Grogan, Brandon R
2010-05-01
This report presents a novel method for removing scattering effects from Nuclear Materials Identification System (NMIS) imaging. The NMIS uses fast neutron radiography to generate images of the internal structure of objects nonintrusively. If the correct attenuation through the object is measured, the positions and macroscopic cross sections of features inside the object can be determined. The cross sections can then be used to identify the materials, and a 3D map of the interior of the object can be reconstructed. Unfortunately, the measured attenuation values are always too low because scattered neutrons contribute to the unattenuated neutron signal. Previous efforts to remove the scatter from NMIS imaging have focused on minimizing the fraction of scattered neutrons that are misidentified as directly transmitted by electronically collimating and time tagging the source neutrons. The parameterized scatter removal algorithm (PSRA) approaches the problem from an entirely new direction by using Monte Carlo simulations to estimate the point scatter functions (PScFs) produced by neutrons scattering in the object. PScFs have been used to remove scattering successfully in other applications, but only with simple 2D detector models. This work represents the first time PScFs have ever been applied to an imaging detector geometry as complicated as the NMIS. By fitting the PScFs using a Gaussian function, they can be parameterized, and the proper scatter for a given problem can be removed without the need for rerunning the simulations each time. In order to model the PScFs, an entirely new method for simulating NMIS measurements was developed for this work. The development of the new models and the codes required to simulate them are presented in detail. The PSRA was used on several simulated and experimental measurements, and chi-squared goodness of fit tests were used to compare the corrected values to the ideal values that would be expected with no scattering. Using the
Grogan, Brandon R
2010-03-01
This dissertation presents a novel method for removing scattering effects from Nuclear Materials Identification System (NMIS) imaging. The NMIS uses fast neutron radiography to generate images of the internal structure of objects non-intrusively. If the correct attenuation through the object is measured, the positions and macroscopic cross-sections of features inside the object can be determined. The cross sections can then be used to identify the materials and a 3D map of the interior of the object can be reconstructed. Unfortunately, the measured attenuation values are always too low because scattered neutrons contribute to the unattenuated neutron signal. Previous efforts to remove the scatter from NMIS imaging have focused on minimizing the fraction of scattered neutrons which are misidentified as directly transmitted by electronically collimating and time tagging the source neutrons. The parameterized scatter removal algorithm (PSRA) approaches the problem from an entirely new direction by using Monte Carlo simulations to estimate the point scatter functions (PScFs) produced by neutrons scattering in the object. PScFs have been used to remove scattering successfully in other applications, but only with simple 2D detector models. This work represents the first time PScFs have ever been applied to an imaging detector geometry as complicated as the NMIS. By fitting the PScFs using a Gaussian function, they can be parameterized and the proper scatter for a given problem can be removed without the need for rerunning the simulations each time. In order to model the PScFs, an entirely new method for simulating NMIS measurements was developed for this work. The development of the new models and the codes required to simulate them are presented in detail. The PSRA was used on several simulated and experimental measurements and chi-squared goodness of fit tests were used to compare the corrected values to the ideal values that would be expected with no scattering. Using
Comment on S-matrix parameterizations in NN-scattering
Mulders, P. J.
1981-08-01
The parameterization of the S-matrix used for the elastic part of the NN-scattering matrix in, for example, the Virginia Polytechnic Institute ineractive nucleon-nucleon program SAID, is not general enough to parameterize any 2 by 2 submatrix of a unitary matrix.
Parameterization of single-scattering properties of snow
NASA Astrophysics Data System (ADS)
Räisänen, P.; Kokhanovsky, A.; Guyot, G.; Jourdan, O.; Nousiainen, T.
2015-02-01
Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat phase function typical of deformed non-spherical particles, this is still a rather ad-hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ = 0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function P11 as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons to spheres and distorted Koch fractals.
Parameterization of single-scattering properties of snow
NASA Astrophysics Data System (ADS)
Räisänen, P.; Kokhanovsky, A.; Guyot, G.; Jourdan, O.; Nousiainen, T.
2015-06-01
Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat phase function typical of deformed non-spherical particles, this is still a rather ad hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ = 0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function P11 as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons to spheres and distorted Koch fractals.
Parameterization of single-scattering properties of snow
NASA Astrophysics Data System (ADS)
Räisänen, Petri; Kokhanovsky, Alexander; Guyot, Gwennole; Jourdan, Olivier; Nousiainen, Timo
2015-04-01
Snow consists of non-spherical ice grains of various shapes and sizes, which are surrounded by air and sometimes covered by films of liquid water. Still, in many studies, homogeneous spherical snow grains have been assumed in radiative transfer calculations, due to the convenience of using Mie theory. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat scattering phase function typical of deformed non-spherical particles, this is still a rather ad-hoc choice. Here, angular scattering measurements for blowing snow conducted during the CLimate IMpacts of Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund, Svalbard, are used to construct a reference phase function for snow. Based on this phase function, an optimized habit combination (OHC) consisting of severely rough (SR) droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The single-scattering properties of snow are then computed for the OHC as a function of wavelength λ and snow grain volume-to-projected area equivalent radius rvp. Parameterization equations are developed for λ=0.199-2.7 μm and rvp = 10-2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter g and the phase function as functions of the size parameter and the real and imaginary parts of the refractive index. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and g. This is also true for the phase function parameterization, except for strongly absorbing cases (β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested snow optics parameterization, making comparisons with spheres and distorted Koch fractals. Further evaluation and validation of the proposed approach against (e.g.) bidirectional reflectance and polarization measurements for snow is planned. At any rate, it seems safe to assume that the OHC selected here
NASA Astrophysics Data System (ADS)
Fu, Qiang
1991-02-01
A radiation model has been developed to calculate the radiative fluxes and heating rates in plane parallel, vertically nonhomogeneous, multiple scattering atmospheres with an accuracy of better than 5%. This scheme is appropriate for use in climate and numerical prediction models to study the effect of cloud and radiation interactions. Parameterization of nongray gaseous absorption in vertically nonhomogeneous atmospheres has been developed based upon the correlated K-distribution method. The entire radiation spectrum is divided into 18 intervals: 6 in the solar and 12 in the infrared. By using a minimum number of quadrature points within each wavelength interval to represent the gaseous absorption and to treat overlap, we need to perform 121 spectral calculations for each vertical profile to obtain total radiative fluxes and heating rates. The treatment of gaseous absorption introduces errors less than 0.05 K/day in the heating rates below 30 km and and relative errors less than 0.5% in the fluxes. The single-scattering properties of water/ice clouds have been parameterized in terms of the effective size and liquid/ice water contents, based on Mie-scattering/ray -tracing computations with the best available size distributions. The parameterization gives an accuracy within about 1% in the solar and 5% in the infrared. By using the delta-four-stream approximation, a single algorithm has been developed for radiative transfer calculations. For vertically nonhomogeneous atmospheres, this code is numerically stable and computationally efficient. The accuracy of the algorithm is generally better than 5%, but it can produce more accurate results in the limit of no scattering. Compared with line-by-line results from clear -sky longwave calculations when all constituents were included, the errors in heating rates calculated by the new radiation model are less than 0.1 K/day in the troposphere and lower stratosphere. The errors in radiative fluxes are less than 1% both at
Parameterization of radiative processes in vertically nonhomogeneous multiple scattering atmospheres
NASA Astrophysics Data System (ADS)
Fu, Qiang
1991-05-01
A radiation model has been developed to calculate the radiative fluxes and heating rates in plane parallel, vertically nonhomogeneous, multiple scattering atmospheres with an accuracy of better than 5 percent. This scheme is appropriate for use in climate and numerical prediction models to study the effect of cloud and radiation interactions. Parameterization of nongray gaseous absorption in vertically nonhomogeneous atmospheres has been developed based upon the correlated K-distribution method. The entire radiation spectrum is divided into 18 intervals: 6 in the solar and 12 in the infrared. By using a minimum number of quadrature points within each wavelength interval to represent the gaseous absorption and to treat overlap, we need to perform 121 spectral calculations for each vertical profile to obtain total radiative fluxes and heating rates. The treatment of gaseous absorption introduces errors less than 0.05 K/day in the heating rates below 30 km and relative errors less than 0.5 percent in the fluxes. The single-scattering properties of water/ice clouds have been parameterized in terms of the effective size and liquid/ice water contents, based on Mie-scattering/ray-tracing computations with the best available size distributions. The parameterization gives an accuracy within about 1 percent in the solar and 5 percent in the infrared. By using the delta-four-stream approximation, a single algorithm has been developed for radiative transfer calculations. For vertically nonhomogeneous atmospheres, this code is numerically stable and computationally efficient. The accuracy of the algorithm is generally better than 5 percent, but it can produce more accurate results in the limit of no scattering. Compared with line-by-line results from clear-sky longwave calculations when all constituents were included, the errors in heating rates calculated by the new radiation model are less than 0.1 K/day in the troposphere and lower stratosphere. The errors in radiative
Cross section parameterizations for cosmic ray nuclei. 1: Single nucleon removal
NASA Technical Reports Server (NTRS)
Norbury, John W.; Townsend, Lawrence W.
1992-01-01
Parameterizations of single nucleon removal from electromagnetic and strong interactions of cosmic rays with nuclei are presented. These parameterizations are based upon the most accurate theoretical calculations available to date. They should be very suitable for use in cosmic ray propagation through interstellar space, the Earth's atmosphere, lunar samples, meteorites, spacecraft walls and lunar and martian habitats.
NASA Astrophysics Data System (ADS)
Yang, Ping; Liou, Kuo-Nan; Bi, Lei; Liu, Chao; Yi, Bingqi; Baum, Bryan A.
2015-01-01
Presented is a review of the radiative properties of ice clouds from three perspectives: light scattering simulations, remote sensing applications, and broadband radiation parameterizations appropriate for numerical models. On the subject of light scattering simulations, several classical computational approaches are reviewed, including the conventional geometric-optics method and its improved forms, the finite-difference time domain technique, the pseudo-spectral time domain technique, the discrete dipole approximation method, and the T-matrix method, with specific applications to the computation of the single-scattering properties of individual ice crystals. The strengths and weaknesses associated with each approach are discussed. With reference to remote sensing, operational retrieval algorithms are reviewed for retrieving cloud optical depth and effective particle size based on solar or thermal infrared (IR) bands. To illustrate the performance of the current solar- and IR-based retrievals, two case studies are presented based on spaceborne observations. The need for a more realistic ice cloud optical model to obtain spectrally consistent retrievals is demonstrated. Furthermore, to complement ice cloud property studies based on passive radiometric measurements, the advantage of incorporating lidar and/or polarimetric measurements is discussed. The performance of ice cloud models based on the use of different ice habits to represent ice particles is illustrated by comparing model results with satellite observations. A summary is provided of a number of parameterization schemes for ice cloud radiative properties that were developed for application to broadband radiative transfer submodels within general circulation models (GCMs). The availability of the single-scattering properties of complex ice habits has led to more accurate radiation parameterizations. In conclusion, the importance of using nonspherical ice particle models in GCM simulations for climate
NASA Astrophysics Data System (ADS)
Alvarado, Matthew J.; Lonsdale, Chantelle R.; Macintyre, Helen L.; Bian, Huisheng; Chin, Mian; Ridley, David A.; Heald, Colette L.; Thornhill, Kenneth L.; Anderson, Bruce E.; Cubison, Michael J.; Jimenez, Jose L.; Kondo, Yutaka; Sahu, Lokesh K.; Dibb, Jack E.; Wang, Chien
2016-07-01
Accurate modeling of the scattering and absorption of ultraviolet and visible radiation by aerosols is essential for accurate simulations of atmospheric chemistry and climate. Closure studies using in situ measurements of aerosol scattering and absorption can be used to evaluate and improve models of aerosol optical properties without interference from model errors in aerosol emissions, transport, chemistry, or deposition rates. Here we evaluate the ability of four externally mixed, fixed size distribution parameterizations used in global models to simulate submicron aerosol scattering and absorption at three wavelengths using in situ data gathered during the 2008 Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS) campaign. The four models are the NASA Global Modeling Initiative (GMI) Combo model, GEOS-Chem v9-02, the baseline configuration of a version of GEOS-Chem with online radiative transfer calculations (called GC-RT), and the Optical Properties of Aerosol and Clouds (OPAC v3.1) package. We also use the ARCTAS data to perform the first evaluation of the ability of the Aerosol Simulation Program (ASP v2.1) to simulate submicron aerosol scattering and absorption when in situ data on the aerosol size distribution are used, and examine the impact of different mixing rules for black carbon (BC) on the results. We find that the GMI model tends to overestimate submicron scattering and absorption at shorter wavelengths by 10-23 %, and that GMI has smaller absolute mean biases for submicron absorption than OPAC v3.1, GEOS-Chem v9-02, or GC-RT. However, the changes to the density and refractive index of BC in GC-RT improve the simulation of submicron aerosol absorption at all wavelengths relative to GEOS-Chem v9-02. Adding a variable size distribution, as in ASP v2.1, improves model performance for scattering but not for absorption, likely due to the assumption in ASP v2.1 that BC is present at a constant mass fraction
Laser scattering measurement for laser removal of graffiti
NASA Astrophysics Data System (ADS)
Tearasongsawat, Watcharawee; Kittiboonanan, Phumipat; Luengviriya, Chaiya; Ratanavis, Amarin
2015-07-01
In this contribution, a technical development of the laser scattering measurement for laser removal of graffiti is reported. This study concentrates on the removal of graffiti from metal surfaces. Four colored graffiti paints were applied to stainless steel samples. Cleaning efficiency was evaluated by the laser scattering system. In this study, an angular laser removal of graffiti was attempted to examine the removal process under practical conditions. A Q-switched Nd:YAG laser operating at 1.06 microns with the repetition rate of 1 Hz was used to remove graffiti from stainless steel samples. The laser fluence was investigated from 0.1 J/cm2 to 7 J/cm2. The laser parameters to achieve the removal effectiveness were determined by using the laser scattering system. This study strongly leads to further development of the potential online surface inspection for the removal of graffiti.
A modified Fresnel scattering model for the parameterization of Fresnel returns, part 2.3A
NASA Technical Reports Server (NTRS)
Gage, K. S.; Ecklund, W. L.; Balsley, B. B.
1984-01-01
A modified Fresnel scatter model is presented and the revised model is compared with observations from the Poker Flat, Alaska, radar, the SOUSY radar and the Jimcamarca radar. The modifications to the original model have been made to better account for the pulse width dependence and height dependence of backscattered power observed at vertical incidence at lower VHF. Vertical profiles of backscattered power calculated using the revised model and routine radiosonde data show good agreement with observed backscattered power profiles. Relative comparisons of backscattered power using climatological data for the model agree fairly well with observed backscattered power profiles from Poker Flat, Jicamarca, and SOUSY.
Scattering Removal for Finger-Vein Image Restoration
Yang, Jinfeng; Zhang, Ben; Shi, Yihua
2012-01-01
Finger-vein recognition has received increased attention recently. However, the finger-vein images are always captured in poor quality. This certainly makes finger-vein feature representation unreliable, and further impairs the accuracy of finger-vein recognition. In this paper, we first give an analysis of the intrinsic factors causing finger-vein image degradation, and then propose a simple but effective image restoration method based on scattering removal. To give a proper description of finger-vein image degradation, a biological optical model (BOM) specific to finger-vein imaging is proposed according to the principle of light propagation in biological tissues. Based on BOM, the light scattering component is sensibly estimated and properly removed for finger-vein image restoration. Finally, experimental results demonstrate that the proposed method is powerful in enhancing the finger-vein image contrast and in improving the finger-vein image matching accuracy. PMID:22737028
Scattering removal for finger-vein image restoration.
Yang, Jinfeng; Zhang, Ben; Shi, Yihua
2012-01-01
Finger-vein recognition has received increased attention recently. However, the finger-vein images are always captured in poor quality. This certainly makes finger-vein feature representation unreliable, and further impairs the accuracy of finger-vein recognition. In this paper, we first give an analysis of the intrinsic factors causing finger-vein image degradation, and then propose a simple but effective image restoration method based on scattering removal. To give a proper description of finger-vein image degradation, a biological optical model (BOM) specific to finger-vein imaging is proposed according to the principle of light propagation in biological tissues. Based on BOM, the light scattering component is sensibly estimated and properly removed for finger-vein image restoration. Finally, experimental results demonstrate that the proposed method is powerful in enhancing the finger-vein image contrast and in improving the finger-vein image matching accuracy. PMID:22737028
NASA Astrophysics Data System (ADS)
Pokhrel, Rudra P.; Wagner, Nick L.; Langridge, Justin M.; Lack, Daniel A.; Jayarathne, Thilina; Stone, Elizabeth A.; Stockwell, Chelsea E.; Yokelson, Robert J.; Murphy, Shane M.
2016-08-01
Single-scattering albedo (SSA) and absorption Ångström exponent (AAE) are two critical parameters in determining the impact of absorbing aerosol on the Earth's radiative balance. Aerosol emitted by biomass burning represent a significant fraction of absorbing aerosol globally, but it remains difficult to accurately predict SSA and AAE for biomass burning aerosol. Black carbon (BC), brown carbon (BrC), and non-absorbing coatings all make substantial contributions to the absorption coefficient of biomass burning aerosol. SSA and AAE cannot be directly predicted based on fuel type because they depend strongly on burn conditions. It has been suggested that SSA can be effectively parameterized via the modified combustion efficiency (MCE) of a biomass burning event and that this would be useful because emission factors for CO and CO2, from which MCE can be calculated, are available for a large number of fuels. Here we demonstrate, with data from the FLAME-4 experiment, that for a wide variety of globally relevant biomass fuels, over a range of combustion conditions, parameterizations of SSA and AAE based on the elemental carbon (EC) to organic carbon (OC) mass ratio are quantitatively superior to parameterizations based on MCE. We show that the EC / OC ratio and the ratio of EC / (EC + OC) both have significantly better correlations with SSA than MCE. Furthermore, the relationship of EC / (EC + OC) with SSA is linear. These improved parameterizations are significant because, similar to MCE, emission factors for EC (or black carbon) and OC are available for a wide range of biomass fuels. Fitting SSA with MCE yields correlation coefficients (Pearson's r) of ˜ 0.65 at the visible wavelengths of 405, 532, and 660 nm while fitting SSA with EC / OC or EC / (EC + OC) yields a Pearson's r of 0.94-0.97 at these same wavelengths. The strong correlation coefficient at 405 nm (r = 0.97) suggests that parameterizations based on EC / OC or EC / (EC + OC) have good predictive
NASA Astrophysics Data System (ADS)
Xu, Hai-Bo; Zheng, Na
2015-07-01
A version of Geant4 has been developed to treat high-energy proton radiography. This article presents the results of calculations simulating the effects of nuclear elastic scattering for various test step wedges. Comparisons with experimental data are also presented. The traditional expressions of the transmission should be correct if the angle distribution of the scattering is Gaussian multiple Coulomb scattering. The mean free path (which depends on the collimator angle) and the radiation length are treated as empirical parameters, according to transmission as a function of thickness obtained by simulations. The results can be used in density reconstruction, which depends on the transmission expressions. Supported by NSAF (11176001) and Science and Technology Developing Foundation of China Academy of Engineering Physics (2012A0202006)
Seed removal by scatter-hoarding rodents: the effects of tannin and nutrient concentration.
Wang, Bo; Yang, Xiaolan
2015-04-01
The mutualistic interaction between scatter-hoarding rodents and seed plants have a long co-evolutionary history. Plants are believed to have evolved traits that influence the foraging behavior of rodents, thus increasing the probability of seed removal and caching, which benefits the establishment of seedlings. Tannin and nutrient content in seeds are considered among the most essential factors in this plant-animal interaction. However, most previous studies used different species of plant seeds, rendering it difficult to tease apart the relative effect of each single nutrient on rodent foraging behavior due to confounding combinations of nutrient contents across seed species. Hence, to further explore how tannin and different nutritional traits of seed affect scatter-hoarding rodent foraging preferences, we manipulated tannin, fat, protein and starch content levels, and also seed size levels by using an artificial seed system. Our results showed that both tannin and various nutrients significantly affected rodent foraging preferences, but were also strongly affected by seed size. In general, rodents preferred to remove seeds with less tannin. Fat addition could counteract the negative effect of tannin on seed removal by rodents, while the effect of protein addition was weaker. Starch by itself had no effect, but it interacted with tannin in a complex way. Our findings shed light on the effects of tannin and nutrient content on seed removal by scatter-hoarding rodents. We therefore, believe that these and perhaps other seed traits should interactively influence this important plant-rodent interaction. However, how selection operates on seed traits to counterbalance these competing interests/factors merits further study. PMID:25625425
NASA Astrophysics Data System (ADS)
Ryu, Y.; Kobayashi, H.; Welles, J.; Norman, J.
2011-12-01
Correct estimation of gap fraction is essential to quantify canopy architectural variables such as leaf area index and clumping index, which mainly control land-atmosphere interactions. However, gap fraction measurements from optical sensors are contaminated by scattered radiation by canopy and ground surface. In this study, we propose a simple invertible bidirectional transmission model to remove scattering effects from gap fraction measurements. The model shows that 1) scattering factor appears highest where leaf area index is 1-2 in non-clumped canopy, 2) relative scattering factor (scattering factor/measured gap fraction) increases with leaf area index, 3) bright land surface (e.g. snow and bright soil) can contribute a significant scattering factor, 4) the scattering factor is not marginal even in highly diffused sky condition. By incorporating the model with LAI2200 data collected in an open savanna ecosystem, we find that the scattering factor causes significant underestimation of leaf area index (25%) and significant overestimation of clumping index (6 %). The results highlight that some LAI-2000-based LAI estimates from around the world may be underestimated, particularly in highly clumped broad-leaf canopies. Fortunately, the importance of scattering could be assessed with software from LICOR, Inc., which will incorporate the scattering model from this study in a post processing mode after data has been collected by a LAI-2000 or LAI-2200.
Radiation properties and emissivity parameterization of high level thin clouds
NASA Technical Reports Server (NTRS)
Wu, M.-L. C.
1984-01-01
To parameterize emissivity of clouds at 11 microns, a study has been made in an effort to understand the radiation field of thin clouds. The contributions to the intensity and flux from different sources and through different physical processes are calculated by using the method of successive orders of scattering. The effective emissivity of thin clouds is decomposed into the effective absorption emissivity, effective scattering emissivity, and effective reflection emissivity. The effective absorption emissivity depends on the absorption and emission of the cloud; it is parameterized in terms of optical thickness. The effective scattering emissivity depends on the scattering properties of the cloud; it is parameterized in terms of optical thickness and single scattering albedo. The effective reflection emissivity follows the similarity relation as in the near infrared cases. This is parameterized in terms of the similarity parameter and optical thickness, as well as the temperature difference between the cloud and ground.
NASA Astrophysics Data System (ADS)
Rana, R.; Jain, A.; Shankar, A.; Bednarek, D. R.; Rudin, S.
2016-03-01
In radiography, one of the best methods to eliminate image-degrading scatter radiation is the use of anti-scatter grids. However, with high-resolution dynamic imaging detectors, stationary anti-scatter grids can leave grid-line shadows and moiré patterns on the image, depending upon the line density of the grid and the sampling frequency of the x-ray detector. Such artifacts degrade the image quality and may mask small but important details such as small vessels and interventional device features. Appearance of these artifacts becomes increasingly severe as the detector spatial resolution is improved. We have previously demonstrated that, to remove these artifacts by dividing out a reference grid image, one must first subtract the residual scatter that penetrates the grid; however, for objects with anatomic structure, scatter varies throughout the FOV and a spatially differing amount of scatter must be subtracted. In this study, a standard stationary Smit-Rontgen X-ray grid (line density - 70 lines/cm, grid ratio - 13:1) was used with a high-resolution CMOS detector, the Dexela 1207 (pixel size - 75 micron) to image anthropomorphic head phantoms. For a 15 x 15cm FOV, scatter profiles of the anthropomorphic head phantoms were estimated then iteratively modified to minimize the structured noise due to the varying grid-line artifacts across the FOV. Images of the anthropomorphic head phantoms taken with the grid, before and after the corrections, were compared demonstrating almost total elimination of the artifact over the full FOV. Hence, with proper computational tools, antiscatter grid artifacts can be corrected, even during dynamic sequences.
Andresen, Kurt; Jimenez-Useche, Isabel; Howell, Steven C; Yuan, Chongli; Qiu, Xiangyun
2013-01-01
Using a combination of small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) measurements we have determined the role of the H3 and H4 histone tails, independently, in stabilizing the nucleosome DNA terminal ends from unwrapping from the nucleosome core. We have performed solution scattering experiments on recombinant wild-type, H3 and H4 tail-removed mutants and fit all scattering data with predictions from PDB models and compared these experiments to complementary DNA-end FRET experiments. Based on these combined SAXS and FRET studies, we find that while all nucleosomes exhibited DNA unwrapping, the extent of this unwrapping is increased for nucleosomes with the H3 tails removed but, surprisingly, decreased in nucleosomes with the H4 tails removed. Studies of salt concentration effects show a minimum amount of DNA unwrapping for all complexes around 50-100mM of monovalent ions. These data exhibit opposite roles for the positively-charged nucleosome tails, with the ability to decrease access (in the case of the H3 histone) or increase access (in the case of the H4 histone) to the DNA surrounding the nucleosome. In the range of salt concentrations studied (0-200mM KCl), the data point to the H4 tail-removed mutant at physiological (50-100mM) monovalent salt concentration as the mononucleosome with the least amount of DNA unwrapping. PMID:24265699
Andresen, Kurt; Jimenez-Useche, Isabel; Howell, Steven C.; Yuan, Chongli; Qiu, Xiangyun
2013-01-01
Using a combination of small-angle X-ray scattering (SAXS) and fluorescence resonance energy transfer (FRET) measurements we have determined the role of the H3 and H4 histone tails, independently, in stabilizing the nucleosome DNA terminal ends from unwrapping from the nucleosome core. We have performed solution scattering experiments on recombinant wild-type, H3 and H4 tail-removed mutants and fit all scattering data with predictions from PDB models and compared these experiments to complementary DNA-end FRET experiments. Based on these combined SAXS and FRET studies, we find that while all nucleosomes exhibited DNA unwrapping, the extent of this unwrapping is increased for nucleosomes with the H3 tails removed but, surprisingly, decreased in nucleosomes with the H4 tails removed. Studies of salt concentration effects show a minimum amount of DNA unwrapping for all complexes around 50-100mM of monovalent ions. These data exhibit opposite roles for the positively-charged nucleosome tails, with the ability to decrease access (in the case of the H3 histone) or increase access (in the case of the H4 histone) to the DNA surrounding the nucleosome. In the range of salt concentrations studied (0-200mM KCl), the data point to the H4 tail-removed mutant at physiological (50-100mM) monovalent salt concentration as the mononucleosome with the least amount of DNA unwrapping. PMID:24265699
Stochastic Convection Parameterizations
NASA Technical Reports Server (NTRS)
Teixeira, Joao; Reynolds, Carolyn; Suselj, Kay; Matheou, Georgios
2012-01-01
computational fluid dynamics, radiation, clouds, turbulence, convection, gravity waves, surface interaction, radiation interaction, cloud and aerosol microphysics, complexity (vegetation, biogeochemistry, radiation versus turbulence/convection stochastic approach, non-linearities, Monte Carlo, high resolutions, large-Eddy Simulations, cloud structure, plumes, saturation in tropics, forecasting, parameterizations, stochastic, radiation-clod interaction, hurricane forecasts
The Influence of Microphysical Cloud Parameterization on Microwave Brightness Temperatures
NASA Technical Reports Server (NTRS)
Skofronick-Jackson, Gail M.; Gasiewski, Albin J.; Wang, James R.; Zukor, Dorothy J. (Technical Monitor)
2000-01-01
The microphysical parameterization of clouds and rain-cells plays a central role in atmospheric forward radiative transfer models used in calculating passive microwave brightness temperatures. The absorption and scattering properties of a hydrometeor-laden atmosphere are governed by particle phase, size distribution, aggregate density., shape, and dielectric constant. This study identifies the sensitivity of brightness temperatures with respect to the microphysical cloud parameterization. Cloud parameterizations for wideband (6-410 GHz observations of baseline brightness temperatures were studied for four evolutionary stages of an oceanic convective storm using a five-phase hydrometeor model in a planar-stratified scattering-based radiative transfer model. Five other microphysical cloud parameterizations were compared to the baseline calculations to evaluate brightness temperature sensitivity to gross changes in the hydrometeor size distributions and the ice-air-water ratios in the frozen or partly frozen phase. The comparison shows that, enlarging the rain drop size or adding water to the partly Frozen hydrometeor mix warms brightness temperatures by up to .55 K at 6 GHz. The cooling signature caused by ice scattering intensifies with increasing ice concentrations and at higher frequencies. An additional comparison to measured Convection and Moisture LA Experiment (CAMEX 3) brightness temperatures shows that in general all but, two parameterizations produce calculated T(sub B)'s that fall within the observed clear-air minima and maxima. The exceptions are for parameterizations that, enhance the scattering characteristics of frozen hydrometeors.
Yoon, Y; Park, M; Kim, H; Kim, K; Kim, J; Morishita, J
2015-06-15
Purpose: This study aims to identify the feasibility of a novel cesium-iodine (CsI)-based flat-panel detector (FPD) for removing scatter radiation in diagnostic radiology. Methods: The indirect FPD comprises three layers: a substrate, scintillation, and thin-film-transistor (TFT) layer. The TFT layer has a matrix structure with pixels. There are ineffective dimensions on the TFT layer, such as the voltage and data lines; therefore, we devised a new FPD system having net-like lead in the substrate layer, matching the ineffective area, to block the scatter radiation so that only primary X-rays could reach the effective dimension.To evaluate the performance of this new FPD system, we conducted a Monte Carlo simulation using MCNPX 2.6.0 software. Scatter fractions (SFs) were acquired using no grid, a parallel grid (8:1 grid ratio), and the new system, and the performances were compared.Two systems having different thicknesses of lead in the substrate layer—10 and 20μm—were simulated. Additionally, we examined the effects of different pixel sizes (153×153 and 163×163μm) on the image quality, while keeping the effective area of pixels constant (143×143μm). Results: In case of 10μm lead, the SFs of the new system (∼11%) were lower than those of the other system (∼27% with no grid, ∼16% with parallel grid) at 40kV. However, as the tube voltage increased, the SF of new system (∼19%) was higher than that of parallel grid (∼18%) at 120kV. In the case of 20μm lead, the SFs of the new system were lower than those of the other systems at all ranges of the tube voltage (40–120kV). Conclusion: The novel CsI-based FPD system for removing scatter radiation is feasible for improving the image contrast but must be optimized with respect to the lead thickness, considering the system’s purposes and the ranges of the tube voltage in diagnostic radiology. This study was supported by a grant(K1422651) from Institute of Health Science, Korea University.
[Characteristics and Parameterization for Atmospheric Extinction Coefficient in Beijing].
Chen, Yi-na; Zhao, Pu-sheng; He, Di; Dong, Fan; Zhao, Xiu-juan; Zhang, Xiao-ling
2015-10-01
In order to study the characteristics of atmospheric extinction coefficient in Beijing, systematic measurements had been carried out for atmospheric visibility, PM2.5 concentration, scattering coefficient, black carbon, reactive gases, and meteorological parameters from 2013 to 2014. Based on these data, we compared some published fitting schemes of aerosol light scattering enhancement factor [ f(RH)], and discussed the characteristics and the key influence factors for atmospheric extinction coefficient. Then a set of parameterization models of atmospheric extinction coefficient for different seasons and different polluted levels had been established. The results showed that aerosol scattering accounted for more than 94% of total light extinction. In the summer and autumn, the aerosol hygroscopic growth caused by high relative humidity had increased the aerosol scattering coefficient by 70 to 80 percent. The parameterization models could reflect the influencing mechanism of aerosol and relative humidity upon ambient light extinction, and describe the seasonal variations of aerosol light extinction ability. PMID:26841588
Parameterization of sub-grid scale convection
NASA Technical Reports Server (NTRS)
Frank, William; Molinari, John; Kain, Jack; Moncrieff, Mitch; Karyampudi, Mohan; Grell, Georg
1993-01-01
The following topics are discussed: an overview of the cumulus parameterization problem; interactions between explicit and implicit processes in mesoscale models; effects of model grid size on the cumulus parameterization problem; parameterizing convective effects on momentum fields in mesoscale models; differences between slantwise and vertical cumulus parameterization; experiments with different closure hypotheses; and coupling cumulus parameterizations to boundary layer, stable cloud, and radiation schemes.
Parameterization of solar cells
NASA Astrophysics Data System (ADS)
Appelbaum, J.; Chait, A.; Thompson, D.
1992-10-01
The aggregation (sorting) of the individual solar cells into an array is commonly based on a single operating point on the current-voltage (I-V) characteristic curve. An alternative approach for cell performance prediction and cell screening is provided by modeling the cell using an equivalent electrical circuit, in which the parameters involved are related to the physical phenomena in the device. These analytical models may be represented by a double exponential I-V characteristic with seven parameters, by a double exponential model with five parameters, or by a single exponential equation with four or five parameters. In this article we address issues concerning methodologies for the determination of solar cell parameters based on measured data points of the I-V characteristic, and introduce a procedure for screening of solar cells for arrays. We show that common curve fitting techniques, e.g., least squares, may produce many combinations of parameter values while maintaining a good fit between the fitted and measured I-V characteristics of the cell. Therefore, techniques relying on curve fitting criteria alone cannot be directly used for cell parameterization. We propose a consistent procedure which takes into account the entire set of parameter values for a batch of cells. This procedure is based on a definition of a mean cell representing the batch, and takes into account the relative contribution of each parameter to the overall goodness of fit. The procedure is demonstrated on a batch of 50 silicon cells for Space Station Freedom.
Parameterization of solar cells
NASA Technical Reports Server (NTRS)
Appelbaum, J.; Chait, A.; Thompson, D.
