Tidal downwelling and implications for the carbon biogeochemistry of cold-water corals in relation to future ocean acidification and warming.

PubMed

Findlay, Helen S; Artioli, Yuri; Moreno Navas, Juan; Hennige, Sebastian J; Wicks, Laura C; Huvenne, Veerle A I; Woodward, E Malcolm S; Roberts, J Murray

2013-09-01

Cold-water coral (CWC) reefs are recognized as ecologically and biologically significant areas that generate habitats and diversity. The interaction between hydrodynamics and CWCs has been well studied at the Mingulay Reef Complex, a relatively shallow area of reefs found on the continental shelf off Scotland, UK. Within 'Mingulay Area 01' a rapid tidal downwelling of surface waters, brought about as an internal wave, is known to supply warmer, phytoplankton-rich waters to corals growing on the northern flank of an east-west trending seabed ridge. This study shows that this tidal downwelling also causes short-term perturbations in the inorganic carbon (CT ) and nutrient dynamics through the water column and immediately above the reef. Over a 14 h period, corresponding to one semi-diurnal tidal cycle, seawater pH overlying the reef varied by ca. 0.1 pH unit, while pCO2 shifted by >60 μatm, a shift equivalent to a ca. 25 year jump into the future, with respect to atmospheric pCO2 . During the summer stratified period, these downwelling events result in the reef being washed over with surface water that has higher pH, is warmer, nutrient depleted, but rich in phytoplankton-derived particles compared to the deeper waters in which the corals sit. Empirical observations, together with outputs from the European Regional Shelf Sea Ecosystem Model, demonstrate that the variability that the CWC reefs experience changes through the seasons and into the future. Hence, as ocean acidification and warming increase into the future, the downwelling event specific to this site could provide short-term amelioration of corrosive conditions at certain times of the year; however, it could additionally result in enhanced detrimental impacts of warming on CWCs. Natural variability in the CT and nutrient conditions, as well as local hydrodynamic regimes, must be accounted for in any future predictions concerning the responses of marine ecosystems to climate change. © 2013 John Wiley & Sons Ltd.

Plate Like Convection with Viscous Strain Weakening and Corresponding Surface Deformation Pattern

NASA Astrophysics Data System (ADS)

Fuchs, L.; Becker, T. W.

2017-12-01

How plate tectonic surface motions are generated by mantle convection on Earth and possibly other terrestrial type planets has recently become more readily accessible with fully dynamic convection computations. However, it remains debated how plate-like the behavior in such models truly is, and in particular how the well plate boundary dynamics are captured in models which typically exclude the effects of deformation history and memory. Here, we analyze some of the effects of viscous strain weakening on plate behavior and the interactions between interior convection dynamics and surface deformation patterns. We use the finite element code CitcomCU to model convection in a 3D Cartesian model setup. The models are internally heated, with an Arrhenius-type temperature dependent viscosity including plastic yielding and viscous strain weakening (VSW) and healing (VSWH). VSW can mimic first order features of more complex damage mechanisms such as grain-size dependent rheology. Besides plate diagnostic parameters (Plateness, Mobility, and Toroidal: Poloidal ratio) to analyze the tectonic behavior our models, we also explore how "plate boundaries" link to convective patterns. In a first model series, we analyze general surface deformation patterns without VSW. In the early stages, deformation patterns are clearly co-located with up- and downwelling limbs of convection. Along downwellings strain-rates are high and localized, whereas upwellings tend to lead to broad zones of high deformation. At a more advanced stage, however, the plates' interior is highly deformed due to continuous strain accumulation and resurfaced inherited strain. Including only VSW leads to more localized deformation along downwellings. However, at a more advanced stage plate-like convection fails due an overall weakening of the material. This is prevented including strain healing. Deformation pattern at the surface more closely coincide with the internal convection patterns. The average surface deformation is reduced significantly and mainly governed by the location of the up- and downwellings. VSWH thereby affects plate dynamics due to two main properties: the intensity of weakening with increasing strain and the strain healing rate. As both increase, mobility increases as well and strain becomes more localized at the downwellings.

Upwelling and downwelling induced by mesoscale circulation in the DeSoto Canyon region

NASA Astrophysics Data System (ADS)

Nguyen, T. T.; Chassignet, E.; Morey, S. L.; Dukhovskoy, D. S.

2014-12-01

Ocean dynamics are complex over irregular topography areas, and the northeastern Gulf of Mexico, specifically the DeSoto Canyon region, is a challenge for modelers and oceanographers. Vertical movement of waters, especially upwelling, is observed to take place over the canyon's head and along the coast; however, it is not well understood. We focus on upwelling/downwelling processes induced by the Loop Current and its associated eddy field using multi-decadal Hybrid Coordinate Ocean Model simulations. The Loop Current, part of the Gulf Stream, can develop northward into the Gulf through the Yucatan Channel and exit through the Florida Straits. It can reach the continental slope of the study domain and directly depress the isopycnals. Cyclonic eddies in front of the Loop Current also induce upwelling underneath. On the other hand, the Loop Current sometimes impinges on the West Florida Shelf and generates a high pressure disturbance, which travels northward along the shelf into the study region. Consequently, large-scale downwelling occurs across the continental slopes. Our analysis of sea surface height shows that the Loop Current pressure disturbance tends to propagate along the shallow isobaths of 100 to 300 m in the topographic wave direction from south of the West Florida Shelf to the Mississippi Delta. In addition, after shedding a large anticyclonic eddy, the Loop Current retracts southward and can touch the southeastern corner of the West Florida Shelf. This can result in a higher pressure disturbance, and therefore stronger large-scale downwelling in the DeSoto Canyon region.

Effects of fine sediment, hyporheic flow, and spawning site characteristics on survival and development of bull trout embryos

USGS Publications Warehouse

Bowerman, Tracy; Neilson, Bethany; Budy, Phaedra

2014-01-01

Successful spawning is imperative for the persistence of salmonid populations, but relatively little research has been conducted to evaluate factors affecting early life-stage survival for bull trout (Salvelinus confluentus), a threatened char. We conducted a field experiment to assess the relationship between site-specific environmental factors and bull trout embryo survival and fry emergence timing. Survival from egg to hatch was negatively related to percent fine sediment (<1 mm) in the redd and positively related to the strength of downwelling at spawning sites. Survival of eggs to fry emergence was also negatively related to fine sediment, and the best statistical models included additional variables that described the rate of downwelling and intragravel flow within the incubation environment. Fry emerged at an earlier stage in development from redds with high percentages of fine sediment. Increased hydraulic conductivity via redd construction and selection of spawning sites with strong downwelling appear to enhance hyporheic flow rates and bull trout egg survival, but early life-stage success may ultimately be limited by intrusion of fine sediment into the incubation environment.

Incubation success and habitat selection of shore-spawning kokanee Onchorhynchus nerka: effects of water level regulation and habitat characteristics.

USGS Publications Warehouse

Whitlock, Steven L.; Quist, Michael C.; Dux, Andrew M.

2014-01-01

Changes to water-level regimes have been known to restructure fish assemblages and interfere with the population dynamics of both littoral and pelagic species. The effect of altered water-level regimes on shore-spawning kokanee Oncorhynchus nerka incubation success was evaluated using a comprehensive in situ study in Lake Pend Oreille, ID, USA. Survival was not related to substrate size composition or depth, indicating that shore-spawning kokanee do not currently receive a substrate-mediated survival benefit from higher winter water levels. Substrate composition also did not differ among isobaths in the nearshore area. On average, the odds of an egg surviving to the preemergent stage were more than three times greater for sites in downwelling areas than those lacking downwelling. This study revealed that shoreline spawning habitat is not as limited as previously thought. Downwelling areas appear to contribute substantially to shore-spawning kokanee recruitment. This research illustrates the value of rigorous in situ studies both for testing potential mechanisms underlying population trends and providing insight into spawning habitat selection.

BOREAS AFM-1 NOAA/ATDD Long-EZ Aircraft Flux data Over the SSA

NASA Technical Reports Server (NTRS)

Crawford, Timothy L.; Baldocchi, Dennis; Hall, Forrest G. (Editor); Knapp, David E. (Editor); Gunter, Laureen; Dumas, Ed; Smith, David E. (Technical Monitor)

2000-01-01

This data set contains measurements from the Airborne Flux and Meteorology (AFM)-1 National Oceanographic and Atmospheric Administration/Atmospheric Turbulence and Diffusion Division (NOAA/ATDD) Long-EZ Aircraft collected during the 1994 Intensive Field Campaigns (IFCs) at the southern study area (SSA). These measurements were made from various instruments mounted on the aircraft. The data that were collected include aircraft altitude, wind direction, wind speed, air temperature, potential temperature, water mixing ratio, U and V components of wind velocity, static pressure, surface radiative temperature, downwelling and upwelling total radiation, downwelling and upwelling longwave radiation, net radiation, downwelling and upwelling photosynthectically active radiation (PAR), greenness index, CO2 concentration, O3 concentration, and CH4 concentration. There are also various columns that indicate the standard deviation, skewness, kurtosis, and trend of some of these data. The data are stored in tabular ASCII files. The NOAA/ATDD Long-EZ aircraft flux data are available from the Earth Observing System Data and Information System (EOSDIS) Oak Ridge National Laboratory (ORNL) Distributed Active Archive Center (DAAC). The data files are available on a CD-ROM (see document number 20010000884).

