burden from 2005 to 2013, the cloud fraction was an important factor that determined the distribution pattern of indirect forcing. The heaviest aerosol loading in North China did not cause a strong radiative effect because of the low cloud fraction over this region.

Solar forcing for CMIP6 (v3.2)

NASA Astrophysics Data System (ADS)

Matthes, Katja; Funke, Bernd; Andersson, Monika E.; Barnard, Luke; Beer, Jürg; Charbonneau, Paul; Clilverd, Mark A.; Dudok de Wit, Thierry; Haberreiter, Margit; Hendry, Aaron; Jackman, Charles H.; Kretzschmar, Matthieu; Kruschke, Tim; Kunze, Markus; Langematz, Ulrike; Marsh, Daniel R.; Maycock, Amanda C.; Misios, Stergios; Rodger, Craig J.; Scaife, Adam A.; Seppälä, Annika; Shangguan, Ming; Sinnhuber, Miriam; Tourpali, Kleareti; Usoskin, Ilya; van de Kamp, Max; Verronen, Pekka T.; Versick, Stefan

2017-06-01

This paper describes the recommended solar forcing dataset for CMIP6 and highlights changes with respect to CMIP5. The solar forcing is provided for radiative properties, namely total solar irradiance (TSI), solar spectral irradiance (SSI), and the F10.7 index as well as particle forcing, including geomagnetic indices Ap and Kp, and ionization rates to account for effects of solar protons, electrons, and galactic cosmic rays. This is the first time that a recommendation for solar-driven particle forcing has been provided for a CMIP exercise. The solar forcing datasets are provided at daily and monthly resolution separately for the CMIP6 preindustrial control, historical (1850-2014), and future (2015-2300) simulations. For the preindustrial control simulation, both constant and time-varying solar forcing components are provided, with the latter including variability on 11-year and shorter timescales but no long-term changes. For the future, we provide a realistic scenario of what solar behavior could be, as well as an additional extreme Maunder-minimum-like sensitivity scenario. This paper describes the forcing datasets and also provides detailed recommendations as to their implementation in current climate models.For the historical simulations, the TSI and SSI time series are defined as the average of two solar irradiance models that are adapted to CMIP6 needs: an empirical one (NRLTSI2-NRLSSI2) and a semi-empirical one (SATIRE). A new and lower TSI value is recommended: the contemporary solar-cycle average is now 1361.0 W m-2. The slight negative trend in TSI over the three most recent solar cycles in the CMIP6 dataset leads to only a small global radiative forcing of -0.04 W m-2. In the 200-400 nm wavelength range, which is important for ozone photochemistry, the CMIP6 solar forcing dataset shows a larger solar-cycle variability contribution to TSI than in CMIP5 (50 % compared to 35 %).We compare the climatic effects of the CMIP6 solar forcing dataset to its CMIP5 predecessor by using time-slice experiments of two chemistry-climate models and a reference radiative transfer model. The differences in the long-term mean SSI in the CMIP6 dataset, compared to CMIP5, impact on climatological stratospheric conditions (lower shortwave heating rates of -0.35 K day-1 at the stratopause), cooler stratospheric temperatures (-1.5 K in the upper stratosphere), lower ozone abundances in the lower stratosphere (-3 %), and higher ozone abundances (+1.5 % in the upper stratosphere and lower mesosphere). Between the maximum and minimum phases of the 11-year solar cycle, there is an increase in shortwave heating rates (+0.2 K day-1 at the stratopause), temperatures ( ˜ 1 K at the stratopause), and ozone (+2.5 % in the upper stratosphere) in the tropical upper stratosphere using the CMIP6 forcing dataset. This solar-cycle response is slightly larger, but not statistically significantly different from that for the CMIP5 forcing dataset.CMIP6 models with a well-resolved shortwave radiation scheme are encouraged to prescribe SSI changes and include solar-induced stratospheric ozone variations, in order to better represent solar climate variability compared to models that only prescribe TSI and/or exclude the solar-ozone response. We show that monthly-mean solar-induced ozone variations are implicitly included in the SPARC/CCMI CMIP6 Ozone Database for historical simulations, which is derived from transient chemistry-climate model simulations and has been developed for climate models that do not calculate ozone interactively. CMIP6 models without chemistry that perform a preindustrial control simulation with time-varying solar forcing will need to use a modified version of the SPARC/CCMI Ozone Database that includes solar variability. CMIP6 models with interactive chemistry are also encouraged to use the particle forcing datasets, which will allow the potential long-term effects of particles to be addressed for the first time. The consideration of particle forcing has been shown to significantly improve the representation of reactive nitrogen and ozone variability in the polar middle atmosphere, eventually resulting in further improvements in the representation of solar climate variability in global models.

Estimation of shortwave direct aerosol radiative forcing at four locations on the Indo-Gangetic plains: Model results and ground measurement

NASA Astrophysics Data System (ADS)

Bibi, Humera; Alam, Khan; Bibi, Samina

2017-08-01

This study provides observational results of aerosol optical and radiative characteristics over four locations in IGP. Spectral variation of Aerosol Optical Depth (AOD), Single Scattering Albedo (SSA) and Asymmetry Parameter (AP) were analysed using AErosol RObotic NETwork (AERONET) data. The analysis revealed that coarse particles were dominant in summer and pre-monsoon, while fine particles were more pronounced in winter and post-monsoon. Furthermore, the spatio-temporal variations of Shortwave Direct Aerosol Radiative Forcing (SDARF) and Shortwave Direct Aerosol Radiative Forcing Efficiency (SDARFE) at the Top Of Atmosphere (TOA), SURface (SUR) and within ATMosphere (ATM) were calculated using SBDART model. The atmospheric Heating Rate (HR) associated with SDARFATM were also computed. It was observed that the monthly averaged SDARFTOA and SDARFSUR were found to be negative leading to positive SDARFATM during all the months over all sites. The increments in net atmospheric forcing lead to maximum HR in November-December and May. The seasonal analysis of SDARF revealed that SDARFTOA and SDARFSUR were negative during all seasons. The SW atmospheric absorption translates to highest atmospheric HR during summer over Karachi and during pre-monsoon over Lahore, Jaipur and Kanpur. Like SDARF, the monthly and seasonal variations of SDARFETOA and SDARFESUR were found to be negative, resulting in positive atmospheric forcing. Additionally, to compare the model estimated forcing against AERONET derived forcing, the regression analysis of AERONET-SBDART forcing were carried out. It was observed that SDARF at SUR and TOA showed relatively higher correlation over Lahore, moderate over Jaipur and Kanpur and lower over Karachi. Finally, the analysis of National Oceanic and Atmospheric Administration Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model revealed that air masses were arriving from multiple source locations.

Assessment of Global Annual Atmospheric Energy Balance from Satellite Observations

NASA Technical Reports Server (NTRS)

Lin, Bing; Stackhouse, Paul; Minnis, Patrick; Wielicki, Bruce A.; Hu, Yongxiang; Sun, Wenbo; Fan, Tai-Fang (Alice); Hinkelman, Laura

2008-01-01

Global atmospheric energy balance is one of the fundamental processes for the earth's climate system. This study uses currently available satellite data sets of radiative energy at the top of atmosphere (TOA) and surface and latent and sensible heat over oceans for the year 2000 to assess the global annual energy budget. Over land, surface radiation data are used to constrain assimilated results and to force the radiation, turbulent heat, and heat storage into balance due to a lack of observation-based turbulent heat flux estimations. Global annual means of the TOA net radiation obtained from both direct measurements and calculations are close to zero. The net radiative energy fluxes into the surface and the surface latent heat transported into the atmosphere are about 113 and 86 Watts per square meter, respectively. The estimated atmospheric and surface heat imbalances are about -8 9 Watts per square meter, values that are within the uncertainties of surface radiation and sea surface turbulent flux estimates and likely systematic biases in the analyzed observations. The potential significant additional absorption of solar radiation within the atmosphere suggested by previous studies does not appear to be required to balance the energy budget the spurious heat imbalances in the current data are much smaller (about half) than those obtained previously and debated at about a decade ago. Progress in surface radiation and oceanic turbulent heat flux estimations from satellite measurements significantly reduces the bias errors in the observed global energy budgets of the climate system.

Modeling East Asian Dust and Its Radiative Feedbacks in CAM4-BAM

DOE PAGES

Xie, Xiaoning; Liu, Xiaodong; Che, Huizheng; ...

2018-01-18

East Asian dust and its radiative feedbacks are analyzed by the use of the fourth version of the Community Atmosphere Model (CAM4) with a bulk aerosol model parameterization (BAM) for the dust size distribution (CAM4-BAM). Two numerical experiments are conducted and intercompared: one with (Active) and one without (Passive) the radiative effects of dust aerosols. This CAM4-BAM captures the main spatial distribution of the dust aerosol optical depth (AOD) and the dust surface concentrations over East Asia, with positive correlations with the local observational data on annual and seasonal means. A comparative analysis of the Active and Passive experiments revealsmore » that consideration of the dust-radiation interaction can significantly reduce dust emissions, loading, transport, and dry and wet depositions over East Asia, which is opposite to the enhanced dust cycle over North Africa. Further analysis of the contrasting dust-radiation feedbacks between North Africa and East Asia shows that over North Africa, the dust radiative forcing significantly increases the surface temperature and 10-m wind speed, whereas it decreases the surface temperature and the surface wind speeds over East Asia. These contrasting radiative effects, in turn, result in distinct dust cycle changes over these two regions. Thus, mechanistic analysis reveals that the radiative contrasts between East Asia and North Africa are mainly due to the differences in their regional surface albedo, dust vertical distribution and size distribution.« less

Modeling East Asian Dust and Its Radiative Feedbacks in CAM4-BAM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Xiaoning; Liu, Xiaodong; Che, Huizheng

East Asian dust and its radiative feedbacks are analyzed by the use of the fourth version of the Community Atmosphere Model (CAM4) with a bulk aerosol model parameterization (BAM) for the dust size distribution (CAM4-BAM). Two numerical experiments are conducted and intercompared: one with (Active) and one without (Passive) the radiative effects of dust aerosols. This CAM4-BAM captures the main spatial distribution of the dust aerosol optical depth (AOD) and the dust surface concentrations over East Asia, with positive correlations with the local observational data on annual and seasonal means. A comparative analysis of the Active and Passive experiments revealsmore » that consideration of the dust-radiation interaction can significantly reduce dust emissions, loading, transport, and dry and wet depositions over East Asia, which is opposite to the enhanced dust cycle over North Africa. Further analysis of the contrasting dust-radiation feedbacks between North Africa and East Asia shows that over North Africa, the dust radiative forcing significantly increases the surface temperature and 10-m wind speed, whereas it decreases the surface temperature and the surface wind speeds over East Asia. These contrasting radiative effects, in turn, result in distinct dust cycle changes over these two regions. Thus, mechanistic analysis reveals that the radiative contrasts between East Asia and North Africa are mainly due to the differences in their regional surface albedo, dust vertical distribution and size distribution.« less

A simulation technique for 3D MR-guided acoustic radiation force imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Payne, Allison, E-mail: apayne@ucair.med.utah.edu; Bever, Josh de; Farrer, Alexis

2015-02-15

Purpose: In magnetic resonance-guided focused ultrasound (MRgFUS) therapies, the in situ characterization of the focal spot location and quality is critical. MR acoustic radiation force imaging (MR-ARFI) is a technique that measures the tissue displacement caused by the radiation force exerted by the ultrasound beam. This work presents a new technique to model the displacements caused by the radiation force of an ultrasound beam in a homogeneous tissue model. Methods: When a steady-state point-source force acts internally in an infinite homogeneous medium, the displacement of the material in all directions is given by the Somigliana elastostatic tensor. The radiation forcemore » field, which is caused by absorption and reflection of the incident ultrasound intensity pattern, will be spatially distributed, and the tensor formulation takes the form of a convolution of a 3D Green’s function with the force field. The dynamic accumulation of MR phase during the ultrasound pulse can be theoretically accounted for through a time-of-arrival weighting of the Green’s function. This theoretical model was evaluated experimentally in gelatin phantoms of varied stiffness (125-, 175-, and 250-bloom). The acoustic and mechanical properties of the phantoms used as parameters of the model were measured using independent techniques. Displacements at focal depths of 30- and 45-mm in the phantoms were measured by a 3D spin echo MR-ARFI segmented-EPI sequence. Results: The simulated displacements agreed with the MR-ARFI measured displacements for all bloom values and focal depths with a normalized RMS difference of 0.055 (range 0.028–0.12). The displacement magnitude decreased and the displacement pattern broadened with increased bloom value for both focal depths, as predicted by the theory. Conclusions: A new technique that models the displacements caused by the radiation force of an ultrasound beam in a homogeneous tissue model theory has been rigorously validated through comparison with experimentally obtained 3D displacement data in homogeneous gelatin phantoms using a 3D MR-ARFI sequence. The agreement of the experimentally measured and simulated results demonstrates the potential to use MR-ARFI displacement data in MRgFUS therapies.« less

The Indian ocean experiment: aerosol forcing obtained from satellite data

NASA Astrophysics Data System (ADS)

Rajeev, K.; Ramanathan, V.