1992-01-01
The aggregation (sorting) of the individual solar cells into an array is commonly based on a single operating point on the current-voltage (I-V) characteristic curve. An alternative approach for cell performance prediction and cell screening is provided by modeling the cell using an equivalent electrical circuit, in which the parameters involved are related to the physical phenomena in the device. These analytical models may be represented by a double exponential I-V characteristic with seven parameters, by a double exponential model with five parameters, or by a single exponential equation with four or five parameters. In this article we address issues concerning methodologies for the determination of solar cell parameters based on measured data points of the I-V characteristic, and introduce a procedure for screening of solar cells for arrays. We show that common curve fitting techniques, e.g., least squares, may produce many combinations of parameter values while maintaining a good fit between the fitted and measured I-V characteristics of the cell. Therefore, techniques relying on curve fitting criteria alone cannot be directly used for cell parameterization. We propose a consistent procedure which takes into account the entire set of parameter values for a batch of cells. This procedure is based on a definition of a mean cell representing the batch, and takes into account the relative contribution of each parameter to the overall goodness of fit. The procedure is demonstrated on a batch of 50 silicon cells for Space Station Freedom.
A Flexible Parameterization for Shortwave Optical Properties of Ice Crystals
NASA Technical Reports Server (NTRS)
VanDiedenhoven, Bastiaan; Ackerman, Andrew S.; Cairns, Brian; Fridlind, Ann M.
2014-01-01
A parameterization is presented that provides extinction cross section sigma (sub e), single-scattering albedo omega, and asymmetry parameter (g) of ice crystals for any combination of volume, projected area, aspect ratio, and crystal distortion at any wavelength in the shortwave. Similar to previous parameterizations, the scheme makes use of geometric optics approximations and the observation that optical properties of complex, aggregated ice crystals can be well approximated by those of single hexagonal crystals with varying size, aspect ratio, and distortion levels. In the standard geometric optics implementation used here, sigma (sub e) is always twice the particle projected area. It is shown that omega is largely determined by the newly defined absorption size parameter and the particle aspect ratio. These dependences are parameterized using a combination of exponential, lognormal, and polynomial functions. The variation of (g) with aspect ratio and crystal distortion is parameterized for one reference wavelength using a combination of several polynomials. The dependences of g on refractive index and omega are investigated and factors are determined to scale the parameterized (g) to provide values appropriate for other wavelengths. The parameterization scheme consists of only 88 coefficients. The scheme is tested for a large variety of hexagonal crystals in several wavelength bands from 0.2 to 4 micron, revealing absolute differences with reference calculations of omega and (g) that are both generally below 0.015. Over a large variety of cloud conditions, the resulting root-mean-squared differences with reference calculations of cloud reflectance, transmittance, and absorptance are 1.4%, 1.1%, and 3.4%, respectively. Some practical applications of the parameterization in atmospheric models are highlighted.
Assessment of Mixed Layer Mesoscale Parameterization in Eddy Resolving Simulations.
NASA Astrophysics Data System (ADS)
Clayson, C. A.; Luneva, M. V.; Dubovikov, M. S.
2014-12-01
In eddy resolving simulations we test a mixed layer mesoscale parameterization, developed recently by Canuto and Dubovikov (2011). The parameterization yields the horizontal and vertical mesoscale fluxes in terms of coarse-resolution fields and eddy kinetic energy. An expression for the later in terms of mean fields has been found too to get a closed parameterization in terms of the mean fields only. In 40 numerical experiments we simulated the two types of flows: idealized flows driven by baroclinic instabilities only, and more realistic flows, driven by wind and surface fluxes as well as by inflow-outflow in shallow and narrow straits. The diagnosed quasi-instantaneous horizontal and vertical mesoscale buoyancy fluxes (averaged over 1o - 2o and 10 days) demonstrate a strong scatter typical for turbulent flows, however, the fluxes are highly correlated with the parameterization. After averaged over 3-4 months, diffusivities diagnosed from the eddy resolving simulations, are quite consistent with the parameterization for a broad range of parameters. Diagnosed vertical mesoscale fluxes restratify mixed layer and are in a good agreement with the parameterization unless vertical turbulent mixing in the upper layer becomes strong enough to compare with mesoscale advection. In the later case, numerical simulations demonstrate that the deviation of the fluxes from the parameterization is controlled by the dimensionless parameter γ, estimating the ratio of vertical diffusion term to a mesoscale advection. The empirical dependence of vertical flux on γ is found. An analysis using a modified omega-equation reveals that the effects of the vertical mixing of vorticity is responsible for the two-three fold amplification of vertical mesoscale flux. Possible physical mechanisms, responsible for the amplification of vertical mesoscale flux are discussed.
Summary of Cumulus Parameterization Workshop
NASA Technical Reports Server (NTRS)
Tao, Wei-Kuo; Starr, David OC.; Hou, Arthur; Newman, Paul; Sud, Yogesh
2002-01-01
A workshop on cumulus parameterization took place at the NASA Goddard Space Flight Center from December 3-5, 2001. The major objectives of this workshop were (1) to review the problem of representation of moist processes in large-scale models (mesoscale models, Numerical Weather Prediction models and Atmospheric General Circulation Models), (2) to review the state-of-the-art in cumulus parameterization schemes, and (3) to discuss the need for future research and applications. There were a total of 31 presentations and about 100 participants from the United States, Japan, the United Kingdom, France and South Korea. The specific presentations and discussions during the workshop are summarized in this paper.
Su, Jing-Wei; Hsu, Wei-Chen; Tjiu, Jeng-Wei; Chiang, Chun-Pin; Huang, Chao-Wei; Sung, Kung-Bin
2014-01-01
The scattering properties and refractive indices (RI) of tissue are important parameters in tissue optics. These parameters can be determined from quantitative phase images of thin slices of tissue blocks. However, the changes in RI and structure of cells due to fixation and paraffin embedding might result in inaccuracies in the estimation of the scattering properties of tissue. In this study, three-dimensional RI distributions of cells were measured using digital holographic microtomography to obtain total scattering cross sections (TSCS) of the cells based on the first-order Born approximation. We investigated the slight loss of dry mass and drastic shrinkage of cells due to paraformaldehyde fixation and paraffin embedding removal processes. We propose a method to compensate for the correlated changes in volume and RI of cells. The results demonstrate that the TSCS of live cells can be estimated using restored cells. The percentage deviation of the TSCS between restored cells and live cells was only −8%. Spatially resolved RI and scattering coefficients of unprocessed oral epithelium ranged from 1.35 to 1.39 and from 100 to 450 cm−1, respectively, estimated from paraffinembedded oral epithelial tissue after restoration of RI and volume. PMID:25069007
NASA Astrophysics Data System (ADS)
Su, Jing-Wei; Hsu, Wei-Chen; Tjiu, Jeng-Wei; Chiang, Chun-Pin; Huang, Chao-Wei; Sung, Kung-Bin
2014-07-01
The scattering properties and refractive indices (RI) of tissue are important parameters in tissue optics. These parameters can be determined from quantitative phase images of thin slices of tissue blocks. However, the changes in RI and structure of cells due to fixation and paraffin embedding might result in inaccuracies in the estimation of the scattering properties of tissue. In this study, three-dimensional RI distributions of cells were measured using digital holographic microtomography to obtain total scattering cross sections (TSCS) of the cells based on the first-order Born approximation. We investigated the slight loss of dry mass and drastic shrinkage of cells due to paraformaldehyde fixation and paraffin embedding removal processes. We propose a method to compensate for the correlated changes in volume and RI of cells. The results demonstrate that the TSCS of live cells can be estimated using restored cells. The percentage deviation of the TSCS between restored cells and live cells was only -8%. Spatially resolved RI and scattering coefficients of unprocessed oral epithelium ranged from 1.35 to 1.39 and from 100 to 450 cm-1, respectively, estimated from paraffin-embedded oral epithelial tissue after restoration of RI and volume.
ARM Data for Cloud Parameterization
Xu, Kuan-Man
2006-10-02
The PI's ARM investigation (DE-IA02-02ER633 18) developed a physically-based subgrid-scale saturation representation that fully considers the direct interactions of the parameterized subgrid-scale motions with subgrid-scale cloud microphysical and radiative processes. Major accomplishments under the support of that interagency agreement are summarized in this paper.
Parameterized Beyond-Einstein Growth
Linder, Eric; Linder, Eric V.; Cahn, Robert N.
2007-09-17
A single parameter, the gravitational growth index gamma, succeeds in characterizing the growth of density perturbations in the linear regime separately from the effects of the cosmic expansion. The parameter is restricted to a very narrow range for models of dark energy obeying the laws of general relativity but can take on distinctly different values in models of beyond-Einstein gravity. Motivated by the parameterized post-Newtonian (PPN) formalism for testing gravity, we analytically derive and extend the gravitational growth index, or Minimal Modified Gravity, approach to parameterizing beyond-Einstein cosmology. The analytic formalism demonstrates how to apply the growth index parameter to early dark energy, time-varying gravity, DGP braneworld gravity, and some scalar-tensor gravity.
Recursive Abstractions for Parameterized Systems
NASA Astrophysics Data System (ADS)
Jaffar, Joxan; Santosa, Andrew E.
We consider a language of recursively defined formulas about arrays of variables, suitable for specifying safety properties of parameterized systems. We then present an abstract interpretation framework which translates a paramerized system as a symbolic transition system which propagates such formulas as abstractions of underlying concrete states. The main contribution is a proof method for implications between the formulas, which then provides for an implementation of this abstract interpreter.
The predictive consequences of parameterization
NASA Astrophysics Data System (ADS)
White, J.; Hughes, J. D.; Doherty, J. E.
2013-12-01
In numerical groundwater modeling, parameterization is the process of selecting the aspects of a computer model that will be allowed to vary during history matching. This selection process is dependent on professional judgment and is, therefore, inherently subjective. Ideally, a robust parameterization should be commensurate with the spatial and temporal resolution of the model and should include all uncertain aspects of the model. Limited computing resources typically require reducing the number of adjustable parameters so that only a subset of the uncertain model aspects are treated as estimable parameters; the remaining aspects are treated as fixed parameters during history matching. We use linear subspace theory to develop expressions for the predictive error incurred by fixing parameters. The predictive error is comprised of two terms. The first term arises directly from the sensitivity of a prediction to fixed parameters. The second term arises from prediction-sensitive adjustable parameters that are forced to compensate for fixed parameters during history matching. The compensation is accompanied by inappropriate adjustment of otherwise uninformed, null-space parameter components. Unwarranted adjustment of null-space components away from prior maximum likelihood values may produce bias if a prediction is sensitive to those components. The potential for subjective parameterization choices to corrupt predictions is examined using a synthetic model. Several strategies are evaluated, including use of piecewise constant zones, use of pilot points with Tikhonov regularization and use of the Karhunen-Loeve transformation. The best choice of parameterization (as defined by minimum error variance) is strongly dependent on the types of predictions to be made by the model.
Fu, Q.; Sun, W.B.; Yang, P.
1998-09-01
An accurate parameterization is presented for the infrared radiative properties of cirrus clouds. For the single-scattering calculations, a composite scheme is developed for randomly oriented hexagonal ice crystals by comparing results from Mie theory, anomalous diffraction theory (ADT), the geometric optics method (GOM), and the finite-difference time domain technique. This scheme employs a linear combination of single-scattering properties from the Mie theory, ADT, and GOM, which is accurate for a wide range of size parameters. Following the approach of Q. Fu, the extinction coefficient, absorption coefficient, and asymmetry factor are parameterized as functions of the cloud ice water content and generalized effective size (D{sub ge}). The present parameterization of the single-scattering properties of cirrus clouds is validated by examining the bulk radiative properties for a wide range of atmospheric conditions. Compared with reference results, the typical relative error in emissivity due to the parameterization is {approximately}2.2%. The accuracy of this parameterization guarantees its reliability in applications to climate models. The present parameterization complements the scheme for the solar radiative properties of cirrus clouds developed by Q. Fu for use in numerical models.
A Thermal Infrared Radiation Parameterization for Atmospheric Studies
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Suarez, Max J.; Liang, Xin-Zhong; Yan, Michael M.-H.; Cote, Charles (Technical Monitor)
2001-01-01
This technical memorandum documents the longwave radiation parameterization developed at the Climate and Radiation Branch, NASA Goddard Space Flight Center, for a wide variety of weather and climate applications. Based on the 1996-version of the Air Force Geophysical Laboratory HITRAN data, the parameterization includes the absorption due to major gaseous absorption (water vapor, CO2, O3) and most of the minor trace gases (N2O, CH4, CFCs), as well as clouds and aerosols. The thermal infrared spectrum is divided into nine bands. To achieve a high degree of accuracy and speed, various approaches of computing the transmission function are applied to different spectral bands and gases. The gaseous transmission function is computed either using the k-distribution method or the table look-up method. To include the effect of scattering due to clouds and aerosols, the optical thickness is scaled by the single-scattering albedo and asymmetry factor. The parameterization can accurately compute fluxes to within 1% of the high spectral-resolution line-by-line calculations. The cooling rate can be accurately computed in the region extending from the surface to the 0.01-hPa level.
NASA Technical Reports Server (NTRS)
Hong, Byungsik; Maung, Khin Maung; Wilson, John W.; Buck, Warren W.
1989-01-01
The derivations of the Lippmann-Schwinger equation and Watson multiple scattering are given. A simple optical potential is found to be the first term of that series. The number density distribution models of the nucleus, harmonic well, and Woods-Saxon are used without t-matrix taken from the scattering experiments. The parameterized two-body inputs, which are kaon-nucleon total cross sections, elastic slope parameters, and the ratio of the real to the imaginary part of the forward elastic scattering amplitude, are presented. The eikonal approximation was chosen as our solution method to estimate the total and absorptive cross sections for the kaon-nucleus scattering.
Quantum Consequences of Parameterizing Geometry
NASA Astrophysics Data System (ADS)
Wanas, M. I.
2002-12-01
The marriage between geometrization and quantization is not successful, so far. It is well known that quantization of gravity , using known quantization schemes, is not satisfactory. It may be of interest to look for another approach to this problem. Recently, it is shown that geometries with torsion admit quantum paths. Such geometries should be parameterizied in order to preserve the quantum properties appeared in the paths. The present work explores the consequences of parameterizing such geometry. It is shown that quantum properties, appeared in the path equations, are transferred to other geometric entities.
Infrared radiation parameterizations in numerical climate models
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Kratz, David P.; Ridgway, William
1991-01-01
This study presents various approaches to parameterizing the broadband transmission functions for utilization in numerical climate models. One-parameter scaling is applied to approximate a nonhomogeneous path with an equivalent homogeneous path, and the diffuse transmittances are either interpolated from precomputed tables or fit by analytical functions. Two-parameter scaling is applied to parameterizing the carbon dioxide and ozone transmission functions in both the lower and middle atmosphere. Parameterizations are given for the nitrous oxide and methane diffuse transmission functions.
Independent component analysis of parameterized ECG signals.
Tanskanen, Jarno M A; Viik, Jari J; Hyttinen, Jari A K
2006-01-01
Independent component analysis (ICA) of measured signals yields the independent sources, given certain fulfilled requirements. Properly parameterized signals provide a better view to the considered system aspects, while reducing the amount of data. It is little acknowledged that appropriately parameterized signals may be subjected to ICA, yielding independent components (ICs) displaying more clearly the investigated properties of the sources. In this paper, we propose ICA of parameterized signals, and demonstrate the concept with ICA of ST and R parameterizations of electrocardiogram (ECG) signals from ECG exercise test measurements from two coronary artery disease (CAD) patients. PMID:17945912
Parameterization of precipitating shallow convection
NASA Astrophysics Data System (ADS)
Seifert, Axel
2015-04-01
Shallow convective clouds play a decisive role in many regimes of the atmosphere. They are abundant in the trade wind regions and essential for the radiation budget in the sub-tropics. They are also an integral part of the diurnal cycle of convection over land leading to the formation of deeper modes of convection later on. Errors in the representation of these small and seemingly unimportant clouds can lead to misforecasts in many situations. Especially for high-resolution NWP models at 1-3 km grid spacing which explicitly simulate deeper modes of convection, the parameterization of the sub-grid shallow convection is an important issue. Large-eddy simulations (LES) can provide the data to study shallow convective clouds and their interaction with the boundary layer in great detail. In contrast to observation, simulations provide a complete and consistent dataset, which may not be perfectly realistic due to the necessary simplifications, but nevertheless enables us to study many aspects of those clouds in a self-consistent way. Today's supercomputing capabilities make it possible to use domain sizes that not only span several NWP grid boxes, but also allow for mesoscale self-organization of the cloud field, which is an essential behavior of precipitating shallow convection. By coarse-graining the LES data to the grid of an NWP model, the sub-grid fluctuations caused by shallow convective clouds can be analyzed explicitly. These fluctuations can then be parameterized in terms of a PDF-based closure. The necessary choices for such schemes like the shape of the PDF, the number of predicted moments, etc., will be discussed. For example, it is shown that a universal three-parameter distribution of total water may exist at scales of O(1 km) but not at O(10 km). In a next step the variance budgets of moisture and temperature in the cloud-topped boundary layer are studied. What is the role and magnitude of the microphysical correlation terms in these equations, which
A Solar Radiation Parameterization for Atmospheric Studies. Volume 15
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Suarez, Max J. (Editor)
1999-01-01
The solar radiation parameterization (CLIRAD-SW) developed at the Goddard Climate and Radiation Branch for application to atmospheric models are described. It includes the absorption by water vapor, O3, O2, CO2, clouds, and aerosols and the scattering by clouds, aerosols, and gases. Depending upon the nature of absorption, different approaches are applied to different absorbers. In the ultraviolet and visible regions, the spectrum is divided into 8 bands, and single O3 absorption coefficient and Rayleigh scattering coefficient are used for each band. In the infrared, the spectrum is divided into 3 bands, and the k-distribution method is applied for water vapor absorption. The flux reduction due to O2 is derived from a simple function, while the flux reduction due to CO2 is derived from precomputed tables. Cloud single-scattering properties are parameterized, separately for liquid drops and ice, as functions of water amount and effective particle size. A maximum-random approximation is adopted for the overlapping of clouds at different heights. Fluxes are computed using the Delta-Eddington approximation.
Parameterization of solar flare dose
Lamarche, A.H.; Poston, J.W.
1996-12-31
A critical aspect of missions to the moon or Mars will be the safety and health of the crew. Radiation in space is a hazard for astronauts, especially high-energy radiation following certain types of solar flares. A solar flare event can be very dangerous if astronauts are not adequately shielded because flares can deliver a very high dose in a short period of time. The goal of this research was to parameterize solar flare dose as a function of time to see if it was possible to predict solar flare occurrence, thus providing a warning time. This would allow astronauts to take corrective action and avoid receiving a dose greater than the recommended limit set by the National Council on Radiation Protection and Measurements (NCRP).
New Approaches to Parameterizing Convection
NASA Technical Reports Server (NTRS)
Randall, David A.; Lappen, Cara-Lyn
1999-01-01
Many general circulation models (GCMs) currently use separate schemes for planetary boundary layer (PBL) processes, shallow and deep cumulus (Cu) convection, and stratiform clouds. The conventional distinctions. among these processes are somewhat arbitrary. For example, in the stratocumulus-to-cumulus transition region, stratocumulus clouds break up into a combination of shallow cumulus and broken stratocumulus. Shallow cumulus clouds may be considered to reside completely within the PBL, or they may be regarded as starting in the PBL but terminating above it. Deeper cumulus clouds often originate within the PBL with also can originate aloft. To the extent that our models separately parameterize physical processes which interact strongly on small space and time scales, the currently fashionable practice of modularization may be doing more harm than good.
Automated Classification and Stellar Parameterization .
NASA Astrophysics Data System (ADS)
Giridhar, S.; Muneer, S.; Goswami, A.
2006-08-01
Different approaches for automated spectral classification are critically reviewed. We also summarize ANN based methods which would be very efficient in quick handling of the large volumes of data generated by different surveys. We have obtained medium resolution spectra for a large sample of stars using 2.3m telescope at VBO, Kavalur, India. Our sample contains uniform distribution of stars in temperature range 4000 to 8000K, log g range of 2.0 to 5.0 and [Fe/H] range of 0 to -3. We have explored the application of artificial neural network for parameterization of these stars. We have used a set of stars with well determined atmospheric parameters for training the networks for temperature, gravity and metallicity estimations. We use these trained network to estimate metallicities for a sample of metal-poor candidate stars.
Visibility Parameterization For Forecasting Model Applications
NASA Astrophysics Data System (ADS)
Gultepe, I.; Milbrandt, J.; Binbin, Z.
2010-07-01
In this study, the visibility parameterizations developed during Fog Remote Sensing And Modeling (FRAM) projects, conducted in central and eastern Canada, will be summarized and their use for forecasting/nowcasting applications will be discussed. Parameterizations developed for reductions in visibility due to 1) fog, 2) rain, 3) snow, and 4) relative humidity (RH) during FRAM will be given and uncertainties in the parameterizations will be discussed. Comparisons made between Canadian GEM NWP model (with 1 and 2.5 km horizontal grid spacing) and observations collected during the Science of Nowcasting Winter Weather for Vancouver 2010 (SNOW-V10) project and FRAM projects, using the new parameterizations, will be given Observations used in this study were obtained using a fog measuring device (FMD) for fog parameterization, a Vaisala all weather precipitation sensor called FD12P for rain and snow parameterizations and visibility measurements, and a total precipitation sensor (TPS), and distrometers called OTT ParSiVel and Laser Precipitation Measurement (LPM) for rain/snow particle spectra. The results from the three SNOW-V10 sites suggested that visibility values given by the GEM model using the new parameterizations were comparable with observed visibility values when model based input parameters such as liquid water content, RH, and precipitation rate for visibility parameterizations were predicted accurately.
An approach for parameterizing mesoscale precipitating systems
Weissbluth, M.J.; Cotton, W.R.
1991-01-01
A cumulus parameterization laboratory has been described which uses a reference numerical model to fabricate, calibrate and verify a cumulus parameterization scheme suitable for use in mesoscale models. Key features of this scheme include resolution independence and the ability to provide hydrometeor source functions to the host model. Thus far, only convective scale drafts have been parameterized, limiting the use of the scheme to those models which can resolve the mesoscale circulations. As it stands, the scheme could probably be incorporated into models having a grid resolution greater than 50 km with results comparable to the existing schemes for the large-scale models. We propose, however, to quantify the mesoscale circulations through the use of the cumulus parameterization laboratory. The inclusion of these mesoscale drafts in the existing scheme will hopefully allow the correct parameterization of the organized mesoscale precipitating systems.
An approach for parameterizing mesoscale precipitating systems
Weissbluth, M.J.; Cotton, W.R.
1991-12-31
A cumulus parameterization laboratory has been described which uses a reference numerical model to fabricate, calibrate and verify a cumulus parameterization scheme suitable for use in mesoscale models. Key features of this scheme include resolution independence and the ability to provide hydrometeor source functions to the host model. Thus far, only convective scale drafts have been parameterized, limiting the use of the scheme to those models which can resolve the mesoscale circulations. As it stands, the scheme could probably be incorporated into models having a grid resolution greater than 50 km with results comparable to the existing schemes for the large-scale models. We propose, however, to quantify the mesoscale circulations through the use of the cumulus parameterization laboratory. The inclusion of these mesoscale drafts in the existing scheme will hopefully allow the correct parameterization of the organized mesoscale precipitating systems.
Parameterized Linear Longitudinal Airship Model
NASA Technical Reports Server (NTRS)
Kulczycki, Eric; Elfes, Alberto; Bayard, David; Quadrelli, Marco; Johnson, Joseph
2010-01-01
A parameterized linear mathematical model of the longitudinal dynamics of an airship is undergoing development. This model is intended to be used in designing control systems for future airships that would operate in the atmospheres of Earth and remote planets. Heretofore, the development of linearized models of the longitudinal dynamics of airships has been costly in that it has been necessary to perform extensive flight testing and to use system-identification techniques to construct models that fit the flight-test data. The present model is a generic one that can be relatively easily specialized to approximate the dynamics of specific airships at specific operating points, without need for further system identification, and with significantly less flight testing. The approach taken in the present development is to merge the linearized dynamical equations of an airship with techniques for estimation of aircraft stability derivatives, and to thereby make it possible to construct a linearized dynamical model of the longitudinal dynamics of a specific airship from geometric and aerodynamic data pertaining to that airship. (It is also planned to develop a model of the lateral dynamics by use of the same methods.) All of the aerodynamic data needed to construct the model of a specific airship can be obtained from wind-tunnel testing and computational fluid dynamics
Automated classification and stellar parameterization
NASA Astrophysics Data System (ADS)
Giridhar, Sunetra; Muneer, S.; Goswami, Aruna
Different approaches for automated spectral classification are critically reviewed. We describe in detail ANN based methods which are very efficient in quick handling of the large volumes of data generated by different surveys. We summarize the application of ANN in various surveys covering UV, visual and IR spectral regions and the accuracies obtained. We also present the preliminary results obtained with medium resolution spectra (R ˜ 1000) for a modest sample of stars using the 2.3 m Vainu Bappu Telescope at Kavalur observatory, India. Our sample contains uniform distribution of stars in temperature range 4500 to 8000 K, log g range of 1.5 to 5.0 and [Fe/H] range of 0 to -3. We have explored the application of artificial neural network for parameterization of these stars. We have used a set of stars with well determined atmospheric parameters for training the networks for temperature, gravity and metallicity estimations. We could get an accuracy of 200 K in temperature, 0.4 in log g and 0.3 dex in [Fe/H] in our preliminary efforts.
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Lee, Kyu-Tae; Yang, Ping; Lau, William K. M. (Technical Monitor)
2002-01-01
Based on the single-scattering optical properties pre-computed with an improved geometric optics method, the bulk absorption coefficient, single-scattering albedo, and asymmetry factor of ice particles have been parameterized as a function of the effective particle size of a mixture of ice habits, the ice water amount, and spectral band. The parameterization has been applied to computing fluxes for sample clouds with various particle size distributions and assumed mixtures of particle habits. It is found that flux calculations are not overly sensitive to the assumed particle habits if the definition of the effective particle size is consistent with the particle habits that the parameterization is based. Otherwise, the error in the flux calculations could reach a magnitude unacceptable for climate studies. Different from many previous studies, the parameterization requires only an effective particle size representing all ice habits in a cloud layer, but not the effective size of individual ice habits.
A Two-Habit Ice Cloud Optical Property Parameterization for GCM Application
NASA Technical Reports Server (NTRS)
Yi, Bingqi; Yang, Ping; Minnis, Patrick; Loeb, Norman; Kato, Seiji
2014-01-01
We present a novel ice cloud optical property parameterization based on a two-habit ice cloud model that has been proved to be optimal for remote sensing applications. The two-habit ice model is developed with state-of-the-art numerical methods for light scattering property calculations involving individual columns and column aggregates with the habit fractions constrained by in-situ measurements from various field campaigns. Band-averaged bulk ice cloud optical properties including the single-scattering albedo, the mass extinction/absorption coefficients, and the asymmetry factor are parameterized as functions of the effective particle diameter for the spectral bands involved in the broadband radiative transfer models. Compared with other parameterization schemes, the two-habit scheme generally has lower asymmetry factor values (around 0.75 at the visible wavelengths). The two-habit parameterization scheme was widely tested with the broadband radiative transfer models (i.e. Rapid Radiative Transfer Model, GCM version) and global circulation models (GCMs, i.e. Community Atmosphere Model, version 5). Global ice cloud radiative effects at the top of the atmosphere are also analyzed from the GCM simulation using the two-habit parameterization scheme in comparison with CERES satellite observations.
Methods of testing parameterizations: Vertical ocean mixing
NASA Technical Reports Server (NTRS)
Tziperman, Eli
1992-01-01
The ocean's velocity field is characterized by an exceptional variety of scales. While the small-scale oceanic turbulence responsible for the vertical mixing in the ocean is of scales a few centimeters and smaller, the oceanic general circulation is characterized by horizontal scales of thousands of kilometers. In oceanic general circulation models that are typically run today, the vertical structure of the ocean is represented by a few tens of discrete grid points. Such models cannot explicitly model the small-scale mixing processes, and must, therefore, find ways to parameterize them in terms of the larger-scale fields. Finding a parameterization that is both reliable and plausible to use in ocean models is not a simple task. Vertical mixing in the ocean is the combined result of many complex processes, and, in fact, mixing is one of the less known and less understood aspects of the oceanic circulation. In present models of the oceanic circulation, the many complex processes responsible for vertical mixing are often parameterized in an oversimplified manner. Yet, finding an adequate parameterization of vertical ocean mixing is crucial to the successful application of ocean models to climate studies. The results of general circulation models for quantities that are of particular interest to climate studies, such as the meridional heat flux carried by the ocean, are quite sensitive to the strength of the vertical mixing. We try to examine the difficulties in choosing an appropriate vertical mixing parameterization, and the methods that are available for validating different parameterizations by comparing model results to oceanographic data. First, some of the physical processes responsible for vertically mixing the ocean are briefly mentioned, and some possible approaches to the parameterization of these processes in oceanographic general circulation models are described in the following section. We then discuss the role of the vertical mixing in the physics of the
NASA Technical Reports Server (NTRS)
Chou, Ming-Dah; Lee, Kyu-Tae; Yang, Ping; Lau, William K. M. (Technical Monitor)
2002-01-01
Based on the single-scattering optical properties that are pre-computed using an improve geometric optics method, the bulk mass absorption coefficient, single-scattering albedo, and asymmetry factor of ice particles have been parameterized as a function of the mean effective particle size of a mixture of ice habits. The parameterization has been applied to compute fluxes for sample clouds with various particle size distributions and assumed mixtures of particle habits. Compared to the parameterization for a single habit of hexagonal column, the solar heating of clouds computed with the parameterization for a mixture of habits is smaller due to a smaller cosingle-scattering albedo. Whereas the net downward fluxes at the TOA and surface are larger due to a larger asymmetry factor. The maximum difference in the cloud heating rate is approx. 0.2 C per day, which occurs in clouds with an optical thickness greater than 3 and the solar zenith angle less than 45 degrees. Flux difference is less than 10 W per square meters for the optical thickness ranging from 0.6 to 10 and the entire range of the solar zenith angle. The maximum flux difference is approximately 3%, which occurs around an optical thickness of 1 and at high solar zenith angles.
Shortwave radiation parameterization scheme for subgrid topography
NASA Astrophysics Data System (ADS)
Helbig, N.; LöWe, H.
2012-02-01
Topography is well known to alter the shortwave radiation balance at the surface. A detailed radiation balance is therefore required in mountainous terrain. In order to maintain the computational performance of large-scale models while at the same time increasing grid resolutions, subgrid parameterizations are gaining more importance. A complete radiation parameterization scheme for subgrid topography accounting for shading, limited sky view, and terrain reflections is presented. Each radiative flux is parameterized individually as a function of sky view factor, slope and sun elevation angle, and albedo. We validated the parameterization with domain-averaged values computed from a distributed radiation model which includes a detailed shortwave radiation balance. Furthermore, we quantify the individual topographic impacts on the shortwave radiation balance. Rather than using a limited set of real topographies we used a large ensemble of simulated topographies with a wide range of typical terrain characteristics to study all topographic influences on the radiation balance. To this end slopes and partial derivatives of seven real topographies from Switzerland and the United States were analyzed and Gaussian statistics were found to best approximate real topographies. Parameterized direct beam radiation presented previously compared well with modeled values over the entire range of slope angles. The approximation of multiple, anisotropic terrain reflections with single, isotropic terrain reflections was confirmed as long as domain-averaged values are considered. The validation of all parameterized radiative fluxes showed that it is indeed not necessary to compute subgrid fluxes in order to account for all topographic influences in large grid sizes.
Parameterization of the three-dimensional room transfer function in horizontal plane.
Bu, Bing; Abhayapala, Thushara D; Bao, Chang-chun; Zhang, Wen
2015-09-01
This letter proposes an efficient parameterization of the three-dimensional room transfer function (RTF) which is robust for the position variations of source and receiver in respective horizontal planes. Based on azimuth harmonic analysis, the proposed method exploits the underlying properties of the associated Legendre functions to remove a portion of the spherical harmonic coefficients of RTF which have no contribution in the horizontal plane. This reduction leads to a flexible measuring-point structure consisting of practical concentric circular arrays to extract horizontal plane RTF coefficients. The accuracy of the above parameterization is verified through numerical simulations. PMID:26428827
POET: Parameterized Optimization for Empirical Tuning
Yi, Q; Seymour, K; You, H; Vuduc, R; Quinlan, D
2007-01-29
The excessive complexity of both machine architectures and applications have made it difficult for compilers to statically model and predict application behavior. This observation motivates the recent interest in performance tuning using empirical techniques. We present a new embedded scripting language, POET (Parameterized Optimization for Empirical Tuning), for parameterizing complex code transformations so that they can be empirically tuned. The POET language aims to significantly improve the generality, flexibility, and efficiency of existing empirical tuning systems. We have used the language to parameterize and to empirically tune three loop optimizations-interchange, blocking, and unrolling-for two linear algebra kernels. We show experimentally that the time required to tune these optimizations using POET, which does not require any program analysis, is significantly shorter than that when using a full compiler-based source-code optimizer which performs sophisticated program analysis and optimizations.
Optical closure of parameterized bio-optical relationships
NASA Astrophysics Data System (ADS)
He, Shuangyan; Fischer, Jürgen; Schaale, Michael; He, Ming-xia
2014-03-01
An optical closure study on bio-optical relationships was carried out using radiative transfer model matrix operator method developed by Freie Universität Berlin. As a case study, the optical closure of bio-optical relationships empirically parameterized with in situ data for the East China Sea was examined. Remote-sensing reflectance ( R rs) was computed from the inherent optical properties predicted by these biooptical relationships and compared with published in situ data. It was found that the simulated R rs was overestimated for turbid water. To achieve optical closure, bio-optical relationships for absorption and scattering coefficients for suspended particulate matter were adjusted. Furthermore, the results show that the Fournier and Forand phase functions obtained from the adjusted relationships perform better than the Petzold phase function. Therefore, before bio-optical relationships are used for a local sea area, the optical closure should be examined.