Nauru Island Effect Detection Data Set

DOE Data Explorer

Long, Chuck

2010-07-15

During Nauru99 it was noted that the island was producing small clouds that advected over the ARM site. The Nauru Island Effect Study was run for 1.5 years and the methodology developed to detect the occurrence. Nauru ACRF downwelling SW, wind direction, and air temperature data are used, along with downwelling SW data from Licor radiometers located on the southern end of the island near the airport landing strip. A statistical analysis and comparison of data from the two locations is used to detect the likely occurrence of an island influence on the Nauru ACRF site data

Morphology-flow interactions lead to stage-selective vertical transport of larval sand dollars in shear flow.

PubMed

Clay, T W; Grünbaum, D

2010-04-01

Many larvae and other plankton have complex and variable morphologies of unknown functional significance. We experimentally and theoretically investigated the functional consequences of the complex morphologies of larval sand dollars, Dendraster excentricus (Eschscholtz), for hydrodynamic interactions between swimming and turbulent water motion. Vertical shearing flows (horizontal gradients of vertical flow) tilt organisms with simple geometries (e.g. spheres, ellipsoids), causing these organisms to move horizontally towards downwelling water and compromising their abilities to swim upwards. A biomechanical model of corresponding hydrodynamic interactions between turbulence-induced shear and the morphologically complex four-, six- and eight-armed stages of sand dollar larvae suggests that the movements of larval morphologies differ quantitatively and qualitatively across stages and shear intensities: at shear levels typical of calm conditions in estuarine and coastal environments, all modeled larval stages moved upward. However, at higher shears, modeled four- and eight-armed larvae moved towards downwelling, whereas six-armed larvae moved towards upwelling. We also experimentally quantified larval movement by tracking larvae swimming in low-intensity shear while simultaneously mapping the surrounding flow fields. Four- and eight-armed larvae moved into downwelling water, but six-armed larvae did not. Both the model and experiments suggest that stage-dependent changes to larval morphology lead to differences in larval movement: four- and eight-armed stages are more prone than the six-armed stage to moving into downwelling water. Our results suggest a mechanism by which differences can arise in the vertical distribution among larval stages. The ability to mitigate or exploit hydrodynamic interactions with shear is a functional consequence that potentially shapes larval evolution and development.

Surface Measurements of Solar Spectral Radiative Flux in the Cloud-Free Atmosphere

NASA Technical Reports Server (NTRS)

Pilewskie, Peter; Goetz, A. F. H.; Bergstrom, R.; Beal, D.; Gore, Warren J. Y. (Technical Monitor)

1997-01-01

Recent studies (Charlock, et al.; Kato, et. al) have indicated a potential discrepancy between measured solar irradiance in the cloud-free atmosphere and model derived downwelling solar irradiance. These conclusions were based primarily on broadband integrated solar flux. Extinction (both absorption and scattering) phenomena, however, typically have spectral characteristics that would be present in moderate resolution (e.g., 10 nm) spectra, indicating the need for such measurements to thoroughly investigate the cause of any discrepancies. The 1996 Department of Energy Atmospheric Radiation Measurement Program (ARM) Intensive Observation Period (IOP), held simultaneously with the NASA Subsonic Aircraft: Contrail and Cloud Effects Special Study (SUCCESS) Program, provided an opportunity for two simultaneous but independent measurements of moderate resolution solar spectral downwelling irradiance at the surface. The instruments were the NASA Ames Solar Spectral Flux Radiometer and the Analytical Spectral Devices, Inc., FieldSpecT-FR. Spectral and band integrated quantities from both sets of measurements will be presented, along with estimates of the downwelling solar irradiance from band model and line by line calculations, in an effort to determine the compatibility between measured and calculated solar irradiance in the cloud-free atmosphere.

a Study of the Bioluminescence of Larger Zooplankton and the Effects of Low-Level Light Changes on Their Behavior.

NASA Astrophysics Data System (ADS)

van Keuren, Jeffrey Robert

A bio-optical study was undertaken to quantify the relationships which exist between counter-illuminating organisms and the downwelling spectral light field in which they exist. The basic hypothesis behind counter-illumination is that the animal emits light using ventrally-oriented photophores to disrupt or eliminate the shadowed area on ventral surfaces. An organism lacking photophores sharply silhouettes against the highly directional downwelling irradiance, whereas by distributing photophores over the ventral surface of the body and closely matching the spectral and intensity characteristics of the downwelling light, this silhouette is obscured. Analysis carried out on changes in vertical distribution patterns in response to low-level intensity changes in ambient surface light suggested that diel migrating organisms begin to shift vertically in the water column when surface scalar irradiance decreased below or increased above 1.0 times10^{-2} muEin m^{-2} sec^ {-1}. Maximum aggregations of organisms, as defined by MOCNESS net sampling or single-frequency acoustic backscatter, appeared to remain within definable in situ blue-green isolume ranges varying less than a factor of ten throughout each night. Comparisons made between organism counter-illumination capacity and modeled in situ downwelling irradiance levels suggested that euphausiids, decapods and myctophids use between 1-10 percent of their maximum counter-illumination capacity to match the ambient downwelling light conditions. Modeling also suggested that up to 40 percent of the maximum measured bioluminescence output is required to match ambient irradiance in the shallower surface zones where aggregations of copepods, potential food sources, were commonly found at night. An optical study to quantify the radiative transfer of bioluminescence from a point source revealed that non -isotropic point sources produce radiance patterns that cannot be simply explained by inverse square losses. Therefore simple inverse-square estimates of bioluminescent propagation loss rates from organisms in the ocean are an oversimplification of the radiative transfer processes that occur when these emissions occur. Additionally, in evaluating counter-illumination, the distance of the receptor, such as the eyes of a potential predator, is critical in determining the effectiveness of the organisms in matching the uniform light field of their surrounding environment and ultimately avoiding detection and predation.

Time Evolution of the Mantle Thermal Structure in the African Hemisphere Before and After the Formation of Pangea

NASA Astrophysics Data System (ADS)

Zhang, N.; Zhong, S.

2008-12-01

The present-day mantle structure is characterized by the African and Pacific superplumes surrounded by subduction slabs. This structure has been demonstrated to result from dynamic interaction between mantle convection and surface plate motion history in the last 120 Ma. With similar techniques, mantle structure has been constructed back to about 100 Ma ago. However, due to the lack in global plate motion reconstructions further back in time, mantle structure for earlier times is poorly understood, despite of their importance in understanding the continental tectonics and volcanisms. Zhong et al. (2007) suggested that the mantle structures alternate between spherical harmonic degrees-1 and -2 structures, modulated by supercontinent processes. In their model, a supercontinent forms in the hemisphere with cold downwellings, and after supercontinent formation, the cold downwellings are replaced with hot upwellings due to return flows associated with circum-supercontinent subduction. This model implies that the African superplume is younger than 330 Ma when Pangea was formed, which is supported by volcanic activities recorded on continents around Pangea time. By using paleomagnetic-geologically reconstructed continental motions between 500 and 200 Ma in a three-dimensional spherical models of mantle convection, this study, for the first time, investigates the time evolution of mantle structures in the African hemisphere associated with Pangea formation. We show that cold downwellings first develop in the mantle between the colliding Laurentia and Gondwana, and that the downwellings are then replaced by upwellings after the formation of Pangea and as circum-Pangea subduction is initiated, consistent with Zhong et al. (2007) and Li et al. (2008). We find that the return flows in response to the circum-Pangea subduction are responsible for the upwellings below Pangea. We also find that even if the mantle in the African hemisphere is initially occupied by hot upwellings, the cold downwellings associated with convergence between Laurentia and Gondwana would destroy the hot upwellings and cause the hemisphere to be cold. These results are insensitive to model parameters such as convective vigor, internal heating rate, and the plate motions in the oceanic hemisphere. We therefore suggest that the African superplume is younger than 330 Ma when Pangea was formed.

African hot spot volcanism: small-scale convection in the upper mantle beneath cratons.