The tropical Indian Ocean provides an ideal and unique natural laboratory to observe and understand the role of anthropogenic aerosols in climate forcing. Since 1996, an international team of American, European and Indian scientists have been collecting aerosol, chemical and radiation data from ships and surface stations, which culminated in a multi-platform field experiment conducted during January to March of 1999. A persistent haze layer that spread over most of the northern Indian Ocean during wintertime was discovered. The layer, a complex mix of organics, black carbon, sulfates, nitrates and other species, subjects the lower atmosphere to a strong radiative heating and a larger reduction in the solar heating of the ocean. We present here the regional distribution of aerosols and the resulting clear sky aerosol radiative forcing at top-of-atmosphere (TOA) observed over the Indian Ocean during the winter months of 1997, 1998 and 1999 based on the aerosol optical depth (AOD) estimated using NOAA14-AVHRR and the TOA radiation budget data from CERES on board TRMM. Using the ratio of surface to TOA clear sky aerosol radiative forcing observed during the same period over the Indian Ocean island of Kaashidhoo (Satheesh and Ramanathan, 2000), the clear sky aerosol radiative forcing at the surface and the atmosphere are discussed. The regional maps of AVHRR derived AOD show abnormally large aerosol concentration during the winter of 1999 which is about 1.5 to 2 times larger than the AOD during the corresponding period of 1997 and 1998. A large latitudinal gradient in AOD is observed during all the three years of observation, with maximum AOD in the northern hemisphere. The diurnal mean clear sky aerosol forcing at TOA in the northern hemisphere Indian Ocean is in the range of -4 to -16 Wm -2 and had large spatio-temporal variations while in the southern hemisphere Indian Ocean it is in the range of 0 to -6Wm -2. The importance of integrating in-situ data with satellite data to get reliable picture of the regional scale aerosol forcing is demonstrated.

A randomized controlled trial of gabapentin for chronic low back pain with and without a radiating component

PubMed Central

Atkinson, J. Hampton; Slater, Mark A.; Capparelli, Edmund V.; Patel, Shetal M.; Wolfson, Tanya; Gamst, Anthony; Abramson, Ian S.; Wallace, Mark S.; Funk, Stephen D.; Rutledge, Thomas R.; Wetherell, Julie Loebach; Matthews, Scott C.; Zisook, Sidney; Garfin, Steven R.

2016-01-01

Gabapentin is prescribed for analgesia in chronic low back pain, yet there are no controlled trials supporting this practice. This randomized, two-arm, 12-week, parallel group study compared gabapentin (forced titration up to 3600 mg daily) to inert placebo. The primary efficacy measure was change in pain intensity from baseline to the last week on treatment measured by the Descriptor Differential Scale; the secondary outcome was disability (Oswestry Disability Index). The intention-to-treat analysis comprised 108 randomized chronic back pain patients (daily pain for ≥ 6 months) whose pain did (43%) or did not radiate into the lower extremity. Random effects regression models which did not impute missing scores were used to analyze outcome data. Pain intensity decreased significantly over time (p < .0001) with subjects on gabapentin or placebo reporting reductions of about 30% from baseline, but did not differ significantly between groups (p = .423). The same results pertained for disability scores. In responder analyses of those who completed 12 weeks (N=72), the proportion reporting at least 30% or 50% reduction in pain intensity, or at least “Minimal Improvement” on the Physician Clinical Global Impression of Change did not differ significantly between groups. There were no significant differences in analgesia between participants with radiating (n = 46) and non-radiating (n = 62) pain either within or between treatment arms. There was no significant correlation between gabapentin plasma concentration and pain intensity. Gabapentin appears to be ineffective for analgesia in chronic low back pain with or without a radiating component. PMID:26963844

Anthropogenic aerosol optical and radiative properties in the typical urban/suburban regions in China

NASA Astrophysics Data System (ADS)

Gong, Chongshui; Xin, Jinyuan; Wang, Shigong; Wang, Yuesi; Zhang, Tiejun

2017-11-01

The effect of high anthropogenic aerosols on the aerosol optical and radiative properties was aggravated from west to east in China. The annual mean (from 2004 to 2007) aerosol optical depth (AOD), Ångström exponents (α), absorptive aerosol optical depth (AAOD), and single-scattering albedo (SSA) were from 0.16 to 0.73, from - 0.01 to 1.15, from 0.03 to 0.04, and from 0.78 to 0.94, respectively. In addition, the annual mean of aerosol direct radiative forcing at the top of the atmosphere (TOA) were from - 7.2 to 18.5 W/m2. High anthropogenic aerosol exhibited the effect of heating the atmosphere (ATM) (48-52 W/m2) and cooling the surface (SFC) (- 48 to - 56 W/m2) in eastern China. In Lanzhou where there is more serious pollution of heavy industry, aerosol-induced surface cooling reached - 61 W/m2. The radiative forcing was higher in winter and spring than that in summer and autumn. Aerosol heating effect on the atmosphere was obvious; there was significantly linear correlation between AOD and TOA, SSA and TOA. The slopes of AOD vs TOA were from - 20.8 to - 42.6. The slopes of SSA vs TOA were from - 58 to - 302. The aerosol was cooling the Earth-atmosphere system with AOD or SSA increasing. In the meantime, AAOD (x) exhibited significantly linear correlation with the heating effect in the atmosphere (ATM: y) (y = 1053.7x + 10.5, R2 = 0.85). And the effect of AOD (x) on the SFC (y) cooling was also obvious (y = - 47.1x - 24.5, R2 = 0.56). Therefore, the thermodynamic effects of anthropogenic aerosols on the atmosphere circulation and structure should be taken into consideration in East Asia.

Changes in Light Absorptivity of Molecular Weight Separated Brown Carbon Due to Photolytic Aging.

PubMed

Wong, Jenny P S; Nenes, Athanasios; Weber, Rodney J

2017-08-01

Brown carbon (BrC) consists of those organic compounds in atmospheric aerosols that absorb solar radiation and may play an important role in planetary radiative forcing and climate. However, little is known about the production and loss mechanisms of BrC in the atmosphere. Here, we study how the light absorptivity of BrC from wood smoke and secondary BrC generated from the reaction of ammonium sulfate with methylglyoxal changes under photolytic aging by UVA radiation in the aqueous phase. Owing to its chemical complexity, BrC is separated by molecular weight using size exclusion chromatography, and the response of each molecular weight fraction to aging is studied. Photolytic aging induced significant changes in the light absorptivity of BrC for all molecular weight fractions; secondary BrC was rapidly photoblenched, whereas for wood smoke BrC, both photoenhancement and photobleaching were observed. Initially, large biomass burning BrC molecules were rapidly photoenhanced, followed by slow photolysis. As a result, large BrC molecules dominated the total light absorption of aged biomass burning BrC. These experimental results further support earlier observations that large molecular weight BrC compounds from biomass burning can be relatively long-lived components in atmospheric aerosols, thus more likely to have larger impacts on aerosol radiative forcing and could serve as biomass burning tracers.

A-Train Aerosol Observations Preliminary Comparisons with AeroCom Models and Pathways to Observationally Based All-Sky Estimates

NASA Technical Reports Server (NTRS)

Redemann, J.; Livingston, J.; Shinozuka, Y.; Kacenelenbogen, M.; Russell, P.; LeBlanc, S.; Vaughan, M.; Ferrare, R.; Hostetler, C.; Rogers, R.;

Radiation-induced changes in gustatory function comparison of effects of neutron and photon irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mossman, K.L.; Chencharick, J.D.; Scheer, A.C.

1979-04-01

Changes in gustatory function were measured in 51 patients with various forms of cancer who received radiation to the head and neck region. Forty patients (group I) were treated with conventional photon radiation (e.g. 66 Gy/7 weeks), and 11 patients (group II) were treated with cyclotron produced fast neutrons (e.g. 22 Gy/7 weeks). Taste acuity was measured for four taste qualities (salt, sweet, sour, and bitter) by a forced choice-three stimulus drop technique which measured detection and recognition thresholds and by a forced scaling technique which measured taste intensity responsiveness. Subjective complaints of anorexia, dysgeusia, taste loss, and xerostomia weremore » also recorded. Patients were studied before, during and up to two months after therapy. Prior to therapy, detection and recognition thresholds, intensity responsiveness, and the frequency of subjective complaints in patients from groups I and II were statistically equivalent. During and up to 2 months after therapy, taste impairment and frequency of subjective complaints increased significantly in neutron and photon treated patients, but were statistically equivalent. Results of this study indicate that gustatory tissue response as measured by taste detection and recognition and intensity responsiveness, and the frequency of subjective complaints related to taste are statistically equivalent in patients before, during, or up 2 months after they were given either neutron or photon radiation for tumors of the head and neck.« less

Quantifying the impact of smoke aerosol on the UV radiation

NASA Astrophysics Data System (ADS)

Sokolik, I. N.; Tatarskii, V.; Hall, S. R.; Petropavlovskikh, I. V.

2017-12-01

We present an analysis of the impact of smoke on the UV radiation. The analysis is performed for a case study by combining the modeling and measurements. The case study is focusing in wildfires occurred in California in ????. The fires have been affecting the environment in the region, posing a serious threat to the human well - being.The modeling is performed using a fully couple WRF- Chem- SMOKE model. The model uses the FRP MODIS satellite data to generate the smoke emission for an actual event. The smoke aerosol is treated in a size and composition resolved manner. The optical properties are computed online and provided to the TUV model that is incorporated in the WRF - Chem-SMOKE model. The analysis of the impact of smoke on the UV radiation is performed. We assess the impact of smoke on the TOA radiative forcing. Our results show a significant impact of smoke on the radiative regime of the atmosphere.

[Standards and guidelines of radiation protection and safety in dental X-ray examinations].

PubMed

Guo, X L; Li, G; Cheng, Y; Yu, Q; Wang, H; Zhang, Z Y

2017-12-09

With the rapid development of imaging technology, the application of dental imaging in diagnosis, treatment planning, intraoperative surgical navigation, monitoring of treatment or lesion development and assessment of treatment outcomes is playing an essential role in oral healthcare. The increased total number of dental X-ray examinations is accompanied by a relatively significant increase in collective dose to patients as well as to dental healthcare workers, which is harmful to human bodies to a certain degree. Some radiation protection standards and guidelines in dental radiology have been published in European countries, US, Canada and Australia, etc. Adherence to these standards and guidelines helps to achieve images with diagnostic quality and avoid unnecessary and repeated exposures. However, no radiation protection standard or guideline with regard to dental X-ray examinations has been put in force so far in mainland China. Therefore, a literature review on available radiation protection standards and guidelines was conducted to provide reference to the development of radiation protection standards or guidelines in mainland China.

Estimation of the global climate effect of brown carbon

NASA Astrophysics Data System (ADS)

Zhang, A.; Wang, Y.; Zhang, Y.; Weber, R. J.; Song, Y.

2017-12-01

Carbonaceous aerosols significantly affect global radiative forcing and climate through absorption and scattering of sunlight. Black carbon (BC) and brown carbon (BrC) are light-absorbing carbonaceous aerosols. The global distribution and climate effect of BrC is uncertain. A recent study suggests that BrC absorption is comparable to BC in the upper troposphere over biomass burning region and that the resulting heating tends to stabilize the atmosphere. Yet current climate models do not include proper treatments of BrC. In this study, we derived a BrC global biomass burning emission inventory from Global Fire Emissions Database 4 (GFED4) and developed a BrC module in the Community Atmosphere Model version 5 (CAM5) of Community Earth System Model (CESM) model. The model simulations compared well to BrC observations of the Studies of Emissions, Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS) and Deep Convective Clouds and Chemistry Project (DC-3) campaigns and includes BrC bleaching. Model results suggested that BrC in the upper troposphere due to convective transport is as important an absorber as BC globally. Upper tropospheric BrC radiative forcing is particularly significant over the tropics, affecting the atmosphere stability and Hadley circulation.

Economic Value of Narrowing the Uncertainty in Climate Sensitivity: Decadal Change in Shortwave Cloud Radiative Forcing and Low Cloud Feedback

NASA Astrophysics Data System (ADS)

Wielicki, B. A.; Cooke, R. M.; Golub, A. A.; Mlynczak, M. G.; Young, D. F.; Baize, R. R.

2016-12-01

Several previous studies have been published on the economic value of narrowing the uncertainty in climate sensitivity (Cooke et al. 2015, Cooke et al. 2016, Hope, 2015). All three of these studies estimated roughly 10 Trillion U.S. dollars for the Net Present Value and Real Option Value at a discount rate of 3%. This discount rate is the nominal discount rate used in the U.S. Social Cost of Carbon Memo (2010). The Cooke et al studies approached this problem by examining advances in accuracy of global temperature measurements, while the Hope 2015 study did not address the type of observations required. While temperature change is related to climate sensitivity, large uncertainties of a factor of 3 in current anthropogenic radiative forcing (IPCC, 2013) would need to be solved for advanced decadal temperature change observations to assist the challenge of narrowing climate sensitivity. The present study takes a new approach by extending the Cooke et al. 2015,2016 papers to replace observations of temperature change to observations of decadal change in the effects of changing clouds on the Earths radiative energy balance, a measurement known as Cloud Radiative Forcing, or Cloud Radiative Effect. Decadal change in this observation is direclty related to the largest uncertainty in climate sensitivity which is cloud feedback from changing amount of low clouds, primarily low clouds over the world's oceans. As a result, decadal changes in shortwave cloud radiative forcing are more directly related to cloud feedback uncertainty which is the dominant uncertainty in climate sensitivity. This paper will show results for the new approach, and allow an examination of the sensitivity of economic value results to different observations used as a constraint on uncertainty in climate sensitivity. The analysis suggests roughly a doubling of economic value to 20 Trillion Net Present Value or Real Option Value at 3% discount rate. The higher economic value results from two changes: a larger increase in accuracy for SW cloud radiative forcing vs temperature, and from a lower confounding noise from natural variability in the cloud radiative forcing variable compared to temperature. In particular, global average temperature is much more sensitive to the climate noise of ENSO cycles.