Parameterization of lattice spacings for lipid multilayers in ionic solutions
NASA Astrophysics Data System (ADS)
Petrache, Horia; Johnson, Merrell; Harries, Daniel; Seifert, Soenke
Lipids, which are molecules found in biological cells, form highly regular layered structures called multilamellar lipid vesicles (MLVs). The repeat lattice spacings of MLVs depend on van der Waals and electrostatic forces between neighboring membranes and are sensitive to the presence of salt. For example, addition of salt ions such as sodium and potassium makes the MLVs swell, primarily due to changes in electrical polarizabilities. However, a more complicated behavior is found in some ionic solutions such as those containing lithium ions. Using x-ray scattering, we show experimentally how the interactions between membranes depend on the type of monovalent ions and construct parameterizations of MLVs swelling curves that can help analyze van der Waals interactions.
Approaches for Subgrid Parameterization: Does Scaling Help?
NASA Astrophysics Data System (ADS)
Yano, Jun-Ichi
2016-04-01
Arguably the scaling behavior is a well-established fact in many geophysical systems. There are already many theoretical studies elucidating this issue. However, the scaling law is slow to be introduced in "operational" geophysical modelling, notably for weather forecast as well as climate projection models. The main purpose of this presentation is to ask why, and try to answer this question. As a reference point, the presentation reviews the three major approaches for traditional subgrid parameterization: moment, PDF (probability density function), and mode decomposition. The moment expansion is a standard method for describing the subgrid-scale turbulent flows both in the atmosphere and the oceans. The PDF approach is intuitively appealing as it directly deals with a distribution of variables in subgrid scale in a more direct manner. The third category, originally proposed by Aubry et al (1988) in context of the wall boundary-layer turbulence, is specifically designed to represent coherencies in compact manner by a low--dimensional dynamical system. Their original proposal adopts the proper orthogonal decomposition (POD, or empirical orthogonal functions, EOF) as their mode-decomposition basis. However, the methodology can easily be generalized into any decomposition basis. The mass-flux formulation that is currently adopted in majority of atmospheric models for parameterizing convection can also be considered a special case of the mode decomposition, adopting the segmentally-constant modes for the expansion basis. The mode decomposition can, furthermore, be re-interpreted as a type of Galarkin approach for numerically modelling the subgrid-scale processes. Simple extrapolation of this re-interpretation further suggests us that the subgrid parameterization problem may be re-interpreted as a type of mesh-refinement problem in numerical modelling. We furthermore see a link between the subgrid parameterization and downscaling problems along this line. The mode
A uniform parameterization of moment tensors
NASA Astrophysics Data System (ADS)
Tape, C.; Tape, W.
2015-12-01
A moment tensor is a 3 x 3 symmetric matrix that expresses an earthquake source. We construct a parameterization of the five-dimensional space of all moment tensors of unit norm. The coordinates associated with the parameterization are closely related to moment tensor orientations and source types. The parameterization is uniform, in the sense that equal volumes in the coordinate domain of the parameterization correspond to equal volumes of moment tensors. Uniformly distributed points in the coordinate domain therefore give uniformly distributed moment tensors. A cartesian grid in the coordinate domain can be used to search efficiently over moment tensors. We find that uniformly distributed moment tensors have uniformly distributed orientations (eigenframes), but that their source types (eigenvalue triples) are distributed so as to favor double couples. An appropriate choice of a priori moment tensor probability is a prerequisite for parameter estimation. As a seemingly sensible choice, we consider the homogeneous probability, in which equal volumes of moment tensors are equally likely. We believe that it will lead to improved characterization of source processes.
Soil processes parameterization in meteorological model.
NASA Astrophysics Data System (ADS)
Mazur, Andrzej; Duniec, Grzegorz
2014-05-01
In August 2012 Polish Institute Meteorology and Water Management - National Research Institute (IMWM-NRI) started a collaboration with the Institute of Agrophysics - Polish Academy of Science (IA-PAS) in order to improve soil processes parameterization in COSMO meteorological model of high resolution (horizontal grid size equal to 2,8 km). This cooperation turned into a project named "New approach to parameterization of physical processes in soil in numerical model". The new set of soil processes parameterizations is being developed considering many physical and microphysical processes in soil. Currently, main effort is focused on description of bare soil evaporation, soil water transport and the runoff from soil layers. The preliminary results from new mathematical formulation of bare soil evaporation implemented in COSMO model will be presented. Moreover, during the Conference authors (realizing a constant need for further improvement) would like to show future plans and topics for further studies. It is planned to combine the mentioned new approach with TILE and MOSAIC parameterizations, previously investigated as a part of TERRA-MultiLevel module of COSMO model, and to use measurements data received from IA-PAS and from Satellite Remote Sensing Center in soil-related COSMO model numerical experiments.
Empirical parameterization of setup, swash, and runup
Stockdon, H.F.; Holman, R.A.; Howd, P.A.; Sallenger, A.H., Jr.
2006-01-01
Using shoreline water-level time series collected during 10 dynamically diverse field experiments, an empirical parameterization for extreme runup, defined by the 2% exceedence value, has been developed for use on natural beaches over a wide range of conditions. Runup, the height of discrete water-level maxima, depends on two dynamically different processes; time-averaged wave setup and total swash excursion, each of which is parameterized separately. Setup at the shoreline was best parameterized using a dimensional form of the more common Iribarren-based setup expression that includes foreshore beach slope, offshore wave height, and deep-water wavelength. Significant swash can be decomposed into the incident and infragravity frequency bands. Incident swash is also best parameterized using a dimensional form of the Iribarren-based expression. Infragravity swash is best modeled dimensionally using offshore wave height and wavelength and shows no statistically significant linear dependence on either foreshore or surf-zone slope. On infragravity-dominated dissipative beaches, the magnitudes of both setup and swash, modeling both incident and infragravity frequency components together, are dependent only on offshore wave height and wavelength. Statistics of predicted runup averaged over all sites indicate a - 17 cm bias and an rms error of 38 cm: the mean observed runup elevation for all experiments was 144 cm. On intermediate and reflective beaches with complex foreshore topography, the use of an alongshore-averaged beach slope in practical applications of the runup parameterization may result in a relative runup error equal to 51% of the fractional variability between the measured and the averaged slope.
A Simple Parameterization of 3 x 3 Magic Squares
ERIC Educational Resources Information Center
Trenkler, Gotz; Schmidt, Karsten; Trenkler, Dietrich
2012-01-01
In this article a new parameterization of magic squares of order three is presented. This parameterization permits an easy computation of their inverses, eigenvalues, eigenvectors and adjoints. Some attention is paid to the Luoshu, one of the oldest magic squares.
Hu, Y.X.; Stamnes, K. )
1993-04-01
A new parameterization of the radiative Properties of water clouds is presented. Cloud optical properties for valent radius throughout the solar and both solar and terrestrial spectra and for cloud equivalent radii in the range 2.5-60 [mu]m are calculated from Mie theory. It is found that cloud optical properties depend mainly on equivalent radius throughout the solar and terrestrial spectrum and are insensitive to the details of the droplet size distribution, such as shape, skewness, width, and modality (single or bimodal). This suggests that in cloud models, aimed at predicting the evolution of cloud microphysics with climate change, it is sufficient to determine the third and the second moments of the size distribution (the ratio of which determines the equivalent radius). It also implies that measurements of the cloud liquid water content and the extinction coefficient are sufficient to determine cloud optical properties experimentally (i.e., measuring the complete droplet size distribution is not required). Based on the detailed calculations, the optical properties are parameterized as a function of cloud liquid water path and equivalent cloud droplet radius by using a nonlinear least-square fitting. The parameterization is performed separately for the range of radii 2.5-12 [mu]m, 12-30,[mu]m, and 30-60 [mu]m. Cloud heating and cooling rates are computed from this parameterization by using a comprehensive radiation model. Comparison with similar results obtained from exact Mie scattering calculations shows that this parameterization yields very accurate results and that it is several thousand times faster. This parameterization separates the dependence of cloud optical properties on droplet size and liquid water content, and is suitable for inclusion into climate models. 22 refs., 7 figs., 6 tabs.
Control of shortwave radiation parameterization on tropical climate SST-forced simulation
NASA Astrophysics Data System (ADS)
Crétat, Julien; Masson, Sébastien; Berthet, Sarah; Samson, Guillaume; Terray, Pascal; Dudhia, Jimy; Pinsard, Françoise; Hourdin, Christophe
2016-01-01
SST-forced tropical-channel simulations are used to quantify the control of shortwave (SW) parameterization on the mean tropical climate compared to other major model settings (convection, boundary layer turbulence, vertical and horizontal resolutions), and to pinpoint the physical mechanisms whereby this control manifests. Analyses focus on the spatial distribution and magnitude of the net SW radiation budget at the surface (SWnet_SFC), latent heat fluxes, and rainfall at the annual timescale. The model skill and sensitivity to the tested settings are quantified relative to observations and using an ensemble approach. Persistent biases include overestimated SWnet_SFC and too intense hydrological cycle. However, model skill is mainly controlled by SW parameterization, especially the magnitude of SWnet_SFC and rainfall and both the spatial distribution and magnitude of latent heat fluxes over ocean. On the other hand, the spatial distribution of continental rainfall (SWnet_SFC) is mainly influenced by convection parameterization and horizontal resolution (boundary layer parameterization and orography). Physical understanding of the control of SW parameterization is addressed by analyzing the thermal structure of the atmosphere and conducting sensitivity experiments to O3 absorption and SW scattering coefficient. SW parameterization shapes the stability of the atmosphere in two different ways according to whether surface is coupled to atmosphere or not, while O3 absorption has minor effects in our simulations. Over SST-prescribed regions, increasing the amount of SW absorption warms the atmosphere only because surface temperatures are fixed, resulting in increased atmospheric stability. Over land-atmosphere coupled regions, increasing SW absorption warms both atmospheric and surface temperatures, leading to a shift towards a warmer state and a more intense hydrological cycle. This turns in reversal model behavior between land and sea points, with the SW scheme that
Parameterization of contrail radiative properties for climate studies
NASA Astrophysics Data System (ADS)
Xie, Yu; Yang, Ping; Liou, Kuo-Nan; Minnis, Patrick; Duda, David P.
2012-12-01
The study of contrails and their impact on global climate change requires a cloud model that statistically represents contrail radiative properties. In this study, the microphysical properties of global contrails are statistically analyzed using collocated Moderate Resolution Imaging Spectroradiometer (MODIS) and Cloud Aerosol Lidar with Orthogonal Polarization (CALIOP) observations. The MODIS contrail pixels are detected using an automated contrail detection algorithm and a manual technique using the brightness temperature differences between the MODIS 11 and 12 μm channels. The scattering and absorption properties of typical contrail ice crystals are used to determine an appropriate contrail model to minimize the uncertainties arising from the assumptions in a particular cloud model. The depolarization ratio is simulated with a variety of ice crystal habit fractions and matched to the collocated MODIS and CALIOP observations. The contrail habit fractions are determined and used to compute the bulk-scattering properties of contrails. A parameterization of shortwave and longwave contrail optical properties is developed for the spectral bands of the Rapid Radiative Transfer Model (RRTM). The contrail forcing at the top of the atmosphere is investigated using the RRTM and compared with spherical and hexagonal ice cloud models. Contrail forcing is overestimated when spherical ice crystals are used to represent contrails, but if a hexagonal ice cloud model is used, the forcing is underestimated for small particles and overestimated for large particles in comparison to the contrail model developed in this study.
Parameterization of cloud effects on the absorption of solar radiation
NASA Technical Reports Server (NTRS)
Davies, R.
1983-01-01
A radiation parameterization for the NASA Goddard climate model was developed, tested, and implemented. Interactive and off-hire experiments with the climate model to determine the limitations of the present parameterization scheme are summarized. The parameterization of Cloud absorption in terms of solar zeith angle, column water vapors about the cloud top, and cloud liquid water content is discussed.
Cloud parameterization for climate modeling - Status and prospects
NASA Technical Reports Server (NTRS)
Randall, David A.
1989-01-01
The current status of cloud parameterization research is reviewed. It is emphasized that the upper tropospheric stratiform clouds associated with deep convection are both physically important and poorly parameterized in current models. Emerging parameterizations are described in general terms, with emphasis on prognostic cloud water and fractional cloudiness, and how these relate to the problem just mentioned.
Numerical Archetypal Parameterization for Mesoscale Convective Systems
NASA Astrophysics Data System (ADS)
Yano, J. I.
2015-12-01
Vertical shear tends to organize atmospheric moist convection into multiscale coherent structures. Especially, the counter-gradient vertical transport of horizontal momentum by organized convection can enhance the wind shear and transport kinetic energy upscale. However, this process is not represented by traditional parameterizations. The present paper sets the archetypal dynamical models, originally formulated by the second author, into a parameterization context by utilizing a nonhydrostatic anelastic model with segmentally-constant approximation (NAM-SCA). Using a two-dimensional framework as a starting point, NAM-SCA spontaneously generates propagating tropical squall-lines in a sheared environment. A high numerical efficiency is achieved through a novel compression methodology. The numerically-generated archetypes produce vertical profiles of convective momentum transport that are consistent with the analytic archetype.
Rapid Parameterization Schemes for Aircraft Shape Optimization
NASA Technical Reports Server (NTRS)
Li, Wu
2012-01-01
A rapid shape parameterization tool called PROTEUS is developed for aircraft shape optimization. This tool can be applied directly to any aircraft geometry that has been defined in PLOT3D format, with the restriction that each aircraft component must be defined by only one data block. PROTEUS has eight types of parameterization schemes: planform, wing surface, twist, body surface, body scaling, body camber line, shifting/scaling, and linear morphing. These parametric schemes can be applied to two types of components: wing-type surfaces (e.g., wing, canard, horizontal tail, vertical tail, and pylon) and body-type surfaces (e.g., fuselage, pod, and nacelle). These schemes permit the easy setup of commonly used shape modification methods, and each customized parametric scheme can be applied to the same type of component for any configuration. This paper explains the mathematics for these parametric schemes and uses two supersonic configurations to demonstrate the application of these schemes.
Aerosol water parameterization: a single parameter framework
NASA Astrophysics Data System (ADS)
Metzger, S.; Steil, B.; Abdelkader, M.; Klingmüller, K.; Xu, L.; Penner, J. E.; Fountoukis, C.; Nenes, A.; Lelieveld, J.
2015-11-01
We introduce a framework to efficiently parameterize the aerosol water uptake for mixtures of semi-volatile and non-volatile compounds, based on the coefficient, νi. This solute specific coefficient was introduced in Metzger et al. (2012) to accurately parameterize the single solution hygroscopic growth, considering the Kelvin effect - accounting for the water uptake of concentrated nanometer sized particles up to dilute solutions, i.e., from the compounds relative humidity of deliquescence (RHD) up to supersaturation (Köhler-theory). Here we extend the νi-parameterization from single to mixed solutions. We evaluate our framework at various levels of complexity, by considering the full gas-liquid-solid partitioning for a comprehensive comparison with reference calculations using the E-AIM, EQUISOLV II, ISORROPIA II models as well as textbook examples. We apply our parameterization in EQSAM4clim, the EQuilibrium Simplified Aerosol Model V4 for climate simulations, implemented in a box model and in the global chemistry-climate model EMAC. Our results show: (i) that the νi-approach enables to analytically solve the entire gas-liquid-solid partitioning and the mixed solution water uptake with sufficient accuracy, (ii) that, e.g., pure ammonium nitrate and mixed ammonium nitrate - ammonium sulfate mixtures can be solved with a simple method, and (iii) that the aerosol optical depth (AOD) simulations are in close agreement with remote sensing observations for the year 2005. Long-term evaluation of the EMAC results based on EQSAM4clim and ISORROPIA II will be presented separately.
A Survey of Shape Parameterization Techniques
NASA Technical Reports Server (NTRS)
Samareh, Jamshid A.
1999-01-01
This paper provides a survey of shape parameterization techniques for multidisciplinary optimization and highlights some emerging ideas. The survey focuses on the suitability of available techniques for complex configurations, with suitability criteria based on the efficiency, effectiveness, ease of implementation, and availability of analytical sensitivities for geometry and grids. The paper also contains a section on field grid regeneration, grid deformation, and sensitivity analysis techniques.
Implicit Shape Parameterization for Kansei Design Methodology
NASA Astrophysics Data System (ADS)
Nordgren, Andreas Kjell; Aoyama, Hideki
Implicit shape parameterization for Kansei design is a procedure that use 3D-models, or concepts, to span a shape space for surfaces in the automotive field. A low-dimensional, yet accurate shape descriptor was found by Principal Component Analysis of an ensemble of point-clouds, which were extracted from mesh-based surfaces modeled in a CAD-program. A theoretical background of the procedure is given along with step-by-step instructions for the required data-processing. The results show that complex surfaces can be described very efficiently, and encode design features by an implicit approach that does not rely on error-prone explicit parameterizations. This provides a very intuitive way to explore shapes for a designer, because various design features can simply be introduced by adding new concepts to the ensemble. Complex shapes have been difficult to analyze with Kansei methods due to the large number of parameters involved, but implicit parameterization of design features provides a low-dimensional shape descriptor for efficient data collection, model-building and analysis of emotional content in 3D-surfaces.
Parameterization Impacts on Linear Uncertainty Calculation
NASA Astrophysics Data System (ADS)
Fienen, M. N.; Doherty, J.; Reeves, H. W.; Hunt, R. J.
2009-12-01
Efficient linear calculation of model prediction uncertainty can be an insightful diagnostic metric for decision-making. Specifically, the contributions of parameter uncertainty or the location and type of data to prediction uncertainty can be used to evaluate which types of information are most valuable. Information that most significantly reduces prediction uncertainty can be considered to have greater worth. Prediction uncertainty is commonly calculated including or excluding specific information and compared to a base scenario. The quantitative difference in uncertainty with or without the information is indicative of that information's worth in the decision-making process. These results can be calculated at many hypothetical locations to guide network design (i.e., where to install new wells/stream gages/etc.) or used to indicate which parameters are the most important to understand thus likely candidates for future characterization work. We examine a hypothetical case in which an inset model is created from a large regional model in order to better represent a surface stream network and make predictions of head near and flux in a stream due to installation and pumping of a large well near a stream headwater. Parameterization and edge boundary conditions are inherited from the regional model, the simple act of refining discretization and stream geometry shows improvement in the representation of the streams. Even visual inspection of the simulated head field highlights the need to recalibrate and potentially re-parametrize the inset model. A network of potential head observations is evaluated and contoured in the shallowest two layers of the six-layer model to assess their worth in both predicting flux at a specific gage, and head at a specific location near the stream. Three hydraulic conductivity parameterization scenarios are evaluated: using a single multiplier on hydraulic conductivity acting on the inherited hydraulic conductivity zonation using; the
NASA Astrophysics Data System (ADS)
Vidot, Jérôme; Baran, Anthony J.; Brunel, Pascal
2015-07-01
A new ice cloud optical property database in the thermal infrared has been parameterized for the RTTOV radiative transfer model. The Self-Consistent Scattering Model (SCSM) database is based on an ensemble model of ice crystals and a parameterization of the particle size distribution. This convolution can predict the radiative properties of cirrus without the need of a priori information on the ice particle shape and an estimate of the ice crystal effective dimension. The ice cloud optical properties are estimated through linear parameterizations of ambient temperature and ice water content. We evaluate the new parameterization against existing parameterizations used in RTTOV. We compare infrared observations from Imaging Infrared Radiometer, on board CALIPSO, against RTTOV simulations of the observations. The simulations are performed using two different products of ice cloud profiles, retrieved from the synergy between space-based radar and lidar observations. These are the 2C-ICE and DARDAR products. We optimized the parameterization by testing different SCSM databases, derived from different shapes of the particle size distribution, and weighting the volume extinction coefficient of the ensemble model. By selecting a large global data set of ice cloud profiles of visible optical depths between 0.03 and 4, we found that the simulations, based on the optimized SCSM database parameterization, reproduces the observations with a mean bias of only 0.43 K and a standard deviation of 6.85 K. The optimized SCSM database parameterization can also be applied to any other radiative transfer model.
New Parameterization of Neutron Absorption Cross Sections
NASA Technical Reports Server (NTRS)
Tripathi, Ram K.; Wilson, John W.; Cucinotta, Francis A.
1997-01-01
Recent parameterization of absorption cross sections for any system of charged ion collisions, including proton-nucleus collisions, is extended for neutron-nucleus collisions valid from approx. 1 MeV to a few GeV, thus providing a comprehensive picture of absorption cross sections for any system of collision pairs (charged or uncharged). The parameters are associated with the physics of the problem. At lower energies, optical potential at the surface is important, and the Pauli operator plays an increasingly important role at intermediate energies. The agreement between the calculated and experimental data is better than earlier published results.
Lightning parameterization in a storm electrification model
NASA Technical Reports Server (NTRS)
Helsdon, John H., Jr.; Farley, Richard D.; Wu, Gang
1988-01-01
The parameterization of an intracloud lightning discharge has been implemented in our Storm Electrification Model. The initiation, propagation direction, termination and charge redistribution of the discharge are approximated assuming overall charge neutrality. Various simulations involving differing amounts of charge transferred have been done. The effects of the lightning-produced ions on the hydrometeor charges, electric field components and electrical energy depend strongly on the charge transferred. A comparison between the measured electric field change of an actual intracloud flash and the field change due to the simulated discharge show favorable agreement.
A natural spline interpolation and exponential parameterization
NASA Astrophysics Data System (ADS)
Kozera, R.; Wilkołazka, M.
2016-06-01
We consider here a natural spline interpolation based on reduced data and the so-called exponential parameterization (depending on parameter λ ∈ [0, 1]). In particular, the latter is studied in the context of the trajectory approximation in arbitrary euclidean space. The term reduced data refers to an ordered collection of interpolation points without provision of the corresponding knots. The numerical verification of the intrinsic asymptotics α(λ) in γ approximation by natural spline γ^3'N is conducted here for regular and sufficiently smooth curve γ sampled more-or-less uniformly. We select in this paper the substitutes for the missing knots according to the exponential parameterization. The outcomes of the numerical tests manifest sharp linear convergence orders α(λ) = 1, for all λ ∈ [0, 1). In addition, the latter results in unexpected left-hand side dis-continuity at λ = 1, since as shown again here a sharp quadratic order α(1) = 2 prevails. Remarkably, the case of α(1)=2 (derived for reduced data) coincides with the well-known asymptotics established for a natural spline to fit non-reduced data determined by the sequence of interpolation points supplemented with the corresponding knots (see e.g. [1]).
Mixing parameterizations in ocean climate modeling
NASA Astrophysics Data System (ADS)
Moshonkin, S. N.; Gusev, A. V.; Zalesny, V. B.; Byshev, V. I.
2016-03-01
Results of numerical experiments with an eddy-permitting ocean circulation model on the simulation of the climatic variability of the North Atlantic and the Arctic Ocean are analyzed. We compare the ocean simulation quality with using different subgrid mixing parameterizations. The circulation model is found to be sensitive to a mixing parametrization. The computation of viscosity and diffusivity coefficients by an original splitting algorithm of the evolution equations for turbulence characteristics is found to be as efficient as traditional Monin-Obukhov parameterizations. At the same time, however, the variability of ocean climate characteristics is simulated more adequately. The simulation of salinity fields in the entire study region improves most significantly. Turbulent processes have a large effect on the circulation in the long-term through changes in the density fields. The velocity fields in the Gulf Stream and in the entire North Atlantic Subpolar Cyclonic Gyre are reproduced more realistically. The surface level height in the Arctic Basin is simulated more faithfully, marking the Beaufort Gyre better. The use of the Prandtl number as a function of the Richardson number improves the quality of ocean modeling.
Parameterized BLOSUM Matrices for Protein Alignment.
Song, Dandan; Chen, Jiaxing; Chen, Guang; Li, Ning; Li, Jin; Fan, Jun; Bu, Dongbo; Li, Shuai Cheng
2015-01-01
Protein alignment is a basic step for many molecular biology researches. The BLOSUM matrices, especially BLOSUM62, are the de facto standard matrices for protein alignments. However, after widely utilization of the matrices for 15 years, programming errors were surprisingly found in the initial version of source codes for their generation. And amazingly, after bug correction, the "intended" BLOSUM62 matrix performs consistently worse than the "miscalculated" one. In this paper, we find linear relationships among the eigenvalues of the matrices and propose an algorithm to find optimal unified eigenvectors. With them, we can parameterize matrix BLOSUMx for any given variable x that could change continuously. We compare the effectiveness of our parameterized isentropic matrix with BLOSUM62. Furthermore, an iterative alignment and matrix selection process is proposed to adaptively find the best parameter and globally align two sequences. Experiments are conducted on aligning 13,667 families of Pfam database and on clustering MHC II protein sequences, whose improved accuracy demonstrates the effectiveness of our proposed method. PMID:26357279
A subgrid parameterization scheme for precipitation
NASA Astrophysics Data System (ADS)
Turner, S.; Brenguier, J.-L.; Lac, C.
2011-07-01
With increasing computing power, the horizontal resolution of numerical weather prediction (NWP) models is improving and today reaches 1 to 5 km. Nevertheless, clouds and precipitation are still subgrid scale processes for most cloud types, such as cumulus and stratocumulus. Subgrid scale parameterizations for water vapor condensation have been in use for many years and are based on a prescribed PDF of relative humidity spatial variability within the grid, thus providing a diagnosis of the cloud fraction. A similar scheme is developed and tested here. It is based on a prescribed PDF of cloud water variability and a threshold value of liquid water content for droplet collection to derive a rain fraction within the model grid. Precipitation of rainwater raises additional concerns relative to the overlap of cloud and rain fractions, however. The scheme is developed following an analysis of data collected during field campaigns in stratocumulus (DYCOMS-II) and fair weather cumulus (RICO) and tested in a 1-D framework against large eddy simulations of these observed cases. The new parameterization is then implemented in a 3-D NWP model with a horizontal resolution of 2.5 km to simulate real cases of precipitating cloud systems over France.
A subgrid parameterization scheme for precipitation
NASA Astrophysics Data System (ADS)
Turner, S.; Brenguier, J.-L.; Lac, C.
2012-04-01
With increasing computing power, the horizontal resolution of numerical weather prediction (NWP) models is improving and today reaches 1 to 5 km. Nevertheless, clouds and precipitation formation are still subgrid scale processes for most cloud types, such as cumulus and stratocumulus. Subgrid scale parameterizations for water vapor condensation have been in use for many years and are based on a prescribed probability density function (PDF) of relative humidity spatial variability within the model grid box, thus providing a diagnosis of the cloud fraction. A similar scheme is developed and tested here. It is based on a prescribed PDF of cloud water variability and a threshold value of liquid water content for droplet collection to derive a rain fraction within the model grid. Precipitation of rainwater raises additional concerns relative to the overlap of cloud and rain fractions, however. The scheme is developed following an analysis of data collected during field campaigns in stratocumulus (DYCOMS-II) and fair weather cumulus (RICO) and tested in a 1-D framework against large eddy simulations of these observed cases. The new parameterization is then implemented in a 3-D NWP model with a horizontal resolution of 2.5 km to simulate real cases of precipitating cloud systems over France.
A new parameterization of spectral and broadband ocean surface albedo.
Jin, Zhonghai; Qiao, Yanli; Wang, Yingjian; Fang, Yonghua; Yi, Weining
2011-12-19
A simple yet accurate parameterization of spectral and broadband ocean surface albedo has been developed. To facilitate the parameterization and its applications, the albedo is parameterized for the direct and diffuse incident radiation separately, and then each of them is further divided into two components: the contributions from surface and water, respectively. The four albedo components are independent of each other, hence, altering one will not affect the others. Such a designed parameterization scheme is flexible for any future update. Users can simply replace any of the adopted empirical formulations (e.g., the relationship between foam reflectance and wind speed) as desired without a need to change the parameterization scheme. The parameterization is validated by in situ measurements and can be easily implemented into a climate or radiative transfer model. PMID:22274228
Parameterization of Star-Shaped Volumes Using Green's Functions
NASA Astrophysics Data System (ADS)
Xia, Jiazhi; He, Ying; Han, Shuchu; Fu, Chi-Wing; Luo, Feng; Gu, Xianfeng
Parameterizations have a wide range of applications in computer graphics, geometric design and many other fields of science and engineering. Although surface parameterizations have been widely studied and are well developed, little research exists on the volumetric data due to the intrinsic difficulties in extending surface parameterization algorithms to volumetric domain. In this paper, we present a technique for parameterizing star-shaped volumes using the Green's functions. We first show that the Green's function on the star shape has a unique critical point. Then we prove that the Green's functions can induce a diffeomorphism between two star-shaped volumes. We develop algorithms to parameterize star shapes to simple domains such as balls and star-shaped polycubes, and also demonstrate the volume parameterization applications: volumetric morphing, anisotropic solid texture transfer and GPU-based volumetric computation.
Mallia, Rupananda J; McVeigh, Patrick Z; Veilleux, Israel; Wilson, Brian C
2012-07-01
As molecular imaging moves towards lower detection limits, the elimination of endogenous background signals becomes imperative. We present a facile background-suppression technique that specifically segregates the signal from surface-enhanced Raman scattering (SERS)-active nanoparticles (NPs) from the tissue autofluorescence background in vivo. SERS NPs have extremely narrow spectral peaks that do not overlap significantly with endogenous Raman signals. This can be exploited, using specific narrow-band filters, to image picomolar (pM) concentrations of NPs against a broad tissue autofluorescence background in wide-field mode, with short integration times that compare favorably with point-by-point mapping typically used in SERS imaging. This advance will facilitate the potential applications of SERS NPs as contrast agents in wide-field multiplexed biomarker-targeted imaging in vivo. PMID:22894500
Extensions and applications of a second-order landsurface parameterization
NASA Technical Reports Server (NTRS)
Andreou, S. A.; Eagleson, P. S.
1983-01-01
Extensions and applications of a second order land surface parameterization, proposed by Andreou and Eagleson are developed. Procedures for evaluating the near surface storage depth used in one cell land surface parameterizations are suggested and tested by using the model. Sensitivity analysis to the key soil parameters is performed. A case study involving comparison with an "exact" numerical model and another simplified parameterization, under very dry climatic conditions and for two different soil types, is also incorporated.
Parameterizing mesoscale and large-scale ice clouds in general circulation models
NASA Technical Reports Server (NTRS)
Donner, Leo J.
1990-01-01
The paper discusses GCM parameterizations for two types of ice clouds: (1) ice clouds formed by large-scale lifting, often of limited vertical extent but usually of large-scale horizontal extent; and (2) ice clouds formed as anvils in convective systems, often of moderate vertical extent but of mesoscale size horizontally. It is shown that the former type of clouds can be parameterized with reference to an equilibrium between ice generation by deposition from vapor, and ice removal by crystal settling. The same mechanisms operate in the mesoscale clouds, but the ice content in these cases is considered to be more closely linked to the moisture supplied to the anvil by cumulus towers. It is shown that a GCM can simulate widespread ice clouds of both types.
A Genus Oblivious Approach to Cross Parameterization
Bennett, J C; Pascucci, V; Joy, K I
2008-06-16
In this paper we present a robust approach to construct a map between two triangulated meshes, M and M{prime} of arbitrary and possibly unequal genus. We introduce a novel initial alignment scheme that allows the user to identify 'landmark tunnels' and/or a 'constrained silhouette' in addition to the standard landmark vertices. To describe the evolution of non-landmark tunnels we automatically derive a continuous deformation from M to M{prime} using a variational implicit approach. Overall, we achieve a cross parameterization scheme that is provably robust in the sense that it can map M to M{prime} without constraints on their relative genus. We provide a number of examples to demonstrate the practical effectiveness of our scheme between meshes of different genus and shape.
Toward parameterization of the stable boundary layer
NASA Technical Reports Server (NTRS)
Wetzel, P. J.
1982-01-01
Wangara data is used to examine the depth of the nocturnal boundary layer (NBL) and the height to which surface-linked turbulence extends. It is noted that a linearity of virtual temperature profiles has been found to extend up to a significant portion of the NBL, and then diverge where the wind shear rides over the surface-induced turbulence. A series of Richardson numbers are examined for varying degrees of turbulence and the significant cooling region is observed to have greater depth than the depth of the linear relationship layer. A three-layer parameterization of the thermodynamic structure of the NBL is developed so that a system of five equations must be solved when the wind velocity profile and the temperature at the surface are known. A correlation between the bulk Richardson number and the depth of the linear layer was found to be 0.89.
Universal Parameterization of Absorption Cross Sections
NASA Technical Reports Server (NTRS)
Tripathi, R. K.; Cucinotta, Francis A.; Wilson, John W.
1997-01-01
This paper presents a simple universal parameterization of total reaction cross sections for any system of colliding nuclei that is valid for the entire energy range from a few AMeV to a few AGeV. The universal picture presented here treats proton-nucleus collision as a special case of nucleus-nucleus collision, where the projectile has charge and mass number of one. The parameters are associated with the physics of the collision system. In general terms, Coulomb interaction modifies cross sections at lower energies, and the effects of Pauli blocking are important at higher energies. The agreement between the calculated and experimental data is better than all earlier published results.
Optika : a GUI framework for parameterized applications.
Nusbaum, Kurtis L.
2011-06-01
In the field of scientific computing there are many specialized programs designed for specific applications in areas such as biology, chemistry, and physics. These applications are often very powerful and extraordinarily useful in their respective domains. However, some suffer from a common problem: a non-intuitive, poorly-designed user interface. The purpose of Optika is to address this problem and provide a simple, viable solution. Using only a list of parameters passed to it, Optika can dynamically generate a GUI. This allows the user to specify parameters values in a fashion that is much more intuitive than the traditional 'input decks' used by some parameterized scientific applications. By leveraging the power of Optika, these scientific applications will become more accessible and thus allow their designers to reach a much wider audience while requiring minimal extra development effort.
The Doppler spread theory and parameterization revisited
NASA Astrophysics Data System (ADS)
Hines, Colin O.