PubMed

King, S D; Ritsema, J

2000-11-10

Numerical models demonstrate that small-scale convection develops in the upper mantle beneath the transition of thick cratonic lithosphere and thin oceanic lithosphere. These models explain the location and geochemical characteristics of intraplate volcanos on the African and South American plates. They also explain the presence of relatively high seismic shear wave velocities (cold downwellings) in the mantle transition zone beneath the western margin of African cratons and the eastern margin of South American cratons. Small-scale, edge-driven convection is an alternative to plumes for explaining intraplate African and South American hot spot volcanism, and small-scale convection is consistent with mantle downwellings beneath the African and South American lithosphere.

The Discrepancy Between Measured and Modeled Downwelling Solar Irradiance at the Ground: Dependence on Water Vapor

NASA Technical Reports Server (NTRS)

Pilewski, P.; Rabbette, M.; Bergstrom, R.; Marquez, J.; Schmid, B.; Russell, P. B.

2000-01-01

Moderate resolution spectra of the downwelling solar irradiance at the ground in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under-cloud-free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model-measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 Wm per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.

The Discrepancy Between Measured and Modeled Downwelling Solar Irradiance at the Ground: Dependence on Water Vapor

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Rabbette, M.; Bergstrom, R.; Marquez, J.; Schmid, B.; Russell, P. B.

2000-01-01

Moderate resolution spectra of the downwelling solar irradiance at the ground in north central Oklahoma were measured during the Department of Energy Atmospheric Radiation Measurement Program Intensive Observation Period in the fall of 1997. Spectra obtained under cloud-free conditions were compared with calculations using a coarse resolution radiative transfer model to examine the dependency of model-measurement bias on water vapor. It was found that the bias was highly correlated with water vapor and increased at a rate of 9 Wm(exp -2) per cm of water. The source of the discrepancy remains undetermined because of the complex dependencies of other variables, most notably aerosol optical depth, on water vapor.

How well-connected is the surface of the global ocean?

PubMed

Froyland, Gary; Stuart, Robyn M; van Sebille, Erik

2014-09-01

The Ekman dynamics of the ocean surface circulation is known to contain attracting regions such as the great oceanic gyres and the associated garbage patches. Less well-known are the extents of the basins of attractions of these regions and how strongly attracting they are. Understanding the shape and extent of the basins of attraction sheds light on the question of the strength of connectivity of different regions of the ocean, which helps in understanding the flow of buoyant material like plastic litter. Using short flow time trajectory data from a global ocean model, we create a Markov chain model of the surface ocean dynamics. The surface ocean is not a conservative dynamical system as water in the ocean follows three-dimensional pathways, with upwelling and downwelling in certain regions. Using our Markov chain model, we easily compute net surface upwelling and downwelling, and verify that it matches observed patterns of upwelling and downwelling in the real ocean. We analyze the Markov chain to determine multiple attracting regions. Finally, using an eigenvector approach, we (i) identify the five major ocean garbage patches, (ii) partition the ocean into basins of attraction for each of the garbage patches, and (iii) partition the ocean into regions that demonstrate transient dynamics modulo the attracting garbage patches.

Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors.

PubMed

Croze, Ottavio A; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A; Brandt, Luca

2013-04-06

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design.

Dispersion of swimming algae in laminar and turbulent channel flows: consequences for photobioreactors

PubMed Central

Croze, Ottavio A.; Sardina, Gaetano; Ahmed, Mansoor; Bees, Martin A.; Brandt, Luca

2013-01-01

Shear flow significantly affects the transport of swimming algae in suspension. For example, viscous and gravitational torques bias bottom-heavy cells to swim towards regions of downwelling fluid (gyrotaxis). It is necessary to understand how such biases affect algal dispersion in natural and industrial flows, especially in view of growing interest in algal photobioreactors. Motivated by this, we here study the dispersion of gyrotactic algae in laminar and turbulent channel flows using direct numerical simulation (DNS) and a previously published analytical swimming dispersion theory. Time-resolved dispersion measures are evaluated as functions of the Péclet and Reynolds numbers in upwelling and downwelling flows. For laminar flows, DNS results are compared with theory using competing descriptions of biased swimming cells in shear flow. Excellent agreement is found for predictions that employ generalized Taylor dispersion. The results highlight peculiarities of gyrotactic swimmer dispersion relative to passive tracers. In laminar downwelling flow the cell distribution drifts in excess of the mean flow, increasing in magnitude with Péclet number. The cell effective axial diffusivity increases and decreases with Péclet number (for tracers it merely increases). In turbulent flows, gyrotactic effects are weaker, but discernable and manifested as non-zero drift. These results should have a significant impact on photobioreactor design. PMID:23407572

Spatial and Temporal Dynamics of Dissolved Oxygen Concentrations and Bioactivity in the Hyporheic Zone

NASA Astrophysics Data System (ADS)

Reeder, W. Jeffery; Quick, Annika M.; Farrell, Tiffany B.; Benner, Shawn G.; Feris, Kevin P.; Tonina, Daniele

2018-03-01

Dissolved oxygen (DO) concentrations and consumption rates are primary indicators of heterotrophic respiration and redox conditions in the hyporheic zone (HZ). Due to the complexity of hyporheic flow and interactions between hyporheic hydraulics and the biogeochemical processes, a detailed, mechanistic, and predictive understanding of the biogeochemical activity in the HZ has not yet been developed. Previous studies of microbial activity in the HZ have treated the metabolic DO consumption rate constant (KDO) as a temporally fixed and spatially homogeneous property that is determined primarily by the concentration of bioavailable carbon. These studies have generally treated bioactivity as temporally steady state, failing to capture the temporal dynamics of a changeable system. We demonstrate that hyporheic hydraulics controls rate constants in a hyporheic system that is relatively abundant in bioavailable carbon, such that KDO is a linear function of the local downwelling flux. We further demonstrate that, for triangular dunes, the downwelling velocities are lognormally distributed, as are the KDO values. By comparing measured and modeled DO profiles, we demonstrate that treating KDO as a function of the downwelling flux yields a significant improvement in the accuracy of predicted DO profiles. Additionally, our results demonstrate the temporal effect of carbon consumption on microbial respiration rates.

The formation processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean

NASA Astrophysics Data System (ADS)

Chang, Yu-Lin; Miyazawa, Yasumasa; Oey, Lie-Yauw; Kodaira, Tsubasa; Huang, Shihming

2017-05-01

In this study, we investigate the processes of phytoplankton growth and decline in mesoscale eddies in the western North Pacific Ocean based on the in situ chlorophyll data obtained from 52 cruises conducted by the Japan Meteorological Agency together with idealized numerical simulations. Both the observation and model results suggest that chlorophyll/phytoplankton concentrations are higher in cold than in warm eddies in near-surface water (z > -70 m). In the idealized simulation, the isopycnal movements associated with upwelling/downwelling transport phytoplankton and nutrients to different vertical depths during eddy formation (stage A). Phytoplankton and nutrients in cold eddies is transported toward shallower waters while those in warm eddies move toward deeper waters. In the period after the eddy has formed (stage B), sunlight and initially upwelled nutrients together promote the growth of phytoplankton in cold eddies. Phytoplankton in warm eddies decays due to insufficient sunlight in deeper waters. In stage B, upwelling and downwelling coexist in both warm and cold eddies, contributing nearly equally to vertical displacement. The upwelling/downwelling-induced nitrate flux accounts for a small percentage (˜3%) of the total nitrate flux in stage B. The vertical velocity caused by propagating eddies, therefore, is not the primary factor causing differences in phytoplankton concentrations between stage-B warm and cold eddies.

Surface distribution of brachyuran megalopae and ichthyoplankton in the Columbia River plume during transition from downwelling to upwelling conditions

NASA Astrophysics Data System (ADS)

Roegner, G. Curtis; Daly, Elizabeth A.; Brodeur, Richard D.

2013-06-01

In the California Current coastal boundary zone, the spring transition between downwelling and upwelling conditions, along with the fluctuating structure of the Columbia River plume, creates highly dynamic interactions. In this study, we investigated whether the surface distribution of brachyuran larvae and ichthyoplankton would track the dynamics of the Columbia River plume. By happenstance, the cruise period coincided with the spring transition from downwelling to sustained upwelling conditions in 2010, a year when the transition was delayed and Columbia River flow was substantially higher than average. We used time series of wind and freshwater input to evaluate the influence of physical forcing on oceanographic patterns, and sampled hydrography and surface plankton concentrations within a 182 km2 grid off Willapa Bay, WA. Additionally, two longer transects, one cross-shelf and the other along-shore, were made to discern the extent of plume influence on larval crab and fish abundance. We found that plume waters that were trapped in a northward-flowing coastal-boundary current during downwelling conditions were advected offshore after several days of upwelling-favorable winds. Neustonic collections of brachyuran larvae and ichthyoplankton varied in response to this large seaward advective event. Megalopae of cancrid crabs exhibited patterns of both offshore transport (Cancer oregonensis/productus) and nearshore retention (C. magister). Additionally, abundant numbers of large juvenile widow (Sebastes entomelas) and yellowtail (S. flavidus) rockfish of a size appropriate for settlement were sampled during a period when ocean conditions favored high recruitment success. These results demonstrated that the response of planktonic crab larvae and ichthyoplankton to large-scale advection varied by species, with larger and more vagile fish exhibiting less evidence of passive transport than smaller crab larvae. Importantly, portions of the planktonic fish and crab community were able to maintain nearshore distributions in favorable settlement habitat, despite physical advection offshore.