First Global Estimates of Anthropogenic Shortwave Forcing by Methane

NASA Astrophysics Data System (ADS)

Collins, William; Feldman, Daniel; Kuo, Chaincy

2017-04-01

Although the primary well-mixed greenhouse gases (WMGHGs) absorb both shortwave and longwave radiation, to date assessments of the effects from human-induced increases in atmospheric concentrations of WMGHGs have focused almost exclusively on quantifying the longwave radiative forcing of these gases. However, earlier studies have shown that the shortwave effects of WMGHGs are comparable to many less important longwave forcing agents routinely in these assessments, for example the effects of aircraft contrails, stratospheric anthropogenic methane, and stratospheric water vapor from the oxidation of this methane. These earlier studies include the Radiative Transfer Model Intercomparison Project (RTMIP; Collins et al. 2006) conducted using line-by-line radiative transfer codes as well as the radiative parameterizations from most of the global climate models (GCMs) assembled for the Coupled Model Intercomparison Project (CMIP-3). In this talk, we discuss the first global estimates of the shortwave radiative forcing by methane due to the anthropogenic increase in CH4 between pre-industrial and present-day conditions. This forcing is a balance between reduced heating due to absorption of downwelling sunlight in the stratosphere and increased heating due to absorption of upwelling sunlight reflected from the surface as well clouds and aerosols in the troposphere. These estimates are produced using the Observing System Simulation Experiment (OSSE) framework we have developed for NASA's upcoming Climate Absolute Radiance and Refractivity Observatory (CLARREO) mission. The OSSE is designed to compute the monthly mean shortwave radiative forcing based upon global gridded atmospheric and surface conditions extracted from either the meteorological reanalyses collected for the Analysis for MIPs (Ana4MIPs) or the CMIP-5 multi-GCM archive analyzed in the Fifth Assessment Report (AR-5) of the Intergovernmental Panel on Climate Change (IPCC). The OSSE combines these atmospheric conditions with an observationally derived prescription for the Earth's spectral surface albedo as inputs to the MODerate resolution atmospheric TRANsmission (MODTRAN) code. MODTRAN is designed to model atmospheric propagation of electromagnetic radiation for the 100-50,000 1/cm (0.2 to 100 micrometers) spectral range. This covers the spectrum from middle ultraviolet to visible light to far infrared. The most recently released version of the code, MODTRAN6, provides a spectral resolution of 0.2 1/cm using its 0.1 1/cm band model algorithm.

Cloud Forcing and the Earth's Radiation Budget: New Ideas and New Observations

NASA Technical Reports Server (NTRS)

Barkstrom, Bruce R.

1997-01-01

1. NEW PERSPECTIVES ON CLOUD-RADIATIVE FORCING. When the Earth Radiation Budget Experiment (ERBE) produced the first measurements of cloud-radiative forcing, the climate community interpreted the results from a context in which the atmosphere was a single column, strongly coupled to the Earth's surface. 2. NEW PERSPECTIVES ON CLOUD-RADIATION OBSERVATIONS. The climate community is also on the verge of adding a new dimension to its observational capability. In classic thinking about atmospheric circulation and climate, surface pressure was a readily available quantity. As meteorology developed, it was possible to develop quantitative predictions of future weather by bringing together a network of surface pressure observations and then of profiles of temperature and humidity obtained from balloons. 3. ON COMBINING OBSERVATIONS AND THE - ORY. With this new capability, it is natural to seek recognizable features in the observations we make of the Earth. There are techniques we can use to group the remotely sensed data in the individual footprints into objects that we can track. We will present one such image-processing application to radiation budget data, showing how we can interpret the radiation budget data in terms of cloud systems that are organized into systematic patterns of behavior - an ecosystem-like view of cloud behavior.

Parametric Investigation of the Effect of Hub Pitching Moment on Blade Vortex Interaction (BVI) Noise of an Isolated Rotor

NASA Technical Reports Server (NTRS)

Malpica, Carlos; Greenwood, Eric; Sim, Ben

2016-01-01

At the most fundamental level, main rotor loading noise is caused by the harmonically-varying aerodynamic loads (acoustic pressures) exerted by the rotating blades on the air. Rotorcraft main rotor noise is therefore, in principle, a function of rotor control inputs, and thus the forces and moments required to achieve steady, or "trim", flight equilibrium. In certain flight conditions, the ensuing aerodynamic loading on the rotor(s) can result in highly obtrusive harmonic noise. The effect of the propulsive force, or X-force, on Blade-Vortex Interaction (BVI) noise is well documented. This paper presents an acoustics parametric sensitivity analysis of the effect of varying rotor aerodynamic pitch hub trim moments on BVI noise radiated by an S-70 helicopter main rotor. Results show that changing the hub pitching moment for an isolated rotor, trimmed in nominal 80 knot, 6 and 12 deg descent, flight conditions, alters the miss distance between the blades and the vortex in ways that have varied and noticeable effects on the BVI radiated-noise directionality. Peak BVI noise level is however not significantly altered. The application of hub pitching moment allows the attitude of the fuselage to be controlled; for example, to compensate for the uncomfortable change in fuselage pitch attitude introduced by a fuselage-mounted X-force controller.

Numerical Computation of Flame Spread over a Thin Solid in Forced Concurrent Flow with Gas-phase Radiation

NASA Technical Reports Server (NTRS)

Jiang, Ching-Biau; T'ien, James S.

1994-01-01

Excerpts from a paper describing the numerical examination of concurrent-flow flame spread over a thin solid in purely forced flow with gas-phase radiation are presented. The computational model solves the two-dimensional, elliptic, steady, and laminar conservation equations for mass, momentum, energy, and chemical species. Gas-phase combustion is modeled via a one-step, second order finite rate Arrhenius reaction. Gas-phase radiation considering gray non-scattering medium is solved by a S-N discrete ordinates method. A simplified solid phase treatment assumes a zeroth order pyrolysis relation and includes radiative interaction between the surface and the gas phase.

Theory of acoustic radiation pressure for actual fluids

NASA Astrophysics Data System (ADS)

Doinikov, Alexander A.

1996-12-01

A body irradiated by a sound field is known to experience a steady force that is called the acoustic radiation pressure. This force plays an important role in many physical phenomena, such as cavitation, sonoluminescence, acoustic levitation, etc. The existing theory of acoustic radiation pressure neglects dissipative effects. The present paper develops a theory that takes these effects into account, both dissipative mechanisms, viscous and thermal, being considered. It is shown that, when they are no longer negligible, the dissipative effects drastically change the radiation pressure. As a result, its magnitude and sign become different from those predicted by the ``classical'' theory neglecting losses.

Relative Contributions of Regional and Sector Emissions to the Radiative Forcing of Aerosol-Radiation and Aerosol-Cloud Interactions Based on the AeroCOM Phase III/HTAP2 Experiment

NASA Astrophysics Data System (ADS)

Takemura, T.; Chin, M.

2014-12-01

It is important to understand relative contributions of each regional and sector emission of aerosols and their precursor gases to the regional and global mean radiative forcing of aerosol-radiation and aerosol-cloud interactions. This is because it is useful for international cooperation on controls of air pollution and anthropogenic climate change along most suitable reduction path of their emissions from each region and sector. The Task Force on Hemispheric Transport of Air Pollution (TF HTAP) under the United Nations researches the intercontinental transport of air pollutants including aerosols with strong support of the Aerosol Comparisons between Observations and Models (AeroCOM). The ongoing AeroCOM Phase III/HTAP2 experiment assesses relative contributions of regional and sector sources of aerosols and their precursor gases to the air quality using global aerosol transport models with latest emission inventories. In this study, the extended analyses on the relative contributions of each regional and sector emission to the radiative forcing of aerosol-radiation and aerosol-cloud interactions are done from the AeroCOM Phase III/HTAP2 experiment. Simulated results from MIROC-SPRINTARS and other some global aerosol models participating in the the AeroCOM Phase III/HTAP2 experiment are assessed. Acknowledgements: This study is based on the AeroCOM Phase III/HTAP2 experiment and partly supported by the Environment Research and Technology Development Fund (S-12-3) of the Ministry of the Environment, Japan.

Direct Aerosol Radiative Forcing from Combined A-Train Observations - Preliminary Comparisons with AeroCom Models and Pathways to Observationally Based All-sky Estimates

NASA Astrophysics Data System (ADS)

Redemann, J.; Livingston, J. M.; Shinozuka, Y.; Kacenelenbogen, M. S.; Russell, P. B.; LeBlanc, S. E.; Vaughan, M.; Ferrare, R. A.; Hostetler, C. A.; Rogers, R. R.; Burton, S. P.; Torres, O.; Remer, L. A.; Stier, P.; Schutgens, N.

2014-12-01

We describe a technique for combining CALIOP aerosol backscatter, MODIS spectral AOD (aerosol optical depth), and OMI AAOD (absorption aerosol optical depth) retrievals for the purpose of estimating full spectral sets of aerosol radiative properties, and ultimately for calculating the 3-D distribution of direct aerosol radiative forcing. We present results using one year of data collected in 2007 and show comparisons of the aerosol radiative property estimates to collocated AERONET retrievals. Use of the recently released MODIS Collection 6 data for aerosol optical depths derived with the dark target and deep blue algorithms has extended the coverage of the multi-sensor estimates towards higher latitudes. Initial calculations of seasonal clear-sky aerosol radiative forcing based on our multi-sensor aerosol retrievals compare well with over-ocean and top of the atmosphere IPCC-2007 model-based results, and with more recent assessments in the "Climate Change Science Program Report: Atmospheric Aerosol Properties and Climate Impacts" (2009). For the first time, we present comparisons of our multi-sensor aerosol direct radiative forcing estimates to values derived from a subset of models that participated in the latest AeroCom initiative. We discuss the major challenges that exist in extending our clear-sky results to all-sky conditions. On the basis of comparisons to suborbital measurements, we present some of the limitations of the MODIS and CALIOP retrievals in the presence of adjacent or underlying clouds. Strategies for meeting these challenges are discussed.

Determination of the viscous acoustic field for liquid drop positioning/forcing in an acoustic levitation chamber in microgravity

NASA Technical Reports Server (NTRS)

Lyell, Margaret J.

1992-01-01

The development of acoustic levitation systems has provided a technology with which to undertake droplet studies as well as do containerless processing experiments in a microgravity environment. Acoustic levitation chambers utilize radiation pressure forces to position/manipulate the drop. Oscillations can be induced via frequency modulation of the acoustic wave, with the modulated acoustic radiation vector acting as the driving force. To account for tangential as well as radial forcing, it is necessary that the viscous effects be included in the acoustic field. The method of composite expansions is employed in the determination of the acoustic field with viscous effects.

GNSS orbit determination by precise modeling of non-gravitational forces acting on satellite's body

NASA Astrophysics Data System (ADS)

Wielgosz, Agata; Kalarus, Maciej; Liwosz, Tomasz

2016-04-01

Satellites orbiting around Earth are affected by gravitational forces and non-gravitational perturbations (NGP). While the perturbations caused by gravitational forces, which are due to central body gravity (including high-precision geopotential field) and its changes (due to secular variations and tides), solar bodies attraction and relativistic effects are well-modeled, the perturbations caused by the non-gravitational forces are the most limiting factor in Precise Orbit Determination (POD). In this work we focused on very precise non-gravitational force modeling for medium Earth orbit satellites by applying the various models of solar radiation pressure including changes in solar irradiance and Earth/Moon shadow transition, Earth albedo and thermal radiation. For computing influence of aforementioned forces on spacecraft the analytical box-wing satellite model was applied. Smaller effects like antenna thrust or spacecraft thermal radiation were also included. In the process of orbit determination we compared the orbit with analytically computed NGP with the standard procedure in which CODE model is fitted for NGP recovery. We considered satellites from several systems and on different orbits and for different periods: when the satellite is all the time in full sunlight and when transits the umbra and penumbra regions.

Deformation of red blood cells using acoustic radiation forces

PubMed Central

Mishra, Puja; Hill, Martyn; Glynne-Jones, Peter

2014-01-01

Acoustic radiation forces have been used to manipulate cells and bacteria in a number of recent microfluidic applications. The net force on a cell has been subject to careful investigation over a number of decades. We demonstrate that the radiation forces also act to deform cells. An ultrasonic standing wave field is created in a 0.1 mm glass capillary at a frequency of 7.9 MHz. Using osmotically swollen red-blood cells, we show observable deformations up to an aspect ratio of 1.35, comparable to deformations created by optical tweezing. In contrast to optical technologies, ultrasonic devices are potentially capable of deforming thousands of cells simultaneously. We create a finite element model that includes both the acoustic environment of the cell, and a model of the cell membrane subject to forces resulting from the non-linear aspects of the acoustic field. The model is found to give reasonable agreement with the experimental results, and shows that the deformation is the result of variation in an acoustic force that is directed outwards at all points on the cell membrane. We foresee applications in diagnostic devices, and in the possibility of mechanically stimulating cells to promote differentiation and physiological effects. PMID:25379070

Ponderomotive force on solitary structures created during radiation pressure acceleration of thin foils

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tripathi, Vipin K.; Sharma, Anamika

2013-05-15

We estimate the ponderomotive force on an expanded inhomogeneous electron density profile, created in the later phase of laser irradiated diamond like ultrathin foil. When ions are uniformly distributed along the plasma slab and electron density obeys the Poisson's equation with space charge potential equal to negative of ponderomotive potential, φ=−φ{sub p}=−(mc{sup 2}/e)(γ−1), where γ=(1+|a|{sup 2}){sup 1/2}, and |a| is the normalized local laser amplitude inside the slab; the net ponderomotive force on the slab per unit area is demonstrated analytically to be equal to radiation pressure force for both overdense and underdense plasmas. In case electron density is takenmore » to be frozen as a Gaussian profile with peak density close to relativistic critical density, the ponderomotive force has non-monotonic spatial variation and sums up on all electrons per unit area to equal radiation pressure force at all laser intensities. The same result is obtained for the case of Gaussian ion density profile and self consistent electron density profile, obeying Poisson's equation with φ=−φ{sub p}.« less

Linkages Between Ozone-depleting Substances, Tropospheric Oxidation and Aerosols

NASA Technical Reports Server (NTRS)

Voulgarakis, A.; Shindell, D. T.; Faluvegi, G.