2004-07-01
The author's earlier Doppler Spread Theory (DST) and Doppler Spread Parameterization (DSP) are revisited with a new understanding of the dichotomous roles played by nonlinearity in Eulerian and Lagrangian coordinates, respectively. An embryo Lagrangian DST is introduced and employed to assess the original DST. Earlier results near the Eulerian spectral peak are found to be reasonably valid, whereas those at greater vertical wavenumber are confirmed to have produced too much spreading. The earlier DSP is found to need little if any change, though specific values are suggested for its two most important ``fudge factors''. In a more general context, the continuing identity of a wave undergoing certain nonlinear interactions with other waves is discussed.
Cumulus parameterizations in chemical transport models
NASA Astrophysics Data System (ADS)
Mahowald, Natalie M.; Rasch, Philip J.; Prinn, Ronald G.
1995-12-01
Global three-dimensional chemical transport models (CTMs) are valuable tools for studying processes controlling the distribution of trace constituents in the atmosphere. A major uncertainty in these models is the subgrid-scale parametrization of transport by cumulus convection. This study seeks to define the range of behavior of moist convective schemes and point toward more reliable formulations for inclusion in chemical transport models. The emphasis is on deriving convective transport from meteorological data sets (such as those from the forecast centers) which do not routinely include convective mass fluxes. Seven moist convective parameterizations are compared in a column model to examine the sensitivity of the vertical profile of trace gases to the parameterization used in a global chemical transport model. The moist convective schemes examined are the Emanuel scheme [Emanuel, 1991], the Feichter-Crutzen scheme [Feichter and Crutzen, 1990], the inverse thermodynamic scheme (described in this paper), two versions of a scheme suggested by Hack [Hack, 1994], and two versions of a scheme suggested by Tiedtke (one following the formulation used in the ECMWF (European Centre for Medium-Range Weather Forecasting) and ECHAM3 (European Centre and Hamburg Max-Planck-Institut) models [Tiedtke, 1989], and one formulated as in the TM2 (Transport Model-2) model (M. Heimann, personal communication, 1992). These convective schemes vary in the closure used to derive the mass fluxes, as well as the cloud model formulation, giving a broad range of results. In addition, two boundary layer schemes are compared: a state-of-the-art nonlocal boundary layer scheme [Holtslag and Boville, 1993] and a simple adiabatic mixing scheme described in this paper. Three tests are used to compare the moist convective schemes against observations. Although the tests conducted here cannot conclusively show that one parameterization is better than the others, the tests are a good measure of the
A parameterization of cloud droplet nucleation
Ghan, S.J. ); Chuang, C.; Penner, J.E. )
1993-01-01
Droplet nucleation is a fundamental cloud process. The number of aerosols activated to form cloud droplets influences not only the number of aerosols scavenged by clouds but also the size of the cloud droplets. Cloud droplet size influences the cloud albedo and the conversion of cloud water to precipitation. Global aerosol models are presently being developed with the intention of coupling with global atmospheric circulation models to evaluate the influence of aerosols and aerosol-cloud interactions on climate. If these and other coupled models are to address issues of aerosol-cloud interactions, the droplet nucleation process must be adequately represented. Here we introduce a droplet nucleation parametrization that offers certain advantages over the popular Twomey (1959) parameterization.
Climate impacts of parameterized Nordic Sea overflows
NASA Astrophysics Data System (ADS)
Danabasoglu, Gokhan; Large, William G.; Briegleb, Bruce P.
2010-11-01
A new overflow parameterization (OFP) of density-driven flows through ocean ridges via narrow, unresolved channels has been developed and implemented in the ocean component of the Community Climate System Model version 4. It represents exchanges from the Nordic Seas and the Antarctic shelves, associated entrainment, and subsequent injection of overflow product waters into the abyssal basins. We investigate the effects of the parameterized Denmark Strait (DS) and Faroe Bank Channel (FBC) overflows on the ocean circulation, showing their impacts on the Atlantic Meridional Overturning Circulation and the North Atlantic climate. The OFP is based on the Marginal Sea Boundary Condition scheme of Price and Yang (1998), but there are significant differences that are described in detail. Two uncoupled (ocean-only) and two fully coupled simulations are analyzed. Each pair consists of one case with the OFP and a control case without this parameterization. In both uncoupled and coupled experiments, the parameterized DS and FBC source volume transports are within the range of observed estimates. The entrainment volume transports remain lower than observational estimates, leading to lower than observed product volume transports. Due to low entrainment, the product and source water properties are too similar. The DS and FBC overflow temperature and salinity properties are in better agreement with observations in the uncoupled case than in the coupled simulation, likely reflecting surface flux differences. The most significant impact of the OFP is the improved North Atlantic Deep Water penetration depth, leading to a much better comparison with the observational data and significantly reducing the chronic, shallow penetration depth bias in level coordinate models. This improvement is due to the deeper penetration of the southward flowing Deep Western Boundary Current. In comparison with control experiments without the OFP, the abyssal ventilation rates increase in the North
Born approximation, scattering, and algorithm
NASA Astrophysics Data System (ADS)
Martinez, Alex; Hu, Mengqi; Gu, Haicheng; Qiao, Zhijun
2015-05-01
In the past few decades, there were many imaging algorithms designed in the case of the absence of multiple scattering. Recently, we discussed an algorithm for removing high order scattering components from collected data. This paper is a continuation of our previous work. First, we investigate the current state of multiple scattering in SAR. Then, we revise our method and test it. Given an estimate of our target reflectivity, we compute the multi scattering effects in the target region for various frequencies. Furthermore, we propagate this energy through free space towards our antenna, and remove it from the collected data.
Parameterization of Heat Transport in a Fjord
NASA Astrophysics Data System (ADS)
Hossainzadeh, S.; Tulaczyk, S. M.
2012-12-01
We aim to improve the coupling in the Regional Arctic System Model (RASM) between the ocean model, Parallel Ocean Program (POP), and the ice sheet model, Community Ice Sheet Model (CISM), by developing a parameterization for the dominant processes in a typical Greenland fjord. The termini of tidewater glaciers and ice shelves may prove to be a critical forcing on outlet glacier mass balance. Recent studies have shown that warm deep water masses have penetrated far up-stream in fjords and sub-ice shelf cavities. We analyze the effects of bottom bathymetry, entrainment rate at the ice face due to freshwater plumes, surface outflow rates, undulating fjord geometries, and open ocean conditions at the fjord mouth on heat transport up-fjord. The fjord is represented as a two-layer (stratified) open channel flow with a substantial and sudden geometric widening at the mouth. Horizontal force balances as well as mass, salt and heat continuity relations of the upper layer provides an analytical solution for the velocity and thickness distribution along-fjord. Subsequently, the sensitivity of the bottom layer's up-fjord flow and heat transport to the ice face is determined and forms the basis of the parameterization of along-fjord processes. Open ocean scenarios (temperature, salinity and velocity profiles), typical of Arctic oceanographic conditions on the Greenland shelf, are prescribed from results of a coupled ocean-sea ice model configured at a regional scale for the pan-Arctic domain. The model was spun up for 48 years and forced by daily averaged atmospheric reanalysis data from the European Centre for Medium-Range Weather Forecasts. We validate this data from several decades-long time series of in situ data from the Gulf of Alaska and West Greenland. Our results provide ice melt rates which agree with current estimates.
Parameterized reduced order modeling of misaligned stacked disks rotor assemblies
NASA Astrophysics Data System (ADS)
Ganine, Vladislav; Laxalde, Denis; Michalska, Hannah; Pierre, Christophe
2011-01-01
Light and flexible rotating parts of modern turbine engines operating at supercritical speeds necessitate application of more accurate but rather computationally expensive 3D FE modeling techniques. Stacked disks misalignment due to manufacturing variability in the geometry of individual components constitutes a particularly important aspect to be included in the analysis because of its impact on system dynamics. A new parametric model order reduction algorithm is presented to achieve this goal at affordable computational costs. It is shown that the disks misalignment leads to significant changes in nominal system properties that manifest themselves as additional blocks coupling neighboring spatial harmonics in Fourier space. Consequently, the misalignment effects can no longer be accurately modeled as equivalent forces applied to a nominal unperturbed system. The fact that the mode shapes become heavily distorted by extra harmonic content renders the nominal modal projection-based methods inaccurate and thus numerically ineffective in the context of repeated analysis of multiple misalignment realizations. The significant numerical bottleneck is removed by employing an orthogonal projection onto the subspace spanned by first few Fourier harmonic basis vectors. The projected highly sparse systems are shown to accurately approximate the specific misalignment effects, to be inexpensive to solve using direct sparse methods and easy to parameterize with a small set of measurable eccentricity and tilt angle parameters. Selected numerical examples on an industrial scale model are presented to illustrate the accuracy and efficiency of the algorithm implementation.
ERIC Educational Resources Information Center
Young, Andrew T.
1982-01-01
The correct usage of such terminology as "Rayleigh scattering,""Rayleigh lines,""Raman lines," and "Tyndall scattering" is resolved during an historical excursion through the physics of light-scattering by gas molecules. (Author/JN)
Adaptive resolution refinement for high-fidelity continuum parameterizations
Anderson, J.W.; Khamayseh, A.; Jean, B.A.
1996-10-01
This paper describes an algorithm the adaptively samples a parametric continuum so that a fidelity metric is satisfied. Using the divide-and-conquer strategy of adaptive sampling eliminates the guesswork of traditional uniform parameterization techniques. The space and time complexity of parameterization are increased in a controllable manner so that a desired fidelity is obtained.
Benchmarking longwave multiple scattering in cirrus environments
NASA Astrophysics Data System (ADS)
Kuo, C.; Feldman, D.; Yang, P.; Flanner, M.; Huang, X.
2015-12-01
Many global climate models currently assume that longwave photons are non-scattering in clouds, and also have overly simplistic treatments of surface emissivity. Multiple scattering of longwave radiation and non-unit emissivity could lead to substantial discrepancies between the actual Earth's radiation budget and its parameterized representation in the infrared, especially at wavelengths longer than 15 µm. The evaluation of the parameterization of longwave spectral multiple scattering in radiative transfer codes for global climate models is critical and will require benchmarking across a wide range atmospheric conditions with more accurate, though computationally more expensive, multiple scattering models. We therefore present a line-by-line radiative transfer solver that includes scattering, run on a supercomputer from the National Energy Research Scientific Computing that exploits the embarrassingly parallel nature of 1-D radiative transfer solutions with high effective throughput. When paired with an advanced ice-particle optical property database with spectral values ranging from the 0.2 to 100 μm, a particle size and habit distribution derived from MODIS Collection 6, and a database for surface emissivity which extends to 100 μm, this benchmarking result can densely sample the thermodynamic and condensate parameter-space, and therefore accelerate the development of an advanced infrared radiative parameterization for climate models, which could help disentangle forcings and feedbacks in CMIP6.
Parameterizing Size Distribution in Ice Clouds
DeSlover, Daniel; Mitchell, David L.
2009-09-25
PARAMETERIZING SIZE DISTRIBUTIONS IN ICE CLOUDS David L. Mitchell and Daniel H. DeSlover ABSTRACT An outstanding problem that contributes considerable uncertainty to Global Climate Model (GCM) predictions of future climate is the characterization of ice particle sizes in cirrus clouds. Recent parameterizations of ice cloud effective diameter differ by a factor of three, which, for overcast conditions, often translate to changes in outgoing longwave radiation (OLR) of 55 W m-2 or more. Much of this uncertainty in cirrus particle sizes is related to the problem of ice particle shattering during in situ sampling of the ice particle size distribution (PSD). Ice particles often shatter into many smaller ice fragments upon collision with the rim of the probe inlet tube. These small ice artifacts are counted as real ice crystals, resulting in anomalously high concentrations of small ice crystals (D < 100 µm) and underestimates of the mean and effective size of the PSD. Half of the cirrus cloud optical depth calculated from these in situ measurements can be due to this shattering phenomenon. Another challenge is the determination of ice and liquid water amounts in mixed phase clouds. Mixed phase clouds in the Arctic contain mostly liquid water, and the presence of ice is important for determining their lifecycle. Colder high clouds between -20 and -36 oC may also be mixed phase but in this case their condensate is mostly ice with low levels of liquid water. Rather than affecting their lifecycle, the presence of liquid dramatically affects the cloud optical properties, which affects cloud-climate feedback processes in GCMs. This project has made advancements in solving both of these problems. Regarding the first problem, PSD in ice clouds are uncertain due to the inability to reliably measure the concentrations of the smallest crystals (D < 100 µm), known as the “small mode”. Rather than using in situ probe measurements aboard aircraft, we employed a treatment of ice
Recognizing parameterized three-dimensional objects
NASA Astrophysics Data System (ADS)
Goldberg, Robert R.
1994-10-01
Complex object models require multiple components affixed to each other in specific and variable geometric paths. This paper expands upon earlier research to present an unified approach for relating components' coordinate systems to each other in the same model. Particularly, we show that rather complex relationships such as ball joints and geometric transformations about arbitrary axes are no more complicated than describing the model base in terms of the camera coordinate system. These require only simple rotations and translations about the major axes. This modeling approach was next integrated with a verification module of a model based vision system. We recovered from a single 2D image the original model and camera parameters that would align the projected model edges with the image segments by solving a nonlinear least squares system. A specific example of the theory is implemented. A lamp head is seceded to its base by a ball joint with three parameters of rotational freedom. From a wide range of initial guess error, the numerical system converged to the correct set of model and camera parameters. Thus, the theory of parameterized affixments and the numerical implementation to obtain these values from 2D images will aid in associated recognition tasks and in real-time tracking of complex conglomerate objects.
Parameterizing deep convection using the assumed probability density function method
Storer, R. L.; Griffin, B. M.; Hoft, Jan; Weber, J. K.; Raut, E.; Larson, Vincent E.; Wang, Minghuai; Rasch, Philip J.
2015-01-06
Due to their coarse horizontal resolution, present-day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method.The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and mid-latitude deep convection.These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing is weak. The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way.
Parameterizing deep convection using the assumed probability density function method
NASA Astrophysics Data System (ADS)
Storer, R. L.; Griffin, B. M.; Höft, J.; Weber, J. K.; Raut, E.; Larson, V. E.; Wang, M.; Rasch, P. J.
2015-01-01
Due to their coarse horizontal resolution, present-day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method. The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and midlatitude deep convection. These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing is weak. The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way.
Parameterizing deep convection using the assumed probability density function method
Storer, R. L.; Griffin, B. M.; Höft, J.; Weber, J. K.; Raut, E.; Larson, V. E.; Wang, M.; Rasch, P. J.
2014-06-11
Due to their coarse horizontal resolution, present-day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method. The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and mid-latitude deep convection. These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing ismore » weak. The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way.« less
Parameterizing deep convection using the assumed probability density function method
Storer, R. L.; Griffin, B. M.; Höft, J.; Weber, J. K.; Raut, E.; Larson, V. E.; Wang, M.; Rasch, P. J.
2015-01-06
Due to their coarse horizontal resolution, present-day climate models must parameterize deep convection. This paper presents single-column simulations of deep convection using a probability density function (PDF) parameterization. The PDF parameterization predicts the PDF of subgrid variability of turbulence, clouds, and hydrometeors. That variability is interfaced to a prognostic microphysics scheme using a Monte Carlo sampling method. The PDF parameterization is used to simulate tropical deep convection, the transition from shallow to deep convection over land, and midlatitude deep convection. These parameterized single-column simulations are compared with 3-D reference simulations. The agreement is satisfactory except when the convective forcing ismore » weak. The same PDF parameterization is also used to simulate shallow cumulus and stratocumulus layers. The PDF method is sufficiently general to adequately simulate these five deep, shallow, and stratiform cloud cases with a single equation set. This raises hopes that it may be possible in the future, with further refinements at coarse time step and grid spacing, to parameterize all cloud types in a large-scale model in a unified way.« less
Brain Surface Conformal Parameterization Using Riemann Surface Structure
Wang, Yalin; Lui, Lok Ming; Gu, Xianfeng; Hayashi, Kiralee M.; Chan, Tony F.; Toga, Arthur W.; Thompson, Paul M.; Yau, Shing-Tung
2011-01-01
In medical imaging, parameterized 3-D surface models are useful for anatomical modeling and visualization, statistical comparisons of anatomy, and surface-based registration and signal processing. Here we introduce a parameterization method based on Riemann surface structure, which uses a special curvilinear net structure (conformal net) to partition the surface into a set of patches that can each be conformally mapped to a parallelogram. The resulting surface subdivision and the parameterizations of the components are intrinsic and stable (their solutions tend to be smooth functions and the boundary conditions of the Dirichlet problem can be enforced). Conformal parameterization also helps transform partial differential equations (PDEs) that may be defined on 3-D brain surface manifolds to modified PDEs on a two-dimensional parameter domain. Since the Jacobian matrix of a conformal parameterization is diagonal, the modified PDE on the parameter domain is readily solved. To illustrate our techniques, we computed parameterizations for several types of anatomical surfaces in 3-D magnetic resonance imaging scans of the brain, including the cerebral cortex, hippocampi, and lateral ventricles. For surfaces that are topologically homeomorphic to each other and have similar geometrical structures, we show that the parameterization results are consistent and the subdivided surfaces can be matched to each other. Finally, we present an automatic sulcal landmark location algorithm by solving PDEs on cortical surfaces. The landmark detection results are used as constraints for building conformal maps between surfaces that also match explicitly defined landmarks. PMID:17679336
Carbody structural lightweighting based on implicit parameterized model
NASA Astrophysics Data System (ADS)
Chen, Xin; Ma, Fangwu; Wang, Dengfeng; Xie, Chen
2014-05-01
Most of recent research on carbody lightweighting has focused on substitute material and new processing technologies rather than structures. However, new materials and processing techniques inevitably lead to higher costs. Also, material substitution and processing lightweighting have to be realized through body structural profiles and locations. In the huge conventional workload of lightweight optimization, model modifications involve heavy manual work, and it always leads to a large number of iteration calculations. As a new technique in carbody lightweighting, the implicit parameterization is used to optimize the carbody structure to improve the materials utilization rate in this paper. The implicit parameterized structural modeling enables the use of automatic modification and rapid multidisciplinary design optimization (MDO) in carbody structure, which is impossible in the traditional structure finite element method (FEM) without parameterization. The structural SFE parameterized model is built in accordance with the car structural FE model in concept development stage, and it is validated by some structural performance data. The validated SFE structural parameterized model can be used to generate rapidly and automatically FE model and evaluate different design variables group in the integrated MDO loop. The lightweighting result of body-in-white (BIW) after the optimization rounds reveals that the implicit parameterized model makes automatic MDO feasible and can significantly improve the computational efficiency of carbody structural lightweighting. This paper proposes the integrated method of implicit parameterized model and MDO, which has the obvious practical advantage and industrial significance in the carbody structural lightweighting design.
Climate and the equilibrium state of land surface hydrology parameterizations
NASA Technical Reports Server (NTRS)
Entekhabi, Dara; Eagleson, Peter S.
1991-01-01
For given climatic rates of precipitation and potential evaporation, the land surface hydrology parameterizations of atmospheric general circulation models will maintain soil-water storage conditions that balance the moisture input and output. The surface relative soil saturation for such climatic conditions serves as a measure of the land surface parameterization state under a given forcing. The equilibrium value of this variable for alternate parameterizations of land surface hydrology are determined as a function of climate and the sensitivity of the surface to shifts and changes in climatic forcing are estimated.
Parameterization of cloud glaciation by atmospheric dust
NASA Astrophysics Data System (ADS)
Nickovic, Slobodan; Cvetkovic, Bojan; Madonna, Fabio; Pejanovic, Goran; Petkovic, Slavko
2016-04-01
The exponential growth of research interest on ice nucleation (IN) is motivated, inter alias, by needs to improve generally unsatisfactory representation of cold cloud formation in atmospheric models, and therefore to increase the accuracy of weather and climate predictions, including better forecasting of precipitation. Research shows that mineral dust significantly contributes to cloud ice nucleation. Samples of residual particles in cloud ice crystals collected by aircraft measurements performed in the upper tropopause of regions distant from desert sources indicate that dust particles dominate over other known ice nuclei such as soot and biological particles. In the nucleation process, dust chemical aging had minor effects. The observational evidence on IN processes has substantially improved over the last decade and clearly shows that there is a significant correlation between IN concentrations and the concentrations of coarser aerosol at a given temperature and moisture. Most recently, due to recognition of the dominant role of dust as ice nuclei, parameterizations for immersion and deposition icing specifically due to dust have been developed. Based on these achievements, we have developed a real-time forecasting coupled atmosphere-dust modelling system capable to operationally predict occurrence of cold clouds generated by dust. We have been thoroughly validated model simulations against available remote sensing observations. We have used the CNR-IMAA Potenza lidar and cloud radar observations to explore the model capability to represent vertical features of the cloud and aerosol vertical profiles. We also utilized the MSG-SEVIRI and MODIS satellite data to examine the accuracy of the simulated horizontal distribution of cold clouds. Based on the obtained encouraging verification scores, operational experimental prediction of ice clouds nucleated by dust has been introduced in the Serbian Hydrometeorological Service as a public available product.
Some applications of parameterized Picard-Vessiot theory
NASA Astrophysics Data System (ADS)
Mitschi, C.
2016-02-01
This is an expository article describing some applications of parameterized Picard-Vessiot theory. This Galois theory for parameterized linear differential equations was Cassidy and Singer's contribution to an earlier volume dedicated to the memory of Andrey Bolibrukh. The main results we present here were obtained for families of ordinary differential equations with parameterized regular singularities in joint work with Singer. They include parametric versions of Schlesinger's theorem and of the weak Riemann-Hilbert problem as well as an algebraic characterization of a special type of monodromy evolving deformations illustrated by the classical Darboux-Halphen equation. Some of these results have recently been applied by different authors to solve the inverse problem of parameterized Picard-Vessiot theory, and were also generalized to irregular singularities. We sketch some of these results by other authors. The paper includes a brief history of the Darboux-Halphen equation as well as an appendix on differentially closed fields.
Parameterization of cirrus optical depth and cloud fraction
Soden, B.
1995-09-01
This research illustrates the utility of combining satellite observations and operational analysis for the evaluation of parameterizations. A parameterization based on ice water path (IWP) captures the observed spatial patterns of tropical cirrus optical depth. The strong temperature dependence of cirrus ice water path in both the observations and the parameterization is probably responsible for the good correlation where it exists. Poorer agreement is found in Southern Hemisphere mid-latitudes where the temperature dependence breaks down. Uncertainties in effective radius limit quantitative validation of the parameterization (and its inclusion into GCMs). Also, it is found that monthly mean cloud cover can be predicted within an RMS error of 10% using ECMWF relative humidity corrected by TOVS Upper Troposphere Humidity. 1 ref., 2 figs.
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Parameter Estimation and Parameterization Uncertainty Using Bayesian Model Averaging
NASA Astrophysics Data System (ADS)
Tsai, F. T.; Li, X.
2007-12-01
This study proposes Bayesian model averaging (BMA) to address parameter estimation uncertainty arisen from non-uniqueness in parameterization methods. BMA provides a means of incorporating multiple parameterization methods for prediction through the law of total probability, with which an ensemble average of hydraulic conductivity distribution is obtained. Estimation uncertainty is described by the BMA variances, which contain variances within and between parameterization methods. BMA shows the facts that considering more parameterization methods tends to increase estimation uncertainty and estimation uncertainty is always underestimated using a single parameterization method. Two major problems in applying BMA to hydraulic conductivity estimation using a groundwater inverse method will be discussed in the study. The first problem is the use of posterior probabilities in BMA, which tends to single out one best method and discard other good methods. This problem arises from Occam's window that only accepts models in a very narrow range. We propose a variance window to replace Occam's window to cope with this problem. The second problem is the use of Kashyap information criterion (KIC), which makes BMA tend to prefer high uncertain parameterization methods due to considering the Fisher information matrix. We found that Bayesian information criterion (BIC) is a good approximation to KIC and is able to avoid controversial results. We applied BMA to hydraulic conductivity estimation in the 1,500-foot sand aquifer in East Baton Rouge Parish, Louisiana.
Faster Parameterized Algorithms for Minor Containment
NASA Astrophysics Data System (ADS)
Adler, Isolde; Dorn, Frederic; Fomin, Fedor V.; Sau, Ignasi; Thilikos, Dimitrios M.
The theory of Graph Minors by Robertson and Seymour is one of the deepest and significant theories in modern Combinatorics. This theory has also a strong impact on the recent development of Algorithms, and several areas, like Parameterized Complexity, have roots in Graph Minors. Until very recently it was a common belief that Graph Minors Theory is mainly of theoretical importance. However, it appears that many deep results from Robertson and Seymour's theory can be also used in the design of practical algorithms. Minor containment testing is one of algorithmically most important and technical parts of the theory, and minor containment in graphs of bounded branchwidth is a basic ingredient of this algorithm. In order to implement minor containment testing on graphs of bounded branchwidth, Hicks [NETWORKS 04] described an algorithm, that in time O(3^{k^2}\\cdot (h+k-1)!\\cdot m) decides if a graph G with m edges and branchwidth k, contains a fixed graph H on h vertices as a minor. That algorithm follows the ideas introduced by Robertson and Seymour in [J'CTSB 95]. In this work we improve the dependence on k of Hicks' result by showing that checking if H is a minor of G can be done in time O(2^{(2k +1 )\\cdot log k} \\cdot h^{2k} \\cdot 2^{2h^2} \\cdot m). Our approach is based on a combinatorial object called rooted packing, which captures the properties of the potential models of subgraphs of H that we seek in our dynamic programming algorithm. This formulation with rooted packings allows us to speed up the algorithm when G is embedded in a fixed surface, obtaining the first single-exponential algorithm for minor containment testing. Namely, it runs in time 2^{O(k)} \\cdot h^{2k} \\cdot 2^{O(h)} \\cdot n, with n = |V(G)|. Finally, we show that slight modifications of our algorithm permit to solve some related problems within the same time bounds, like induced minor or contraction minor containment.
Brydegaard, Mikkel
2015-01-01
In recent years, the field of remote sensing of birds and insects in the atmosphere (the aerial fauna) has advanced considerably, and modern electro-optic methods now allow the assessment of the abundance and fluxes of pests and beneficials on a landscape scale. These techniques have the potential to significantly increase our understanding of, and ability to quantify and manage, the ecological environment. This paper presents a concept whereby laser radar observations of atmospheric fauna can be parameterized and table values for absolute cross sections can be catalogued to allow for the study of focal species such as disease vectors and pests. Wing-beat oscillations are parameterized with a discrete set of harmonics and the spherical scatter function is parameterized by a reduced set of symmetrical spherical harmonics. A first order spherical model for insect scatter is presented and supported experimentally, showing angular dependence of wing beat harmonic content. The presented method promises to give insights into the flight heading directions of species in the atmosphere and has the potential to shed light onto the km-range spread of pests and disease vectors. PMID:26295706
Brydegaard, Mikkel
2015-01-01
In recent years, the field of remote sensing of birds and insects in the atmosphere (the aerial fauna) has advanced considerably, and modern electro-optic methods now allow the assessment of the abundance and fluxes of pests and beneficials on a landscape scale. These techniques have the potential to significantly increase our understanding of, and ability to quantify and manage, the ecological environment. This paper presents a concept whereby laser radar observations of atmospheric fauna can be parameterized and table values for absolute cross sections can be catalogued to allow for the study of focal species such as disease vectors and pests. Wing-beat oscillations are parameterized with a discrete set of harmonics and the spherical scatter function is parameterized by a reduced set of symmetrical spherical harmonics. A first order spherical model for insect scatter is presented and supported experimentally, showing angular dependence of wing beat harmonic content. The presented method promises to give insights into the flight heading directions of species in the atmosphere and has the potential to shed light onto the km-range spread of pests and disease vectors. PMID:26295706
Paluszkiewicz, T.; Hibler, L.F.; Romea, R.D.
1995-01-01
The current generation of ocean general circulation models (OGCMS) uses a convective adjustment scheme to remove static instabilities and to parameterize shallow and deep convection. In simulations used to examine climate-related scenarios, investigators found that in the Arctic regions, the OGCM simulations did not produce a realistic vertical density structure, did not create the correct quantity of deep water, and did not use a time-scale of adjustment that is in agreement with tracer ages or observations. A possible weakness of the models is that the convective adjustment scheme does not represent the process of deep convection adequately. Consequently, a penetrative plume mixing scheme has been developed to parameterize the process of deep open-ocean convection in OGCMS. This new deep convection parameterization was incorporated into the Semtner and Chervin (1988) OGCM. The modified model (with the new parameterization) was run in a simplified Nordic Seas test basin: under a cyclonic wind stress and cooling, stratification of the basin-scale gyre is eroded and deep mixing occurs in the center of the gyre. In contrast, in the OGCM experiment that uses the standard convective adjustment algorithm, mixing is delayed and is wide-spread over the gyre.
How uncertain are the process parameterizations in our models?
NASA Astrophysics Data System (ADS)
Hrachowitz, M.; Gharari, S.; Gupta, H. V.; Fenicia, F.; Matgen, P.; Savenije, H.
2015-12-01
Environmental models are abstract simplifications of real systems. As a result, the elements of these models, including system architecture (structure), process parameterization and parameters inherit a high level of approximation and simplification. In a conventional model building exercise the parameter values are the only elements of a model which can vary while the rest of the modeling elements are often fixed a priori and therefore not subjected to change. Once chosen the process parametrization and model structure usually remains the same throughout the modeling process. The only flexibility comes from the changing parameter values, thereby enabling these models to reproduce the desired observation. This part of modeling practice, parameter identification and uncertainty, has attracted a significant attention in the literature during the last years. However what remains unexplored in our point of view is to what extent the process parameterization and system architecture (model structure) can support each other. In other words "Does a specific form of process parameterization emerge for a specific model given its system architecture and data while no or little assumption has been made about the process parameterization itself? In this study we relax the assumption regarding a specific pre-determined form for the process parameterizations of a rainfall/runoff model and examine how varying the complexity of the system architecture can lead to different or possibly contradictory parameterization forms than what would have been decided otherwise. This comparison implicitly and explicitly provides us with an assessment of how uncertain is our perception of model process parameterization in respect to the extent the data can support.
How certain are the process parameterizations in our models?
NASA Astrophysics Data System (ADS)
Gharari, Shervan; Hrachowitz, Markus; Fenicia, Fabrizio; Matgen, Patrick; Razavi, Saman; Savenije, Hubert; Gupta, Hoshin; Wheater, Howard
2016-04-01
Environmental models are abstract simplifications of real systems. As a result, the elements of these models, including system architecture (structure), process parameterization and parameters inherit a high level of approximation and simplification. In a conventional model building exercise the parameter values are the only elements of a model which can vary while the rest of the modeling elements are often fixed a priori and therefore not subjected to change. Once chosen the process parametrization and model structure usually remains the same throughout the modeling process. The only flexibility comes from the changing parameter values, thereby enabling these models to reproduce the desired observation. This part of modeling practice, parameter identification and uncertainty, has attracted a significant attention in the literature during the last years. However what remains unexplored in our point of view is to what extent the process parameterization and system architecture (model structure) can support each other. In other words "Does a specific form of process parameterization emerge for a specific model given its system architecture and data while no or little assumption has been made about the process parameterization itself? In this study we relax the assumption regarding a specific pre-determined form for the process parameterizations of a rainfall/runoff model and examine how varying the complexity of the system architecture can lead to different or possibly contradictory parameterization forms than what would have been decided otherwise. This comparison implicitly and explicitly provides us with an assessment of how uncertain is our perception of model process parameterization in respect to the extent the data can support.
NASA Technical Reports Server (NTRS)
Molthan, Andrew L.; Petersen, Walter A.; Case, Jonathan L.; Dembek, Scott R.; Jedlovec, Gary J.
2009-01-01
Increases in computational resources have allowed operational forecast centers to pursue experimental, high resolution simulations that resolve the microphysical characteristics of clouds and precipitation. These experiments are motivated by a desire to improve the representation of weather and climate, but will also benefit current and future satellite campaigns, which often use forecast model output to guide the retrieval process. Aircraft, surface and radar data from the Canadian CloudSat/CALIPSO Validation Project are used to check the validity of size distribution and density characteristics for snowfall simulated by the NASA Goddard six-class, single-moment bulk water microphysics scheme, currently available within the Weather Research and Forecast (WRF) Model. Widespread snowfall developed across the region on January 22, 2007, forced by the passing of a midlatitude cyclone, and was observed by the dual-polarimetric, C-band radar King City, Ontario, as well as the NASA 94 GHz CloudSat Cloud Profiling Radar. Combined, these data sets provide key metrics for validating model output: estimates of size distribution parameters fit to the inverse-exponential equations prescribed within the model, bulk density and crystal habit characteristics sampled by the aircraft, and representation of size characteristics as inferred by the radar reflectivity at C- and W-band. Specified constants for distribution intercept and density differ significantly from observations throughout much of the cloud depth. Alternate parameterizations are explored, using column-integrated values of vapor excess to avoid problems encountered with temperature-based parameterizations in an environment where inversions and isothermal layers are present. Simulation of CloudSat reflectivity is performed by adopting the discrete-dipole parameterizations and databases provided in literature, and demonstrate an improved capability in simulating radar reflectivity at W-band versus Mie scattering
NASA Technical Reports Server (NTRS)
Molthan, Andrew L.; Petersen, Walter A.; Case, Jonathan L.; Dembek, Scott R.
2009-01-01
CloudSat reflectivity is performed by adopting the discrete-dipole parameterizations and databases provided in literature, and demonstrate an improved capability in simulating radar reflectivity at W-band versus Mie scattering assumptions.
Optimal Aerosol Parameterization for Remote Sensing Retrievals
NASA Technical Reports Server (NTRS)
Newchurch, Michael J.
2004-01-01
discrepancy in the lower stratosphere is attributable to natural variation, and is also seen in comparisons between lidar and ozonesonde measurements. NO2 profiles obtained with our algorithm were compared to those obtained through the SAGE III operational algorithm and exhibited differences of 20 - 40%. Our retrieved profiles agree with the HALOE NO2 measurements significantly better than those of the operational retrieval. In other work (described below), we are extending our aerosol retrievals into the infrared regime and plan to perform retrievals from combined uv-visible-infrared spectra. This work will allow us to use the spectra to derive the size and composition of aerosols, and we plan to employ our algorithms in the analysis of PSC spectra. We are presently also developing a limb-scattering algorithm to retrieve aerosol data from limb measurements of solar scattered radiation.