The Impact of Changing Cloud Cover on the High Arctic's Primary Cooling-to-space Windows

NASA Astrophysics Data System (ADS)

Mariani, Zen; Rowe, Penny; Strong, Kimberly; Walden, Von; Drummond, James

2014-05-01

In the Arctic, most of the infrared energy emitted by the surface escapes to space in two atmospheric windows at 10 and 20 μm. As the Arctic warms, the 20 μm cooling-to-space window becomes increasingly opaque (or "closed"), trapping more surface infrared radiation in the atmosphere, with implications for the Arctic's radiative energy balance. Since 2006, the Canadian Network for the Detection of Atmospheric Change (CANDAC) has measured downwelling infrared radiance with an Atmospheric Emitted Radiance Interferometer (AERI) at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Canada, providing the first long-term measurements of the 10 and 20 μm windows in the high Arctic. In this work, measurements of the distribution of downwelling 10 and 20 µm brightness temperatures at Eureka are separated based on cloud cover, providing a comparison to an existing climatology from the Southern Great Plains (SGP). Measurements of the downwelling radiance at both 10 and 20 μm exhibit strong seasonal variability as a result of changes in temperature and water vapour, in addition to variability with cloud cover. When separated by season, brightness temperatures in the 20 µm window are found to be independent of cloud thickness in the summertime, indicating that this window is closed in the summer. Radiance trends in three-month averages are positive and are significantly larger (factor > 5) than the trends detected at the SGP, indicating that changes in the downwelling radiance are accelerated in the high Arctic compared to lower latitudes. This statistically significant increase (> 5% / yr) in radiance at 10 μm occurs only when the 20 μm window is mostly transparent, or "open" (i.e., in all seasons except summer), and may have long-term consequences, particularly as warmer temperatures and increased water vapour "close" the dirty window for a prolonged period. These surface-based measurements of radiative forcing can be used to quantify changes in the high-Arctic energy budget and evaluate general circulation model simulations.

Nitrogen uptake of phytoplankton assemblages under contrasting upwelling and downwelling conditions: The Ría de Vigo, NW Iberia

NASA Astrophysics Data System (ADS)

Seeyave, Sophie; Probyn, Trevor; Álvarez-Salgado, Xosé Antón; Figueiras, Francisco G.; Purdie, Duncan A.; Barton, Eric D.; Lucas, Michael

2013-06-01

Regenerated production (including organic nitrogen) is shown here to be important in the Ría de Vigo (Galicia, NW Iberia) in supporting both harmful algal bloom communities during the downwelling season, but also (to a lesser extent) diatom communities during stratified periods of weak to moderate upwelling. The Galician Rías, situated in the Iberian upwelling system, are regularly affected by blooms of toxic dinoflagellates, which pose serious threats to the local mussel farming industry. These tend to occur towards the end of summer, during the transition from upwelling to downwelling favourable seasons, when cold bottom shelf waters in the rías are replaced by warm surface shelf waters. Nitrate, ammonium and urea uptake rates were measured in the Ría de Vigo during a downwelling event in September 2006 and during an upwelling event in June 2007. In September the ría was well mixed, with a downwelling front observed towards the middle of the ría and relatively high nutrient concentrations (1.0-2.6 μmol L-1 nitrate; 1.0-5.6 μmol L-1 ammonium; 0.1-0.8 μmol L-1 phosphate; 2.0-9.0 μmol L-1 silicic acid) were present throughout the water column. Ammonium represented more than 80% of the nitrogenous nutrients, and the phytoplankton assemblage was dominated by dinoflagellates and small flagellates. In June the water column was stratified, with nutrient-rich, upwelled water below the thermocline and warm, nutrient-depleted water in the surface. At this time, nitrate represented more than 80% of the nitrogenous nutrients, and a mixed diatom assemblage was present. Primary phytoplankton production during both events was mainly sustained by regenerated nitrogen, with ammonium uptake rates of 0.035-0.063 μmol N L-1 h-1 in September and 0.078-0.188 μmol N L-1 h-1 in June. Although f-ratios were generally low (<0.2) in both June and September, a maximum of 0.61 was reached in June due to higher nitrate uptake (0.225 μmol N L-1 h-1). Total nitrogen uptake was also higher during the upwelling event (0.153-0.366 in June and 0.053-0.096 μmol N L-1 h-1 in September). Nitrogen uptake kinetics demonstrated a strong preference for ammonium and urea over nitrate in June.

Cloud cover classification through simultaneous ground-based measurements of solar and infrared radiation

NASA Astrophysics Data System (ADS)

Orsini, Antonio; Tomasi, Claudio; Calzolari, Francescopiero; Nardino, Marianna; Cacciari, Alessandra; Georgiadis, Teodoro

2002-04-01

Simultaneous measurements of downwelling short-wave solar irradiance and incoming total radiation flux were performed at the Reeves Nevè glacier station (1200 m MSL) in Antarctica on 41 days from late November 1994 to early January 1995, employing the upward sensors of an albedometer and a pyrradiometer. The downwelling short-wave radiation measurements were analysed following the Duchon and O'Malley [J. Appl. Meteorol. 38 (1999) 132] procedure for classifying clouds, using the 50-min running mean values of standard deviation and the ratio of scaled observed to scaled clear-sky irradiance. Comparing these measurements with the Duchon and O'Malley rectangular boundaries and the local human observations of clouds collected on 17 days of the campaign, we found that the Duchon and O'Malley classification method obtained a success rate of 93% for cirrus and only 25% for cumulus. New decision criteria were established for some polar cloud classes providing success rates of 94% for cirrus, 67% for cirrostratus and altostratus, and 33% for cumulus and altocumulus. The ratios of the downwelling short-wave irradiance measured for cloudy-sky conditions to that calculated for clear-sky conditions were analysed in terms of the Kasten and Czeplak [Sol. Energy 24 (1980) 177] formula together with simultaneous human observations of cloudiness, to determine the empirical relationship curves providing reliable estimates of cloudiness for each of the three above-mentioned cloud classes. Using these cloudiness estimates, the downwelling long-wave radiation measurements (obtained as differences between the downward fluxes of total and short-wave radiation) were examined to evaluate the downwelling long-wave radiation flux normalised to totally overcast sky conditions. Calculations of the long-wave radiation flux were performed with the MODTRAN 3.7 code [Kneizys, F.X., Abreu, L.W., Anderson, G.P., Chetwynd, J.H., Shettle, E.P., Berk, A., Bernstein, L.S., Robertson, D.C., Acharya, P., Rothman, L.S., Selby, J.E.A., Gallery, W.O., Clough, S.A., 1996. In: Abreu, L.W., Anderson, G.P. (Eds.), The MODTRAN 2/3 Report and LOWTRAN 7 MODEL. Contract F19628-91-C.0132, Phillips Laboratory, Geophysics Directorate, PL/GPOS, Hanscom AFB, MA, 261 pp.] for both clear-sky and cloudy-sky conditions, considering various cloud types characterised by different cloud base altitudes and vertical thicknesses. From these evaluations, best-fit curves of the downwelling long-wave radiation flux were defined as a function of the cloud base height for the three polar cloud classes. Using these relationship curves, average estimates of the cloud base height were obtained from the three corresponding sub-sets of long-wave radiation measurements. The relative frequency histograms of the cloud base height defined by examining these three sub-sets were found to present median values of 4.7, 1.7 and 3.6 km for cirrus, cirrostratus/altostratus and cumulus/altocumulus, respectively, while median values of 6.5, 1.8 and 2.9 km were correspondingly determined by analysing only the measurements taken together with simultaneous cloud observations.