2013-01-01

Coupling between the stratosphere and the troposphere allows changes in stratospheric ozone abundances to affect tropospheric chemistry. Large-scale effects from such changes on chemically produced tropospheric aerosols have not been systematically examined in past studies. We use a composition-climate model to investigate potential past and future impacts of changes in stratospheric ozone depleting substances (ODS) on tropospheric oxidants and sulfate aerosols. In most experiments, we find significant responses in tropospheric photolysis and oxidants, with small but significant effects on methane radiative forcing. The response of sulfate aerosols is sizeable when examining the effect of increasing future nitrous oxide (N2O) emissions. We also find that without the regulation of chlorofluorocarbons (CFCs) through the Montreal Protocol, sulfate aerosols could have increased by 2050 by a comparable amount to the decreases predicted due to relatively stringent sulfur emissions controls. The individual historical radiative forcings of CFCs and N2O through their indirect effects on methane (-22.6mW/sq. m for CFCs and -6.7mW/sq. m for N2O) and sulfate aerosols (-3.0mW/sq. m for CFCs and +6.5mW/sq. m for N2O when considering the direct aerosol effect) discussed here are non-negligible when compared to known historical ODS forcing. Our results stress the importance of accounting for stratosphere-troposphere, gas-aerosol and composition-climate interactions when investigating the effects of changing emissions on atmospheric composition and climate.

Response to marine cloud brightening in a multi-model ensemble

NASA Astrophysics Data System (ADS)

Stjern, Camilla W.; Muri, Helene; Ahlm, Lars; Boucher, Olivier; Cole, Jason N. S.; Ji, Duoying; Jones, Andy; Haywood, Jim; Kravitz, Ben; Lenton, Andrew; Moore, John C.; Niemeier, Ulrike; Phipps, Steven J.; Schmidt, Hauke; Watanabe, Shingo; Egill Kristjánsson, Jón

2018-01-01

Here we show results from Earth system model simulations from the marine cloud brightening experiment G4cdnc of the Geoengineering Model Intercomparison Project (GeoMIP). The nine contributing models prescribe a 50 % increase in the cloud droplet number concentration (CDNC) of low clouds over the global oceans in an experiment dubbed G4cdnc, with the purpose of counteracting the radiative forcing due to anthropogenic greenhouse gases under the RCP4.5 scenario. The model ensemble median effective radiative forcing (ERF) amounts to -1.9 W m-2, with a substantial inter-model spread of -0.6 to -2.5 W m-2. The large spread is partly related to the considerable differences in clouds and their representation between the models, with an underestimation of low clouds in several of the models. All models predict a statistically significant temperature decrease with a median of (for years 2020-2069) -0.96 [-0.17 to -1.21] K relative to the RCP4.5 scenario, with particularly strong cooling over low-latitude continents. Globally averaged there is a weak but significant precipitation decrease of -2.35 [-0.57 to -2.96] % due to a colder climate, but at low latitudes there is a 1.19 % increase over land. This increase is part of a circulation change where a strong negative top-of-atmosphere (TOA) shortwave forcing over subtropical oceans, caused by increased albedo associated with the increasing CDNC, is compensated for by rising motion and positive TOA longwave signals over adjacent land regions.

Oscillatory radiatively-forced internal convection

NASA Astrophysics Data System (ADS)

Llewellyn Smith, Stefan

2017-11-01

Internal convection, in which stably stratified fluid is destabilized by internal heating, shows interesting differences from the canonical situation of Rayleigh-Benard convection with forcing at the boundaries. We consider the case when the thermal forcing is the result of radiative heating, yielding an exponential profile in the vertical, rather than a uniformly distributed source of buoyancy, and when the forcing is oscillatory in time. These two effects do not appear to have been treated together previously. We examine the linear instability problem considering steady, harmonic and more general periodic forcings. We also discuss nonlinear effects. The underlying problem is relevant to Springtime heating in the Great Lakes, in which case heating destabilizes the water column because the temperature is in the anomalous regime when water becomes denser with heating.

Evaluation of Dust Absorption and Radiative Forcing of Climate Using Satellite and Ground Based Remote Sensing

NASA Technical Reports Server (NTRS)

Kaufman, Yoram J.

1999-01-01

Simultaneous spaceborne and ground based measurements of the scattered solar radiation, create a powerful tool for determination of dust absorption. Absorption of solar radiation is a key component in understanding dust impact on radiative forcing at the top of the atmosphere, on the temperature profile and on cloud formation. We use Landsat spaceborne measurements at seven spectral channels in the range of 0.47 to 2.2 microns over Senegal with corresponding measurements of the aerosol spectral optical thickness by ground based sunphotometers, to find that Saharan dust absorption of solar radiation is two to four times smaller than measured in situ and represented in models. Though dust was found to absorb in the blue (single scattering albedo wo = 0.88), almost no absorption, wo = 0.98, was found for 1 greater than 0.6 microns. The results are in agreement with dust radiative measurements reported in the literature, and explain some previously reported but unexplained dust radiative properties. Therefore, the new finding should be of general relevance. The new finding increases by 50% recently estimated solar radiative forcing by dust at the top of the atmosphere and decreases the estimated dust heating of the lower troposphere due to absorption of solar radiation. Dust transported from Asia shows slightly higher absorption for wavelengths under 1 @im, that can be explained by the presence of black carbon from urban/industrial pollution associated with the submicron size mode.

Influence of inhomogeneous surface heat capacity on the estimation of radiative response coefficients in a two-zone energy balance model

NASA Astrophysics Data System (ADS)

Park, Jungmin; Choi, Yong-Sang

2018-04-01

Observationally constrained values of the global radiative response coefficient are pivotal to assess the reliability of modeled climate feedbacks. A widely used approach is to measure transient global radiative imbalance related to surface temperature changes. However, in this approach, a potential error in the estimate of radiative response coefficients may arise from surface inhomogeneity in the climate system. We examined this issue theoretically using a simple two-zone energy balance model. Here, we dealt with the potential error by subtracting the prescribed radiative response coefficient from those calculated within the two-zone framework. Each zone was characterized by the different magnitude of the radiative response coefficient and the surface heat capacity, and the dynamical heat transport in the atmosphere between the zones was parameterized as a linear function of the temperature difference between the zones. Then, the model system was forced by randomly generated monthly varying forcing mimicking time-varying forcing like an observation. The repeated simulations showed that inhomogeneous surface heat capacity causes considerable miscalculation (down to -1.4 W m-2 K-1 equivalent to 31.3% of the prescribed value) in the global radiative response coefficient. Also, the dynamical heat transport reduced this miscalculation driven by inhomogeneity of surface heat capacity. Therefore, the estimation of radiative response coefficients using the surface temperature-radiation relation is appropriate for homogeneous surface areas least affected by the exterior.

The Impact of Aerosol Microphysical Representation in Models on the Direct Radiative Effect

NASA Astrophysics Data System (ADS)

Ridley, D. A.; Heald, C. L.

2017-12-01

Aerosol impacts the radiative balance of the atmosphere both directly and indirectly. There is considerable uncertainty remaining in the aerosol direct radiative effect (DRE), hampering understanding of the present magnitude of anthropogenic aerosol forcing and how future changes in aerosol loading will influence climate. Computationally expensive explicit aerosol microphysics are usually reserved for modelling of the aerosol indirect radiative effects that depend upon aerosol particle number. However, the direct radiative effects of aerosol are also strongly dependent upon the aerosol size distribution, especially particles between 0.2µm - 2µm diameter. In this work, we use a consistent model framework and consistent emissions to explore the impact of prescribed size distributions (bulk scheme) relative to explicit microphysics (sectional scheme) on the aerosol radiative properties. We consider the difference in aerosol burden, water uptake, and extinction efficiency resulting from the two representations, highlighting when and where the bulk and sectional schemes diverge significantly in their estimates of the DRE. Finally, we evaluate the modelled size distributions using in-situ measurements over a range of regimes to provide constraints on both the accumulation and coarse aerosol sizes.

Intense acoustic bursts as a signal-enhancement mechanism in ultrasound-modulated optical tomography.

PubMed

Kim, Chulhong; Zemp, Roger J; Wang, Lihong V

2006-08-15

Biophotonic imaging with ultrasound-modulated optical tomography (UOT) promises ultrasonically resolved imaging in biological tissues. A key challenge in this imaging technique is a low signal-to-noise ratio (SNR). We show significant UOT signal enhancement by using intense time-gated acoustic bursts. A CCD camera captured the speckle pattern from a laser-illuminated tissue phantom. Differences in speckle contrast were observed when ultrasonic bursts were applied, compared with when no ultrasound was applied. When CCD triggering was synchronized with burst initiation, acoustic-radiation-force-induced displacements were detected. To avoid mechanical contrast in UOT images, the CCD camera acquisition was delayed several milliseconds until transient effects of acoustic radiation force attenuated to a satisfactory level. The SNR of our system was sufficiently high to provide an image pixel per acoustic burst without signal averaging. Because of the substantially improved SNR, the use of intense acoustic bursts is a promising signal enhancement strategy for UOT.

Radiative amplification of sound waves in the winds of O and B stars

NASA Technical Reports Server (NTRS)

Macgregor, K. B.; Hartmann, L.; Raymond, J. C.

1979-01-01

The velocity perturbation associated with an outwardly propagating sound wave in a radiation-driven stellar wind gives rise to a periodic Doppler shifting of absorption lines formed in the flow. A linearized theory applicable to optically thin waves is used to show that the resulting fluctuation in the absorption-line force can cause the wave amplitude to grow. Detailed calculations of the acceleration due to a large number of lines indicate that significant amplification can occur throughout the high-velocity portion of winds in which the dominant force-producing lines have appreciable optical depths. In the particular case of the wind of Zeta Pup (O4f), it is found that the e-folding distance for wave growth is considerably shorter than the scale lengths over which the physical properties of the flow vary. A qualitative estimate of the rate at which mechanical energy due to nonlinear waves can be dissipated suggests that this mechanism may be important in heating the supersonic portion of winds of early-type stars.

Radioactive fallout projections and arms control agreements: INF (Intermediate-range Nuclear Forces) and START (Strategic Arms Reduction Treaty)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shapiro, C.S.

1988-02-01

Projections of levels of radioactive fallout from a nuclear war are sensitive to assumptions about the structure of the nuclear stockpiles as well as the assumed scenarios for a nuclear war. Recent arms control proposals would change these parameters. This paper examines the implications of the proposed (Intermediate-range Nuclear Forces) INF treaty and (Strategic Arms Reduction Treaty) START on fallout projections from a major nuclear war. We conclude that the INF reductions are likely to have negligible effects on estimates of global and local fallout, whereas the START reductions could result in reductions in estimates of local fallout that rangemore » from significant to dramatic, depending upon the nature of the reduced strategic forces. Should a major war occur, projections of total fatalities from direct effects of blast, thermal radiation, a nd fallout, and the phenomenon known as nuclear winter, would not be significantly affected by INF and START initiatives as now drafted. 14 refs.« less

Air Circulation and Heat Exchange Under Reduced Pressures

NASA Technical Reports Server (NTRS)

Rygalov, V.; Wheeler, R.; Dixon, M.; Fowler, P.; Hillhouse, L.

2010-01-01

Heat exchange rates decrease non-linearly with reductions in atmospheric pressure. This decrease creates risk of thermal stress (elevated leaf temperatures) for plants under reduced pressures. Forced convection (fans) significantly increases heat exchange rate under almost all pressures except below 10 kPa. Plant cultivation techniques under reduced pressures will require forced convection. The cooling curve technique is a reliable means of assessing the influence of environmental variables like pressure and gravity on gas exchange of plant. These results represent the extremes of gas exchange conditions for simple systems under variable pressures. In reality, dense plant canopies will exhibit responses in between these extremes. More research is needed to understand the dependence of forced convection on atmospheric pressure. The overall thermal balance model should include latent and radiative exchange components.

Potential theory of radiation

NASA Technical Reports Server (NTRS)

Chiu, Huei-Huang

1989-01-01

A theoretical method is being developed by which the structure of a radiation field can be predicted by a radiation potential theory, similar to a classical potential theory. The introduction of a scalar potential is justified on the grounds that the spectral intensity vector is irrotational. The vector is also solenoidal in the limits of a radiation field in complete radiative equilibrium or in a vacuum. This method provides an exact, elliptic type equation that will upgrade the accuracy and the efficiency of the current CFD programs required for the prediction of radiation and flow fields. A number of interesting results emerge from the present study. First, a steady state radiation field exhibits an optically modulated inverse square law distribution character. Secondly, the unsteady radiation field is structured with two conjugate scalar potentials. Each is governed by a Klein-Gordon equation with a frictional force and a restoring force. This steady potential field structure and the propagation of radiation potentials are consistent with the well known results of classical electromagnetic theory. The extension of the radiation potential theory for spray combustion and hypersonic flow is also recommended.