Functional parameterization for hydraulic conductivity inversion with uncertainty quantification
NASA Astrophysics Data System (ADS)
Jiao, Jianying; Zhang, Ye
2015-05-01
Functional inversion based on local approximate solutions (LAS) is developed for steady-state flow in heterogeneous aquifers. The method employs a set of LAS of flow to impose spatial continuity of hydraulic head and Darcy fluxes in the solution domain, which are conditioned to limited measurements. Hydraulic conductivity is first parameterized as piecewise continuous, which requires the addition of a smoothness constraint to reduce inversion artifacts. Alternatively, it is formulated as piecewise constant, for which the smoothness constraint is not required, but the data requirement is much higher. Success of the inversion with both parameterizations is demonstrated for both one-dimensional synthetic examples and an oil-field permeability profile. When measurement errors are increased, estimation becomes less accurate but the solution is stable, i.e., estimation errors remain bounded. Compared to piecewise constant parameterization, piecewise continuous parameterization leads to more stable and accurate inversion. Moreover, conductivity variation can also be captured at two spatial scales reflecting sub-facies smooth-varying heterogeneity as well as abrupt changes at facies boundaries. By combining inversion with geostatistical simulation, uncertainty in the estimated conductivity and the hydraulic head field can be quantified. For a given measurement dataset, inversion accuracy and estimation uncertainty with the piecewise continuous parameterization is not sensitive to increasing conductivity contrast.
Parameterizing the power spectrum: Beyond the truncated Taylor expansion
Abazajian, Kevork; Kadota, Kenji; Stewart, Ewan D.; /KAIST, Taejon /Canadian Inst. Theor. Astrophys.
2005-07-01
The power spectrum is traditionally parameterized by a truncated Taylor series: ln P(k) = ln P{sub *} + (n{sub *} - 1) ln(k/k{sub *}) + 1/2 n'{sub *} ln{sup 2} (k/k{sub *}). It is reasonable to truncate the Taylor series if |n'{sub *} ln(k/k{sub *})| << |n{sub *} - 1|, but it is not if |n'{sub *} ln(k/k{sub *})| {approx}> |n{sub *} - 1|. We argue that there is no good theoretical reason to prefer |n'{sub *}| << |n{sub *} - 1|, and show that current observations are consistent with |n*{sub *} ln(k/k{sub *})| {approx} |n{sub *} - 1| even for |ln(k/k{sub *})| {approx} 1. Thus, there are regions of parameter space, which are both theoretically and observationally relevant, for which the traditional truncated Taylor series parameterization is inconsistent, and hence it can lead to incorrect parameter estimations. Motivated by this, we propose a simple extension of the traditional parameterization, which uses no extra parameters, but that, unlike the traditional approach, covers well motivated inflationary spectra with |n'{sub *}| {approx} |n{sub *} - 1|. Our parameterization therefore covers not only standard-slow-roll inflation models but also a much wider class of inflation models. We use this parameterization to perform a likelihood analysis for the cosmological parameters.
Uncertainties in gas exchange parameterization during the SAGE dual-tracer experiment
NASA Astrophysics Data System (ADS)
Smith, Murray J.; Ho, David T.; Law, Cliff S.; McGregor, John; Popinet, Stéphane; Schlosser, Peter
2011-03-01
A dual tracer experiment was carried out during the SAGE experiment using the inert tracers SF 6 and 3He, in order to determine the gas transfer velocity, k, at high wind speeds in the Southern Ocean. Wind speed/gas exchange parameterization is characterised by significant variability and we examine the major measurement uncertainties that contribute to that scatter. Correction for the airflow distortion over the research vessel, as determined by computational fluid dynamics (CFD) modelling, had the effect of increasing the calculated value of k by 30%. On the short time scales of such experiments, the spatial variability of the wind field resulted in differences between ship and satellite QuikSCAT winds, which produced significant differences in transfer velocity. With such variability between wind estimates, the comparison between gas exchange parameterizations from diverse experiments should clearly be made on the basis of the same wind product. Uncertainty in mixed layer depth of ˜10% arose from mixed layer deepening at high wind speed and limited resolution of vertical sampling. However the assumption of equal mixing of the two tracers is borne out by the experiment. Two dual tracer releases were carried out during SAGE, and showed no significant difference in transfer velocities using QuikSCAT winds, despite the differences in wind history. In the SAGE experiment, duration limitation on the development of waves was shown to be an important factor for Southern Ocean waves, despite the presence of long fetches.
Parameterization of and Brine Storage in MOR Hydrothermal Systems
NASA Astrophysics Data System (ADS)
Hoover, J.; Lowell, R. P.; Cummings, K. B.
2009-12-01
Single-pass parameterized models of high-temperature hydrothermal systems at oceanic spreading centers use observational constraints such as vent temperature, heat output, vent field area, and the area of heat extraction from the sub-axial magma chamber to deduce fundamental hydrothermal parameters such as total mass flux Q, bulk permeability k, and the thickness of the conductive boundary layer at the base of the system, δ. Of the more than 300 known systems, constraining data are available for less than 10%. Here we use the single pass model to estimate Q, k, and δ for all the seafloor hydrothermal systems for which the constraining data are available. Mean values of Q, k, and δ are 170 kg/s, 5.0x10-13 m2, and 20 m, respectively; which is similar to results obtained from the generic model. There is no apparent correlation with spreading rate. Using observed vent field lifetimes, the rate of magma replenishment can also be calculated. Essentially all high-temperature hydrothermal systems at oceanic spreading centers undergo phase separation, yielding a low chlorinity vapor and a high salinity brine. Some systems such as the Main Endeavour Field on the Juan de Fuca Ridge and the 9°50’N sites on the East Pacific Rise vent low chlorinity vapor for many years, while the high density brine remains sequestered beneath the seafloor. In an attempt to further understand the brine storage at the EPR, we used the mass flux Q determined above, time series of vent salinity and temperature, and the depth of the magma chamber to determine the rate of brine production at depth. We found thicknesses ranging from 0.32 meters to ~57 meters over a 1 km2 area from 1994-2002. These calculations suggest that brine maybe being stored within the conductive boundary layer without a need for lateral transport or removal by other means. We plan to use the numerical code FISHES to further test this idea.
Development of a hybrid cloud parameterization for general circulation models
Kao, C.Y.J.; Kristjansson, J.E.; Langley, D.L.
1995-04-01
We have developed a cloud package with state-of-the-art physical schemes that can parameterize low-level stratus or stratocumulus, penetrative cumulus, and high-level cirrus. Such parameterizations will improve cloud simulations in general circulation models (GCMs). The principal tool in this development comprises the physically based Arakawa-Schubert scheme for convective clouds and the Sundqvist scheme for layered, nonconvective clouds. The term {open_quotes}hybrid{close_quotes} addresses the fact that the generation of high-attitude layered clouds can be associated with preexisting convective clouds. Overall, the cloud parameterization package developed should better determine cloud heating and drying effects in the thermodynamic budget, realistic precipitation patterns, cloud coverage and liquid/ice water content for radiation purposes, and the cloud-induced transport and turbulent diffusion for atmospheric trace gases.
Cloud-radiation interactions and their parameterization in climate models
NASA Technical Reports Server (NTRS)
1994-01-01
This report contains papers from the International Workshop on Cloud-Radiation Interactions and Their Parameterization in Climate Models met on 18-20 October 1993 in Camp Springs, Maryland, USA. It was organized by the Joint Working Group on Clouds and Radiation of the International Association of Meteorology and Atmospheric Sciences. Recommendations were grouped into three broad areas: (1) general circulation models (GCMs), (2) satellite studies, and (3) process studies. Each of the panels developed recommendations on the themes of the workshop. Explicitly or implicitly, each panel independently recommended observations of basic cloud microphysical properties (water content, phase, size) on the scales resolved by GCMs. Such observations are necessary to validate cloud parameterizations in GCMs, to use satellite data to infer radiative forcing in the atmosphere and at the earth's surface, and to refine the process models which are used to develop advanced cloud parameterizations.
Parameterized reduced-order models using hyper-dual numbers.
Fike, Jeffrey A.; Brake, Matthew Robert
2013-10-01
The goal of most computational simulations is to accurately predict the behavior of a real, physical system. Accurate predictions often require very computationally expensive analyses and so reduced order models (ROMs) are commonly used. ROMs aim to reduce the computational cost of the simulations while still providing accurate results by including all of the salient physics of the real system in the ROM. However, real, physical systems often deviate from the idealized models used in simulations due to variations in manufacturing or other factors. One approach to this issue is to create a parameterized model in order to characterize the effect of perturbations from the nominal model on the behavior of the system. This report presents a methodology for developing parameterized ROMs, which is based on Craig-Bampton component mode synthesis and the use of hyper-dual numbers to calculate the derivatives necessary for the parameterization.
A numerical model of aerosol scavenging: Part 1, Microphysics parameterization
Molenkamp, C.R.; Bradley, M.M.
1991-09-01
We have developed a three-dimensional numerical model (OCTET) to simulate the dynamics and microphysics of clouds and the transport, diffusion and precipitation scavenging of aerosol particles. In this paper we describe the cloud microphysics and scavenging parameterizations. The representation of cloud microphysics is a bulk- water parameterization which includes water vapor and five types of hydrometeors (cloud droplets, rain drops, ice crystals, snow, and graupel). A parallel parameterization represents the scavenging interactions between pollutant particles and hydrometeors including collection of particles because of condensation nucleation, Brownian and phoretic attachment, and inertial capture, resuspension because of evaporation and sublimation; and transfer interactions where particles collected by one type of hydrometeor are transferred to another type of freezing, melting, accretion, riming and autoconversion.
Cloud-radiation interactions and their parameterization in climate models
1994-11-01
This report contains papers from the International Workshop on Cloud-Radiation Interactions and Their Parameterization in Climate Models met on 18--20 October 1993 in Camp Springs, Maryland, USA. It was organized by the Joint Working Group on Clouds and Radiation of the International Association of Meteorology and Atmospheric Sciences. Recommendations were grouped into three broad areas: (1) general circulation models (GCMs), (2) satellite studies, and (3) process studies. Each of the panels developed recommendations on the. themes of the workshop. Explicitly or implicitly, each panel independently recommended observations of basic cloud microphysical properties (water content, phase, size) on the scales resolved by GCMs. Such observations are necessary to validate cloud parameterizations in GCMs, to use satellite data to infer radiative forcing in the atmosphere and at the earth`s surface, and to refine the process models which are used to develop advanced cloud parameterizations.
Isogeometric analysis for parameterized LSM-based structural topology optimization
NASA Astrophysics Data System (ADS)
Wang, Yingjun; Benson, David J.
2016-01-01
In this paper, we present an accurate and efficient isogeometric topology optimization method that integrates the non-uniform rational B-splines based isogeometric analysis and the parameterized level set method for minimal compliance problems. The same NURBS basis functions are used to parameterize the level set function and evaluate the objective function, and therefore the design variables are associated with the control points. The coefficient matrix that parameterizes the level set function is set up by a collocation method that uses the Greville abscissae. The zero-level set boundary is obtained from the interpolation points corresponding to the vertices of the knot spans. Numerical examples demonstrate the validity and efficiency of the proposed method.
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NASA Astrophysics Data System (ADS)
Gladish, James C.; Duncan, Donald D.
2016-05-01
Liquid crystal variable retarders (LCVRs) are computer-controlled birefringent devices that contain nanometer-sized birefringent liquid crystals (LCs). These devices impart retardance effects through a global, uniform orientation change of the LCs, which is based on a user-defined drive voltage input. In other words, the LC structural organization dictates the device functionality. The LC structural organization also produces a spectral scatter component which exhibits an inverse power law dependence. We investigate LC structural organization by measuring the voltage-dependent LC spectral scattering signature with an integrating sphere and then relate this observable to a fractal-Born model based on the Born approximation and a Von Kármán spectrum. We obtain LCVR light scattering spectra at various drive voltages (i.e., different LC orientations) and then parameterize LCVR structural organization with voltage-dependent correlation lengths. The results can aid in determining performance characteristics of systems using LCVRs and can provide insight into interpreting structural organization measurements.
Berg, Larry K.; Shrivastava, ManishKumar B.; Easter, Richard C.; Fast, Jerome D.; Chapman, Elaine G.; Liu, Ying
2015-01-01
A new treatment of cloud-aerosol interactions within parameterized shallow and deep convection has been implemented in WRF-Chem that can be used to better understand the aerosol lifecycle over regional to synoptic scales. The modifications to the model to represent cloud-aerosol interactions include treatment of the cloud dropletnumber mixing ratio; key cloud microphysical and macrophysical parameters (including the updraft fractional area, updraft and downdraft mass fluxes, and entrainment) averaged over the population of shallow clouds, or a single deep convective cloud; and vertical transport, activation/resuspension, aqueous chemistry, and wet removal of aerosol and trace gases in warm clouds. Thesechanges have been implemented in both the WRF-Chem chemistry packages as well as the Kain-Fritsch cumulus parameterization that has been modified to better represent shallow convective clouds. Preliminary testing of the modified WRF-Chem has been completed using observations from the Cumulus Humilis Aerosol Processing Study (CHAPS) as well as a high-resolution simulation that does not include parameterized convection. The simulation results are used to investigate the impact of cloud-aerosol interactions on the regional scale transport of black carbon (BC), organic aerosol (OA), and sulfate aerosol. Based on the simulations presented here, changes in the column integrated BC can be as large as -50% when cloud-aerosol interactions are considered (due largely to wet removal), or as large as +35% for sulfate in non-precipitating conditions due to the sulfate production in the parameterized clouds. The modifications to WRF-Chem version 3.2.1 are found to account for changes in the cloud drop number concentration (CDNC) and changes in the chemical composition of cloud-drop residuals in a way that is consistent with observations collected during CHAPS. Efforts are currently underway to port the changes described here to WRF-Chem version 3.5, and it is anticipated that they
IMPLEMENTATION OF AN URBAN CANOPY PARAMETERIZATION IN MM5
The Pennsylvania State University/National Center for Atmospheric Research Mesoscale Model (MM5) (Grell et al. 1994) has been modified to include an urban canopy parameterization (UCP) for fine-scale urban simulations (~1-km horizontal grid spacing). The UCP accounts for drag ...
Parameterizations in high resolution isopycanl wind-driven ocean models
Jensen, T.G.; Randall, D.A.
1993-01-01
For the CHAMMP project, we proposed to implement and test new numerical schemes, parameterizations of boundary layer flow and development and implement mixed layer physics in an existing isopycnal models. The objectives for the proposed research were; implement the Arakawa and Hsu, scheme in an existing isopycnal model of the Indian Ocean; recode the new model for a highly parallel architecture; determine effects of various parameterizations of islands; determine the correct lateral boundary condition for boundary layer currents, as for instance the Gulf Stream and other western boundary currents.; and incorporate a oceanic mixed layer on top of the isopycnal deep layers. This is, primarily a model development project, with emphasis on determining the influence and parameterization of narrow flows along continents and through chains of small islands on the large scale oceanic circulation, which is resolved by climate models. The new model is based on the multi-layer FSU Indian Ocean model. Our research strategy is to; recode a one-layer version of the Indian Ocean Model for a highly parallel computer; add thermodynamics to a rectangular domain version of the new model; implement the irregular domain from the Indian Ocean Model into the box model; change the numerical scheme for the continuity equation to the scheme proposed by; perform parameterization experiments with various coast line and island geometries. This report discusses project progress for period August 1, 1992 through December 31, 1992.
Comparison of Soil Hydraulic Parameterizations for Mesoscale Meteorological Models.
NASA Astrophysics Data System (ADS)
Braun, Frank J.; Schädler, Gerd
2005-07-01
Soil water contents, calculated with seven soil hydraulic parameterizations, that is, soil hydraulic functions together with the corresponding parameter sets, are compared with observational data. The parameterizations include the Campbell/Clapp-Hornberger parameterization that is often used by meteorologists and the van Genuchten/Rawls-Brakensiek parameterization that is widespread among hydrologists. The observations include soil water contents at several soil depths and atmospheric surface data; they were obtained within the Regio Klima Projekt (REKLIP) at three sites in the Rhine Valley in southern Germany and cover up to 3 yr with 10-min temporal resolution. Simulations of 48-h episodes, as well as series of daily simulations initialized anew every 24 h and covering several years, were performed with the “VEG3D” soil-vegetation model in stand-alone mode; furthermore, 48-h episodes were simulated with the model coupled to a one-dimensional atmospheric model. For the cases and soil types considered in this paper, the van Genuchten/Rawls-Brakensiek model gives the best agreement between observed and simulated soil water contents on average. Especially during episodes with medium and high soil water content, the van Genuchten/Rawls-Brakensiek model performs better than the Campbell/Clapp-Hornberger model.
CLOUD PARAMETERIZATIONS, CLOUD PHYSICS, AND THEIR CONNECTIONS: AN OVERVIEW.
LIU,Y.; DAUM,P.H.; CHAI,S.K.; LIU,F.
2002-02-12
This paper consists of three parts. The first part is concerned with the parameterization of cloud microphysics in climate models. We demonstrate the crucial importance of spectral dispersion of the cloud droplet size distribution in determining radiative properties of clouds (e.g., effective radius), and underline the necessity of specifying spectral dispersion in the parameterization of cloud microphysics. It is argued that the inclusion of spectral dispersion makes the issue of cloud parameterization essentially equivalent to that of the droplet size distribution function, bringing cloud parameterization to the forefront of cloud physics. The second part is concerned with theoretical investigations into the spectral shape of droplet size distributions in cloud physics. After briefly reviewing the mainstream theories (including entrainment and mixing theories, and stochastic theories), we discuss their deficiencies and the need for a paradigm shift from reductionist approaches to systems approaches. A systems theory that has recently been formulated by utilizing ideas from statistical physics and information theory is discussed, along with the major results derived from it. It is shown that the systems formalism not only easily explains many puzzles that have been frustrating the mainstream theories, but also reveals such new phenomena as scale-dependence of cloud droplet size distributions. The third part is concerned with the potential applications of the systems theory to the specification of spectral dispersion in terms of predictable variables and scale-dependence under different fluctuating environments.
Parameterization of HONO sources in Mega-Cities
NASA Astrophysics Data System (ADS)
Li, G.; Zhang, R.; Tie, X.; Molina, L. T.
2013-05-01
Nitrous acid (HONO) plays an important role in the photochemistry of the troposphere because the photolysis of HONO is a primary source of the hydroxyl radical (OH) in the early morning. However, the formation or sources of HONO are still poorly understood in the troposphere and thence the representation of the HONO sources in chemical transport models (CTMs) is lack of comprehensive consideration. In the present study, the observed HONO, NOx, and aerosols at an urban supersite T0 during the MCMA-2006 field campaign in Mexico City are used to interpret the HONO formation in association with the suggested HONO sources from literature. The HONO source parameterizations are proposed and incorporated into the WRF-CHEM model. Homogeneous sources of HONO include the reaction of NO with OH and excited NO2 with H2O. Four HONO heterogeneous sources are considered: NO2 reaction with semivolatile organics, NO2 reaction with freshly emitted soot, NO2 reaction on aerosol and ground surfaces. Four cases are used in the present study to evaluate the proposed HONO parameterizations during four field campaigns in which HONO measurements are available, including MCMA-2003 and MCMA-2006 (Mexico City Metropolitan Area, Mexico), MIRAGE-2009 (Shanghai, China), and SHARP (Houston, USA). The WRF-CHEM model with the proposed HONO parameterizations performs moderately well in reproducing the observed diurnal variation of HONO concentrations, showing that the HONO parameterizations in the study are reasonable and potentially useful in improving the HONO simulation in CTMs.
Parameterization of HONO sources in Mega-Cities
NASA Astrophysics Data System (ADS)
Li, Guohui; Zhang, Renyi; Tie, Xuxie; Molina, Luisa
2013-04-01
Nitrous acid (HONO) plays an important role in the photochemistry of the troposphere because the photolysis of HONO is a primary source of the hydroxyl radical (OH) in the early morning. However, the formation or sources of HONO are still poorly understood in the troposphere; hence the representation of the HONO sources in chemical transport models (CTMs) has lack comprehensive consideration. In the present study, the observed HONO, NOx, and aerosols at an urban supersite T0 during the MCMA-2006 field campaign in Mexico City are used to interpret the HONO formation in association with the suggested HONO sources from literature. The HONO source parameterizations are proposed and incorporated into the WRF-CHEM model. Homogeneous sources of HONO include the reaction of NO with OH and excited NO2 with H2O. Four HONO heterogeneous sources are considered: NO2 reaction with semivolatile organics, NO2 reaction with freshly emitted soot, NO2 reaction on aerosol and ground surfaces. Four cases are used in the present study to evaluate the proposed HONO parameterizations during four field campaigns in which HONO measurements are available, including MCMA-2003 and MCMA-2006 (Mexico City Metropolitan Area, Mexico), MIRAGE-2009 (Shanghai, China), and SHARP (Houston, USA). The WRF-CHEM model with the proposed HONO parameterizations performs moderately well in reproducing the observed diurnal variation of HONO concentrations, showing that the HONO parameterizations in the study are reasonable and potentially useful in improving the HONO simulation in CTMs.
Validation of an Urban Parameterization in a Mesoscale Model
Leach, M.J.; Chin, H.
2001-07-19
The Atmospheric Science Division at Lawrence Livermore National Laboratory uses the Naval Research Laboratory's Couple Ocean-Atmosphere Mesoscale Prediction System (COAMPS) for both operations and research. COAMPS is a non-hydrostatic model, designed as a multi-scale simulation system ranging from synoptic down to meso, storm and local terrain scales. As model resolution increases, the forcing due to small-scale complex terrain features including urban structures and surfaces, intensifies. An urban parameterization has been added to the Naval Research Laboratory's mesoscale model, COAMPS. The parameterization attempts to incorporate the effects of buildings and urban surfaces without explicitly resolving them, and includes modeling the mean flow to turbulence energy exchange, radiative transfer, the surface energy budget, and the addition of anthropogenic heat. The Chemical and Biological National Security Program's (CBNP) URBAN field experiment was designed to collect data to validate numerical models over a range of length and time scales. The experiment was conducted in Salt Lake City in October 2000. The scales ranged from circulation around single buildings to flow in the entire Salt Lake basin. Data from the field experiment includes tracer data as well as observations of mean and turbulence atmospheric parameters. Wind and turbulence predictions from COAMPS are used to drive a Lagrangian particle model, the Livermore Operational Dispersion Integrator (LODI). Simulations with COAMPS and LODI are used to test the sensitivity to the urban parameterization. Data from the field experiment, including the tracer data and the atmospheric parameters, are also used to validate the urban parameterization.
Overview of an Urban Canopy Parameterization in COAMPS
Leach, M J; Chin, H S
2006-02-09
The Coupled Atmosphere/Ocean Mesoscale Prediction System (COAMPS) model (Hodur, 1997) was developed at the Naval Research Laboratory. COAMPS has been used at resolutions as small as 2 km to study the role of complex topography in generating mesoscale circulation (Doyle, 1997). The model has been adapted for use in the Atmospheric Science Division at LLNL for both research and operational use. The model is a fully, non-hydrostatic model with several options for turbulence parameterization, cloud processes and radiative transfer. We have recently modified the COAMPS code to include building and other urban surfaces effects in the mesoscale model by incorporating an urban canopy parameterization (UCP) (Chin et al., 2005). This UCP is a modification of the original parameterization of (Brown and Williams, 1998), based on Yamada's (1982) forest canopy parameterization and includes modification of the TKE and mean momentum equations, modification of radiative transfer, and an anthropogenic heat source. COAMPS is parallelized for both shared memory (OpenMP) and distributed memory (MPI) architecture.
Momentum Transport by Cumulus Clouds and its Parameterization.
NASA Astrophysics Data System (ADS)
Zhang, Guang Jun
The effect of cumulus convection on the large -scale momentum field is examined in this thesis. A parameterization scheme is developed to calculate the vertical transport of momentum by cumulus clouds. The effect of the perturbation pressure field induced by cumulus convection on the cloud momentum and its vertical transport is taken into account for the first time. It is shown that a perturbation pressure field is required to balance the irrotational component of the local Coriolis force produced by the interaction of the large-scale flow field with the cumulus-scale circulation. To facilitate quantitative evaluation of the horizontal pressure gradient force across the cloud, a simple cloud model which specifies the dynamic and the thermodynamic structures in cloud is developed. The parameterization scheme is applied to several convective events in the tropics and the midlatitudes. The first case is the average of six convective periods observed in Phase III of GATE. The second one is the numerical simulation of a convective band observed in Phase II of GATE by Soong and Tao (1984). It is shown that the cloud mean wind obtained from the parameterization scheme changes significantly with height if the environmental wind has strong vertical shear. The perturbation pressure gradient force across the cloud plays an important role in changing the cloud mean momentum. The vertical transport of the horizontal momentum by cumulus clouds is parameterized and compared to observations and numerical simulations. Good agreement is found between the computed and the observed/simulated cumulus effects on the momentum field in both cases. The third case is a mesoscale convective complex observed in PRE-STORM. The evolution of the storm is analyzed; and the dynamic and the thermodynamic budgets are computed. Comparison between the residuals of the momentum budgets and the cumulus effects from the parameterization again shows good agreement. Sensitivity tests are performed to
NASA Astrophysics Data System (ADS)
Liu, J.; Chen, Z.; Horowitz, L. W.; Carlton, A. M. G.; Fan, S.; Cheng, Y.; Ervens, B.; Fu, T. M.; He, C.; Tao, S.
2014-12-01
Secondary organic aerosols (SOA) have a profound influence on air quality and climate, but large uncertainties exist in modeling SOA on the global scale. In this study, five SOA parameterization schemes, including a two-product model (TPM), volatility basis-set (VBS) and three cloud SOA schemes (Ervens et al. (2008, 2014), Fu et al. (2008) , and He et al. (2013)), are implemented into the global chemical transport model (MOZART-4). For each scheme, model simulations are conducted with identical boundary and initial conditions. The VBS scheme produces the highest global annual SOA production (close to 35 Tg·y-1), followed by three cloud schemes (26-30 Tg·y-1) and TPM (23 Tg·y-1). Though sharing a similar partitioning theory to the TPM scheme, the VBS approach simulates the chemical aging of multiple generations of VOCs oxidation products, resulting in a much larger SOA source, particularly from aromatic species, over Europe, the Middle East and Eastern America. The formation of SOA in VBS, which represents the net partitioning of semi-volatile organic compounds from vapor to condensed phase, is highly sensitivity to the aging and wet removal processes of vapor-phase organic compounds. The production of SOA from cloud processes (SOAcld) is constrained by the coincidence of liquid cloud water and water-soluble organic compounds. Therefore, all cloud schemes resolve a fairly similar spatial pattern over the tropical and the mid-latitude continents. The spatiotemporal diversity among SOA parameterizations is largely driven by differences in precursor inputs. Therefore, a deeper understanding of the evolution, wet removal, and phase partitioning of semi-volatile organic compounds, particularly above remote land and oceanic areas, is critical to better constrain the global-scale distribution and related climate forcing of secondary organic aerosols.
Zhang, Yang; Zhang, Xin; Wang, Kai; He, Jian; Leung, Lai-Yung R.; Fan, Jiwen; Nenes, Athanasios
2015-07-22
Aerosol activation into cloud droplets is an important process that governs aerosol indirect effects. The advanced treatment of aerosol activation by Fountoukis and Nenes (2005) and its recent updates, collectively called the FN series, have been incorporated into a newly developed regional coupled climate-air quality model based on the Weather Research and Forecasting model with the physics package of the Community Atmosphere Model version 5 (WRF-CAM5) to simulate aerosol-cloud interactions in both resolved and convective clouds. The model is applied to East Asia for two full years of 2005 and 2010. A comprehensive model evaluation is performed for model predictions of meteorological, radiative, and cloud variables, chemical concentrations, and column mass abundances against satellite data and surface observations from air quality monitoring sites across East Asia. The model performs overall well for major meteorological variables including near-surface temperature, specific humidity, wind speed, precipitation, cloud fraction, precipitable water, downward shortwave and longwave radiation, and column mass abundances of CO, SO2, NO2, HCHO, and O3 in terms of both magnitudes and spatial distributions. Larger biases exist in the predictions of surface concentrations of CO and NOx at all sites and SO2, O3, PM2.5, and PM10 concentrations at some sites, aerosol optical depth, cloud condensation nuclei over ocean, cloud droplet number concentration (CDNC), cloud liquid and ice water path, and cloud optical thickness. Compared with the default Abdul-Razzack Ghan (2000) parameterization, simulations with the FN series produce ~107–113% higher CDNC, with half of the difference attributable to the higher aerosol activation fraction by the FN series and the remaining half due to feedbacks in subsequent cloud microphysical processes. With the higher CDNC, the FN series are more skillful in simulating cloud water path, cloud optical thickness, downward shortwave radiation
Parameterizing Coefficients of a POD-Based Dynamical System
NASA Technical Reports Server (NTRS)
Kalb, Virginia L.
2010-01-01
A method of parameterizing the coefficients of a dynamical system based of a proper orthogonal decomposition (POD) representing the flow dynamics of a viscous fluid has been introduced. (A brief description of POD is presented in the immediately preceding article.) The present parameterization method is intended to enable construction of the dynamical system to accurately represent the temporal evolution of the flow dynamics over a range of Reynolds numbers. The need for this or a similar method arises as follows: A procedure that includes direct numerical simulation followed by POD, followed by Galerkin projection to a dynamical system has been proven to enable representation of flow dynamics by a low-dimensional model at the Reynolds number of the simulation. However, a more difficult task is to obtain models that are valid over a range of Reynolds numbers. Extrapolation of low-dimensional models by use of straightforward Reynolds-number-based parameter continuation has proven to be inadequate for successful prediction of flows. A key part of the problem of constructing a dynamical system to accurately represent the temporal evolution of the flow dynamics over a range of Reynolds numbers is the problem of understanding and providing for the variation of the coefficients of the dynamical system with the Reynolds number. Prior methods do not enable capture of temporal dynamics over ranges of Reynolds numbers in low-dimensional models, and are not even satisfactory when large numbers of modes are used. The basic idea of the present method is to solve the problem through a suitable parameterization of the coefficients of the dynamical system. The parameterization computations involve utilization of the transfer of kinetic energy between modes as a function of Reynolds number. The thus-parameterized dynamical system accurately predicts the flow dynamics and is applicable to a range of flow problems in the dynamical regime around the Hopf bifurcation. Parameter
Lievens, Hans; Vernieuwe, Hilde; Álvarez-Mozos, Jesús; De Baets, Bernard; Verhoest, Niko E.C.
2009-01-01
In the past decades, many studies on soil moisture retrieval from SAR demonstrated a poor correlation between the top layer soil moisture content and observed backscatter coefficients, which mainly has been attributed to difficulties involved in the parameterization of surface roughness. The present paper describes a theoretical study, performed on synthetical surface profiles, which investigates how errors on roughness parameters are introduced by standard measurement techniques, and how they will propagate through the commonly used Integral Equation Model (IEM) into a corresponding soil moisture retrieval error for some of the currently most used SAR configurations. Key aspects influencing the error on the roughness parameterization and consequently on soil moisture retrieval are: the length of the surface profile, the number of profile measurements, the horizontal and vertical accuracy of profile measurements and the removal of trends along profiles. Moreover, it is found that soil moisture retrieval with C-band configuration generally is less sensitive to inaccuracies in roughness parameterization than retrieval with L-band configuration. PMID:22399956
NASA Astrophysics Data System (ADS)
Liou, K. N.; Takano, Y.; He, C.; Yang, P.; Leung, L. R.; Gu, Y.; Lee, W. L.
2014-06-01
A stochastic approach has been developed to model the positions of BC (black carbon)/dust internally mixed with two snow grain types: hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine BC/dust single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), the action of internal mixing absorbs substantially more light than external mixing. The snow grain shape effect on absorption is relatively small, but its effect on asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions of BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2-5 µm) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4 µm, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo substantially more than external mixing and that the snow grain shape plays a critical role in snow albedo calculations through its forward scattering strength. Also, multiple inclusion of BC/dust significantly reduces snow albedo as compared to an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization involving contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountain/snow topography.
Validation of parameterization scheme for eddy diffusion from satellite data
NASA Technical Reports Server (NTRS)
Sassi, F.; Visconti, G.; Gille, J. C.
1990-01-01
The eddy diffusion coefficient K(yy) has been calculated usign LIMS for the months of December 1978 and January and February 1979. Two methods have been used. The first implements the suggestion made by Tung (1987) to parameterize the eddy transport as a diffusive process along isentropes. The second method integrates the equation relating the parcel displacements to the eddy velocity fields. The latter method uses a filtering on both space and time domains to isolate transients and is referred to as the 'spectral method'. Results from the first method are shown to be reliable only for quiescent periods, breaking down when the meridional gradient of potential vorticity is negligible. Results from the two methods are in agreement only for very disturbed conditions, when transience is readily isolated. It is concluded that the parameterizations suggested for eddy transport and calculated in this paper may be meaningful for quiet periods, but are not reliable for unsteady and very large amplitude disturbances.
Parameterized neural networks for high-energy physics
NASA Astrophysics Data System (ADS)
Baldi, Pierre; Cranmer, Kyle; Faucett, Taylor; Sadowski, Peter; Whiteson, Daniel
2016-05-01
We investigate a new structure for machine learning classifiers built with neural networks and applied to problems in high-energy physics by expanding the inputs to include not only measured features but also physics parameters. The physics parameters represent a smoothly varying learning task, and the resulting parameterized classifier can smoothly interpolate between them and replace sets of classifiers trained at individual values. This simplifies the training process and gives improved performance at intermediate values, even for complex problems requiring deep learning. Applications include tools parameterized in terms of theoretical model parameters, such as the mass of a particle, which allow for a single network to provide improved discrimination across a range of masses. This concept is simple to implement and allows for optimized interpolatable results.