Impact of cirrus on the surface radiative environment at the FIRE ETLA Palisades, NY site

NASA Technical Reports Server (NTRS)

Robinson, David A.; Kukla, George; Frei, Allan

1990-01-01

FIRE Extended Time Limited Area (ETLA) observations provide year round information critical to gaining a better understanding of cloud/climate interactions. The Lamont/Rutgers team has participated in the ETLS program through the collection and analysis of shortwave and longwave downwelling irradiances at Palisades, NY. These data are providing useful information on surface radiative fluxes with respect to sky condition, solar zenith angle and season. Their utility extends to the calibration and validation of cloud/radiative models and satellite cloud and radiative retrievals. The impact cirrus clouds have on the surface radiative environment is examined using Palisades ETLA information on atmospheric transmissivities and downwelling longwave fluxes for winter and summer cirrus and clear sky episodes in 1987.

Solar Spectral Radiative Forcing Due to Dust Aerosol During the Puerto Rico Dust Experiment

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Bergstrom, R.; Rabbette, M.; Livingston, J.; Russell, P.; Gore, Warren J. (Technical Monitor)

2000-01-01

During the Puerto Rico Dust Experiment (PRIDE) upwelling and downwelling solar spectral irradiance was measured on board the SPAWAR Navajo and downwelling solar spectral flux was measured at a surface site using the NASA Ames Solar Spectral Flux Radiometer. These data will be used to determine the net solar radiative forcing of dust aerosol and to quantify the solar spectral radiative energy budget in the presence of elevated aerosol loading. We will assess the variability in spectral irradiance using formal principal component analysis procedures and relate the radiative variability to aerosol microphysical properties. Finally, we will characterize the sea surface reflectance to improve aerosol optical depth retrievals from the AVHRR satellite and to validate SeaWiFS ocean color products.

The effects of downwelling radiance on MER surface spectra: the evil that atmospheres do

NASA Astrophysics Data System (ADS)

Wolff, M.; Ghosh, A.; Arvidson, R.; Christensen, P.; Guinness, E.; Ruff, S.; Seelos, F.; Smith, M.; Athena Science

2004-11-01

While it may not be surprising to some that downwelling radiation in the martian atmosphere may contribute a non-negligible fraction of the radiance for a given surface scene, others remain shocked and surprised (and often dismayed) to discover this fact; particularly with regard to mini-TES observations. Naturally, the relative amplitude of this sky ``contamination'' is often a complicated function of meteorological conditions, viewing geometry, surface properties, and (for the IR) surface temperature. Ideally, one would use a specialized observations to mimic the actual hemispherical-directional nature of the problem. Despite repeated attempts to obtain Pancam complete sky observations and mini-TES sky octants, such observations are not available in the MER observational database. As a result, one is left with the less-enviable, though certainly more computationally intensive, task of connecting point observations (radiance and derived meteorological parameters) to a hemispherical integral of downwelling radiance. Naturally, one must turn to a radiative transfer analysis, despite oft-repeated attempts to assert otherwise. In our presentation, we offer insight into the conditions under which one must worry about atmospheric removal, as well as semi-empirical approaches (based upon said radiative transfer efforts) for producing the correction factors from the available MER atmospheric observations. This work is proudly supported by the MER program through NASA/JPL Contract No. 1242889 (MJW), as well as the contracts for the co-authors.

FIRE_ACE_C130_RAMS

Atmospheric Science Data Center

2017-04-26

... NCAR C-130 Instrument:  Radiation Measurement System Spatial Coverage:  Fairbanks, Alaska and the ... Parameters:  Upwelling and Downwelling Total Solar Flux Infrared Flux and Narrowband Flux Order Data:  ...

Geothermal down well pumping system

NASA Technical Reports Server (NTRS)

Matthews, H. B.; Mcbee, W. D.

1974-01-01

A key technical problem in the exploitation of hot water geothermal energy resources is down-well pumping to inhibit mineral precipitation, improve thermal efficiency, and enhance flow. A novel approach to this problem involves the use of a small fraction of the thermal energy of the well water to boil and super-heat a clean feedwater flow in a down-hole exchanger adjacent to the pump. This steam powers a high-speed turbine-driven pump. The exhaust steam is brought to the surface through an exhaust pipe, condensed, and recirculated. A small fraction of the high-pressure clean feedwater is diverted to lubricate the turbine pump bearings and prevent leakage of brine into the turbine-pump unit. A project demonstrating the feasibility of this approach by means of both laboratory and down-well tests is discussed.

An analytical two-flow model to simulate the distribution of irradiance in coastal waters with a wind-roughed surface and bottom reflectance

NASA Astrophysics Data System (ADS)

Ma, Wei-Ming

1997-06-01

An analytical two-flow model is derived from the radiative transfer equation to simulate the distribution of irradiance in coastal waters with a wind-roughed surface and bottom reflectance. The model utilizes unique boundary conditions, including the surface slope of the downwelling and upwelling irradiance as well as the influence of wind and bottom reflectance on simulated surface reflectance. The developed model provides a simple mathematical concept for understanding the irradiant light flux and associated processes in coastal or fresh water as well as turbid estuarine waters. The model is applied to data from the Banana River and coastal Atlantic Ocean water off the east coast of central Florida, USA. The two-flow irradiance model is capable of simulating realistic above-surface reflectance signatures under wind-roughened air-water surface given realistic input parameters including a specular flux conversion coefficient, absorption coefficient, backscattering coefficient, atmospheric visibility, bottom reflectance, and water depth. The root-mean-squared error of the calculated above-surface reflectances is approximately 3% in the Banana River and is less than 15% in coastal Atlantic Ocean off the east of Florida. Result of the subsurface reflectance sensitivity analysis indicates that the specular conversion coefficient is the most sensitive parameter in the model, followed by the beam attenuation coefficient, absorption coefficient, water depth, backscattering coefficient, specular irradiance, diffuse irradiance, bottom reflectance, and wind speed. On the other hand, result of the above-surface reflectance sensitivity analysis indicates that the wind speed is the most important parameter, followed by bottom reflectance, attenuation coefficient, water depth, conversion coefficient, specular irradiance, downwelling irradiance, absorption coefficient, and backscattering coefficient. Model results depend on the accuracy of these parameters to a large degree and more important the water depth and value of the bottom reflectance. The results of this work indicates little change of subsurface or in-water reflectances, due to variations of wind speed and observation angle. Simulations of the wind effect on the total downwelling irradiance from the two- flow model indicates that the total downwelling irradiance just below a wind-roughened water surface increases to about 1% of the total downwelling irradiance on a calm water surface when the sun is near zenith and increases to about 3% when the sun is near the horizon. This analytically based model, solved or developed utilizing the unique boundary conditions, can be applied to remote sensing of oceanic upper mixed layer dynamics, plant canopies, primary production, and shallow water environments with different bottom type reflectances. Future applications may include determining effects of sediment resuspension of bottom sediments in the bottom boundary layer on remotely sensed data.

The Design and Analysis of Salmonid Tagging Studies in the Columbia Basin : Volume XVII : Effects of Ocean Covariates and Release Timing on First Ocean-Year Survival of Fall Chinook Salmon from Oregon and Washington Coastal Hatcheries.

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

Burgess, Caitlin; Skalski, John R.

2001-05-01

Effects of oceanographic conditions, as well as effects of release-timing and release-size, on first ocean-year survival of subyearling fall chinook salmon were investigated by analyzing CWT release and recovery data from Oregon and Washington coastal hatcheries. Age-class strength was estimated using a multinomial probability likelihood which estimated first-year survival as a proportional hazards regression against ocean and release covariates. Weight-at-release and release-month were found to significantly effect first year survival (p < 0.05) and ocean effects were therefore estimated after adjusting for weight-at-release. Negative survival trend was modeled for sea surface temperature (SST) during 11 months of the year overmore » the study period (1970-1992). Statistically significant negative survival trends (p < 0.05) were found for SST during April, June, November and December. Strong pairwise correlations (r > 0.6) between SST in April/June, April/November and April/December suggest the significant relationships were due to one underlying process. At higher latitudes (45{sup o} and 48{sup o}N), summer upwelling (June-August) showed positive survival trend with survival and fall (September-November) downwelling showed positive trend with survival, indicating early fall transition improved survival. At 45{sup o} and 48{sup o}, during spring, alternating survival trends with upwelling were observed between March and May, with negative trend occurring in March and May, and positive trend with survival occurring in April. In January, two distinct scenarios of improved survival were linked to upwelling conditions, indicated by (1) a significant linear model effect (p < 0.05) showing improved survival with increasing upwelling, and (2) significant bowl-shaped curvature (p < 0.05) of survival with upwelling. The interpretation of the effects is that there was (1) significantly improved survival when downwelling conditions shifted to upwelling conditions in January (i.e., early spring transition occurred, p < 0.05), (2) improved survival during strong downwelling conditions (Bakun units < -250). Survival decreased during weak downwelling conditions (Bakun units between -180 and -100). Strong to moderately strong correlations between January upwelling and April SST (r = 0.5), June SST (r = 0.6), and the North Pacific Index (NPI) of Aleutian Low strength (r > 0.7) suggest January is a period when important effects originate and play out over ensuing months. Significant inverse trend with survival (p < 0.05) was found for Bakun indices in December, indicating strong downwelling improved survival. Higher-than-average adult return rates were observed for cohorts from brood-years 1982-1983, strong El Nino years. Individual hatcheries were found to have unique age-class strength and age-at-return characteristics.« less