Climate Effect of Greenhouse Gas: Warming or Cooling is Determined by Temperature Gradient

NASA Astrophysics Data System (ADS)

Shia, R.

2011-12-01

The instantaneous radiative forcing (IRF) at the top of the atmosphere (ToA) is the initial change of the total energy in the climate system when the concentration of greenhouse gas (GHG) increases. In my previous presentation at the 2010 Fall AGU meeting (A11J-02, "Mechanism of Radiative Forcing of Greenhouse Gas its Implication to the Global Warming"), it was demonstrated that IRF at TOA is generated by moving up of the emission weighting function. Thus, the temperature gradient plays a critical role in determining the climate effect of GHG. In this presentation the change of the outgoing infrared radiation flux at ToA is studied from a perturbation point of view. After the cancellation between the changes in the outgoing radiation flux from the surface emission and from the reemission of the atmosphere, the derivative of the outgoing flux to the concentration of GHG is found to be proportional to the temperature gradients below the level where the concentration of GHG changes. Therefore, the greenhouse gas contribute only to the magnitude of the radiative forcing, the temperature gradients decide the direction of the radiative forcing, i.e. warming or cooling, in addition to contributing to its magnitude. In response to the question "Does the negative IRF at ToA lead to the surface cooling or it only cools the upper part of the atmosphere?" the Eddington grey radiative equilibrium model is modified to simulate different scenarios. The original model has been used to illustrate the warming effect of GHG in textbooks of the atmospheric physics. It is modified by adding source terms from the absorption of the solar flux and the internal energy exchange in the atmosphere. In two cases the modified model generates atmospheres with a large and warm stratosphere and negative IRF at ToA when GHG increases by 25%. This negative radiative forcing can lead to the cooling of the atmosphere all the way down to the surface. The implications of the cooling effect of GHG to the climate change, including paleoclimatology and the prerequests for climate models to include cooling effect of GHG properly are discussed.

Radiation-reaction force on a small charged body to second order

NASA Astrophysics Data System (ADS)

Moxon, Jordan; Flanagan, Éanna

2018-05-01

In classical electrodynamics, an accelerating charged body emits radiation and experiences a corresponding radiation-reaction force, or self-force. We extend to higher order in the total charge a previous rigorous derivation of the electromagnetic self-force in flat spacetime by Gralla, Harte, and Wald. The method introduced by Gralla, Harte, and Wald computes the self-force from the Maxwell field equations and conservation of stress-energy in a limit where the charge, size, and mass of the body go to zero, and it does not require regularization of a singular self-field. For our higher-order computation, an adjustment of the definition of the mass of the body is necessary to avoid including self-energy from the electromagnetic field sourced by the body in the distant past. We derive the evolution equations for the mass, spin, and center-of-mass position of the body through second order. We derive, for the first time, the second-order acceleration dependence of the evolution of the spin (self-torque), as well as a mixing between the extended body effects and the acceleration-dependent effects on the overall body motion.

Radiation reaction on a classical charged particle: a modified form of the equation of motion.

PubMed

Alcaine, Guillermo García; Llanes-Estrada, Felipe J

2013-09-01

We present and numerically solve a modified form of the equation of motion for a charged particle under the influence of an external force, taking into account the radiation reaction. This covariant equation is integro-differential, as Dirac-Röhrlich's, but has several technical improvements. First, the equation has the form of Newton's second law, with acceleration isolated on the left hand side and the force depending only on positions and velocities: Thus, the equation is linear in the highest derivative. Second, the total four-force is by construction perpendicular to the four-velocity. Third, if the external force vanishes for all future times, the total force and the acceleration automatically vanish at the present time. We show the advantages of this equation by solving it numerically for several examples of external force.

Radiation reaction on a classical charged particle: A modified form of the equation of motion

NASA Astrophysics Data System (ADS)

Alcaine, Guillermo García; Llanes-Estrada, Felipe J.

2013-09-01

We present and numerically solve a modified form of the equation of motion for a charged particle under the influence of an external force, taking into account the radiation reaction. This covariant equation is integro-differential, as Dirac-Röhrlich's, but has several technical improvements. First, the equation has the form of Newton's second law, with acceleration isolated on the left hand side and the force depending only on positions and velocities: Thus, the equation is linear in the highest derivative. Second, the total four-force is by construction perpendicular to the four-velocity. Third, if the external force vanishes for all future times, the total force and the acceleration automatically vanish at the present time. We show the advantages of this equation by solving it numerically for several examples of external force.

Integrating biomass, sulphate and sea-salt aerosol responses into a microphysical chemical parcel model: implications for climate studies.

PubMed

Ghosh, S; Smith, M H; Rap, A

2007-11-15

Aerosols are known to influence significantly the radiative budget of the Earth. Although the direct effect (whereby aerosols scatter and absorb solar and thermal infrared radiation) has a large perturbing influence on the radiation budget, the indirect effect (whereby aerosols modify the microphysical and hence the radiative properties and amounts of clouds) poses a greater challenge to climate modellers. This is because aerosols undergo chemical and physical changes while in the atmosphere, notably within clouds, and are removed largely by precipitation. The way in which aerosols are processed by clouds depends on the type, abundance and the mixing state of the aerosols concerned. A parametrization with sulphate and sea-salt aerosol has been successfully integrated within the Hadley Centre general circulation model (GCM). The results of this combined parametrization indicate a significantly reduced role, compared with previous estimates, for sulphate aerosol in cloud droplet nucleation and, consequently, in indirect radiative forcing. However, in this bicomponent system, the cloud droplet number concentration, N(d) (a crucial parameter that is used in GCMs for radiative transfer calculations), is a smoothly varying function of the sulphate aerosol loading. Apart from sea-salt and sulphate aerosol particles, biomass aerosol particles are also present widely in the troposphere. We find that biomass smoke can significantly perturb the activation and growth of both sulphate and sea-salt particles. For a fixed salt loading, N(d) increases linearly with modest increases in sulphate and smoke masses, but significant nonlinearities are observed at higher non-sea-salt mass loadings. This non-intuitive N(d) variation poses a fresh challenge to climate modellers.

Analysis of the polar amplification pattern of global warming on an aquaplanet in "ghost forcing" experiments with no ice-albedo feedbacks

NASA Astrophysics Data System (ADS)

Alexeev, V. A.; Langen, P. L.

2004-05-01

Non-ice-albedo feedback mechanisms leading to polar amplification, as reported by Alexeev (2003), are explored in three aquaplanet climate model systems of different complexity. We analyze this pattern using three different "ghost forcing" experiments (Hansen et al, 1997). In the first one we uniformly add 4W/m2 to the oceanic mixed layer in order to roughly simulate a 2xCO2 forcing at the surface. The second forcing, of the same magnitude, is applied only within the tropics and the third forcing is applied only polewards of 30 degrees (north and south). It turns out that our systems' equilibrium responses are linear with respect to these forcings. Surprisingly, the response to the tropical-only forcing is essentially non-local with quite significant warming at higher latitudes. The response to the high-latitude-only forcing is more local and has higher amplitude near the poles. Our explanation of the polar amplification obtained in the uniform forcing experiment is therefore two-fold. Firstly, the tropics are much more difficult to warm because of the higher sensitivity of the surface budget to SST changes at higher temperatures. Secondly, any extra heat deposited in the tropics is not easily radiated to outer space because of the high opaqueness of the tropical atmosphere. The energy, most of which is latent, needs to be redistributed by transports to the extra-tropics. Consequently, the tropical "ghost forcing" results in an essentially non-local response, while the extra-tropical one yields a more localized response, because the energy in the atmosphere cannot propagate effectively equator-wards from high latitudes. The paper deals with these mechanisms in three climate model systems with no ice-albedo feedback - an EBM and two different GCMs - one with cloud feedbacks and the other with cloud feedbacks excluded. References. Alexeev, V.A., (2003) Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Climate Dynamics, 20: p.775-787. Hansen, J., Sato M, and R. Ruedy, (1997) Radiative forcing and climate response, JGR, 102, No. D6, 6831-6864.

Future Climate Impacts of Direct Radiative Forcing Anthropogenic Aerosols, Tropospheric Ozone, and Long-lived Greenhouse Gases

NASA Technical Reports Server (NTRS)

Chen, Wei-Ting; Liao, Hong; Seinfeld, John H.

2007-01-01

Long-lived greenhouse gases (GHGs) are the most important driver of climate change over the next century. Aerosols and tropospheric ozone (O3) are expected to induce significant perturbations to the GHG-forced climate. To distinguish the equilibrium climate responses to changes in direct radiative forcing of anthropogenic aerosols, tropospheric ozone, and GHG between present day and year 2100, four 80-year equilibrium climates are simulated using a unified tropospheric chemistry-aerosol model within the Goddard Institute for Space Studies (GISS) general circulation model (GCM) 110. Concentrations of sulfate, nitrate, primary organic (POA) carbon, secondary organic (SOA) carbon, black carbon (BC) aerosols, and tropospheric ozone for present day and year 2100 are obtained a priori by coupled chemistry-aerosol GCM simulations, with emissions of aerosols, ozone, and precursors based on the Intergovernmental Panel on Climate Change (IPCC) Special Report on Emissions Scenario (SRES) A2. Changing anthropogenic aerosols, tropospheric ozone, and GHG from present day to year 2100 is predicted to perturb the global annual mean radiative forcing by +0.18 (considering aerosol direct effects only), +0.65, and +6.54 W m(sup -2) at the tropopause, and to induce an equilibrium global annual mean surface temperature change of +0.14, +0.32, and +5.31 K, respectively, with the largest temperature response occurring at northern high latitudes. Anthropogenic aerosols, through their direct effect, are predicted to alter the Hadley circulation owing to an increasing interhemispheric temperature gradient, leading to changes in tropical precipitation. When changes in both aerosols and tropospheric ozone are considered, the predicted patterns of change in global circulation and the hydrological cycle are similar to those induced by aerosols alone. GHG-induced climate changes, such as amplified warming over high latitudes, weakened Hadley circulation, and increasing precipitation over the Tropics and high latitudes, are consistent with predictions of a number of previous GCM studies. Finally, direct radiative forcing of anthropogenic aerosols is predicted to induce strong regional cooling over East and South Asia. Wintertime rainfall over southeastern China and the Indian subcontinent is predicted to decrease because of the increased atmospheric stability and decreased surface evaporation, while the geographic distribution of precipitation is also predicted to be altered as a result of aerosol-induced changes in wind flow.

Radiation effects and tolerance mechanism in β-eucryptite

NASA Astrophysics Data System (ADS)

Narayanan, Badri; Reimanis, Ivar E.; Huang, Hanchen; Ciobanu, Cristian V.

2013-01-01

Previous studies on Li-silicates have shown that these materials are resistant to radiation damage even in extreme physical and chemical environments, and are thus promising solid-state breeder materials in fusion reactors. Here, we focus on β-eucryptite as a member of Li-Al silicate class of ceramics with potential for nuclear applications, and study the atomic-scale processes induced by radiation. Using molecular dynamics simulations based on a reactive force field, we have found that upon radiation dosage of 0.21 displacements-per-atom or less, the structure largely retains its long-range order while exhibiting (a) disordering of the Li atoms, (b) distortion of the Si and Al tetrahedra defined as the change in their oxygen-coordination number, and (c) tilting of the Si and Al tetrahedra with respect to one another. We find that Si tetrahedra that distort to SiO3 during exposure to radiation recover significantly upon thermal relaxation, and provide the mechanism for this recovery. This mechanism consists in the tilting of AlO5 polyhedra formed upon exposure so as to satisfy the oxygen-coordination of distorted Si tetrahedra. Doubling the dosage results in a significant increase of the concentration of Si-Al antisite defects, which renders the tolerance mechanism inefficient and leads to amorphization.

Force-Free Time-Harmonic Plasmoids

DTIC Science & Technology

1992-10-01

effect of currents or vortical motion are absolutely required for stability. What makes the present model attractive is the minimization of the body ...radiative-mode effects may be very fruitful in the future. For example: Rigid non-radiative composite "particles" containing large numbers of fus- able...12 7. The neutral plasma .......... .......................... 12 8. Forces on a moving electron ....... ......... .............. 13 9. Effects of

A general method for computing the total solar radiation force on complex spacecraft structures

NASA Technical Reports Server (NTRS)

Chan, F. K.

1981-01-01

The method circumvents many of the existing difficulties in computational logic presently encountered in the direct analytical or numerical evaluation of the appropriate surface integral. It may be applied to complex spacecraft structures for computing the total force arising from either specular or diffuse reflection or even from non-Lambertian reflection and re-radiation.

Multi-Model Simulations of Aerosol and Ozone Radiative Forcing Due to Anthropogenic Emission Changes During the Period 1990-2015

NASA Technical Reports Server (NTRS)

Myhre, Gunnar; Aas, Wenche; Ribu, Cherian; Collins, William; Faluvegi, Gregory S.; Flanner, Mark; Forster, Piers; Hodnebrog, Oivind; Klimont, Zbigniew; Lund, Marianne T.