A parameterization of effective soil temperature for microwave emission
NASA Technical Reports Server (NTRS)
Choudhury, B. J.; Schmugge, T. J.; Mo, T. (Principal Investigator)
1981-01-01
A parameterization of effective soil temperature is discussed, which when multiplied by the emissivity gives the brightness temperature in terms of surface (T sub o) and deep (T sub infinity) soil temperatures as T = T sub infinity + C (T sub o - T sub infinity). A coherent radiative transfer model and a large data base of observed soil moisture and temperature profiles are used to calculate the best-fit value of the parameter C. For 2.8, 6.0, 11.0, 21.0 and 49.0 cm wavelengths. The C values are respectively 0.802 + or - 0.006, 0.667 + or - 0.008, 0.480 + or - 0.010, 0.246 + or - 0.009, and 0,084 + or - 0.005. The parameterized equation gives results which are generally within one or two percent of the exact values.
Parameterization of Model Validating Sets for Uncertainty Bound Optimizations. Revised
NASA Technical Reports Server (NTRS)
Lim, K. B.; Giesy, D. P.
2000-01-01
Given measurement data, a nominal model and a linear fractional transformation uncertainty structure with an allowance on unknown but bounded exogenous disturbances, easily computable tests for the existence of a model validating uncertainty set are given. Under mild conditions, these tests are necessary and sufficient for the case of complex, nonrepeated, block-diagonal structure. For the more general case which includes repeated and/or real scalar uncertainties, the tests are only necessary but become sufficient if a collinearity condition is also satisfied. With the satisfaction of these tests, it is shown that a parameterization of all model validating sets of plant models is possible. The new parameterization is used as a basis for a systematic way to construct or perform uncertainty tradeoff with model validating uncertainty sets which have specific linear fractional transformation structure for use in robust control design and analysis. An illustrative example which includes a comparison of candidate model validating sets is given.
An intracloud lightning parameterization scheme for a storm electrification model
NASA Technical Reports Server (NTRS)
Helsdon, John H., Jr.; Wu, Gang; Farley, Richard D.
1992-01-01
The parameterization of an intracloud lightning discharge has been implemented in the present storm electrification model. The initiation, propagation direction, and termination of the discharge are computed using the magnitude and direction of the electric field vector as the determining criteria. The charge redistribution due to the lightning is approximated assuming the channel to be an isolated conductor with zero net charge over its entire length. Various simulations involving differing amounts of charge transferred and distribution of charges have been done. Values of charge transfer, dipole moment change, and electrical energy dissipation computed in the model are consistent with observations. The effects of the lightning-produced ions on the hydrometeor charges and electric field components depend strongly on the amount of charge transferred. A comparison between the measured electric field change of an actual intracloud flash and the field change due to the simulated discharge shows favorable agreement. Limitations of the parameterization scheme are discussed.
Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies
NASA Astrophysics Data System (ADS)
Williams, Paul; Howe, Nicola; Gregory, Jonathan; Smith, Robin; Joshi, Manoj
2016-04-01
In climate simulations, the impacts of the sub-grid scales on the resolved scales are conventionally represented using deterministic closure schemes, which assume that the impacts are uniquely determined by the resolved scales. Stochastic parameterization relaxes this assumption, by sampling the sub-grid variability in a computationally inexpensive manner. This presentation shows that the simulated climatological state of the ocean is improved in many respects by implementing a simple stochastic parameterization of ocean eddies into a coupled atmosphere-ocean general circulation model. Simulations from a high-resolution, eddy-permitting ocean model are used to calculate the eddy statistics needed to inject realistic stochastic noise into a low-resolution, non-eddy-permitting version of the same model. A suite of four stochastic experiments is then run to test the sensitivity of the simulated climate to the noise definition, by varying the noise amplitude and decorrelation time within reasonable limits. The addition of zero-mean noise to the ocean temperature tendency is found to have a non-zero effect on the mean climate. Specifically, in terms of the ocean temperature and salinity fields both at the surface and at depth, the noise reduces many of the biases in the low-resolution model and causes it to more closely resemble the high-resolution model. The variability of the strength of the global ocean thermohaline circulation is also improved. It is concluded that stochastic ocean perturbations can yield reductions in climate model error that are comparable to those obtained by refining the resolution, but without the increased computational cost. Therefore, stochastic parameterizations of ocean eddies have the potential to significantly improve climate simulations. Reference PD Williams, NJ Howe, JM Gregory, RS Smith, and MM Joshi (2016) Improved Climate Simulations through a Stochastic Parameterization of Ocean Eddies. Journal of Climate, under revision.
Parameterization of wind farms in COSMO-LM
NASA Astrophysics Data System (ADS)
Stuetz, E.; Steinfeld, G.; Heinemann, D.; Peinke, J.
2012-04-01
In order to examine the impact of wind farms in the meso scale using numerical simulations parameterizations of wind farms were implemented in a mesoscale model. In 2008/2009 the first wind farm in the german exclusive economic zone - Alpha Ventus - was built. Since then more wind farms are erected in the german exclusive economic zone. Wind farms with up to 80 wind turbines and on an area up to 66 square kilometers are planned - partly only few kilometers apart from one another. Such large wind farms influence the properties of the atmospheric boundary layer at the meso scale by a reduction of the wind speed, a enhancement of the turbulent kinetic energy, but also an alternation of the wind direction. Results of models for the calculation of wakes (wake models), idealistic mesoscale studies as well as observations show, that wind farms of this size produce wakes, which can expand up to a few 10 kilometers downstream. Mesoscale models provide the possibility to investigate the impact of such large wind farms on the atmospheric flow in a larger area and also to examine the effect of wind farms under different weather conditions. For the numerical simulation the mesoscale model COSMO-LM is used. Because the wind turbines of the wind farm cannot be displayed individually due to the large mesh-grid size, the effects of the wind turbine in a numerical model have to be described with the help of a parameterization. Different parameterizations, including the interpretation of a wind farm as enhanced surface roughness or as an impuls deficit and turbulence source, respectively, are implemented into COSMO. The impact of the different wind farm parameterizations on the simulation of the atmospheric boundary layer are presented. as well as first tests of idealistic simulations of wind farms are presented. For this purpose idealistic runs as well as a case study were performed.
A parameterization of the depth of the entrainment zone
NASA Technical Reports Server (NTRS)
Boers, Reinout
1989-01-01
A theory of the parameterization of the entrainment zone depth has been developed based on conservation of energy. This theory suggests that the normalized entrainment zone depth is proportional to the inverse square root of the Richardson number. A comparison of this theory with atmospheric observations indicates excellent agreement. It does not adequately predict the laboratory data, although it improves on parcel theory, which is based on a momentum balance.
Contribution to the cloud droplet effective radius parameterization
Pontikis, C.; Hicks, E. )
1992-11-01
An analytic cloud droplet effective radius expression is derived and validated by using field experiment microphysical data. This expression shows that the effective radius depends simultaneously upon the cloud liquid water content, droplet concentration and droplet spectral dispersion. It further suggests that the variability in these parameters present at all scales, due to turbulent mixing and secondary droplet activation, could limit the accuracy of the effective radius parameterizations used in climate models. 12 refs.
Improved CART Data Products and 6cmm Parameterization for Clouds
Kenneth Sassen
2004-08-23
Reviewed here is the history of the participation in the Atmospheric Radiation Measurement (ARM) Program, with particular emphasis on research performed between 1999 and 2002, before the PI moved from the University of Utah to the University of Alaska, Fairbanks. The research results are divided into the following areas: IOP research, remote sensing algorithm development using datasets and models, cirrus cloud and SCM/GCM parameterizations, student training, and publications.
Parameterization for light ion production from electromagnetic dissociation
NASA Astrophysics Data System (ADS)
Norbury, John
2014-09-01
Light ion (hydrogen and helium isotopes) production from relativistic nucleus-nucleus collisions is important in space radiation protection problems, when galactic cosmic rays interact with spacecraft. In fact, for thick spacecraft shields, such as the International Space Station, light ion and neutron production can dominate the contribution to dose equivalent. Both strong and electromagnetic interactions can contribute to light ion production. The present work extends a previous parameterization of electromagnetically produced light ions, so that particle branching ratios are described more realistically.
NASA Astrophysics Data System (ADS)
Savre, J.; Ekman, A. M. L.
2015-05-01
A new parameterization for heterogeneous ice nucleation constrained by laboratory data and based on classical nucleation theory is introduced. Key features of the parameterization include the following: a consistent and modular modeling framework for treating condensation/immersion and deposition freezing, the possibility to consider various potential ice nucleating particle types (e.g., dust, black carbon, and bacteria), and the possibility to account for an aerosol size distribution. The ice nucleating ability of each aerosol type is described using a contact angle (θ) probability density function (PDF). A new modeling strategy is described to allow the θ PDF to evolve in time so that the most efficient ice nuclei (associated with the lowest θ values) are progressively removed as they nucleate ice. A computationally efficient quasi Monte Carlo method is used to integrate the computed ice nucleation rates over both size and contact angle distributions. The parameterization is employed in a parcel model, forced by an ensemble of Lagrangian trajectories extracted from a three-dimensional simulation of a springtime low-level Arctic mixed-phase cloud, in order to evaluate the accuracy and convergence of the method using different settings. The same model setup is then employed to examine the importance of various parameters for the simulated ice production. Modeling the time evolution of the θ PDF is found to be particularly crucial; assuming a time-independent θ PDF significantly overestimates the ice nucleation rates. It is stressed that the capacity of black carbon (BC) to form ice in the condensation/immersion freezing mode is highly uncertain, in particular at temperatures warmer than -20°C. In its current version, the parameterization most likely overestimates ice initiation by BC.
Parameterization of the influence of organic surfactants on aerosol activation
NASA Astrophysics Data System (ADS)
Abdul-Razzak, Hayder; Ghan, Steven J.
2004-02-01
Surface-active organic compounds, or surfactants, can affect aerosol activation by two mechanisms: lowering surface tension and altering the bulk hygroscopicity of the particles. A numerical model has been developed to predict the activation of aerosol particles consisting of an internally uniform chemical mixture of organic surfactants and inorganic salts in a parcel of air rising adiabatically at constant speed. Equations reflecting water balance of the air parcel were used together with a modified form of Köhler theory to model droplet nucleation while considering surface effects. We also extend a parametric representation of aerosol activation to the case of a mixture of inorganic salts and organic surfactants by modifying the Raoult term in Köhler theory (assuming additive behavior) and using a simplified relationship between surface tension and surfactant molar concentration to account for surface effects at the critical radius for activation. The close agreement (to within 10% for most and 20% for almost all conditions) between numerical and parametric results validates our modifications. Moreover, the form of the relationship is identical to an empirical relationship between surface tension and organic carbon concentration. Thus the modified form of the parameterization provides a framework that can account for the influence of observed organics on the activation of other salts. The modified form of the parameterization is tested successfully with the Po Valley model both for single aerosol size distribution and three-mode size distributions for marine, rural, and urban aerosols. Further measurements are required to extend the parameterization to other organic surfactants.
Optimizing EDMF parameterization for stratocumulus-topped boundary layer
NASA Astrophysics Data System (ADS)
Jones, C. R.; Bretherton, C. S.; Witek, M. L.; Suselj, K.
2014-12-01
We present progress in the development of an Eddy Diffusion / Mass Flux (EDMF) turbulence parameterization, with the goal of improving the representation of the cloudy boundary layer in NCEP's Global Forecast System (GFS), as part of a multi-institution Climate Process Team (CPT). Current GFS versions substantially under-predict cloud amount and cloud radiative impact over much of the globe, leading to large biases in the surface and top of atmosphere energy budgets. As part of the effort to correct these biases, the CPT is developing a new EDMF turbulence scheme for GFS, in which local turbulent mixing is represented by an eddy diffusion term while nonlocal shallow convection is represented by a mass flux term. The sum of both contributions provides the total turbulent flux. Our goal is for this scheme to more skillfully simulate cloud radiative properties without negatively impacting other measures of weather forecast skill. One particular challenge faced by an EDMF parameterization is to be able to handle stratocumulus regimes as well as shallow cumulus regimes. In order to isolate the behavior of the proposed EDMF parameterization and aid in its further development, we have implemented the scheme in a portable MATLAB single column model (SCM). We use this SCM framework to optimize the simulation of stratocumulus cloud top entrainment and boundary layer decoupling.
UQ-Guided Selection of Physical Parameterizations in Climate Models
NASA Astrophysics Data System (ADS)
Lucas, D. D.; Debusschere, B.; Ghan, S.; Rosa, D.; Bulaevskaya, V.; Anderson, G. J.; Chowdhary, K.; Qian, Y.; Lin, G.; Larson, V. E.; Zhang, G. J.; Randall, D. A.
2015-12-01
Given two or more parameterizations that represent the same physical process in a climate model, scientists are sometimes faced with difficult decisions about which scheme to choose for their simulations and analysis. These decisions are often based on subjective criteria, such as "which scheme is easier to use, is computationally less expensive, or produces results that look better?" Uncertainty quantification (UQ) and model selection methods can be used to objectively rank the performance of different physical parameterizations by increasing the preference for schemes that fit observational data better, while at the same time penalizing schemes that are overly complex or have excessive degrees-of-freedom. Following these principles, we are developing a perturbed-parameter UQ framework to assist in the selection of parameterizations for a climate model. Preliminary results will be presented on the application of the framework to assess the performance of two alternate schemes for simulating tropical deep convection (CLUBB-SILHS and ZM-trigmem) in the U.S. Dept. of Energy's ACME climate model. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344, is supported by the DOE Office of Science through the Scientific Discovery Through Advanced Computing (SciDAC), and is released as LLNL-ABS-675799.
Parameterization of effective ice particle size for high-latitude clouds
NASA Astrophysics Data System (ADS)
Boudala, Faisal S.; Isaac, George A.; Fu, Qiang; Cober, Stewart G.
2002-08-01
A parameterization has been developed for mean effective size Dge in terms of ice water content (IWC) and temperature using in situ measurements of ice crystal spectra, cloud particle shapes and particle cross-sectional area A from four research projects conducted in latitudes north of 45° N. The cloud microphysical measurements were made using PMS 2D optical probes, a PMS forward scattering spectrometer probe (FSSP), and Nevzorov total water and liquid water content probes. The IWCs derived from particle spectra using three different methods were compared with IWC measured with the Nevzorov probe (IWCNev). The contribution of small particles to the total mass was estimated by integrating a gamma distribution function that was fitted to match the measured FSSP concentrations. The Dge was calculated from the derived IWC and total cross-sectional area per unit volume Ac. This analysis indicates that there are significant differences among the schemes used to derive the IWC. It was found that the IWC derived based on the Cunningham scheme and IWCNev have the highest correlation: r2 = 0.78. After considering small particles, the derived IWC almost matched the IWCNev. The average estimated contribution of small particles to the Ac was 43%. The average estimated contribution of small particles to the total IWC, however, was 20%. Since Dge is directly proportional to the ratio IWC/Ac, the addition of small particles reduced the derived Dge considerably. The largest changes in Dge associated with small particles, however, occur at the coldest temperature and at low IWC, reaching up to 45% for temperatures less than -25° C. Generally, Dge and IWC increase with increasing temperature. Good agreement between the parameterized Dge and derived Dge from measurements were found when small particles were included.
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NASA Technical Reports Server (NTRS)
Yao, Mao-Sung; Stone, Peter H.
1987-01-01
The moist convection parameterization used in the GISS 3-D GCM is adapted for use in a two-dimensional (2-D) zonally averaged statistical-dynamical model. Experiments with different versions of the parameterization show that its impact on the general circulation in the 2-D model does not parallel its impact in the 3-D model unless the effect of zonal variations is parameterized in the moist convection calculations. A parameterization of the variations in moist static energy is introduced in which the temperature variations are calculated from baroclinic stability theory, and the relative humidity is assumed to be constant. Inclusion of the zonal variations of moist static energy in the 2-D moist convection parameterization allows just a fraction of a latitude circle to be unstable and enhances the amount of deep convection. This leads to a 2-D simulation of the general circulation very similar to that in the 3-D model. The experiments show that the general circulation is sensitive to the parameterized amount of deep convection in the subsident branch of the Hadley cell. The more there is, the weaker are the Hadley cell circulations and the westerly jets. The experiments also confirm the effects of momentum mixing associated with moist convection found by earlier investigators and, in addition, show that the momentum mixing weakens the Ferrel cell. An experiment in which the moist convection was removed while the hydrological cycle was retained and the eddy forcing was held fixed shows that moist convection by itself stabilizes the tropics, reduces the Hadley circulation, and reduces the maximum speeds in the westerly jets.
Scattering in Quantum Lattice Gases
NASA Astrophysics Data System (ADS)
O'Hara, Andrew; Love, Peter
2009-03-01
Quantum Lattice Gas Automata (QLGA) are of interest for their use in simulating quantum mechanics on both classical and quantum computers. QLGAs are an extension of classical Lattice Gas Automata where the constraint of unitary evolution is added. In the late 1990s, David A. Meyer as well as Bruce Boghosian and Washington Taylor produced similar models of QLGAs. We start by presenting a unified version of these models and study them from the point of view of the physics of wave-packet scattering. We show that the Meyer and Boghosian-Taylor models are actually the same basic model with slightly different parameterizations and limits. We then implement these models computationally using the Python programming language and show that QLGAs are able to replicate the analytic results of quantum mechanics (for example reflected and transmitted amplitudes for step potentials and the Klein paradox).
A parameterization method and application in breast tomosynthesis dosimetry
Li, Xinhua; Zhang, Da; Liu, Bob
2013-09-15
Purpose: To present a parameterization method based on singular value decomposition (SVD), and to provide analytical parameterization of the mean glandular dose (MGD) conversion factors from eight references for evaluating breast tomosynthesis dose in the Mammography Quality Standards Act (MQSA) protocol and in the UK, European, and IAEA dosimetry protocols.Methods: MGD conversion factor is usually listed in lookup tables for the factors such as beam quality, breast thickness, breast glandularity, and projection angle. The authors analyzed multiple sets of MGD conversion factors from the Hologic Selenia Dimensions quality control manual and seven previous papers. Each data set was parameterized using a one- to three-dimensional polynomial function of 2–16 terms. Variable substitution was used to improve accuracy. A least-squares fit was conducted using the SVD.Results: The differences between the originally tabulated MGD conversion factors and the results computed using the parameterization algorithms were (a) 0.08%–0.18% on average and 1.31% maximum for the Selenia Dimensions quality control manual, (b) 0.09%–0.66% on average and 2.97% maximum for the published data by Dance et al. [Phys. Med. Biol. 35, 1211–1219 (1990); ibid. 45, 3225–3240 (2000); ibid. 54, 4361–4372 (2009); ibid. 56, 453–471 (2011)], (c) 0.74%–0.99% on average and 3.94% maximum for the published data by Sechopoulos et al. [Med. Phys. 34, 221–232 (2007); J. Appl. Clin. Med. Phys. 9, 161–171 (2008)], and (d) 0.66%–1.33% on average and 2.72% maximum for the published data by Feng and Sechopoulos [Radiology 263, 35–42 (2012)], excluding one sample in (d) that does not follow the trends in the published data table.Conclusions: A flexible parameterization method is presented in this paper, and was applied to breast tomosynthesis dosimetry. The resultant data offer easy and accurate computations of MGD conversion factors for evaluating mean glandular breast dose in the MQSA
Adatto, Maurice A; Halachmi, Shlomit; Lapidoth, Moshe
2011-01-01
Over 50,000 new tattoos are placed each year in the United States. Studies estimate that 24% of American college students have tattoos and 10% of male American adults have a tattoo. The rising popularity of tattoos has spurred a corresponding increase in tattoo removal. Not all tattoos are placed intentionally or for aesthetic reasons though. Traumatic tattoos due to unintentional penetration of exogenous pigments can also occur, as well as the placement of medical tattoos to mark treatment boundaries, for example in radiation therapy. Protocols for tattoo removal have evolved over history. The first evidence of tattoo removal attempts was found in Egyptian mummies, dated to have lived 4,000 years BC. Ancient Greek writings describe tattoo removal with salt abrasion or with a paste containing cloves of white garlic mixed with Alexandrian cantharidin. With the advent of Q-switched lasers in the late 1960s, the outcomes of tattoo removal changed radically. In addition to their selective absorption by the pigment, the extremely short pulse duration of Q-switched lasers has made them the gold standard for tattoo removal. PMID:21865802
A stochastic parameterization for deep convection using cellular automata
NASA Astrophysics Data System (ADS)
Bengtsson, L.; Steinheimer, M.; Bechtold, P.; Geleyn, J.
2012-12-01
Cumulus parameterizations used in most operational weather and climate models today are based on the mass-flux concept which took form in the early 1970's. In such schemes it is assumed that a unique relationship exists between the ensemble-average of the sub-grid convection, and the instantaneous state of the atmosphere in a vertical grid box column. However, such a relationship is unlikely to be described by a simple deterministic function (Palmer, 2011). Thus, because of the statistical nature of the parameterization challenge, it has been recognized by the community that it is important to introduce stochastic elements to the parameterizations (for instance: Plant and Craig, 2008, Khouider et al. 2010, Frenkel et al. 2011, Bentsson et al. 2011, but the list is far from exhaustive). There are undoubtedly many ways in which stochastisity can enter new developments. In this study we use a two-way interacting cellular automata (CA), as its intrinsic nature possesses many qualities interesting for deep convection parameterization. In the one-dimensional entraining plume approach, there is no parameterization of horizontal transport of heat, moisture or momentum due to cumulus convection. In reality, mass transport due to gravity waves that propagate in the horizontal can trigger new convection, important for the organization of deep convection (Huang, 1988). The self-organizational characteristics of the CA allows for lateral communication between adjacent NWP model grid-boxes, and temporal memory. Thus the CA scheme used in this study contain three interesting components for representation of cumulus convection, which are not present in the traditional one-dimensional bulk entraining plume method: horizontal communication, memory and stochastisity. The scheme is implemented in the high resolution regional NWP model ALARO, and simulations show enhanced organization of convective activity along squall-lines. Probabilistic evaluation demonstrate an enhanced spread in
Sensitivity analysis of volume scattering phase functions.
Tuchow, Noah; Broughton, Jennifer; Kudela, Raphael
2016-08-01
To solve the radiative transfer equation and relate inherent optical properties (IOPs) to apparent optical properties (AOPs), knowledge of the volume scattering phase function is required. Due to the difficulty of measuring the phase function, it is frequently approximated. We explore the sensitivity of derived AOPs to the phase function parameterization, and compare measured and modeled values of both the AOPs and estimated phase functions using data from Monterey Bay, California during an extreme "red tide" bloom event. Using in situ measurements of absorption and attenuation coefficients, as well as two sets of measurements of the volume scattering function (VSF), we compared output from the Hydrolight radiative transfer model to direct measurements. We found that several common assumptions used in parameterizing the radiative transfer model consistently introduced overestimates of modeled versus measured remote-sensing reflectance values. Phase functions from VSF data derived from measurements at multiple wavelengths and a single scattering single angle significantly overestimated reflectances when using the manufacturer-supplied corrections, but were substantially improved using newly published corrections; phase functions calculated from VSF measurements using three angles and three wavelengths and processed using manufacture-supplied corrections were comparable, demonstrating that reasonable predictions can be made using two commercially available instruments. While other studies have reached similar conclusions, our work extends the analysis to coastal waters dominated by an extreme algal bloom with surface chlorophyll concentrations in excess of 100 mg m^{-3}. PMID:27505819
Modeling the clouds on Venus: model development and improvement of a nucleation parameterization
NASA Astrophysics Data System (ADS)
Määttänen, Anni; Bekki, Slimane; Vehkamäki, Hanna; Julin, Jan; Montmessin, Franck; Ortega, Ismael K.; Lebonnois, Sébastien
2014-05-01
As both the clouds of Venus and aerosols in the Earth's stratosphere are composed of sulfuric acid droplets, we use the 1-D version of a model [1,4] developed for stratospheric aerosols and clouds to study the clouds on Venus. We have removed processes and compounds related to the stratospheric clouds so that the only species remaining are water and sulfuric acid, corresponding to the stratospheric sulfate aerosols, and we have added some key processes. The model describes microphysical processes including condensation/evaporation, and sedimentation. Coagulation, turbulent diffusion, and a parameterization for two-component nucleation [8] of water and sulfuric acid have been added in the model. Since the model describes explicitly the size distribution with a large number of size bins (50-500), it can handle multiple particle modes. The validity ranges of the existing nucleation parameterization [7] have been improved to cover a larger temperature range, and the very low relative humidity (RH) and high sulfuric acid concentrations found in the atmosphere of Venus. We have made several modifications to improve the 2002 nucleation parameterization [7], most notably ensuring that the two-component nucleation model behaves as predicted by the analytical studies at the one-component limit reached at extremely low RH. We have also chosen to use a self-consistent cluster distribution [9], constrained by scaling it to recent quantum chemistry calculations [3]. First tests of the cloud model have been carried out with temperature profiles from VIRA [2] and from the LMD Venus GCM [5], and with a compilation of water vapor and sulfuric acid profiles, as in [6]. The temperature and pressure profiles do not evolve with time, but the vapour profiles naturally change with the cloud. However, no chemistry is included for the moment, so the vapor concentrations are only dependent on the microphysical processes. The model has been run for several hundreds of Earth days to reach a
Liou, K. N.; Takano, Y.; He, Cenlin; Yang, P.; Leung, Lai-Yung R.; Gu, Y.; Lee, W- L.
2014-06-27
A stochastic approach to model the positions of BC/dust internally mixed with two snow-grain types has been developed, including hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine their single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), internal mixing absorbs more light than external mixing. The snow-grain shape effect on absorption is relatively small, but its effect on the asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions of BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2 – 5 um) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4 um, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo more than external mixing and that the snow-grain shape plays a critical role in snow albedo calculations through the asymmetry factor. Also, snow albedo reduces more in the case of multiple inclusion of BC/dust compared to that of an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization containing contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountains/snow topography.
Parameterization of the Meridional Eddy Heat and Momentum Fluxes.
NASA Astrophysics Data System (ADS)
Zou, Cheng-Zhi; Gal-Chen, Tzvi
1999-06-01
Green's eddy diffusive transfer representation is used to parameterize the meridional eddy heat flux. The structural function obtained by Branscome for the diagonal component Kyy in the tensor of the transfer coefficients is adopted. A least squares method that uses the observed data of eddy heat flux is proposed to evaluate the magnitude of Kyy and the structure of the nondiagonal component Kyz in the transfer coefficient tensor. The optimum motion characteristic at the steering level is used as a constraint for the relationship between Kyy and Kyz. The obtained magnitude of Kyy is two to three times larger than that of the Branscome's, which is obtained in a linear analysis with the assumption of Kyz = 0.Green's vertically integrated expression for the meridional eddy momentum flux is used to test the coefficients obtained in the eddy heat flux. In this parameterization, the eddy momentum flux is related to the eddy fluxes of two conserved quantities: potential vorticity and potential temperature. The transfer coefficient is taken to be the sum of that obtained in the parameterization of eddy heat flux, plus a correction term suggested by Stone and Yao, which ensures the global net eddy momentum transport to be zero. What makes the present method attractive is that, even though only the data of eddy heat flux are used to evaluate the magnitude of the transfer coefficients, the obtained magnitude of the eddy momentum flux is in good agreement with observations. For the annual mean calculation, the obtained peak values of eddy momentum flux are 94% of the observation for the Northern Hemisphere and 101% for the Southern Hemisphere. This result significantly improves the result of Stone and Yao, who obtained 34% for the Northern Hemisphere and 16% for the Southern Hemisphere in a similar calculation, but in which Kyz = 0 was assumed.
Mechanistic Parameterization of the Kinomic Signal in Peptide Arrays
Dussaq, Alex; Anderson, Joshua C; Willey, Christopher D; Almeida, Jonas S
2016-01-01
Kinases play a role in every cellular process involved in tumorigenesis ranging from proliferation, migration, and protein synthesis to DNA repair. While genetic sequencing has identified most kinases in the human genome, it does not describe the ‘kinome’ at the level of activity of kinases against their substrate targets. An attempt to address that limitation and give researchers a more direct view of cellular kinase activity is found in the PamGene PamChip® system, which records and compares the phosphorylation of 144 tyrosine or serine/threonine peptides as they are phosphorylated by cellular kinases. Accordingly, the kinetics of this time dependent kinomic signal needs to be well understood in order to transduce a parameter set into an accurate and meaningful mathematical model. Here we report the analysis and mathematical modeling of kinomic time series, which achieves a more accurate description of the accumulation of phosphorylated product than the current model, which assumes first order enzyme-substrate kinetics. Reproducibility of the proposed solution was of particular attention. Specifically, the non-linear parameterization procedure is delivered as a public open source web application where kinomic time series can be accurately decomposed into the model’s two parameter values measuring phosphorylation rate and capacity. The ability to deliver model parameterization entirely as a client side web application is an important result on its own given increasing scientific preoccupation with reproducibility. There is also no need for a potentially transitory and opaque server-side component maintained by the authors, nor of exchanging potentially sensitive data as part of the model parameterization process since the code is transferred to the browser client where it can be inspected and executed. PMID:27601856
Data-driven RBE parameterization for helium ion beams
NASA Astrophysics Data System (ADS)
Mairani, A.; Magro, G.; Dokic, I.; Valle, S. M.; Tessonnier, T.; Galm, R.; Ciocca, M.; Parodi, K.; Ferrari, A.; Jäkel, O.; Haberer, T.; Pedroni, P.; Böhlen, T. T.
2016-01-01
Helium ion beams are expected to be available again in the near future for clinical use. A suitable formalism to obtain relative biological effectiveness (RBE) values for treatment planning (TP) studies is needed. In this work we developed a data-driven RBE parameterization based on published in vitro experimental values. The RBE parameterization has been developed within the framework of the linear-quadratic (LQ) model as a function of the helium linear energy transfer (LET), dose and the tissue specific parameter {{(α /β )}\\text{ph}} of the LQ model for the reference radiation. Analytic expressions are provided, derived from the collected database, describing the \\text{RB}{{\\text{E}}α}={α\\text{He}}/{α\\text{ph}} and {{\\text{R}}β}={β\\text{He}}/{β\\text{ph}} ratios as a function of LET. Calculated RBE values at 2 Gy photon dose and at 10% survival (\\text{RB}{{\\text{E}}10} ) are compared with the experimental ones. Pearson’s correlation coefficients were, respectively, 0.85 and 0.84 confirming the soundness of the introduced approach. Moreover, due to the lack of experimental data at low LET, clonogenic experiments have been performed irradiating A549 cell line with {{(α /β )}\\text{ph}}=5.4 Gy at the entrance of a 56.4 MeV u-1He beam at the Heidelberg Ion Beam Therapy Center. The proposed parameterization reproduces the measured cell survival within the experimental uncertainties. A RBE formula, which depends only on dose, LET and {{(α /β )}\\text{ph}} as input parameters is proposed, allowing a straightforward implementation in a TP system.
Numerical simulations of snowfall events: Sensitivity analysis of physical parameterizations
NASA Astrophysics Data System (ADS)
Fernández-González, S.; Valero, F.; Sánchez, J. L.; Gascón, E.; López, L.; García-Ortega, E.; Merino, A.
2015-10-01
Accurate estimation of snowfall episodes several hours or even days in advance is essential to minimize risks to transport and other human activities. Every year, these episodes cause severe traffic problems on the northwestern Iberian Peninsula. In order to analyze the influence of different parameterization schemes, 15 snowfall days were analyzed with the Weather Research and Forecasting (WRF) model, defining three nested domains with resolutions of 27, 9, and 3 km. We implemented four microphysical parameterizations (WRF Single-Moment 6-class scheme, Goddard, Thompson, and Morrison) and two planetary boundary layer schemes (Yonsei University and Mellor-Yamada-Janjic), yielding eight distinct combinations. To validate model estimates, a network of 97 precipitation gauges was used, together with dichotomous data of snowfall presence/absence from snowplow requests to the emergency service of Spain and observatories of the Spanish Meteorological Agency. The results indicate that the most accurate setting of WRF for the study area was that using the Thompson microphysical parameterization and Mellor-Yamada-Janjic scheme, although the Thompson and Yonsei University combination had greater accuracy in determining the temporal distribution of precipitation over 1 day. Combining the eight deterministic members in an ensemble average improved results considerably. Further, the root mean square difference decreased markedly using a multiple linear regression as postprocessing. In addition, our method was able to provide mean ensemble precipitation and maximum expected precipitation,which can be very useful in the management of water resources. Finally, we developed an application that allows determination of the risk of snowfall above a certain threshold.
Longwave radiation parameterization for UCLA/GLAS GCM
NASA Astrophysics Data System (ADS)
Harshvardhan; Corsetti, T.
1984-03-01
This document describes the parameterization of longwave radiation in the UCLA/GLAS general circulation model. Transmittances have been computed from the work of Arking and Chou for water vapor and carbon dioxide and ozone absorptances are computed using a formula due to Rodgers. Cloudiness has been introduced into the code in a manner in which fractional cover and random or maximal overlap can be accommodated. The entire code has been written in a form that is amenable to vectorization on CYBER and CRAY computers. Sample clear sky computations for five standard profiles using the 15- and 9-level versions of the model have been included.