Downwelling radiation at the sea surface in the central Mediterranean: one year of shortwave and longwave irradiance measurements on the Lampedusa buoy

NASA Astrophysics Data System (ADS)

di Sarra, Alcide; Bommarito, Carlo; Anello, Fabrizio; Di Iorio, Tatiana; Meloni, Daniela; Monteleone, Francesco; Pace, Giandomenico; Piacentino, Salvatore; Sferlazzo, Damiano

2017-04-01

An oceanographic buoy has been developed and deployed in August 2015 about 3.3 miles South West of the island of Lampedusa, at 35.49°N, 12.47°E, in the central Mediterranean Sea. The buoy was developed within the Italian RITMARE flagship project, and contributes to the Italian fixed-point oceanographic observation network. The buoy is an elastic beacon type and is intended to study air-sea interactions, propagation of radiation underwater, and oceanographic properties. The buoy measurements complement the atmospheric observations carried out at the long-term Station for Climate Observations on the island of Lampedusa (www.lampedusa.enea.it; 35.52°N, 12.63°E), which is located about 15 km E-NE of the buoy. Underwater instruments and part of the atmospheric sensors are presently being installed on the buoy. Measurements of downwelling shortwave, SW, and longwave, LW, irradiance, have been made since September 2015 with a Kipp and Zonen CMP21 pyranometer and a Kipp and Zonen CGR4 pyrgeometer, respectively. The radiometers are mounted on a small platform at about 7 m above sea level, on an arm protruding southward of the buoy. High time resolution data, at 1 Hz, have been acquired since December 2015, together with the sensors' attitude. Data from the period December 2015-December 2016 are analyzed and compared with measurements made on land at the Station for Climate Observations at 50 m above mean sea level. This study aims at deriving high quality determinations of the downwelling radiation over sea in the central Mediterranean. The following aspects will be discussed: - representativeness of time averaging of irradiance measurements over moving platforms; - comparison of downwelling irradiance measurements made over land and over ocean, and identification of possible correction strategies to infer irradiances over the ocean from close by measurements made over land; - influence of dome cleaning on the quality of measurements; - envisaging possible corrections strategies for varying radiometers' attitude.

Supercontinent Formation in 3-D Spherical Mantle Convection Models With Multiple Continental Blocks

NASA Astrophysics Data System (ADS)

Zhang, N.; Zhong, S.; McNamara, A.

2007-12-01

Much of the large-scale tectonics on the Earth in the last Ga is predominated by the assembly and breakup of supercontinents Rodinia and Pangea. However, the mechanism that is responsible for supercontinent formation remains poorly understood. Zhong et al [2007] recently showed that mantle convection with moderately strong lithosphere and lower mantle is characterized by a largely degree-1 planform in which one hemisphere is predominated by upwellings while the other by downwellings. They further suggested that the downwellings should attract all the continental blocks to merge in the downwelling hemisphere, thus leading to supercontinent formation there. However, Zhong et al. [2007] did not consider drifting and collision processes of continents. In this study, we explore the supercontinent formation mechanisms by including drifting and collision processes of multiple continental blocks in 3-D spherical mantle convection models. We use thermochemical CitcomS code to model 3-D spherical mantle convection with continental blocks. In our models, particles are used to represent continents and to track their motions. We found that for models with mantle viscosity (i.e., moderately strong lithosphere and lower mantle) that leads to degree-1 convection as reported in Zhong et al. [2007], initially evenly- distributed continental blocks always merge to form a supercontinent on a time-scale of about 6 transit times (i.e., corresponding to about 300 Ma). The hemisphere where a supercontinent is formed is predominated by downwellings as continents merge towards there, while the other hemisphere by upwellings. However, after the supercontinent formation, upwellings are generated beneath the supercontinent. This scenario is qualitatively consistent with what Zhong et al. [2007] proposed. We also found that while some convection models with intrinsically small-scale planforms may also lead to formation of a supercontinent, some other models may fail to produce a supercontinent. For these models with intrinsically small-scale planforms, the merged continental blocks promote long-wavelength mantle structure near the continents. However, in non-continental regions, convective wavelengths remain relatively small. We suggest that time-scales for supercontinent formation and convective wavelengths in non-continental area are important parameters that help constrain mechanisms for supercontinent formation.

Downwelling dynamics of the western Adriatic Coastal Current

NASA Astrophysics Data System (ADS)

Geyer, W. R.; Mullenbach, B. L.; Kineke, G. C.; Sherwood, C. R.; Signell, R. P.; Ogston, A. S.; Puig, P.; Traykovski, P.

2004-12-01

The western Adriatic coastal current (WACC) flows for hundreds of kilometers along the east coast of Italy at speeds of 20 to 100 cm/s. It is fed by the buoyancy input from the Po River and other rivers of the northern Adriatic Sea, with typical freshwater discharge rates of 2000 m**3/s. The Bora winds provide the dominant forcing agent of the WACC during the winter months, resulting in peak southeastward flows reaching 100 cm/s. The energy input of the Bora is principally in the northern Adriatic, and the coastal current response is due mainly to the set up of the pressure field, although there is sometimes an accompanying local component of down-coast winds that further augments the coastal current. Downwelling conditions occur during Bora, with or without local wind-forcing, because the bottom Ekman transport occurs in either case. Downwelling results in destratification of the coastal current, due to both vertical mixing and straining of the cross-shore density gradient. The relative contributions of mixing and straining depends on the value of the Kelvin number K=Lf/(g_Oh)**1/2, where L is the width of the coastal current, f is the Coriolis parameter, g_O is reduced gravity, and h is the plume thickness. For a narrow coastal current (K<1), straining occurs more rapidly than vertical mixing. This is the case in the WACC during Bora events, with strain-induced destratification occurring in less than 24 hours. The straining process limits vertical mixing of the coastal current with the ambient Adriatic water, because once the isopycnals become vertical, no more mixing can occur. This limitation of mixing may explain the persistence of the density anomaly of the coastal current in the presence of high stresses. The straining process also has important implications for sediment transport: destratification allows sediment to be distributed throughout the water column during Bora events, resulting in enhanced down-coast fluxes. The influence of the downwelling dynamics on cross-shore sediment transport is still under examination.

Jovian Temperatures--Highest Resolution

NASA Image and Video Library

1997-09-24

This image, bottom panel, from NASA Galileo orbiter indicates the forces powering Jovian winds, and differentiates between areas of strongest upwelling and downwelling winds in the upper part of the atmosphere where winds are strong.

The Response of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo

NASA Technical Reports Server (NTRS)

Aquila, Valentina; Oman, Luke D.; Stolarski, R.; Douglass, A. R.; Newman, P. A.

2012-01-01

Observations have shown that the global mass of nitrogen dioxide decreased in both hemispheres in the year following the eruption of Mt. Pinatubo. In contrast, the observed ozone response was largely asymmetrical with respect to the equator, with a decrease in the northern hemisphere and little change and even a small increase in the southern hemisphere. Simulations including enhanced heterogeneous chemistry due to the presence of the volcanic aerosol reproduce a decrease of ozone in the northern hemisphere, but also produce a comparable ozone decrease in the southern hemisphere, contrary to observations. Our simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and the extratropical downwelling. The enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer-Dobson circulation, increased the ozone in the southern hemisphere and counteracted the ozone depletion due to heterogeneous chemistry on volcanic aerosol.

The Response of Ozone and Nitrogen Dioxide to the Eruption of Mount Pinatubo at Southern and Northern Midlatitudes

NASA Technical Reports Server (NTRS)

Aquila, Valentina; Oman, Luke D.; Stolarski, Richard S.; Douglass, Anne R.; Newman, Paul A.

2013-01-01

Observations have shown that the mass of nitrogen dioxide decreased at both southern and northern midlatitudes in the year following the eruption of Mt. Pinatubo, indicating that the volcanic aerosol had enhanced nitrogen dioxide depletion via heterogeneous chemistry. In contrast, the observed ozone response showed a northern midlatitude decrease and a small southern midlatitude increase. Previous simulations that included an enhancement of heterogeneous chemistry by the volcanic aerosol but no other effect of this aerosol produce ozone decreases in both hemispheres, contrary to observations. The authors simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and Southern Hemisphere extratropical downwelling. This enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer Dobson circulation, increased Southern Hemisphere ozone via advection, counteracting the ozone depletion due to heterogeneous chemistry on the Pinatubo aerosol.