2017-01-01

Over the past few decades, the geographical distribution of emissions of substances that alter the atmospheric energy balance has changed due to economic growth and air pollution regulations. Here, we show the resulting changes to aerosol and ozone abundances and their radiative forcing using recently updated emission data for the period 1990-2015, as simulated by seven global atmospheric composition models. The models broadly reproduce large-scale changes in surface aerosol and ozone based on observations (e.g. 1 to 3 percent per year in aerosols over the USA and Europe). The global mean radiative forcing due to ozone and aerosol changes over the 1990-2015 period increased by 0.17 plus or minus 0.08 watts per square meter, with approximately one-third due to ozone. This increase is more strongly positive than that reported in IPCC AR5 (Intergovernmental Panel on Climate Change Fifth Assessment Report). The main reasons for the increased positive radiative forcing of aerosols over this period are the substantial reduction of global mean SO2 emissions, which is stronger in the new emission inventory compared to that used in the IPCC analysis, and higher black carbon emissions.

aerosol radiative effects and forcing: spatial and temporal distributions

NASA Astrophysics Data System (ADS)

Kinne, Stefan

2014-05-01

A monthly climatology for aerosol optical properties based on a synthesis from global modeling and observational data has been applied to illustrate spatial distributions and global averages of aerosol radiative impacts. With the help of a pre-industrial reference for aerosol optical properties from global modeling, also the aerosol direct forcing (ca -0.35W/m2 globally and annual averaged) and their spatial and seasonal distributions and contributions by individual aerosol components are estimated. Finally, CCN and IN concentrations associated with this climatology are applied to estimate aerosol indirect effects and forcing.

Effects of neutron irradiation on pinning force scaling in state-of-the-art Nb3Sn wires

NASA Astrophysics Data System (ADS)

Baumgartner, T.; Eisterer, M.; Weber, H. W.; Flükiger, R.; Scheuerlein, C.; Bottura, L.

2014-01-01

We present an extensive irradiation study involving five state-of-the-art Nb3Sn wires which were subjected to sequential neutron irradiation up to a fast neutron fluence of 1.6 × 1022 m-2 (E > 0.1 MeV). The volume pinning force of short wire samples was assessed in the temperature range from 4.2 to 15 K in applied fields of up to 7 T by means of SQUID magnetometry in the unirradiated state and after each irradiation step. Pinning force scaling computations revealed that the exponents in the pinning force function differ significantly from those expected for pure grain boundary pinning, and that fast neutron irradiation causes a substantial change in the functional dependence of the volume pinning force. A model is presented, which describes the pinning force function of irradiated wires using a two-component ansatz involving a point-pinning contribution stemming from radiation induced pinning centers. The dependence of this point-pinning contribution on fast neutron fluence appears to be a universal function for all examined wire types.

Guidelines for Finite Element Modeling of Acoustic Radiation Force-Induced Shear Wave Propagation in Tissue-Mimicking Media

PubMed Central

Palmeri, Mark L.; Qiang, Bo; Chen, Shigao; Urban, Matthew W.

2017-01-01

Ultrasound shear wave elastography is emerging as an important imaging modality for evaluating tissue material properties. In its practice, some systematic biases have been associated with ultrasound frequencies, focal depths and configuration, transducer types (linear versus curvilinear), along with displacement estimation and shear wave speed estimation algorithms. Added to that, soft tissues are not purely elastic, so shear waves will travel at different speeds depending on their spectral content, which can be modulated by the acoustic radiation force excitation focusing, duration and the frequency-dependent stiffness of the tissue. To understand how these different acquisition and material property parameters may affect measurements of shear wave velocity, simulations of the propagation of shear waves generated by acoustic radiation force excitations in viscoelastic media are a very important tool. This article serves to provide an in-depth description of how these simulations are performed. The general scheme is broken into three components: (1) simulation of the three-dimensional acoustic radiation force push beam, (2) applying that force distribution to a finite element model, and (3) extraction of the motion data for post-processing. All three components will be described in detail and combined to create a simulation platform that is powerful for developing and testing algorithms for academic and industrial researchers involved in making quantitative shear wave-based measurements of tissue material properties. PMID:28026760

Waves and instability in the atmosphere of Mars: NASA planetary atmospheres program

NASA Technical Reports Server (NTRS)

Barnes, Jeffrey R.

1990-01-01

A broad range of phenomena were addressed by the study including the following: (1) polar warming; (2) forced stationary waves; (3) gravity waves; (4) transient baroclinic eddies; and (5) radiative-dynamical instabilities. A variety of numerical models have been employed in these studies, as well as analytical approaches. Some of the most significant results from this work are very briefly summarized.

Electrons in strong electromagnetic fields: spin effects and radiation reaction (Conference Presentation)

NASA Astrophysics Data System (ADS)

Bauke, Heiko; Wen, Meng; Keitel, Christoph H.

2017-05-01

Various different classical models of electrons including their spin degree of freedom are commonly applied to describe the coupled dynamics of relativistic electron motion and spin precession in strong electromagnetic fields. The spin dynamics is usually governed by the Thomas-Bargmann-Michel-Telegdi equation [1, 2] in these models, while the electron's orbital motion follows the (modified) Lorentz force and a spin-dependent Stern-Gerlach force. Various classical models can lead to different or even contradicting predictions how the spin degree of freedom modifies the electron's orbital motion when the electron moves in strong electromagnetic fields. This discrepancy is rooted in the model-specific energy dependency of the spin induced relativistic Stern-Gerlach force acting on the electron. The Frenkel model [3, 4] and the classical Foldy-Wouthuysen model 5 are compared exemplarily against each other and against the quantum mechanical Dirac equation in order to identify parameter regimes where these classical models make different predictions [6, 7]. Our theoretical results allow for experimental tests of these models. In the setup of the longitudinal Stern-Gerlach effect, the Frenkel model and classical Foldy-Wouthuysen model lead in the relativistic limit to qualitatively different spin effects on the electron trajectory. Furthermore, it is demonstrated that in tightly focused beams in the near infrared the effect of the Stern-Gerlach force of the Frenkel model becomes sufficiently large to be potentially detectable in an experiment. Among the classical spin models, the Frenkel model is certainly prominent for its long history and its wide application. Our results, however, suggest that the classical Foldy-Wouthuysen model is superior as it is qualitatively in better agreement with the quantum mechanical Dirac equation. In ultra strong laser setups at parameter regimes where effects of the Stern-Gerlach force become relevant also radiation reaction effects are expected to set in. We incorporate radiation reaction classically via the Landau-Lifshitz equation and demonstrate that although radiation reaction effects can have a significant effect on the electron trajectory, the Frenkel model and the classical Foldy-Wouthuysen model remain distinguishable also if radiation reaction effects are taken into account. Our calculations are also suitable to verify the Landau-Lifshitz equation for the radiation reaction of electrons and other spin one-half particles. 1. Thomas, L. H., "I. The kinematics of an electron with an axis," The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science 3(13), 1-22 (1927). 2. Bargmann, V., Michel, L., and Telegdi, V. L., "Precession of the polarization of particles moving in a homogeneous electromagnetic field," Phys. Rev. Lett. 2(10), 435-436 (1959). 3. Frenkel, J., "Die Elektrodynamik des rotierenden Elektrons," Z. Phys. 37(4-5), 243-262 (1926). 4. Frenkel, J., "Spinning electrons," Nature (London) 117(2949), 653-654 (1926). 5. Silenko, A. J., "Foldy-Wouthyusen transformation and semiclassical limit for relativistic particles in strong external fields," Phys. Rev. A 77(1), 012116 (2008). 6. Wen, M., Bauke, H., and Keitel, C. H., "Identifying the Stern-Gerlach force of classical electron dynamics," Sci. Rep. 6, 31624 (2016). 7. Wen, M., Keitel, C. H., and Bauke, H., "Spin one-half particles in strong electromagnetic fields: spin effects and radiation reaction," arXiv:1610.08951 (2016).

The use of Acoustic Radiation Force decorrelation-weighted pulse inversion (ADW-PI) for enhanced ultrasound contrast imaging

PubMed Central

Herbst, Elizabeth; Unnikrishnan, Sunil; Wang, Shiying; Klibanov, Alexander L.; Hossack, John A.; Mauldin, F. William

2016-01-01

Objectives The use of ultrasound imaging for cancer diagnosis and screening can be enhanced with the use of molecularly targeted microbubbles. Nonlinear imaging strategies such as pulse inversion (PI) and “contrast pulse sequences” (CPS) can be used to differentiate microbubble signal, but often fail to suppress highly echogenic tissue interfaces. This failure results in false positive detection and potential misdiagnosis. In this study, a novel Acoustic Radiation Force (ARF) based approach was developed for superior microbubble signal detection. The feasibility of this technique, termed ARF-decorrelation-weighted PI (ADW-PI), was demonstrated in vivo using a subcutaneous mouse tumor model. Materials and Methods Tumors were implanted in the hindlimb of C57BL/6 mice by subcutaneous injection of MC38 cells. Lipid-shelled microbubbles were conjugated to anti-VEGFR2 antibody and administered via bolus injection. An image sequence using ARF pulses to generate microbubble motion was combined with PI imaging on a Verasonics Vantage programmable scanner. ADW-PI images were generated by combining PI images with inter-frame signal decorrelation data. For comparison, CPS images of the same mouse tumor were acquired using a Siemens Sequoia clinical scanner. Results Microbubble-bound regions in the tumor interior exhibited significantly higher signal decorrelation than static tissue (n = 9, p < 0.001). The application of ARF significantly increased microbubble signal decorrelation (n = 9, p < 0.01). Using these decorrelation measurements, ADW-PI imaging demonstrated significantly improved microbubble contrast-to-tissue ratio (CTR) when compared to corresponding CPS or PI images (n = 9, p < 0.001). CTR improved with ADW-PI by approximately 3 dB compared to PI images and 2 dB compared to CPS images. Conclusions Acoustic radiation force can be used to generate adherent microbubble signal decorrelation without microbubble bursting. When combined with pulse inversion, measurements of the resulting microbubble signal decorrelation can be used to reconstruct images that exhibit superior suppression of highly echogenic tissue interfaces when compared to PI or CPS alone. PMID:27495188

Acoustic manipulation of active spherical carriers: Generation of negative radiation force

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rajabi, Majid, E-mail: majid_rajabi@iust.ac.ir; Mojahed, Alireza

2016-09-15

This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered asmore » a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.« less

Deflection of the local interstellar dust flow by solar radiation pressure

NASA Technical Reports Server (NTRS)

Landgraf, M.; Augustsson, K.; Grun, E.; Gustafson, B. A.

1999-01-01

Interstellar dust grains intercepted by the dust detectors on the Ulysses and Galileo spacecrafts at heliocentric distances from 2 to 4 astronomical units show a deficit of grains with masses from 1 x 10(-17) to 3 x 10(-16) kilograms relative to grains intercepted outside 4 astronomical units. To divert grains out of the 2- to 4-astronomical unit region, the solar radiation pressure must be 1.4 to 1.8 times the force of solar gravity. These figures are consistent with the optical properties of spherical or elongated grains that consist of astronomical silicates or organic refractory material. Pure graphite grains with diameters of 0.2 to 0.4 micrometer experience a solar radiation pressure force as much as twice the force of solar gravity.

Acoustic levitation of a large solid sphere

NASA Astrophysics Data System (ADS)

Andrade, Marco A. B.; Bernassau, Anne L.; Adamowski, Julio C.

2016-07-01

We demonstrate that acoustic levitation can levitate spherical objects much larger than the acoustic wavelength in air. The acoustic levitation of an expanded polystyrene sphere of 50 mm in diameter, corresponding to 3.6 times the wavelength, is achieved by using three 25 kHz ultrasonic transducers arranged in a tripod fashion. In this configuration, a standing wave is created between the transducers and the sphere. The axial acoustic radiation force generated by each transducer on the sphere was modeled numerically as a function of the distance between the sphere and the transducer. The theoretical acoustic radiation force was verified experimentally in a setup consisting of an electronic scale and an ultrasonic transducer mounted on a motorized linear stage. The comparison between the numerical and experimental acoustic radiation forces presents a good agreement.

Global model comparison of heterogeneous ice nucleation parameterizations in mixed phase clouds

NASA Astrophysics Data System (ADS)

Yun, Yuxing; Penner, Joyce E.

2012-04-01

A new aerosol-dependent mixed phase cloud parameterization for deposition/condensation/immersion (DCI) ice nucleation and one for contact freezing are compared to the original formulations in a coupled general circulation model and aerosol transport model. The present-day cloud liquid and ice water fields and cloud radiative forcing are analyzed and compared to observations. The new DCI freezing parameterization changes the spatial distribution of the cloud water field. Significant changes are found in the cloud ice water fraction and in the middle cloud fractions. The new DCI freezing parameterization predicts less ice water path (IWP) than the original formulation, especially in the Southern Hemisphere. The smaller IWP leads to a less efficient Bergeron-Findeisen process resulting in a larger liquid water path, shortwave cloud forcing, and longwave cloud forcing. It is found that contact freezing parameterizations have a greater impact on the cloud water field and radiative forcing than the two DCI freezing parameterizations that we compared. The net solar flux at top of atmosphere and net longwave flux at the top of the atmosphere change by up to 8.73 and 3.52 W m-2, respectively, due to the use of different DCI and contact freezing parameterizations in mixed phase clouds. The total climate forcing from anthropogenic black carbon/organic matter in mixed phase clouds is estimated to be 0.16-0.93 W m-2using the aerosol-dependent parameterizations. A sensitivity test with contact ice nuclei concentration in the original parameterization fit to that recommended by Young (1974) gives results that are closer to the new contact freezing parameterization.