Improving bulk microphysics parameterizations in simulations of aerosol effects
NASA Astrophysics Data System (ADS)
Wang, Yuan; Fan, Jiwen; Zhang, Renyi; Leung, L. Ruby; Franklin, Charmaine
2013-06-01
To improve the microphysical parameterizations for simulations of the aerosol effects in regional and global climate models, the Morrison double-moment bulk microphysical scheme presently implemented in the Weather Research and Forecasting model is modified by replacing the prescribed aerosols in the original bulk scheme (Bulk-OR) with a prognostic double-moment aerosol representation to predict both aerosol number concentration and mass mixing ratio (Bulk-2M). Sensitivity modeling experiments are performed for two distinct cloud regimes: maritime warm stratocumulus clouds (Sc) over southeast Pacific Ocean from the VOCALS project and continental deep convective clouds in the southeast of China. The results from Bulk-OR and Bulk-2M are compared against atmospheric observations and simulations produced by a spectral bin microphysical scheme (SBM). The prescribed aerosol approach (Bulk-OR) produces unreliable aerosol and cloud properties throughout the simulation period, when compared to the results from those using Bulk-2M and SBM, although all of the model simulations are initiated by the same initial aerosol concentration on the basis of the field observations. The impacts of the parameterizations of diffusional growth and autoconversion of cloud droplets and the selection of the embryonic raindrop radius on the performance of the bulk microphysical scheme are also evaluated by comparing the results from the modified Bulk-2M with those from SBM simulations. Sensitivity experiments using four different types of autoconversion schemes reveal that the autoconversion parameterization is crucial in determining the raindrop number, mass concentration, and drizzle formation for warm stratocumulus clouds. An embryonic raindrop size of 40 µm is determined as a more realistic setting in the autoconversion parameterization. The saturation adjustment employed in calculating condensation/evaporation in the bulk scheme is identified as the main factor responsible for the large
CCPP-ARM Parameterization Testbed Model Forecast Data
Klein, Stephen
2008-01-15
Dataset contains the NCAR CAM3 (Collins et al., 2004) and GFDL AM2 (GFDL GAMDT, 2004) forecast data at locations close to the ARM research sites. These data are generated from a series of multi-day forecasts in which both CAM3 and AM2 are initialized at 00Z every day with the ECMWF reanalysis data (ERA-40), for the year 1997 and 2000 and initialized with both the NASA DAO Reanalyses and the NCEP GDAS data for the year 2004. The DOE CCPP-ARM Parameterization Testbed (CAPT) project assesses climate models using numerical weather prediction techniques in conjunction with high quality field measurements (e.g. ARM data).
Modeling and parameterization of horizontally inhomogeneous cloud radiative properties
NASA Technical Reports Server (NTRS)
Welch, R. M.
1995-01-01
One of the fundamental difficulties in modeling cloud fields is the large variability of cloud optical properties (liquid water content, reflectance, emissivity). The stratocumulus and cirrus clouds, under special consideration for FIRE, exhibit spatial variability on scales of 1 km or less. While it is impractical to model individual cloud elements, the research direction is to model a statistical ensembles of cloud elements with mean-cloud properties specified. The major areas of this investigation are: (1) analysis of cloud field properties; (2) intercomparison of cloud radiative model results with satellite observations; (3) radiative parameterization of cloud fields; and (4) development of improved cloud classification algorithms.
Ricci Flow-based Spherical Parameterization and Surface Registration.
Chen, X; He, H; Zou, G; Zhang, X; Gu, X; Hua, J
2013-09-01
This paper presents an improved Euclidean Ricci flow method for spherical parameterization. We subsequently invent a scale space processing built upon Ricci energy to extract robust surface features for accurate surface registration. Since our method is based on the proposed Euclidean Ricci flow, it inherits the properties of Ricci flow such as conformality, robustness and intrinsicalness, facilitating efficient and effective surface mapping. Compared with other surface registration methods using curvature or sulci pattern, our method demonstrates a significant improvement for surface registration. In addition, Ricci energy can capture local differences for surface analysis as shown in the experiments and applications. PMID:24019739
The causal structure of spacetime is a parameterized Randers geometry
NASA Astrophysics Data System (ADS)
Skakala, Jozef; Visser, Matt
2011-03-01
There is a well-established isomorphism between stationary four-dimensional spacetimes and three-dimensional purely spatial Randers geometries—these Randers geometries being a particular case of the more general class of three-dimensional Finsler geometries. We point out that in stably causal spacetimes, by using the (time-dependent) ADM decomposition, this result can be extended to general non-stationary spacetimes—the causal structure (conformal structure) of the full spacetime is completely encoded in a parameterized (t-dependent) class of Randers spaces, which can then be used to define a Fermat principle, and also to reconstruct the null cones and causal structure.
Parameterization of interatomic potential by genetic algorithms: A case study
Ghosh, Partha S. Arya, A.; Dey, G. K.; Ranawat, Y. S.
2015-06-24
A framework for Genetic Algorithm based methodology is developed to systematically obtain and optimize parameters for interatomic force field functions for MD simulations by fitting to a reference data base. This methodology is applied to the fitting of ThO{sub 2} (CaF{sub 2} prototype) – a representative of ceramic based potential fuel for nuclear applications. The resulting GA optimized parameterization of ThO{sub 2} is able to capture basic structural, mechanical, thermo-physical properties and also describes defect structures within the permissible range.
Improving Bulk Microphysics Parameterizations in Simulations of Aerosol Effects
Wang, Yuan; Fan, Jiwen; Zhang, Renyi; Leung, Lai-Yung R.; Franklin, Charmaine N.
2013-06-05
To improve the microphysical parameterizations for simulations of the aerosol indirect effect (AIE) in regional and global climate models, a double-moment bulk microphysical scheme presently implemented in the Weather Research and Forecasting (WRF) model is modified and the results are compared against atmospheric observations and simulations produced by a spectral bin microphysical scheme (SBM). Rather than using prescribed aerosols as in the original bulk scheme (Bulk-OR), a prognostic doublemoment aerosol representation is introduced to predict both the aerosol number concentration and mass mixing ratio (Bulk-2M). The impacts of the parameterizations of diffusional growth and autoconversion and the selection of the embryonic raindrop radius on the performance of the bulk microphysical scheme are also evaluated. Sensitivity modeling experiments are performed for two distinct cloud regimes, maritime warm stratocumulus clouds (SC) over southeast Pacific Ocean from the VOCALS project and continental deep convective clouds (DCC) in the southeast of China from the Department of Energy/ARM Mobile Facility (DOE/AMF) - China field campaign. The results from Bulk-2M exhibit a much better agreement in the cloud number concentration and effective droplet radius in both the SC and DCC cases with those from SBM and field measurements than those from Bulk-OR. In the SC case particularly, Bulk-2M reproduces the observed drizzle precipitation, which is largely inhibited in Bulk-OR. Bulk-2M predicts enhanced precipitation and invigorated convection with increased aerosol loading in the DCC case, consistent with the SBM simulation, while Bulk-OR predicts the opposite behaviors. Sensitivity experiments using four different types of autoconversion schemes reveal that the autoconversion parameterization is crucial in determining the raindrop number, mass concentration, and drizzle formation for warm 2 stratocumulus clouds. An embryonic raindrop size of 40 μm is determined as a more
NASA Astrophysics Data System (ADS)
Hall, Carlton Raden
A major objective of remote sensing is determination of biochemical and biophysical characteristics of plant canopies utilizing high spectral resolution sensors. Canopy reflectance signatures are dependent on absorption and scattering processes of the leaf, canopy properties, and the ground beneath the canopy. This research investigates, through field and laboratory data collection, and computer model parameterization and simulations, the relationships between leaf optical properties, canopy biophysical features, and the nadir viewed above-canopy reflectance signature. Emphasis is placed on parameterization and application of an existing irradiance radiative transfer model developed for aquatic systems. Data and model analyses provide knowledge on the relative importance of leaves and canopy biophysical features in estimating the diffuse absorption a(lambda,m-1), diffuse backscatter b(lambda,m-1), beam attenuation alpha(lambda,m-1), and beam to diffuse conversion c(lambda,m-1 ) coefficients of the two-flow irradiance model. Data sets include field and laboratory measurements from three plant species, live oak (Quercus virginiana), Brazilian pepper (Schinus terebinthifolius) and grapefruit (Citrus paradisi) sampled on Cape Canaveral Air Force Station and Kennedy Space Center Florida in March and April of 1997. Features measured were depth h (m), projected foliage coverage PFC, leaf area index LAI, and zenith leaf angle. Optical measurements, collected with a Spectron SE 590 high sensitivity narrow bandwidth spectrograph, included above canopy reflectance, internal canopy transmittance and reflectance and bottom reflectance. Leaf samples were returned to laboratory where optical and physical and chemical measurements of leaf thickness, leaf area, leaf moisture and pigment content were made. A new term, the leaf volume correction index LVCI was developed and demonstrated in support of model coefficient parameterization. The LVCI is based on angle adjusted leaf
When EPA sets a regulation ( a maxim contaminant level) for a contaminant, it must also specify the "best available technology" (BAT) that can be used to remove the contaminant. ecause the regulations apply to community water systems, the technologies selected are ones that are c...
Presentation covered five topics; arsenic chemistry, best available technology (BAT), surface water technology, ground water technology and case studies of arsenic removal. The discussion on arsenic chemistry focused on the need and method of speciation for AsIII and AsV. BAT me...
... remove a splinter, first wash your hands with soap and water. Use tweezers to grab the splinter. Carefully pull it out at the same angle it went in. If the splinter is under the skin or hard to grab: Sterilize a pin or needle by ...
Contrail Cirrus Parameterization in the UK Met Office Climate Model
NASA Astrophysics Data System (ADS)
Rap, A.; Forster, P.; Dobbie, S.
2011-12-01
Air travel and its associated emissions are growing faster than other sectors and they are predicted to contribute a significant warming of climate over the coming century. According to current best estimates, the largest single radiative forcing component associated with aviation is due to aviation-induced cloudiness (AIC), which includes contrail cirrus and changes in the natural cirrus caused by air traffic. However, there is still a high level of uncertainty associated with these, and limited estimates for the forcing of the total effect of aviation induced cloudiness exist. This study, as part of the Contrails Spreading into Cirrus (COSIC) project, aimed to build a physically based parameterization of contrails spreading into cirrus within the UK Met Office Unified Model (UM) and thus to give an independent estimate of the climate impact of AIC. In-situ observations of contrails properties and their spreading have been performed during a series of flights with the UK Facility for Airborne Atmospheric Measurements (FAAM) BAe-146 aircraft. These observations were used in the development of the parameterization, which simulates contrail formation and ageing interactively with the natural cirrus module within the UM. Based on this new parameterisation, estimates of global contrail cirrus coverage, optical depth, and radiative forcing are given, investigating also the contrail effect on the natural cirrus cloud and contrail saturation regional effects of future air traffic growth.
The Reduced RUM as a Logit Model: Parameterization and Constraints.
Chiu, Chia-Yi; Köhn, Hans-Friedrich
2016-06-01
Cognitive diagnosis models (CDMs) for educational assessment are constrained latent class models. Examinees are assigned to classes of intellectual proficiency defined in terms of cognitive skills called attributes, which an examinee may or may not have mastered. The Reduced Reparameterized Unified Model (Reduced RUM) has received considerable attention among psychometricians. Markov Chain Monte Carlo (MCMC) or Expectation Maximization (EM) are typically used for estimating the Reduced RUM. Commercial implementations of the EM algorithm are available in the latent class analysis (LCA) routines of Latent GOLD and Mplus, for example. Fitting the Reduced RUM with an LCA routine requires that it be reparameterized as a logit model, with constraints imposed on the parameters. For models involving two attributes, these have been worked out. However, for models involving more than two attributes, the parameterization and the constraints are nontrivial and currently unknown. In this article, the general parameterization of the Reduced RUM as a logit model involving any number of attributes and the associated parameter constraints are derived. As a practical illustration, the LCA routine in Mplus is used for fitting the Reduced RUM to two synthetic data sets and to a real-world data set; for comparison, the results obtained by using the MCMC implementation in OpenBUGS are also provided. PMID:25838247
Comparison of surface radiative flux parameterizations. Part II. Shortwave radiation
NASA Astrophysics Data System (ADS)
Niemelä, Sami; Räisänen, Petri; Savijärvi, Hannu
This paper presents a comparison of several shortwave (SW) downwelling radiative flux parameterizations with hourly averaged pointwise surface radiation observations made at Jokioinen and Sodankylä, Finland, in 1997. Both clear and cloudy conditions are considered. The clear-sky comparisons included six simple SW parameterizations, which use screen level input data, and three radiation schemes from numerical weather prediction (NWP) models: the former European Centre for Medium-Range Weather Forecast (ECMWF) scheme, the Deutscher Wetterdienst (DWD) scheme, and the High Resolution Limited Area Model (HIRLAM) scheme. Atmospheric-sounding profiles were used as input for the NWP schemes. For the cases with clouds, three simple cloud correction methods (mainly dependent on the total cloud cover) were tested. In the SW clear-sky comparisons, the relatively simple scheme by Iqbal provided the best results, surprisingly outperforming even the NWP radiation models. Simple cloud corrections performed poorly in the SW region. Out of these schemes, a new cloud correction method developed using the present data provided the best results.
Evaluation of a New Parameterization for Fair-Weather Cumulus
Berg, Larry K.; Stull, Roland B.
2006-05-25
A new parameterization for boundary layer cumulus clouds, called the cumulus potential (CuP) scheme, is introduced. This scheme uses joint probability density functions (JPDFs) of virtual potential temperature and water-vapor mixing ratio, as well as the mean vertical profiles of virtual potential temperature, to predict the amount and size distribution of boundary layer cloud cover. This model considers the diversity of air parcels over a heterogeneous surface, and recognizes that some parcels rise above their lifting condensation level to become cumulus, while other parcels might rise as clear updrafts. This model has several unique features: 1) surface heterogeneity is represented using the boundary layer JPDF of virtual potential temperature versus water-vapor mixing ratio, 2) clear and cloudy thermals are allowed to coexist at the same altitude, and 3) a range of cloud-base heights, cloud-top heights, and cloud thicknesses are predicted within any one cloud field, as observed. Using data from Boundary Layer Experiment 1996 and a model intercomparsion study using large eddy simulation (LES) based on Barbados Oceanographic and Meteorological Experiment (BOMEX), it is shown that the CuP model does a good job predicting cloud-base height and cloud-top height. The model also shows promise in predicting cloud cover, and is found to give better cloud-cover estimates than three other cumulus parameterizations: one based on relative humidity, a statistical scheme based on the saturation deficit, and a slab model.
Transient Storage Parameterization of Wetland-dominated Stream Reaches
NASA Astrophysics Data System (ADS)
Wilderotter, S. M.; Lightbody, A.; Kalnejais, L. H.; Wollheim, W. M.
2014-12-01
Current understanding of the importance of transient storage in fluvial wetlands is limited. Wetlands that have higher connectivity to the main stream channel are important because they have the potential to retain more nitrogen within the river system than wetlands that receive little direct stream discharge. In this study, we investigated how stream water accesses adjacent fluvial wetlands in New England coastal watersheds to improve parameterization in network-scale models. Break through curves of Rhodamine WT were collected for eight wetlands in the Ipswich and Parker (MA) and Lamprey River (NH) watersheds, USA. The curves were inverse modeled using STAMMT-L to optimize the connectivity and size parameters for each reach. Two approaches were tested, a single dominant storage zone and a range of storage zones represented using a power-law distribution of storage zone connectivity. Multiple linear regression analyses were conducted to relate transient storage parameters to stream discharge, area, length-to-width ratio, and reach slope. Resulting regressions will enable more accurate parameterization of surface water transient storage in network-scale models.
Evaluation of an Urban Canopy Parameterization in a Mesoscale Model
Chin, H S; Leach, M J; Sugiyama, G A; Leone, Jr., J M; Walker, H; Nasstrom, J; Brown, M J
2004-03-18
A modified urban canopy parameterization (UCP) is developed and evaluated in a three-dimensional mesoscale model to assess the urban impact on surface and lower atmospheric properties. This parameterization accounts for the effects of building drag, turbulent production, radiation balance, anthropogenic heating, and building rooftop heating/cooling. USGS land-use data are also utilized to derive urban infrastructure and urban surface properties needed for driving the UCP. An intensive observational period with clear-sky, strong ambient wind and drainage flow, and the absence of land-lake breeze over the Salt Lake Valley, occurring on 25-26 October 2000, is selected for this study. A series of sensitivity experiments are performed to gain understanding of the urban impact in the mesoscale model. Results indicate that within the selected urban environment, urban surface characteristics and anthropogenic heating play little role in the formation of the modeled nocturnal urban boundary layer. The rooftop effect appears to be the main contributor to this urban boundary layer. Sensitivity experiments also show that for this weak urban heat island case, the model horizontal grid resolution is important in simulating the elevated inversion layer. The root mean square errors of the predicted wind and temperature with respect to surface station measurements exhibit substantially larger discrepancies at the urban locations than the rural counterparts. However, the close agreement of modeled tracer concentration with observations fairly justifies the modeled urban impact on the wind direction shift and wind drag effects.
Locally isometric and conformal parameterization of image manifold
NASA Astrophysics Data System (ADS)
Bernstein, A. V.; Kuleshov, A. P.; Yanovich, Yu. A.
2015-12-01
Images can be represented as vectors in a high-dimensional Image space with components specifying light intensities at image pixels. To avoid the `curse of dimensionality', the original high-dimensional image data are transformed into their lower-dimensional features preserving certain subject-driven data properties. These properties can include `information-preserving' when using the constructed low-dimensional features instead of original high-dimensional vectors, as well preserving the distances and angles between the original high-dimensional image vectors. Under the commonly used Manifold assumption that the high-dimensional image data lie on or near a certain unknown low-dimensional Image manifold embedded in an ambient high-dimensional `observation' space, a constructing of the lower-dimensional features consists in constructing an Embedding mapping from the Image manifold to Feature space, which, in turn, determines a low-dimensional parameterization of the Image manifold. We propose a new geometrically motivated Embedding method which constructs a low-dimensional parameterization of the Image manifold and provides the information-preserving property as well as the locally isometric and conformal properties.
Evaluation of six parameterization approaches for the ground heat flux
NASA Astrophysics Data System (ADS)
Liebethal, C.; Foken, T.
2007-01-01
There are numerous approaches to the parameterization of the ground heat flux that use different input data, are valid for different times of the day, and deliver results of different quality. Six of these approaches are tested in this study: three approaches calculating the ground heat flux from net radiation, one approach using the turbulent sensible heat flux, one simplified in situ measurement approach, and the force-restore method. On the basis of a data set recorded during the LITFASS-2003 experiment, the strengths and weaknesses of the approaches are assessed. The quality of the best approaches (simplified measurement and force-restore) approximates that of the measured data set. An approach calculating the ground heat flux from net radiation and the diurnal amplitude of the soil surface temperature also delivers satisfactory daytime results. The remaining approaches all have such serious drawbacks that they should only be applied with care. Altogether, this study demonstrates that ground heat flux parameterization has the potential to produce results matching measured ones very well, if all conditions and restrictions of the respective approaches are taken into account.
Sensitivity of liquid clouds to homogenous freezing parameterizations
Herbert, Ross J; Murray, Benjamin J; Dobbie, Steven J; Koop, Thomas
2015-01-01
Water droplets in some clouds can supercool to temperatures where homogeneous ice nucleation becomes the dominant freezing mechanism. In many cloud resolving and mesoscale models, it is assumed that homogeneous ice nucleation in water droplets only occurs below some threshold temperature typically set at −40°C. However, laboratory measurements show that there is a finite rate of nucleation at warmer temperatures. In this study we use a parcel model with detailed microphysics to show that cloud properties can be sensitive to homogeneous ice nucleation as warm as −30°C. Thus, homogeneous ice nucleation may be more important for cloud development, precipitation rates, and key cloud radiative parameters than is often assumed. Furthermore, we show that cloud development is particularly sensitive to the temperature dependence of the nucleation rate. In order to better constrain the parameterization of homogeneous ice nucleation laboratory measurements are needed at both high (>−35°C) and low (<−38°C) temperatures. Key Points Homogeneous freezing may be significant as warm as −30°C Homogeneous freezing should not be represented by a threshold approximation There is a need for an improved parameterization of homogeneous ice nucleation PMID:26074652
Parameterizing Ocean Eddy Transports From Surface to Bottom
NASA Astrophysics Data System (ADS)
Aiki, H.; Jacobson, T.; Yamagata, T.
2004-12-01
To improve subgrid-scale physics of climate ocean models, in particular near the top and bottom boundaries, we consider new parameterization schemes for the extra transport velocity by waves and eddies in baroclinic instability. These come in the form of elliptic equations, previously unmentioned, which we derive for the eddy-induced overturning stream function. They guarantee decrease of the mean field potential energy. Our principal example gives a relationship between the vertical shear of the overturning velocity and the buoyancy torque of the main geostrophic current. Interestingly the parameterized velocity is nonsingular at the bottom and the sea surface, contrasting with the constant-coefficient Gent and McWilliams (1990)scheme. Idealized two-dimensional numerical experiments uccessfully reproduce meridional overturning circulation even when the background density gradient is uniform everywhere (the Eady problem) or when the bottom is steeply sloped. We further demonstrate that adding an eddy form drag (wave tress) term in the TRM momentum equations yields overturning of the velocity field.
Parameterization of Vegetation Aerodynamic Roughness of Natural Regions Satellite Imagery
NASA Technical Reports Server (NTRS)
Jasinski, Michael F.; Crago, Richard; Stewart, Pamela
1998-01-01
Parameterizations of the frontal area index and canopy area index of natural or randomly distributed plants are developed, and applied to the estimation of local aerodynamic roughness using satellite imagery. The formulas are expressed in terms of the subpixel fractional vegetation cover and one non-dimensional geometric parameter that characterizes the plant's shape. Geometrically similar plants and Poisson distributed plant centers are assumed. An appropriate averaging technique to extend satellite pixel-scale estimates to larger scales is provided. The parameterization is applied to the estimation of aerodynamic roughness using satellite imagery for a 2.3 sq km coniferous portion of the Landes Forest near Lubbon, France, during the 1986 HAPEX-Mobilhy Experiment. The canopy area index is estimated first for each pixel in the scene based on previous estimates of fractional cover obtained using Landsat Thematic Mapper imagery. Next, the results are incorporated into Raupach's (1992, 1994) analytical formulas for momentum roughness and zero-plane displacement height. The estimates compare reasonably well to reference values determined from measurements taken during the experiment and to published literature values. The approach offers the potential for estimating regionally variable, vegetation aerodynamic roughness lengths over natural regions using satellite imagery when there exists only limited knowledge of the vegetated surface.
A Parameterization for the Triggering of Landscape Generated Moist Convection
NASA Technical Reports Server (NTRS)
Lynn, Barry H.; Tao, Wei-Kuo; Abramopoulos, Frank
1998-01-01
A set of relatively high resolution three-dimensional (3D) simulations were produced to investigate the triggering of moist convection by landscape generated mesoscale circulations. The local accumulated rainfall varied monotonically (linearly) with the size of individual landscape patches, demonstrating the need to develop a trigger function that is sensitive to the size of individual patches. A new triggering function that includes the effect of landscapes generated mesoscale circulations over patches of different sizes consists of a parcel's perturbation in vertical velocity (nu(sub 0)), temperature (theta(sub 0)), and moisture (q(sub 0)). Each variable in the triggering function was also sensitive to soil moisture gradients, atmospheric initial conditions, and moist processes. The parcel's vertical velocity, temperature, and moisture perturbation were partitioned into mesoscale and turbulent components. Budget equations were derived for theta(sub 0) and q(sub 0). Of the many terms in this set of budget equations, the turbulent, vertical flux of the mesoscale temperature and moisture contributed most to the triggering of moist convection through the impact of these fluxes on the parcel's temperature and moisture profile. These fluxes needed to be parameterized to obtain theta(sub 0) and q(sub 0). The mesoscale vertical velocity also affected the profile of nu(sub 0). We used similarity theory to parameterize these fluxes as well as the parcel's mesoscale vertical velocity.
Observational Study and Parameterization of Aerosol-fog Interactions
NASA Astrophysics Data System (ADS)
Duan, J.; Guo, X.; Liu, Y.; Fang, C.; Su, Z.; Chen, Y.
2014-12-01
Studies have shown that human activities such as increased aerosols affect fog occurrence and properties significantly, and accurate numerical fog forecasting depends on, to a large extent, parameterization of fog microphysics and aerosol-fog interactions. Furthermore, fogs can be considered as clouds near the ground, and enjoy an advantage of permitting comprehensive long-term in-situ measurements that clouds do not. Knowledge learned from studying aerosol-fog interactions will provide useful insights into aerosol-cloud interactions. To serve the twofold objectives of understanding and improving parameterizations of aerosol-fog interactions and aerosol-cloud interactions, this study examines the data collected from fogs, with a focus but not limited to the data collected in Beijing, China. Data examined include aerosol particle size distributions measured by a Passive Cavity Aerosol Spectrometer Probe (PCASP-100X), fog droplet size distributions measured by a Fog Monitor (FM-120), Cloud Condensation Nuclei (CCN), liquid water path measured by radiometers and visibility sensors, along with meteorological variables measured by a Tethered Balloon Sounding System (XLS-Ⅱ) and Automatic Weather Station (AWS). The results will be compared with low-level clouds for similarities and differences between fogs and clouds.
Convection Parameterization and Double ITCZ in NCAR CCSM3
NASA Astrophysics Data System (ADS)
Zhang, G. J.; Wang, H.
2006-05-01
The appearance of a spurious Inter-Tropical Convergence Zone south of the equator in the eastern and central equatorial Pacific, in addition to the observed one north of the equator, is a common problem in coupled global climate models. Previous theoretical and modeling studies suggest that convection parameterization and the unrealistic simulation of the stratus clouds off Peru are two of the factors that can lead to double ITCZ. The present study investigates this double ITCZ problem in the NCAR CCSM3. It shows that use of a modified convection scheme significantly mitigates the double ITCZ problem in boreal summer. This has a profound impact on the simulated sea surface temperature through cloud radiative forcing feedback. Both the warm bias in the southern ITCZ region and the cold bias in the cold tongue over the equator are reduced. Examination of time series of precipitation, SST and surface energy fluxes shows that depending on the convection parameterization used, double or single ITCZ emerges quickly within the first few months after the model start.
NASA Astrophysics Data System (ADS)
Yang, Z.
2011-12-01
Noah-MP, which improves over the standard Noah land surface model, is unique among all land surface models in that it has multi-parameterization options (hence Noah-MP), capable of producing thousands of parameterization schemes, in addition to its improved physical realism (multi-layer snowpack, groundwater dynamics, and vegetation dynamics). All these features are critical for ensemble hydrological simulations and climate predictions at intraseasonal to decadal timescales. This talk will focus on evaluation of the Noah-MP simulations of energy, water and carbon balances for different sub-basins in the Mississippi River in comparison with various observations. The analysis is performed on daily and monthly scales spanning from January 2000 to December 2009. We will show how different runoff schemes in Noah-MP affect the scatter patterns between runoff and water table depth and between gross primary productivity and total water storage change, a type of analysis that would help us identify the relationships between key water storage terms (groundwater, soil moisture, snow) and fluxes (GPP, sensible heat, evapotranspiration, runoff). Similarly, we want to see how other options affect the patterns, such as the beta parameter (i.e. the soil moisture parameter controlling transpiration of plants), the Ball-Berry and Jarvis options for stomatal resistance, and the dynamic vegetation options (on or off). We will compare the water storage simulations from Noah-MP, observations and other model estimates, which would help determine the strengths and limitations of the Noah-MP groundwater and hydrological schemes.
eblur/dust: a modular python approach for dust extinction and scattering
NASA Astrophysics Data System (ADS)
Corrales, Lia
2016-03-01
I will present a library of python codes -- github.com/eblur/dust -- which calculate dust scattering and extinction properties from the IR to the X-ray. The modular interface allows for custom defined dust grain size distributions, optical constants, and scattering physics. These codes are currently undergoing a major overhaul to include multiple scattering effects, parallel processing, parameterized grain size distributions beyond power law, and optical constants for different grain compositions. I use eblur/dust primarily to study dust scattering images in the X-ray, but they may be extended to applications at other wavelengths.
A Coordinated Effort to Improve Parameterization of High-Latitude Cloud and Radiation Processes
J. O. Pinto, A.H. Lynch
2005-12-14
The goal of this project is the development and evaluation of improved parameterization of arctic cloud and radiation processes and implementation of the parameterizations into a climate model. Our research focuses specifically on the following issues: (1) continued development and evaluation of cloud microphysical parameterizations, focusing on issues of particular relevance for mixed phase clouds; and (2) evaluation of the mesoscale simulation of arctic cloud system life cycles.
Properties of a parameterization of radon projection by the reconstruction on circular disc
NASA Astrophysics Data System (ADS)
Tischenko, O.; Schegerer, A.; Xu, Y.; Hoeschen, C.
2010-04-01
An angular parameterization of parallel Radon projections referred to in this paper as ψ-parameterization is discussed in relevance to the efficiency of reconstruction from fan data. The fact that the ψ-parameterization coincides with the equiangular fan beam parameterization allows us to develop a simple and efficient approach useful for the reconstruction from fan data. Within this approach parallel projections are approximated by groups of semi-parallel rays. The reconstruction is carried out directly, i.e. without any modification of original data, at the speed which is comparable or even higher than that of the parallel Filtered Back Projection (FBP) algorithm.
Shi, Xiangjun; Liu, Xiaohong; Zhang, Kai
2015-01-01
In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmospheric Model version 5.3 (CAM5.3), the effects of preexisting ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of cirrus cloud rather than in the whole area of cirrus cloud. With these improvements, the two unphysical limiters used in the representation of ice nucleation are removed. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The preexisting ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably.Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and preexisting ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24×106 m-2) is obviously less than that from the LP (8.46×106 m-2) and BN (5.62×106 m-2) parameterizations. As a result, experiment using the KL parameterization predicts a much smaller anthropogenic aerosol longwave indirect forcing (0.24 W m-2) than that using the LP (0.46 W m-2
NASA Astrophysics Data System (ADS)
Shi, X.; Liu, X.; Zhang, K.
2014-07-01
In order to improve the treatment of ice nucleation in a more realistic manner in the Community Atmospheric Model version 5.3 (CAM5.3), the effects of preexisting ice crystals on ice nucleation in cirrus clouds are considered. In addition, by considering the in-cloud variability in ice saturation ratio, homogeneous nucleation takes place spatially only in a portion of cirrus cloud rather than in the whole area of cirrus cloud. With these improvements, the two unphysical limiters used in the representation of ice nucleation are removed. Compared to observations, the ice number concentrations and the probability distributions of ice number concentration are both improved with the updated treatment. The preexisting ice crystals significantly reduce ice number concentrations in cirrus clouds, especially at mid- to high latitudes in the upper troposphere (by a factor of ~10). Furthermore, the contribution of heterogeneous ice nucleation to cirrus ice crystal number increases considerably. Besides the default ice nucleation parameterization of Liu and Penner (2005, hereafter LP) in CAM5.3, two other ice nucleation parameterizations of Barahona and Nenes (2009, hereafter BN) and Kärcher et al. (2006, hereafter KL) are implemented in CAM5.3 for the comparison. In-cloud ice crystal number concentration, percentage contribution from heterogeneous ice nucleation to total ice crystal number, and preexisting ice effects simulated by the three ice nucleation parameterizations have similar patterns in the simulations with present-day aerosol emissions. However, the change (present-day minus pre-industrial times) in global annual mean column ice number concentration from the KL parameterization (3.24 × 106 m-2) is obviously less than that from the LP (8.46 × 106 m-2) and BN (5.62 × 106 m-2) parameterizations. As a result, experiment using the KL parameterization predicts a much smaller anthropogenic aerosol longwave indirect forcing (0.24 W m-2) than that using the LP (0.46 W
A simple parameterization of aerosol emissions in RAMS
NASA Astrophysics Data System (ADS)
Letcher, Theodore
Throughout the past decade, a high degree of attention has been focused on determining the microphysical impact of anthropogenically enhanced concentrations of Cloud Condensation Nuclei (CCN) on orographic snowfall in the mountains of the western United States. This area has garnered a lot of attention due to the implications this effect may have on local water resource distribution within the Region. Recent advances in computing power and the development of highly advanced microphysical schemes within numerical models have provided an estimation of the sensitivity that orographic snowfall has to changes in atmospheric CCN concentrations. However, what is still lacking is a coupling between these advanced microphysical schemes and a real-world representation of CCN sources. Previously, an attempt to representation the heterogeneous evolution of aerosol was made by coupling three-dimensional aerosol output from the WRF Chemistry model to the Colorado State University (CSU) Regional Atmospheric Modeling System (RAMS) (Ward et al. 2011). The biggest problem associated with this scheme was the computational expense. In fact, the computational expense associated with this scheme was so high, that it was prohibitive for simulations with fine enough resolution to accurately represent microphysical processes. To improve upon this method, a new parameterization for aerosol emission was developed in such a way that it was fully contained within RAMS. Several assumptions went into generating a computationally efficient aerosol emissions parameterization in RAMS. The most notable assumption was the decision to neglect the chemical processes in formed in the formation of Secondary Aerosol (SA), and instead treat SA as primary aerosol via short-term WRF-CHEM simulations. While, SA makes up a substantial portion of the total aerosol burden (much of which is made up of organic material), the representation of this process is highly complex and highly expensive within a numerical
Parameterization of ion channeling half-angles and minimum yields
NASA Astrophysics Data System (ADS)
Doyle, Barney L.
2016-03-01
A MS Excel program has been written that calculates ion channeling half-angles and minimum yields in cubic bcc, fcc and diamond lattice crystals. All of the tables and graphs in the three Ion Beam Analysis Handbooks that previously had to be manually looked up and read from were programed into Excel in handy lookup tables, or parameterized, for the case of the graphs, using rather simple exponential functions with different power functions of the arguments. The program then offers an extremely convenient way to calculate axial and planar half-angles, minimum yields, effects on half-angles and minimum yields of amorphous overlayers. The program can calculate these half-angles and minimum yields for axes and [h k l] planes up to (5 5 5). The program is open source and available at
Piecewise-quartics and exponential parameterization for interpolating reduced data
NASA Astrophysics Data System (ADS)
Kozera, R.
2016-06-01
We examine the asymptotics of a piecewise-quartic Lagrange interpolation used to fit reduced data in arbitrary Euclidean space which are sampled more-or-less uniformly. The unknown interpolation knots are guessed here according to the so-called exponential parameterization which depends on a single parameter λ ∈ [0, 1]. In this work we demonstrate numerically an abrupt discontinuity in the quality of the discussed interpolation scheme yielding a slow linear convergence order for all λ ∈ [0, 1). On the other hand, as well-known the quality of the curve approximation for λ = 1 sharply increases to the fast sharp quartic order which can be further accelerated for special subfamilies of more-or-less uniform samplings.