The Response of Ozone and Nitrogen Dioxide to the Eruption of Mount Pinatubo

NASA Technical Reports Server (NTRS)

Aquila. Valentina; Oman, Luke D.; Stolarsk, Richard S.; Douglass, Anne R.; Newman, Paul A.

2012-01-01

Observations have shown that the global mass of nitrogen dioxide decreased in both hemispheres in the year following the eruption of Mt. Pinatubo, indicating an enhanced heterogeneous chemistry. In contrast, the observed ozone response was largely asymmetrical with respect to the equator, with a decrease in the northern hemisphere and little change in the southern hemisphere. Simulations including enhanced heterogeneous chemistry due to the presence of the volcanic aerosol reproduce a decrease of ozone in the northern hemisphere, but also produce a comparable ozone decrease in the southern hemisphere, contrary to observations. Our simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and the extratropical downwelling. The enhanced extratropical downwelling, combined with the time of the eruption relative to the phase of the Brewer-Dobson circulation, increased the ozone in the southern hemisphere and counteracted the ozone depletion due to heterogeneous chemistry on volcanic aerosol.

Bathymetric analysis of in-water upwelling-radiance data

NASA Astrophysics Data System (ADS)

Fay, Temple H.; Miller, H. V.; Clark, R. K.

1990-09-01

In June 1988, the Naval Ocean Research and Development Activity (NORDA) collected some "in-water" data using its Towed Underwater Pumping System (TUPS) in the near-shore waters off St. Andrews State Park, Shell Island, Florida. These in situ data include latitude; longitude; depth in meters; narrow-band upwelling at 465 nm, 507 nm, and 532 nm; broad-band downwelling collected at the surface; temperature; salinity; atid transmissivity. In this paper, we investigate the relationship between depth and the normalized upwelling irradiance (upwelling divided by downwelling) in the three bands. Algorithms used to calculate water depth from remotely sensed airborne and satellite multispectral data are applied to the TUPS data and results compared. The TEJPS data have the advantage over most aircraft- and satellite-collected data because they were collected over an essentially uniform bottom type (smooth sandy bottom with steady slope) and have no atmospheric contamination. A new algorithm for depth calculation is proposed.

Geologic Map of the Meskhent Tessera Quadrangle (V-3), Venus: Evidence for Early Formation and Preservation of Regional Topography

NASA Technical Reports Server (NTRS)

Ivanov, M. A.; Head, James W.

2008-01-01

The area of the Meskhent Tessera quadrangle (V-3, 50-75degN, 60-120degE, Fig. 1) corresponds to a transition zone from the uplands of Ishtar Terra to the west to the lowlands of Atalanta Planitia to the east. The topographic configuration, gravity signature, and presence of large tesserae in Ishtar Terra are consistent with extensive areas of thickened crust and tectonically stabilized lithosphere representing ancient and now extinct regimes of mantle convection. The gravity and topographic characteristics of Atalanta Planitia have been cited as evidence for large-scale mantle downwelling. Thus, the region of Meskhent Tessera quadrangle represents an important sample for the study of the regional history of long-wavelength topography (highlands, midlands, and lowlands), interaction between the downwelling and areas of thickened crust/lithosphere, formation of associated tectonic features, and emplacement of volcanic plains.

The Chemical and Dynamical Responses of Ozone and Nitrogen Dioxide to the Eruption of Mt. Pinatubo

NASA Technical Reports Server (NTRS)

Aquila, V.; Oman, L. D.; Stolarski, R.; Douglass, A. R.

2012-01-01

Observations have shown that the concentration of nitrogen dioxide decreased in both hemispheres in the years following the eruption of Mt. Pinatubo. In contrast, the observed ozone response was largely asymmetrical with respect to the equator, with a decrease in the northern hemisphere and little or no change in the southern hemisphere. Simulations including enhanced heterogeneous chemistry due to the presence of the volcanic aerosol reproduce a decrease of ozone in the northern hemisphere, but also produce a comparable ozone decrease in the southern hemisphere contrary to observations. Our simulations show that the heating due to the volcanic aerosol enhanced both the tropical upwelling and the extratropical downwelling. The enhanced extratropical downwelling, combined with the time of the eruption relative to the seasonal phase of the Brewer-Dobson circulation, increased the ozone in the southern hemisphere and counteracted the ozone depletion due to heterogeneous chemistry on volcanic aerosol.

Melt onset over Arctic sea ice controlled by atmospheric moisture transport

NASA Astrophysics Data System (ADS)

Mortin, Jonas; Svensson, Gunilla; Graversen, Rune G.; Kapsch, Marie-Luise; Stroeve, Julienne C.; Boisvert, Linette N.

2016-06-01

The timing of melt onset affects the surface energy uptake throughout the melt season. Yet the processes triggering melt and causing its large interannual variability are not well understood. Here we show that melt onset over Arctic sea ice is initiated by positive anomalies of water vapor, clouds, and air temperatures that increase the downwelling longwave radiation (LWD) to the surface. The earlier melt onset occurs; the stronger are these anomalies. Downwelling shortwave radiation (SWD) is smaller than usual at melt onset, indicating that melt is not triggered by SWD. When melt occurs early, an anomalously opaque atmosphere with positive LWD anomalies preconditions the surface for weeks preceding melt. In contrast, when melt begins late, clearer than usual conditions are evident prior to melt. Hence, atmospheric processes are imperative for melt onset. It is also found that spring LWD increased during recent decades, consistent with trends toward an earlier melt onset.

Earth's interior. Dehydration melting at the top of the lower mantle.

PubMed

Schmandt, Brandon; Jacobsen, Steven D; Becker, Thorsten W; Liu, Zhenxian; Dueker, Kenneth G

2014-06-13

The high water storage capacity of minerals in Earth's mantle transition zone (410- to 660-kilometer depth) implies the possibility of a deep H2O reservoir, which could cause dehydration melting of vertically flowing mantle. We examined the effects of downwelling from the transition zone into the lower mantle with high-pressure laboratory experiments, numerical modeling, and seismic P-to-S conversions recorded by a dense seismic array in North America. In experiments, the transition of hydrous ringwoodite to perovskite and (Mg,Fe)O produces intergranular melt. Detections of abrupt decreases in seismic velocity where downwelling mantle is inferred are consistent with partial melt below 660 kilometers. These results suggest hydration of a large region of the transition zone and that dehydration melting may act to trap H2O in the transition zone. Copyright © 2014, American Association for the Advancement of Science.

The Origin and Mantle Dynamics of Quaternary Intraplate Volcanism in Northeast China From Joint Inversion of Surface Wave and Body Wave

NASA Astrophysics Data System (ADS)

Guo, Zhen; Wang, Kai; Yang, Yingjie; Tang, Youcai; John Chen, Y.; Hung, Shu-Huei

2018-03-01

We present a 3-D model of NE China by joint inversion of body and surface waves. The joint inversion significantly improves the resolution at shallow depths compared with body wave tomography alone and provides seismic evidence for the origin of Quaternary volcanism in NE China. Our model reveals that the mantle upwelling beneath the Changbaishan volcano originates from the transition zone and extends up to 60 km, and spreads at the base of the lithosphere with the upwelling head 5 times wider than the raising tail in the lower upper mantle. However, low velocities beneath the Halaha and Abaga volcanoes in the Xingmeng belt are confined to depths shallower than 150 km, suggesting that magmatism in the Xingmeng belt is more likely caused by localized asthenospheric upwelling at shallow depths rather than from the common deep source. A small-scale sublithospheric mantle convection may control the spatial and temporal distribution of Quaternary magmatism in NE China; that is, the upwelling beneath the Changbaishan volcano triggers the downwelling beneath the southern Songliao basin, where the high velocity imaged extends to 300 km. The downwelling may further induce localized upwelling in the surrounding areas, such as the Halaha and Abaga volcanoes. Thanks to the joint constraints from both surface and body waves, we can estimate the dimension of the convection cell. The convection cell is located between 42°N and 45°N, spreads around 500 km in the W-E direction measured from the distance between centers of downwelling and upwelling, and extends to 300 km vertically.

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

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

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookupmore » table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation ( R 2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.« less

The Interaction of Large Amplitude Internal Seiches with a Shallow Sloping Lakebed: Observations of Benthic Turbulence in Lake Simcoe, Ontario, Canada

PubMed Central

Cossu, Remo; Wells, Mathew G.