Using Radar, Lidar and Radiometer Data from NSA and SHEBA to Quantify Cloud Property Effects on the Surface Heat Budget in the Arctic

DOE Office of Scientific and Technical Information (OSTI.GOV)

Janet Intrieri; Mathhew Shupe

2005-01-01

Cloud and radiation data from two distinctly different Arctic areas are analyzed to study the differences between coastal Alaskan and open Arctic Ocean region clouds and their respective influence on the surface radiation budget. The cloud and radiation datasets were obtained from (1) the DOE North Slope of Alaska (NSA) facility in the coastal town of Barrow, Alaska, and (2) the SHEBA field program, which was conducted from an icebreaker frozen in, and drifting with, the sea-ice for one year in the Western Arctic Ocean. Radar, lidar, radiometer, and sounding measurements from both locations were used to produce annual cyclesmore » of cloud occurrence and height, atmospheric temperature and humidity, surface longwave and shortwave broadband fluxes, surface albedo, and cloud radiative forcing. In general, both regions revealed a similar annual trend of cloud occurrence fraction with minimum values in winter (60-75%) and maximum values during spring, summer and fall (80-90%). However, the annual average cloud occurrence fraction for SHEBA (76%) was lower than the 6-year average cloud occurrence at NSA (92%). Both Arctic areas also showed similar annual cycle trends of cloud forcing with clouds warming the surface through most of the year and a period of surface cooling during the summer, when cloud shading effects overwhelm cloud greenhouse effects. The greatest difference between the two regions was observed in the magnitude of the cloud cooling effect (i.e., shortwave cloud forcing), which was significantly stronger at NSA and lasted for a longer period of time than at SHEBA. This is predominantly due to the longer and stronger melt season at NSA (i.e., albedo values that are much lower coupled with Sun angles that are somewhat higher) than the melt season observed over the ice pack at SHEBA. Longwave cloud forcing values were comparable between the two sites indicating a general similarity in cloudiness and atmospheric temperature and humidity structure between the two regions.« less

Differentiation of benign from malignant liver masses with Acoustic Radiation Force Impulse technique.

PubMed

Yu, Hojun; Wilson, Stephanie R

2011-12-01

The objective of the study was to determine the performance of Acoustic Radiation Force Impulse (ARFI) imaging to differentiate benign from malignant liver masses, both of hepatocellular origin and metastases, by quantification of their stiffness. This study has institutional review board approval and informed consent. Eighty-nine patients (42 female and 47 male patients) with 105 liver masses had ARFI evaluation on ultrasound, S2000 (Siemens, Mountain View, Calif). Mean age of the patients was 53.67 years (range, 27-83 years). Mean diameter of the masses was 2.77 cm (range, 1.0-13.0 cm). Final diagnoses, confirmed by imaging on contrast-enhanced computed tomography, magnetic resonance, or ultrasound or biopsy, include hepatocellular carcinoma (n = 28), metastasis (n = 13), hemangioma (n = 35), focal nodular hyperplasia (n = 15), focal fat sparing (n = 8), focal fat deposit (n = 4), and adenoma (n = 2). Receiver operating characteristic analysis was performed to evaluate the diagnostic accuracy of the ARFI measurement and to extract the optimal cutoff values in the differentiation of benign from malignant disease. Acoustic Radiation Force Impulse values showed a statistically significant difference between benign (1.73 [SD, 0.8] m/sec) and malignant masses (2.57 [SD, 1.01] m/sec) (P < 0.001). However, the area under the receiver operating characteristic curve was 0.744, suggesting only fair accuracy. For differentiation of malignant from benign masses, the sensitivity, specificity, positive predictive value, and negative predictive value were 68% (28/41), 69% (44/64), 58% (28/48), and 77% (44/57), respectively, when 1.9 m/sec was chosen as a cutoff value, reflective of a wide variation of ARFI values in each diagnosis. For differentiation of metastasis from benign masses, sensitivity, specificity, positive predictive value, and NPV were 69% (9/13), 89% (57/64), 56% (9/16), and 93% (57/61), respectively, when 2.72 m/sec was chosen as a cutoff value. Acoustic Radiation Force Impulse measurement may be helpful to differentiate benign masses from metastases, in particular. Otherwise, ARFI measurements alone do not differentiate benign and malignant masses because of variations in stiffness of all types of masses.

A GCM Study of Responses of the Atmospheric Water Cycle of West Africa and the Atlantic to Saharan Dust Radiative Forcing

NASA Technical Reports Server (NTRS)

Lau, K. M.; Kim, K. M.; Sud, Y. C.; Walker, G. K.

2009-01-01

The responses of the atmospheric water cycle and climate of West Africa and the Atlantic to radiative forcing of Saharan dust are studied using the NASA finite volume general circulation model (fvGCM), coupled to a mixed layer ocean. We find evidence of an "elevated heat pump" (EHP) mechanism that underlines the responses of the atmospheric water cycle to dust forcing as follow. During the boreal summerr, as a result of large-scale atmospheric feedback triggered by absorbing dust aerosols, rainfall and cloudiness are ehanIed over the West Africa/Eastern Atlantic ITCZ, and suppressed over the West Atlantic and Caribbean region. Shortwave radiation absorption by dust warms the atmosphere and cools the surface, while longwave has the opposite response. The elevated dust layer warms the air over West Africa and the eastern Atlantic. As the warm air rises, it spawns a large-scale onshore flow carrying the moist air from the eastern Atlantic and the Gulf of Guinea. The onshore flow in turn enhances the deep convection over West Africa land, and the eastern Atlantic. The condensation heating associated with the ensuing deep convection drives and maintains an anomalous large-scale east-west overturning circulation with rising motion over West Africa/eastern Atlantic, and sinking motion over the Caribbean region. The response also includes a strengthening of the West African monsoon, manifested in a northward shift of the West Africa precipitation over land, increased low-level westerlies flow over West Africa at the southern edge of the dust layer, and a near surface westerly jet underneath the dust layer overr the Sahara. The dust radiative forcing also leads to significant changes in surface energy fluxes, resulting in cooling of the West African land and the eastern Atlantic, and warming in the West Atlantic and Caribbean. The EHP effect is most effective for moderate to highly absorbing dusts, and becomes minimized for reflecting dust with single scattering albedo at0.95 or higher.

Soft X-Ray Microscopy Radiation Damage On Fixed Cells Investigated With Synchrotron Radiation FTIR Microscopy.

PubMed

Gianoncelli, A; Vaccari, L; Kourousias, G; Cassese, D; Bedolla, D E; Kenig, S; Storici, P; Lazzarino, M; Kiskinova, M

2015-05-14

Radiation damage of biological samples remains a limiting factor in high resolution X-ray microscopy (XRM). Several studies have attempted to evaluate the extent and the effects of radiation damage, proposing strategies to minimise or prevent it. The present work aims to assess the impact of soft X-rays on formalin fixed cells on a systematic manner. The novelty of this approach resides on investigating the radiation damage not only with XRM, as often reported in relevant literature on the topic, but by coupling it with two additional independent non-destructive microscopy methods: Atomic Force Microscopy (AFM) and FTIR Microscopy (FTIRM). Human Embryonic Kidney 293 cells were exposed to different radiation doses at 1 keV. In order to reveal possible morphological and biochemical changes, the irradiated cells were systematically analysed with AFM and FTIRM before and after. Results reveal that while cell morphology is not substantially affected, cellular biochemical profile changes significantly and progressively when increasing dose, resulting in a severe breakdown of the covalent bonding network. This information impacts most soft XRM studies on fixed cells and adds an in-depth understanding of the radiation damage for developing better prevention strategies.

Soft X-Ray Microscopy Radiation Damage On Fixed Cells Investigated With Synchrotron Radiation FTIR Microscopy

PubMed Central

Gianoncelli, A.; Vaccari, L.; Kourousias, G.; Cassese, D.; Bedolla, D. E.; Kenig, S.; Storici, P.; Lazzarino, M.; Kiskinova, M.

2015-01-01

Radiation damage of biological samples remains a limiting factor in high resolution X-ray microscopy (XRM). Several studies have attempted to evaluate the extent and the effects of radiation damage, proposing strategies to minimise or prevent it. The present work aims to assess the impact of soft X-rays on formalin fixed cells on a systematic manner. The novelty of this approach resides on investigating the radiation damage not only with XRM, as often reported in relevant literature on the topic, but by coupling it with two additional independent non-destructive microscopy methods: Atomic Force Microscopy (AFM) and FTIR Microscopy (FTIRM). Human Embryonic Kidney 293 cells were exposed to different radiation doses at 1 keV. In order to reveal possible morphological and biochemical changes, the irradiated cells were systematically analysed with AFM and FTIRM before and after. Results reveal that while cell morphology is not substantially affected, cellular biochemical profile changes significantly and progressively when increasing dose, resulting in a severe breakdown of the covalent bonding network. This information impacts most soft XRM studies on fixed cells and adds an in-depth understanding of the radiation damage for developing better prevention strategies. PMID:25974639

Climate variability related to the 11 year solar cycle as represented in different spectral solar irradiance reconstructions

NASA Astrophysics Data System (ADS)

Kruschke, Tim; Kunze, Markus; Misios, Stergios; Matthes, Katja; Langematz, Ulrike; Tourpali, Kleareti

2016-04-01

Advanced spectral solar irradiance (SSI) reconstructions differ significantly from each other in terms of the mean solar spectrum, that is the spectral distribution of energy, and solar cycle variability. Largest uncertainties - relative to mean irradiance - are found for the ultraviolet range of the spectrum, a spectral region highly important for radiative heating and chemistry in the stratosphere and troposphere. This study systematically analyzes the effects of employing different SSI reconstructions in long-term (40 years) chemistry-climate model (CCM) simulations to estimate related uncertainties of the atmospheric response. These analyses are highly relevant for the next round of CCM studies as well as climate models within the CMIP6 exercise. The simulations are conducted by means of two state-of-the-art CCMs - CESM1(WACCM) and EMAC - run in "atmosphere-only"-mode. These models are quite different with respect to the complexity of the implemented radiation and chemistry schemes. CESM1(WACCM) features a chemistry module with considerably higher spectral resolution of the photolysis scheme while EMAC employs a radiation code with notably higher spectral resolution. For all simulations, concentrations of greenhouse gases and ozone depleting substances, as well as observed sea surface temperatures (SST) are set to average conditions representative for the year 2000 (for SSTs: mean of decade centered over year 2000) to exclude anthropogenic influences and differences due to variable SST forcing. Only the SSI forcing differs for the various simulations. Four different forcing datasets are used: NRLSSI1 (used as a reference in all previous climate modeling intercomparisons, i.e. CMIP5, CCMVal, CCMI), NRLSSI2, SATIRE-S, and the SSI forcing dataset recommended for the CMIP6 exercise. For each dataset, a solar maximum and minimum timeslice is integrated, respectively. The results of these simulations - eight in total - are compared to each other with respect to their shortwave heating rate differences (additionally collated with line-by-line calculations using libradtran), differences in the photolysis rates, as well as atmospheric circulation features (temperature, zonal wind, geopotential height, etc.). It is shown that atmospheric responses to the different SSI datasets differ significantly from each other. This is a result from direct radiative effects as well as indirect effects induced by ozone feedbacks. Differences originating from using different SSI datasets for the same level of solar activity are in the same order of magnitude as those associated with the 11 year solar cycle within a specific dataset. However, the climate signals related to the solar cycle are quite comparable across datasets.

Note: Measurement system for the radiative forcing of greenhouse gases in a laboratory scale.

PubMed

Kawamura, Yoshiyuki

2016-01-01

The radiative forcing of the greenhouse gases has been studied being based on computational simulations or the observation of the real atmosphere meteorologically. In order to know the greenhouse effect more deeply and to study it from various viewpoints, the study on it in a laboratory scale is important. We have developed a direct measurement system for the infrared back radiation from the carbon dioxide (CO2) gas. The system configuration is similar with that of the practical earth-atmosphere-space system. Using this system, the back radiation from the CO2 gas was directly measured in a laboratory scale, which roughly coincides with meteorologically predicted value.

Impact of radiation frequency, precipitation radiative forcing, and radiation column aggregation on convection-permitting West African monsoon simulations

NASA Astrophysics Data System (ADS)

Matsui, Toshi; Zhang, Sara Q.; Lang, Stephen E.; Tao, Wei-Kuo; Ichoku, Charles; Peters-Lidard, Christa D.

2018-03-01

In this study, the impact of different configurations of the Goddard radiation scheme on convection-permitting simulations (CPSs) of the West African monsoon (WAM) is investigated using the NASA-Unified WRF (NU-WRF). These CPSs had 3 km grid spacing to explicitly simulate the evolution of mesoscale convective systems (MCSs) and their interaction with radiative processes across the WAM domain and were able to reproduce realistic precipitation and energy budget fields when compared with satellite data, although low clouds were overestimated. Sensitivity experiments reveal that (1) lowering the radiation update frequency (i.e., longer radiation update time) increases precipitation and cloudiness over the WAM region by enhancing the monsoon circulation, (2) deactivation of precipitation radiative forcing suppresses cloudiness over the WAM region, and (3) aggregating radiation columns reduces low clouds over ocean and tropical West Africa. The changes in radiation configuration immediately modulate the radiative heating and low clouds over ocean. On the 2nd day of the simulations, patterns of latitudinal air temperature profiles were already similar to the patterns of monthly composites for all radiation sensitivity experiments. Low cloud maintenance within the WAM system is tightly connected with radiation processes; thus, proper coupling between microphysics and radiation processes must be established for each modeling framework.

The atmospheric implications of radiation belt remediation

NASA Astrophysics Data System (ADS)

Rodger, C. J.; Clilverd, M. A.; Ulich, Th.; Verronen, P. T.; Turunen, E.; Thomson, N. R.