Parameterization of Aerosol Sinks in Chemical Transport Models
NASA Technical Reports Server (NTRS)
Colarco, Peter
2012-01-01
The modelers point of view is that the aerosol problem is one of sources, evolution, and sinks. Relative to evolution and sink processes, enormous attention is given to the problem of aerosols sources, whether inventory based (e.g., fossil fuel emissions) or dynamic (e.g., dust, sea salt, biomass burning). On the other hand, aerosol losses in models are a major factor in controlling the aerosol distribution and lifetime. Here we shine some light on how aerosol sinks are treated in modern chemical transport models. We discuss the mechanisms of dry and wet loss processes and the parameterizations for those processes in a single model (GEOS-5). We survey the literature of other modeling studies. We additionally compare the budgets of aerosol losses in several of the ICAP models.
A Step Towards an Advanced Parameterization of Cloud Microphysical Processes
NASA Astrophysics Data System (ADS)
Beheng, K. D.
2002-12-01
Consideration of cloud microphysical properties and processes in atmospheric models usually requires reliable and accurate parameterizations. For describing all hydrometeor types by size distribution functions and corresponding budget equations comprising a multitude of processes in an adapted manner is by far too costly. An alternative is to only deal with certain integrals (i.e. moments of the size spectra as, e.g., water contents) and their tendency equations. Moreover, the parameter formulae should comply with the natural situation of having smaller (cloud) and larger (precipitation) particles which interact by collisions in a complex way. Many years ago this idea has been elaborated by Kessler (1969) for liquid (warm) clouds. Kessler presented a rate equation for the transformation of cloud water content to rainwater mass (autoconversion) which relies on high intuition and another one for accretion, i.e. for the increase of rainwater content by mutual collection of cloud droplets by raindrops, which is based on a simplistic evaluation of the collection integrals of the spectral budget equation for drops. This first approach to parameterize the evolution of rain water from cloud water is a very important one since almost all clouds start as liquid clouds. For a long time and also to date these so-called Kessler formulae were the only parameterization available for warm cloud processes. In adopting this idea corresponding formulations have also been derived and extensively applied for mixed and ice cloud microphysics. The drawback of Kesslers formulation is that it only uses (cloud and rain) water contents such that a differentiation between continental and maritime clouds exhibiting very different size spectra but identical water contents is not possible. To overcome this deficiency and to include typical cloud characteristics several authors extended Kessler's idea by formulating - in addition to the rates of change of mass contents - rates for the
New particle dependant parameterizations of heterogeneous freezing processes.
NASA Astrophysics Data System (ADS)
Diehl, Karoline; Mitra, Subir K.
2014-05-01
For detailed investigations of cloud microphysical processes an adiabatic air parcel model with entrainment is used. It represents a spectral bin model which explicitly solves the microphysical equations. The initiation of the ice phase is parameterized and describes the effects of different types of ice nuclei (mineral dust, soot, biological particles) in immersion, contact, and deposition modes. As part of the research group INUIT (Ice Nuclei research UnIT), existing parameterizations have been modified for the present studies and new parameterizations have been developed mainly on the basis of the outcome of INUIT experiments. Deposition freezing in the model is dependant on the presence of dry particles and on ice supersaturation. The description of contact freezing combines the collision kernel of dry particles with the fraction of frozen drops as function of temperature and particle size. A new parameterization of immersion freezing has been coupled to the mass of insoluble particles contained in the drops using measured numbers of ice active sites per unit mass. Sensitivity studies have been performed with a convective temperature and dew point profile and with two dry aerosol particle number size distributions. Single and coupled freezing processes are studied with different types of ice nuclei (e.g., bacteria, illite, kaolinite, feldspar). The strength of convection is varied so that the simulated cloud reaches different levels of temperature. As a parameter to evaluate the results the ice water fraction is selected which is defined as the relation of the ice water content to the total water content. Ice water fractions between 0.1 and 0.9 represent mixed-phase clouds, larger than 0.9 ice clouds. The results indicate the sensitive parameters for the formation of mixed-phase and ice clouds are: 1. broad particle number size distribution with high number of small particles, 2. temperatures below -25°C, 3. specific mineral dust particles as ice nuclei such
FSP (Full Space Parameterization), Version 2.0
Fries, G.A.; Hacker, C.J.; Pin, F.G.
1995-10-01
This paper describes the modifications made to FSPv1.0 for the Full Space Parameterization (FSP) method, a new analytical method used to resolve underspecified systems of algebraic equations. The optimized code recursively searches for the necessary number of linearly independent vectors that are necessary to form the solution space. While doing this, it ensures that all possible combinations of solutions are checked, if needed, and handles complications which arise due to particular cases. In addition, two particular cases which cause failure of the FSP algorithm were discovered during testing of this new code. These cases are described in the context of how they are recognized and how they are handled by the new code. Finally, testing was performed on the new code using both isolated movements and complex trajectories for various mobile manipulators.
Parameterized modeling and estimation of spatially varying optical blur
NASA Astrophysics Data System (ADS)
Simpkins, Jonathan D.; Stevenson, Robert L.
2015-02-01
Optical blur can display significant spatial variation across the image plane, even for constant camera settings and object depth. Existing solutions to represent this spatially varying blur requires a dense sampling of blur kernels across the image, where each kernel is defined independent of the neighboring kernels. This approach requires a large amount of data collection, and the estimation of the kernels is not as robust as if it were possible to incorporate knowledge of the relationship between adjacent kernels. A novel parameterized model is presented which relates the blur kernels at different locations across the image plane. The model is motivated by well-established optical models, including the Seidel aberration model. It is demonstrated that the proposed model can unify a set of hundreds of blur kernel observations across the image plane under a single 10-parameter model, and the accuracy of the model is demonstrated with simulations and measurement data collected by two separate research groups.
Criteria and algorithms for spectrum parameterization of MST radar signals
NASA Technical Reports Server (NTRS)
Rastogi, P. K.
1984-01-01
The power spectra S(f) of MST radar signals contain useful information about the variance of refractivity fluctuations, the mean radial velocity, and the radial velocity variance in the atmosphere. When noise and other contaminating signals are absent, these quantities can be obtained directly from the zeroth, first and second order moments of the spectra. A step-by-step procedure is outlined that can be used effectively to reduce large amounts of MST radar data-averaged periodograms measured in range and time to a parameterized form. The parameters to which a periodogram can be reduced are outlined and the steps in the procedure, that may be followed selectively, to arrive at the final set of reduced parameters are given. Examples of the performance of the procedure are given and its use with other radars are commented on.
Parameterized Facial Expression Synthesis Based on MPEG-4
NASA Astrophysics Data System (ADS)
Raouzaiou, Amaryllis; Tsapatsoulis, Nicolas; Karpouzis, Kostas; Kollias, Stefanos
2002-12-01
In the framework of MPEG-4, one can include applications where virtual agents, utilizing both textual and multisensory data, including facial expressions and nonverbal speech help systems become accustomed to the actual feelings of the user. Applications of this technology are expected in educational environments, virtual collaborative workplaces, communities, and interactive entertainment. Facial animation has gained much interest within the MPEG-4 framework; with implementation details being an open research area (Tekalp, 1999). In this paper, we describe a method for enriching human computer interaction, focusing on analysis and synthesis of primary and intermediate facial expressions (Ekman and Friesen (1978)). To achieve this goal, we utilize facial animation parameters (FAPs) to model primary expressions and describe a rule-based technique for handling intermediate ones. A relation between FAPs and the activation parameter proposed in classical psychological studies is established, leading to parameterized facial expression analysis and synthesis notions, compatible with the MPEG-4 standard.
Research on aerosol profiles and parameterization scheme in Southeast China
NASA Astrophysics Data System (ADS)
Wang, Gang; Deng, Tao; Tan, Haobo; Liu, Xiantong; Yang, Honglong
2016-09-01
The vertical distribution of the aerosol extinction coefficient serves as a basis for evaluating aerosol radiative forcing and air quality modeling. In this study, MODIS AOD data and ground-based lidar extinction coefficients were employed to verify 6 years (2009-2014) aerosol extinction data obtained via CALIOP for Southeast China. The objective was mainly to provide the parameterization scheme of annual and seasonal aerosol extinction profiles. The results showed that the horizontal and vertical distributions of CALIOP extinction data were highly accurate in Southeast China. The annual average AOD below 2 km accounted for 64% of the total layer, with larger proportions observed in winter (80%) and autumn (80%) and lower proportions observed in summer (70%) and spring (59%). The AOD was maximum in the spring (0.58), followed by the autumn and winter (0.44), and reached a minimum in the summer (0.40). The near-surface extinction coefficient increased from summer, spring, autumn and winter, in that order. The Elterman profile is obviously lower than the profiles observed by CALIOP in Southeast China. The annual average and seasonal aerosol profiles showed an exponential distribution, and could be divided into two sections. Two sections exponential fitting was used in the parameterization scheme. In the first section, the aerosol scale height reached 2200 m with a maximum (3,500 m) in summer and a minimum (1,230 m) in winter, which meant that the aerosol extinction decrease with height slower in summer, but more rapidly in winter. In second section, the aerosol scale height was maximum in spring, which meant that the higher aerosol diffused in spring.
Precisely parameterized experimental and computational models of tissue organization†
Sekar, Rajesh B.; Blake, Robert; Park, JinSeok; Trayanova, Natalia A.; Tung, Leslie; Levchenko, Andre
2016-01-01
Patterns of cellular organization in diverse tissues frequently display a complex geometry and topology tightly related to the tissue function. Progressive disorganization of tissue morphology can lead to pathologic remodeling, necessitating the development of experimental and theoretical methods of analysis of the tolerance of normal tissue function to structural alterations. A systematic way to investigate the relationship of diverse cell organization to tissue function is to engineer two-dimensional cell monolayers replicating key aspects of the in vivo tissue architecture. However, it is still not clear how this can be accomplished on a tissue level scale in a parameterized fashion, allowing for a mathematically precise definition of the model tissue organization and properties down to a cellular scale with a parameter dependent gradual change in model tissue organization. Here, we describe and use a method of designing precisely parameterized, geometrically complex patterns that are then used to control cell alignment and communication of model tissues. We demonstrate direct application of this method to guiding the growth of cardiac cell cultures and developing mathematical models of cell function that correspond to the underlying experimental patterns. Several anisotropic patterned cultures spanning a broad range of multicellular organization, mimicking the cardiac tissue organization of different regions of the heart, were found to be similar to each other and to isotropic cell monolayers in terms of local cell–cell interactions, reflected in similar confluency, morphology and connexin-43 expression. However, in agreement with the model predictions, different anisotropic patterns of cell organization, paralleling in vivo alterations of cardiac tissue morphology, resulted in variable and novel functional responses with important implications for the initiation and maintenance of cardiac arrhythmias. We conclude that variations of tissue geometry and
Arthrodial joint markerless cross-parameterization and biomechanical visualization.
Marai, G Elisabeta; Grimm, Cindy M; Laidlaw, David H
2007-01-01
Abstract-Orthopedists invest significant amounts of effort and time trying to understand the biomechanics of arthrodial (gliding) joints. Although new image acquisition and processing methods currently generate richer-than-ever geometry and kinematic data sets that are individual specific, the computational and visualization tools needed to enable the comparative analysis and exploration of these data sets lag behind. In this paper, we present a framework that enables the cross-data-set visual exploration and analysis of arthrodial joint biomechanics. Central to our approach is a computer-vision-inspired markerless method for establishing pairwise correspondences between individual-specific geometry. Manifold models are subsequently defined and deformed from one individual-specific geometry to another such that the markerless correspondences are preserved while minimizing model distortion. The resulting mutually consistent parameterization and visualization allow the users to explore the similarities and differences between two data sets and to define meaningful quantitative measures. We present two applications of this framework to human-wrist data: articular cartilage transfer from cadaver data to in vivo data and cross-data-set kinematics analysis. The method allows our users to combine complementary geometries acquired through different modalities and thus overcome current imaging limitations. The results demonstrate that the technique is useful in the study of normal and injured anatomy and kinematics of arthrodial joints. In principle, the pairwise cross-parameterization method applies to all spherical topology data from the same class and should be particularly beneficial in instances where identifying salient object features is a nontrivial task. PMID:17622690
Precisely parameterized experimental and computational models of tissue organization.
Molitoris, Jared M; Paliwal, Saurabh; Sekar, Rajesh B; Blake, Robert; Park, JinSeok; Trayanova, Natalia A; Tung, Leslie; Levchenko, Andre
2016-02-01
Patterns of cellular organization in diverse tissues frequently display a complex geometry and topology tightly related to the tissue function. Progressive disorganization of tissue morphology can lead to pathologic remodeling, necessitating the development of experimental and theoretical methods of analysis of the tolerance of normal tissue function to structural alterations. A systematic way to investigate the relationship of diverse cell organization to tissue function is to engineer two-dimensional cell monolayers replicating key aspects of the in vivo tissue architecture. However, it is still not clear how this can be accomplished on a tissue level scale in a parameterized fashion, allowing for a mathematically precise definition of the model tissue organization and properties down to a cellular scale with a parameter dependent gradual change in model tissue organization. Here, we describe and use a method of designing precisely parameterized, geometrically complex patterns that are then used to control cell alignment and communication of model tissues. We demonstrate direct application of this method to guiding the growth of cardiac cell cultures and developing mathematical models of cell function that correspond to the underlying experimental patterns. Several anisotropic patterned cultures spanning a broad range of multicellular organization, mimicking the cardiac tissue organization of different regions of the heart, were found to be similar to each other and to isotropic cell monolayers in terms of local cell-cell interactions, reflected in similar confluency, morphology and connexin-43 expression. However, in agreement with the model predictions, different anisotropic patterns of cell organization, paralleling in vivo alterations of cardiac tissue morphology, resulted in variable and novel functional responses with important implications for the initiation and maintenance of cardiac arrhythmias. We conclude that variations of tissue geometry and topology
Parameterization of tree-ring growth in Siberia
NASA Astrophysics Data System (ADS)
Tychkov, Ivan; Popkova, Margarita; Shishov, Vladimir; Vaganov, Eugene
2016-04-01
No doubt, climate-tree growth relationship is an one of the useful and interesting subject of studying in dendrochronology. It provides an information of tree growth dependency on climatic environment, but also, gives information about growth conditions and whole tree-ring growth process for long-term periods. New parameterization approach of the Vaganov-Shashkin process-based model (VS-model) is developed to described critical process linking climate variables with tree-ring formation. The approach (co-called VS-Oscilloscope) is presented as a computer software with graphical interface. As most process-based tree-ring models, VS-model's initial purpose is to describe variability of tree-ring radial growth due to variability of climatic factors, but also to determinate principal factors limiting tree-ring growth. The principal factors affecting on the growth rate of cambial cells in the VS-model are temperature, day light and soil moisture. Detailed testing of VS-Oscilloscope was done for semi-arid area of southern Siberia (Khakassian region). Significant correlations between initial tree-ring chronologies and simulated tree-ring growth curves were obtained. Direct natural observations confirm obtained simulation results including unique growth characteristic for semi-arid habitats. New results concerning formation of wide and narrow rings under different climate conditions are considered. By itself the new parameterization approach (VS-oscilloscope) is an useful instrument for better understanding of various processes in tree-ring formation. The work was supported by the Russian Science Foundation (RSF # 14-14-00219).
Mesoscale Eddy Parameterization in an Idealized Primitive Equations Model
NASA Astrophysics Data System (ADS)
Anstey, J.; Zanna, L.
2014-12-01
Large-scale ocean currents such as the Gulf Stream and Kuroshio Extension are strongly influenced by mesoscale eddies, which have spatial scales of order 10-100 km. The effects of these eddies are poorly represented in many state-of-the-art ocean general circulation models (GCMs) due to the inadequate spatial resolution of these models. In this study we examine the response of the large-scale ocean circulation to the rectified effects of eddy forcing - i.e., the role played by surface-intensified mesoscale eddies in sustaining and modulating an eastward jet that separates from an intense western boundary current (WBC). For this purpose a primitive equations ocean model (the MITgcm) in an idealized wind-forced double-gyre configuration is integrated at eddy-resolving resolution to reach a forced-dissipative equilibrium state that captures the essential dynamics of WBC-extension jets. The rectified eddy forcing is diagnosed as a stochastic function of the large-scale state, this being characterized by the manner in which potential vorticity (PV) contours become deformed. Specifically, a stochastic function based on the Laplacian of the material rate of change of PV is examined in order to compare the primitive equations results with those of a quasi-geostrophic model in which this function has shown some utility as a parameterization of eddy effects (Porta Mana and Zanna, 2014). The key question is whether an eddy parameterization based on quasi-geostrophic scaling is able to carry over to a system in which this scaling is not imposed (i.e. the primitive equations), in which unbalanced motions occur.
Synthesizing 3D Surfaces from Parameterized Strip Charts
NASA Technical Reports Server (NTRS)
Robinson, Peter I.; Gomez, Julian; Morehouse, Michael; Gawdiak, Yuri
2004-01-01
We believe 3D information visualization has the power to unlock new levels of productivity in the monitoring and control of complex processes. Our goal is to provide visual methods to allow for rapid human insight into systems consisting of thousands to millions of parameters. We explore this hypothesis in two complex domains: NASA program management and NASA International Space Station (ISS) spacecraft computer operations. We seek to extend a common form of visualization called the strip chart from 2D to 3D. A strip chart can display the time series progression of a parameter and allows for trends and events to be identified. Strip charts can be overlayed when multiple parameters need to visualized in order to correlate their events. When many parameters are involved, the direct overlaying of strip charts can become confusing and may not fully utilize the graphing area to convey the relationships between the parameters. We provide a solution to this problem by generating 3D surfaces from parameterized strip charts. The 3D surface utilizes significantly more screen area to illustrate the differences in the parameters and the overlayed strip charts, and it can rapidly be scanned by humans to gain insight. The selection of the third dimension must be a parallel or parameterized homogenous resource in the target domain, defined using a finite, ordered, enumerated type, and not a heterogeneous type. We demonstrate our concepts with examples from the NASA program management domain (assessing the state of many plans) and the computers of the ISS (assessing the state of many computers). We identify 2D strip charts in each domain and show how to construct the corresponding 3D surfaces. The user can navigate the surface, zooming in on regions of interest, setting a mark and drilling down to source documents from which the data points have been derived. We close by discussing design issues, related work, and implementation challenges.
Parameterization of Infrared Absorption in Midlatitude Cirrus Clouds
Sassen, Kenneth; Wang, Zhien; Platt, C.M.R.; Comstock, Jennifer M.
2003-01-01
Employing a new approach based on combined Raman lidar and millimeter-wave radar measurements and a parameterization of the infrared absorption coefficient {sigma}{sub a}(km{sup -1}) in terms of retrieved cloud microphysics, we derive a statistical relation between {sigma}{sub a} and cirrus cloud temperature. The relations {sigma}{sub a} = 0.3949 + 5.3886 x 10{sup -3} T + 1.526 x 10{sup -5} T{sup 2} for ambient temperature (T,{sup o}C), and {sigma}{sub a} = 0.2896 + 3.409 x 10{sup -3} T{sub m} for midcloud temperature (T{sub m}, {sup o}C), are found using a second order polynomial fit. Comparison with two {sigma}{sub a} versus T{sub m} relations obtained primarily from midlatitude cirrus using the combined lidar/infrared radiometer (LIRAD) approach reveals significant differences. However, we show that this reflects both the previous convention used in curve fitting (i. e., {sigma}{sub a} {yields} 0 at {approx} 80 C), and the types of clouds included in the datasets. Without such constraints, convergence is found in the three independent remote sensing datasets within the range of conditions considered valid for cirrus (i.e., cloud optical depth {approx} 3.0 and T{sub m} < {approx}20 C). Hence for completeness we also provide reanalyzed parameterizations for a visible extinction coefficient {sigma}{sub a} versus T{sub m} relation for midlatitude cirrus, and a data sample involving cirrus that evolved into midlevel altostratus clouds with higher optical depths.
Nejadgholi, Isar; Caytak, Herschel; Bolic, Miodrag; Batkin, Izmail; Shirmohammadi, Shervin
2015-05-01
In several applications of bioimpedance spectroscopy, the measured spectrum is parameterized by being fitted into the Cole equation. However, the extracted Cole parameters seem to be inconsistent from one measurement session to another, which leads to a high standard deviation of extracted parameters. This inconsistency is modeled with a source of random variations added to the voltage measurement carried out in the time domain. These random variations may originate from biological variations that are irrelevant to the evidence that we are investigating. Yet, they affect the voltage measured by using a bioimpedance device based on which magnitude and phase of impedance are calculated.By means of simulated data, we showed that Cole parameters are highly affected by this type of variation. We further showed that singular value decomposition (SVD) is an effective tool for parameterizing bioimpedance measurements, which results in more consistent parameters than Cole parameters. We propose to apply SVD as a preprocessing method to reconstruct denoised bioimpedance measurements. In order to evaluate the method, we calculated the relative difference between parameters extracted from noisy and clean simulated bioimpedance spectra. Both mean and standard deviation of this relative difference are shown to effectively decrease when Cole parameters are extracted from preprocessed data in comparison to being extracted from raw measurements.We evaluated the performance of the proposed method in distinguishing three arm positions, for a set of experiments including eight subjects. It is shown that Cole parameters of different positions are not distinguishable when extracted from raw measurements. However, one arm position can be distinguished based on SVD scores. Moreover, all three positions are shown to be distinguished by two parameters, R0/R∞ and Fc, when Cole parameters are extracted from preprocessed measurements. These results suggest that SVD could be considered as an
SU-E-T-597: Parameterization of the Photon Beam Dosimetry for a Commercial Linear Accelerator
Lebron, S; Lu, B; Yan, G; Kahler, D; Li, J; Barraclough, B; Liu, C
2015-06-15
Purpose: In radiation therapy, accurate data acquisition of photon beam dosimetric quantities is important for (1) beam modeling data input into a treatment planning system (TPS), (2) comparing measured and TPS modelled data, (3) a linear accelerator’s (linac) beam characteristics quality assurance process, and (4) establishing a standard data set for data comparison, etcetera. Parameterization of the photon beam dosimetry creates a portable data set that is easy to implement for different applications such as those previously mentioned. The aim of this study is to develop methods to parameterize photon percentage depth doses(PDD), profiles, and total scatter output factors(Scp). Methods: Scp, PDDs and profiles for different field sizes (from 2×2 to 40×40cm{sup 2}), depths and energies were measured in a linac using a three-dimensional water tank. All data were smoothed and profile data were also centered, symmetrized and geometrically scaled. The Scp and PDD data were analyzed using exponential functions. For modelling of open and wedge field profiles, each side was divided into three regions described by exponential, sigmoid and Gaussian equations. The model’s equations were chosen based on the physical principles described by these dosimetric quantities. The equations’ parameters were determined using a least square optimization method with the minimal amount of measured data necessary. The model’s accuracy was then evaluated via the calculation of absolute differences and distance–to–agreement analysis in low gradient and high gradient regions, respectively. Results: All differences in the PDDs’ buildup and the profiles’ penumbra regions were less than 2 mm and 0.5 mm, respectively. Differences in the low gradient regions were 0.20 ± 0.20% and 0.50 ± 0.35% for PDDs and profiles, respectively. For Scp data, all differences were less than 0.5%. Conclusion: This novel analytical model with minimum measurement requirements proved to accurately
Parameterizations for convective transport in various cloud-topped boundary layers
NASA Astrophysics Data System (ADS)
Sikma, M.; Ouwersloot, H. G.
2015-09-01
We investigate the representation of convective transport of atmospheric compounds by boundary layer clouds. We focus on three key parameterizations that, when combined, express this transport: the area fraction of transporting clouds, the upward velocity in the cloud cores and the chemical concentrations at cloud base. The first two parameterizations combined represent the kinematic mass flux by clouds. To investigate the key parameterizations under a wide range of conditions, we use large-eddy simulation model data for 10 meteorological situations, characterized by either shallow cumulus or stratocumulus clouds. The parameterizations have not been previously tested with such large data sets. In the analysis, we show that the parameterization of the area fraction of clouds currently used in mixed-layer models is affected by boundary layer dynamics. Therefore, we (i) simplify the independent variable used for this parameterization, Q1, by considering the variability in moisture rather than in the saturation deficit and update the parameters in the parameterization to account for this simplification. We (ii) next demonstrate that the independent variable has to be evaluated locally to capture cloud presence. Furthermore, we (iii) show that the area fraction of transporting clouds is not represented by the parameterization for the total cloud area fraction, as is currently assumed in literature. To capture cloud transport, a novel active cloud area fraction parameterization is proposed. Subsequently, the scaling of the upward velocity in cloud cores by the Deardorff convective velocity scale and the parameterization for the concentration of atmospheric reactants at cloud base from literature are verified and improved by analysing six shallow cumulus cases. For the latter, we additionally discuss how the parameterization is affected by wind conditions. This study contributes to a more accurate estimation of convective transport, which occurs at sub-grid scales.
NASA Astrophysics Data System (ADS)
Scarpa, Riccardo; Thiene, Mara; Hensher, David A.
2012-01-01
Preferences for attributes of complex goods may differ substantially among members of households. Some of these goods, such as tap water, are jointly supplied at the household level. This issue of jointness poses a series of theoretical and empirical challenges to economists engaged in empirical nonmarket valuation studies. While a series of results have already been obtained in the literature, the issue of how to empirically measure these differences, and how sensitive the results are to choice of model specification from the same data, is yet to be clearly understood. In this paper we use data from a widely employed form of stated preference survey for multiattribute goods, namely choice experiments. The salient feature of the data collection is that the same choice experiment was applied to both partners of established couples. The analysis focuses on models that simultaneously handle scale as well as preference heterogeneity in marginal rates of substitution (MRS), thereby isolating true differences between members of couples in their MRS, by removing interpersonal variation in scale. The models employed are different parameterizations of the mixed logit model, including the willingness to pay (WTP)-space model and the generalized multinomial logit model. We find that in this sample there is some evidence of significant statistical differences in values between women and men, but these are of small magnitude and only apply to a few attributes.
High-precision positioning of radar scatterers
NASA Astrophysics Data System (ADS)
Dheenathayalan, Prabu; Small, David; Schubert, Adrian; Hanssen, Ramon F.
2016-05-01
Remote sensing radar satellites cover wide areas and provide spatially dense measurements, with millions of scatterers. Knowledge of the precise position of each radar scatterer is essential to identify the corresponding object and interpret the estimated deformation. The absolute position accuracy of synthetic aperture radar (SAR) scatterers in a 2D radar coordinate system, after compensating for atmosphere and tidal effects, is in the order of centimeters for TerraSAR-X (TSX) spotlight images. However, the absolute positioning in 3D and its quality description are not well known. Here, we exploit time-series interferometric SAR to enhance the positioning capability in three dimensions. The 3D positioning precision is parameterized by a variance-covariance matrix and visualized as an error ellipsoid centered at the estimated position. The intersection of the error ellipsoid with objects in the field is exploited to link radar scatterers to real-world objects. We demonstrate the estimation of scatterer position and its quality using 20 months of TSX stripmap acquisitions over Delft, the Netherlands. Using trihedral corner reflectors (CR) for validation, the accuracy of absolute positioning in 2D is about 7 cm. In 3D, an absolute accuracy of up to ˜ 66 cm is realized, with a cigar-shaped error ellipsoid having centimeter precision in azimuth and range dimensions, and elongated in cross-range dimension with a precision in the order of meters (the ratio of the ellipsoid axis lengths is 1/3/213, respectively). The CR absolute 3D position, along with the associated error ellipsoid, is found to be accurate and agree with the ground truth position at a 99 % confidence level. For other non-CR coherent scatterers, the error ellipsoid concept is validated using 3D building models. In both cases, the error ellipsoid not only serves as a quality descriptor, but can also help to associate radar scatterers to real-world objects.
NASA Astrophysics Data System (ADS)
Xia, Xiangao
2015-09-01
Aerosols impact clear-sky surface irradiance () through the effects of scattering and absorption. Linear or nonlinear relationships between aerosol optical depth (τa) and have been established to describe the aerosol direct radiative effect on (ADRE). However, considerable uncertainties remain associated with ADRE due to the incorrect estimation of (τa in the absence of aerosols). Based on data from the Aerosol Robotic Network, the effects of τa, water vapor content (w) and the cosine of the solar zenith angle (μ) on are thoroughly considered, leading to an effective parameterization of as a nonlinear function of these three quantities. The parameterization is proven able to estimate with a mean bias error of 0.32 W m-2, which is one order of magnitude smaller than that derived using earlier linear or nonlinear functions. Applications of this new parameterization to estimate τa from , or vice versa, show that the root-mean-square errors were 0.08 and 10.0 Wm-2, respectively. Therefore, this study establishes a straightforward method to derive from τa or estimate τa from measurements if water vapor measurements are available.
Xia, Xiangao
2015-01-01
Aerosols impact clear-sky surface irradiance () through the effects of scattering and absorption. Linear or nonlinear relationships between aerosol optical depth (τa) and have been established to describe the aerosol direct radiative effect on (ADRE). However, considerable uncertainties remain associated with ADRE due to the incorrect estimation of (τa in the absence of aerosols). Based on data from the Aerosol Robotic Network, the effects of τa, water vapor content (w) and the cosine of the solar zenith angle (μ) on are thoroughly considered, leading to an effective parameterization of as a nonlinear function of these three quantities. The parameterization is proven able to estimate with a mean bias error of 0.32 W m−2, which is one order of magnitude smaller than that derived using earlier linear or nonlinear functions. Applications of this new parameterization to estimate τa from , or vice versa, show that the root-mean-square errors were 0.08 and 10.0 Wm−2, respectively. Therefore, this study establishes a straightforward method to derive from τa or estimate τa from measurements if water vapor measurements are available. PMID:26395310
NASA Astrophysics Data System (ADS)
Brown, Steven S.; Dubé, William P.; Fuchs, Hendrik; Ryerson, Thomas B.; Wollny, Adam G.; Brock, Charles A.; Bahreini, Roya; Middlebrook, Ann M.; Neuman, J. Andrew; Atlas, Elliot; Roberts, James M.; Osthoff, Hans D.; Trainer, Michael; Fehsenfeld, Frederick C.; Ravishankara, A. R.
2009-04-01
This paper presents determinations of reactive uptake coefficients for N2O5, γ(N2O5), on aerosols from nighttime aircraft measurements of ozone, nitrogen oxides, and aerosol surface area on the NOAA P-3 during Second Texas Air Quality Study (TexAQS II). Determinations based on both the steady state approximation for NO3 and N2O5 and a plume modeling approach yielded γ(N2O5) substantially smaller than current parameterizations used for atmospheric modeling and generally in the range 0.5-6 × 10-3. Dependence of γ(N2O5) on variables such as relative humidity and aerosol composition was not apparent in the determinations, although there was considerable scatter in the data. Determinations were also inconsistent with current parameterizations of the rate coefficient for homogenous hydrolysis of N2O5 by water vapor, which may be as much as a factor of 10 too large. Nocturnal halogen activation via conversion of N2O5 to ClNO2 on chloride aerosol was not determinable from these data, although limits based on laboratory parameterizations and maximum nonrefractory aerosol chloride content showed that this chemistry could have been comparable to direct production of HNO3 in some cases.
The CCPP-ARM Parameterization Testbed (CAPT): Where Climate Simulation Meets Weather Prediction
Phillips, T J; Potter, G L; Williamson, D L; Cederwall, R T; Boyle, J S; Fiorino, M; Hnilo, J J; Olson, J G; Xie, S; Yio, J J
2003-11-21
To significantly improve the simulation of climate by general circulation models (GCMs), systematic errors in representations of relevant processes must first be identified, and then reduced. This endeavor demands, in particular, that the GCM parameterizations of unresolved processes should be tested over a wide range of time scales, not just in climate simulations. Thus, a numerical weather prediction (NWP) methodology for evaluating model parameterizations and gaining insights into their behavior may prove useful, provied that suitable adaptations are made for implementation in climate GCMs. This method entails the generation of short-range weather forecasts by realistically initialized climate GCM, and the application of six-hourly NWP analyses and observations of parameterized variables to evaluate these forecasts. The behavior of the parameterizations in such a weather-forecasting framework can provide insights on how these schemes might be improved, and modified parameterizations then can be similarly tested. In order to further this method for evaluating and analyzing parameterizations in climate GCMs, the USDOE is funding a joint venture of its Climate Change Prediction Program (CCPP) and Atmospheric Radiation Measurement (ARM) Program: the CCPP-ARM Parameterization Testbed (CAPT). This article elaborates the scientific rationale for CAPT, discusses technical aspects of its methodology, and presents examples of its implementation in a representative climate GCM. Numerical weather prediction methods show promise for improving parameterizations in climate GCMs.
Improved parameterization for the vertical flux of dust aerosols emitted by an eroding soil
Technology Transfer Automated Retrieval System (TEKTRAN)
The representation of the dust cycle in atmospheric circulation models hinges on an accurate parameterization of the vertical dust flux at emission. However, existing parameterizations of the vertical dust flux vary substantially in their scaling with wind friction velocity, require input parameters...
Parameterization of spectral distributions for pion and kaon production in proton-proton collisions
NASA Technical Reports Server (NTRS)
Schneider, John P.; Norbury, John W.; Cucinotta, Frank A.
1995-01-01
Accurate semi-empirical parameterizations of the energy-differential cross sections for charged pion and kaon production from proton-proton collisions are presented at energies relevant to cosmic rays. The parameterizations depend on the outgoing meson momentum and also the proton energy, and are able to be reduced to very simple analytical formulas suitable for cosmic-ray transport.
Impact of Apex Model parameterization strategy on estimated benefit of conservation practices
Technology Transfer Automated Retrieval System (TEKTRAN)
Three parameterized Agriculture Policy Environmental eXtender (APEX) models for corn-soybean rotation on clay pan soils were developed with the objectives, 1. Evaluate model performance of three parameterization strategies on a validation watershed; and 2. Compare predictions of water quality benefi...