2006-08-01

High altitude nuclear explosions (HANEs) and geomagnetic storms can produce large scale injections of relativistic particles into the inner radiation belts. It is recognised that these large increases in >1 MeV trapped electron fluxes can shorten the operational lifetime of low Earth orbiting satellites, threatening a large, valuable population. Therefore, studies are being undertaken to bring about practical human control of the radiation belts, termed "Radiation Belt Remediation" (RBR). Here we consider the upper atmospheric consequences of an RBR system operating over either 1 or 10 days. The RBR-forced neutral chemistry changes, leading to NOx enhancements and Ox depletions, are significant during the timescale of the precipitation but are generally not long-lasting. The magnitudes, time-scales, and altitudes of these changes are no more significant than those observed during large solar proton events. In contrast, RBR-operation will lead to unusually intense HF blackouts for about the first half of the operation time, producing large scale disruptions to radio communication and navigation systems. While the neutral atmosphere changes are not particularly important, HF disruptions could be an important area for policy makers to consider, particularly for the remediation of natural injections.

Efficient Formation of Stratospheric Aerosol for Climate Engineering by Emission of Condensible Vapor from Aircraft

NASA Technical Reports Server (NTRS)

Pierce, Jeffrey R.; Weisenstein, Debra K.; Heckendorn, Patricia; Peter. Thomas; Keith, David W.

2010-01-01

Recent analysis suggests that the effectiveness of stratospheric aerosol climate engineering through emission of non-condensable vapors such as SO2 is limited because the slow conversion to H2SO4 tends to produce aerosol particles that are too large; SO2 injection may be so inefficient that it is difficult to counteract the radiative forcing due to a CO2 doubling. Here we describe an alternate method in which aerosol is formed rapidly in the plume following injection of H2SO4, a condensable vapor, from an aircraft. This method gives better control of particle size and can produce larger radiative forcing with lower sulfur loadings than SO2 injection. Relative to SO2 injection, it may reduce some of the adverse effects of geoengineering such as radiative heating of the lower stratosphere. This method does not, however, alter the fact that such a geoengineered radiative forcing can, at best, only partially compensate for the climate changes produced by CO2.

In-Space technology experiments program. A high efficiency thermal interface (using condensation heat transfer) between a 2-phase fluid loop and heatpipe radiator: Experiment definition phase

NASA Technical Reports Server (NTRS)

Pohner, John A.; Dempsey, Brian P.; Herold, Leroy M.

1990-01-01

Space Station elements and advanced military spacecraft will require rejection of tens of kilowatts of waste heat. Large space radiators and two-phase heat transport loops will be required. To minimize radiator size and weight, it is critical to minimize the temperature drop between the heat source and sink. Under an Air Force contract, a unique, high-performance heat exchanger is developed for coupling the radiator to the transport loop. Since fluid flow through the heat exchanger is driven by capillary forces which are easily dominated by gravity forces in ground testing, it is necessary to perform microgravity thermal testing to verify the design. This contract consists of an experiment definition phase leading to a preliminary design and cost estimate for a shuttle-based flight experiment of this heat exchanger design. This program will utilize modified hardware from a ground test program for the heat exchanger.

Re-evaluation of Dust Absorption and Radiative Forcing of Climate Using Satellite and Ground Based Remote Sensing

NASA Technical Reports Server (NTRS)

Kaufman, Yoram

1999-01-01

Simultaneous spaceborne and ground based measurements of the scattered solar radiation, create a powerful tool for determination of dust absorption and scattering properties. Absorption of solar radiation is a key component in understanding dust impact on radiative forcing at the top of the atmosphere, on the temperature profile and on cloud formation. We use Landsat spaceborne measurements at seven spectral channels in the range of 0.47 to 2.2 microns over Senegal with corresponding measurements of the aerosol spectral optical thickness by ground based sunphotometers, to find that Saharan dust absorption of solar radiation is two to four times smaller than measured in situ and represented in models. Though dust was found to absorb in the blue (single scattering albedo w = 0.88), almost no absorption, w = 0.98, was found for wavelengths > 0.6 microns. The new finding increases by 50% recently estimated solar radiative forcing by dust at the top of the atmosphere and decreases the estimated dust heating of the lower troposphere due to absorption of solar radiation. Dust transported from Asia shows slightly higher absorption for wavelengths under 1 micron, that can be explained by the presence of black carbon from urban/industrial pollution associated with the submicron size mode. In the talk I shall also discuss recent observation of the impact of dust shape on the dust scattering properties.

The rising greenhouse effect: experiments and observations in and around the Alps

NASA Astrophysics Data System (ADS)

Philipona, R.

2010-09-01

The rapid temperature increase of more than 1°C in central Europe over the last three decades is larger than expected from anthropogenic greenhouse warming. Surface radiation flux measurements in and around the Alps in fact confirm that not only thermal longwave radiation but also solar shortwave radiation increased since the 1980s. Surface energy budget analyses reveal the rising surface temperature to be well correlated with the radiative forcing, and also show an increase of the kinetic energy fluxes explaining the rise of atmospheric water vapor. Solar radiation mainly increased due to a strong decline of anthropogenic aerosols since mid of the 1980s. While anthropogenic aerosols were mainly accumulated in the boundary layer, this reduction let solar radiation to recover (solar brightening after several decades of solar dimming) mainly at low altitudes around the Alps. At high elevations in the Alps, solar forcing is much smaller and the respective temperature rise is also found to be smaller than in the lowlands. The fact that temperature increases less in the Alps than at low elevations is unexpected in the concept of greenhouse warming, but the radiation budget analyses clearly shows that in the plains solar forcing due to declining aerosols additionally increased surface temperature, whereas in the Alps temperature increased primarily due to greenhouse warming that is particularly manifested by a strong water vapor feedback.

OUTWARD MOTION OF POROUS DUST AGGREGATES BY STELLAR RADIATION PRESSURE IN PROTOPLANETARY DISKS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tazaki, Ryo; Nomura, Hideko, E-mail: rtazaki@kusastro.kyoto-u.ac.jp

2015-02-01

We study the dust motion at the surface layer of protoplanetary disks. Dust grains in the surface layer migrate outward owing to angular momentum transport via gas-drag force induced by the stellar radiation pressure. In this study we calculate the mass flux of the outward motion of compact grains and porous dust aggregates by the radiation pressure. The radiation pressure force for porous dust aggregates is calculated using the T-Matrix Method for the Clusters of Spheres. First, we confirm that porous dust aggregates are forced by strong radiation pressure even if they grow to be larger aggregates, in contrast tomore » homogeneous and spherical compact grains, for which radiation pressure efficiency becomes lower when their sizes increase. In addition, we find that the outward mass flux of porous dust aggregates with monomer size of 0.1 μm is larger than that of compact grains by an order of magnitude at the disk radius of 1 AU, when their sizes are several microns. This implies that large compact grains like calcium-aluminum-rich inclusions are hardly transported to the outer region by stellar radiation pressure, whereas porous dust aggregates like chondritic-porous interplanetary dust particles are efficiently transported to the comet formation region. Crystalline silicates are possibly transported in porous dust aggregates by stellar radiation pressure from the inner hot region to the outer cold cometary region in the protosolar nebula.« less

Impacts of radiation management techniques on the North Atlantic Oscillation

NASA Astrophysics Data System (ADS)

Adakudlu, Muralidhar; Helge Otterå, Odd; Tjiputra, Jerry; Muri, Helene; Grini, Alf; Schulz, Michael

2017-04-01

The effectiveness of various climate engineering techniques in limiting the global warming signal to reasonable levels has been the topic of state-of-the-art research on climate change. Using an Earth system model, we show that these techniques have the potential to bring down the high CO2 concentration climate in RCP8.5 to a moderate climate similar to RCP4.5 in terms of global temperature. Nevertheless, their influence on the regional aspects of atmospheric circulation is not clear. The regional circulation patterns in the atmosphere are largely characterized by the natural variability modes, such as the North Atlantic Oscillation (NAO). In this study, we assess the impacts of three radiation managment techniques, namely, Stratospheric Aerosol Injection (SAI), Marine Sky Brightening (MSB) and Cirrus Cloud Thinning (CCT), on the structure and features of the NAO. The results indicate an east-northeastward shift as well as intensification of the NAO spatial pattern in the global warming scenarios of RCP4.5 and RCP8.5, with the signal being most intense in the latter. The climate engineering forcings when applied to the RCP8.5 case tend to reduce the strength of the NAO with little impact on its position. The CCT case appears to have the maximum effect on the NAO signal. The patterns of cloud radiative forcing, expressed as the difference between net radiative forcing at TOA under average conditions and clear sky conditions, reveal a northeastward shift of the radiative heating in the north Atlantic region. This implies a possible link between the changes in the NAO signal and the cloud radiative forcing.

Does acoustic radiation force elastography improve the diagnostic capability of ultrasound in the preoperative characterization of masses of the parotid gland?

PubMed

Zengel, Pamela; Notter, Florian; Clevert, Dirk A

2018-06-06

Ultrasound is the method of choice for preoperative evaluation of tumours of the parotid glands. However, existing methods do not allow for clear differentiation between the most common benign tumours and malignant tumours. The aim of our study was to evaluate if acoustic radiation force, Virtual Touch Quantification (VTQ) elastography helps to improve the preoperative evaluation of parotid masses. We investigated the parenchyma of 102 parotid glands, 14 lymph nodes of healthy volunteers and 51 tumours of the parotid gland via ultrasound, colour Doppler ultrasound and VTQ. The results were matched with histopathology and analyzed. The perfusion in pleomorphic adenoma, the most frequent benign tumour of the parotid gland, was significantly lower in comparison to malignant tumours. All tumours showed statistically significant higher perfusion in comparison to the parenchyma or the lymph nodes of the gland. Shear wave velocity of the user-defined region of interest was statistically significant more frequently an overflow value higher than 8.5 m/s in total tumours in comparison to parenchyma or lymph nodes. The different tumour types presented no significant difference in the shear wave velocity. VTQ in combination with classical ultrasound examination provides additional data useful in distinguishing between benign and malignant tumours and thus shows promise for integration into preexisting ultrasound protocols. However, despite the improvement, clear differentiation of tumours is still not possible and further investigation is recommended.

Top-of-atmosphere radiative forcing affected by brown carbon in the upper troposphere

NASA Astrophysics Data System (ADS)

Zhang, Yuzhong; Forrister, Haviland; Liu, Jiumeng; Dibb, Jack; Anderson, Bruce; Schwarz, Joshua P.; Perring, Anne E.; Jimenez, Jose L.; Campuzano-Jost, Pedro; Wang, Yuhang; Nenes, Athanasios; Weber, Rodney J.

2017-07-01

Carbonaceous aerosols affect the global radiative balance by absorbing and scattering radiation, which leads to warming or cooling of the atmosphere, respectively. Black carbon is the main light-absorbing component. A portion of the organic aerosol known as brown carbon also absorbs light. The climate sensitivity to absorbing aerosols rapidly increases with altitude, but brown carbon measurements are limited in the upper troposphere. Here we present aircraft observations of vertical aerosol distributions over the continental United States in May and June 2012 to show that light-absorbing brown carbon is prevalent in the troposphere, and absorbs more short-wavelength radiation than black carbon at altitudes between 5 and 12 km. We find that brown carbon is transported to these altitudes by deep convection, and that in-cloud heterogeneous processing may produce brown carbon. Radiative transfer calculations suggest that brown carbon accounts for about 24% of combined black and brown carbon warming effect at the tropopause. Roughly two-thirds of the estimated brown carbon forcing occurs above 5 km, although most brown carbon is found below 5 km. The highest radiative absorption occurred during an event that ingested a wildfire plume. We conclude that high-altitude brown carbon from biomass burning is an unappreciated component of climate forcing.

Polar Amplification of Global Warming in Models Without Ice-Albedo Feedbacks

NASA Astrophysics Data System (ADS)

Alexeev, V. A.; Langen, P. L.

2004-12-01

Non-ice-albedo feedback mechanisms leading to polar amplification, as reported by Alexeev (2003), are explored in three aquaplanet climate model systems of different complexity. We analyze this pattern using three different "ghost forcing" experiments (Hansen et al, 1997). In the first one we uniformly add 4W/m2 to the oceanic mixed layer in order to roughly simulate a 2xCO2 forcing at the surface. The second forcing, of the same magnitude, is applied only within the tropics and the third forcing is applied only polewards of 30 degrees (north and south). It turns out that our systems' equilibrium responses are linear with respect to these forcings. Surprisingly, the response to the tropical-only forcing is essentially non-local with quite significant warming at higher latitudes. The response to the high-latitude-only forcing is more local and has higher amplitude near the poles. Our explanation of the polar amplification obtained in the uniform forcing experiment is therefore two-fold. Firstly, the tropics are much more difficult to warm because of the higher sensitivity of the surface budget to SST changes at higher temperatures. Secondly, any extra heat deposited in the tropics is not easily radiated to outer space because of the high opaqueness of the tropical atmosphere. The energy, most of which is latent, needs to be redistributed by transports to the extra-tropics. Consequently, the tropical "ghost forcing" results in an essentially non-local response, while the extra-tropical one yields a more localized response, because the energy in the atmosphere cannot propagate effectively equator-wards from high latitudes. The paper deals with these mechanisms in three climate model systems with no ice-albedo feedbacks - an EBM and two different GCMs - one with cloud feedbacks and the other with cloud feedbacks excluded. References. Alexeev, V.A., (2003) Sensitivity to CO2 doubling of an atmospheric GCM coupled to an oceanic mixed layer: a linear analysis. Climate Dynamics, 20: p.775-787. Hansen, J., Sato M, and R. Ruedy, (1997) Radiative forcing and climate response, JGR, 102, No. D6, 6831-6864.