2013-01-01

Observations of the interactions of large amplitude internal seiches with the sloping boundary of Lake Simcoe, Canada show a pronounced asymmetry between up- and downwelling. Data were obtained during a 42-day period in late summer with an ADCP and an array of four thermistor chains located in a 5 km line at the depths where the thermocline intersects the shallow slope of the lakebed. The thermocline is located at depths of 12–14 m during the strongly stratified period of late summer. During periods of strong westerly winds the thermocline is deflected as much as 8 m vertically and interacts directly with the lakebed at depth between 14–18 m. When the thermocline was rising at the boundary, the stratification resembles a turbulent bore that propagates up the sloping lakebed with a speed of 0.05–0.15 m s−1 and a Froude number close to unity. There were strong temperature overturns associated with the abrupt changes in temperature across the bore. Based on the size of overturns in the near bed stratification, we show that the inferred turbulent diffusivity varies by up to two orders of magnitude between up- and downwellings. When the thermocline was rising, estimates of turbulent diffusivity were high with KZ ∼10−4 m2s−1, whereas during downwelling events the near-bed stratification was greatly increased and the turbulence was reduced. This asymmetry is consistent with previous field observations and underlines the importance of shear-induced convection in benthic bottom boundary layers of stratified lakes. PMID:23472085

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

NASA Astrophysics Data System (ADS)

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.; Turner, David D.; Eloranta, Edwin W.

2017-06-01

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookup table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation (R2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21 µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.

Thin ice clouds in the Arctic: cloud optical depth and particle size retrieved from ground-based thermal infrared radiometry

DOE PAGES

Blanchard, Yann; Royer, Alain; O'Neill, Norman T.; ...

2017-06-09

Multiband downwelling thermal measurements of zenith sky radiance, along with cloud boundary heights, were used in a retrieval algorithm to estimate cloud optical depth and effective particle diameter of thin ice clouds in the Canadian High Arctic. Ground-based thermal infrared (IR) radiances for 150 semitransparent ice clouds cases were acquired at the Polar Environment Atmospheric Research Laboratory (PEARL) in Eureka, Nunavut, Canada (80° N, 86° W). We analyzed and quantified the sensitivity of downwelling thermal radiance to several cloud parameters including optical depth, effective particle diameter and shape, water vapor content, cloud geometric thickness and cloud base altitude. A lookupmore » table retrieval method was used to successfully extract, through an optimal estimation method, cloud optical depth up to a maximum value of 2.6 and to separate thin ice clouds into two classes: (1) TIC1 clouds characterized by small crystals (effective particle diameter ≤ 30 µm), and (2) TIC2 clouds characterized by large ice crystals (effective particle diameter > 30 µm). The retrieval technique was validated using data from the Arctic High Spectral Resolution Lidar (AHSRL) and Millimeter Wave Cloud Radar (MMCR). Inversions were performed over three polar winters and results showed a significant correlation ( R 2 = 0.95) for cloud optical depth retrievals and an overall accuracy of 83 % for the classification of TIC1 and TIC2 clouds. A partial validation relative to an algorithm based on high spectral resolution downwelling IR radiance measurements between 8 and 21µm was also performed. It confirms the robustness of the optical depth retrieval and the fact that the broadband thermal radiometer retrieval was sensitive to small particle (TIC1) sizes.« less

Measurements of downwelling far-infrared radiance during the RHUBC-II campaign at Cerro Toco, Chile and comparisons with line-by-line radiative transfer calculations

NASA Astrophysics Data System (ADS)

Mast, Jeffrey C.; Mlynczak, Martin G.; Cageao, Richard P.; Kratz, David P.; Latvakoski, Harri; Johnson, David G.; Turner, David D.; Mlawer, Eli J.

2017-09-01

Downwelling radiances at the Earth's surface measured by the Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument in an environment with integrated precipitable water (IPW) as low as 0.03 cm are compared with calculated spectra in the far-infrared and mid-infrared. FIRST (a Fourier transform spectrometer) was deployed from August through October 2009 at 5.38 km MSL on Cerro Toco, a mountain in the Atacama Desert of Chile. There FIRST took part in the Radiative Heating in Unexplored Bands Campaign Part 2 (RHUBC-II), the goal of which is the assessment of water vapor spectroscopy. Radiosonde water vapor and temperature vertical profiles are input into the Atmospheric and Environmental Research (AER) Line-by-Line Radiative Transfer Model (LBLRTM) to compute modeled radiances. The LBLRTM minus FIRST residual spectrum is calculated to assess agreement. Uncertainties (1-σ) in both the measured and modeled radiances are also determined. Measured and modeled radiances nearly all agree to within combined (total) uncertainties. Features exceeding uncertainties can be corrected into the combined uncertainty by increasing water vapor and model continuum absorption, however this may not be necessary due to 1-σ uncertainties (68% confidence). Furthermore, the uncertainty in the measurement-model residual is very large and no additional information on the adequacy of current water vapor spectral line or continuum absorption parameters may be derived. Similar future experiments in similarly cold and dry environments will require absolute accuracy of 0.1% of a 273 K blackbody in radiance and water vapor accuracy of ∼3% in the profile layers contributing to downwelling radiance at the surface.

Modeling of the mesoscale structure of coupled upwelling/downwelling events and the related input of nutrients to the upper mixed layer in the Gulf of Finland, Baltic Sea

NASA Astrophysics Data System (ADS)

Zhurbas, Victor; Laanemets, Jaan; Vahtera, Emil

2008-05-01

A high resolution numerical study is undertaken to simulate an upwelling event along the northern coast of the Gulf of Finland, 21-29 July 1999, which was documented well by in situ and remote measurements. The simulated sequence of SST maps shows a reasonably good resemblance to that of satellite infrared imagery, including both mesoscale coherent structures (filaments or squirts) and the whole process of post-upwelling relaxation of the temperature field. Upwelling along the northern coast of the Gulf is accompanied by downwelling along the southern coast so that two longshore baroclinic jets and related fronts are developed simultaneously. When the strong westerly winds producing the upwelling/downwelling weaken, the longshore jets become unstable and produce transverse jets, cold/warm water squirts. Using pseudo-random simulated fields of temperature and velocity of currents, the apparent lateral diffusivity due to squirts is directly estimated at 500 m2 s-1. The model is also applied to estimate nutrient transport. Simulated phosphate concentration in the surface layer at the cold side of upwelling front is found to be about 0.3 mmol m-3 which is consistent with observations. The total content of phosphorus and nitrogen in the upper 10 m layer of the Gulf introduced by the upwelling event is estimated to be 387 and 36 tons, respectively. It follows, that the upwelling event transports nutrients into the upper layer with clear excess of phosphorus (N:P = 36:387 = 0.093) compared to the Redfield ratio of 7.2. Therefore phosphorus input caused by upwelling during summer most likely promotes nitrogen-fixing cyanobacteria blooms.

Cold cratonic roots and thermal blankets: How continents affect mantle convection

USGS Publications Warehouse

Trubitsyn, V.P.; Mooney, W.D.; Abbott, D.H.

2003-01-01

Two-dimensional convection models with moving continents show that continents profoundly affect the pattern of mantle convection. If the continents are wider than the wavelength of the convection cells (???3000 km, the thickness of the mantle), they cause neighboring deep mantle thermal upwellings to coalesce into a single focused upwelling. This focused upwelling zone will have a potential temperature anomaly of about 200??C, much higher than the 100??C temperature anomaly of upwelling zones generated beneath typical oceanic lithosphere. Extensive high-temperature melts (including flood basalts and late potassic granites) will be produced, and the excess temperature anomaly will induce continental uplift (as revealed in sea level changes) and the eventual breakup of the supercontinent. The mantle thermal anomaly will persist for several hundred million years after such a breakup. In contrast, small continental blocks (<1000 km diameter) do not induce focused mantle upwelling zones. Instead, small continental blocks are dragged to mantle downwelling zones, where they spend most of their time, and will migrate laterally with the downwelling. As a result of sitting over relatively cold mantle (downwellings), small continental blocks are favored to keep their cratonic roots. This may explain the long-term survival of small cratonic blocks (e.g., the Yilgarn and Pilbara cratons of western Australia, and the West African craton). The optimum size for long-term stability of a continental block is <3000 km. These results show that continents profoundly affect the pattern of mantle convection. These effects are illustrated in terms of the timing and history of supercontinent breakup, the production of high-temperature melts, and sea level changes. Such two-dimensional calculations can be further refined and tested by three-dimensional numerical simulations of mantle convection with moving continental and oceanic plates.

Scaling Coastal Ecosystems to Oceanographic and Climatic Drivers: Making Sense of Community Variation on Rocky Shores Using the Comparative-Experimental Approach in Upwelling and Downwelling Systems

NASA Astrophysics Data System (ADS)

Menge, B. A.; Gouhier, T.; Chan, F.; Hacker, S.; Menge, D.; Nielsen, K. J.

2016-02-01

Ecology focuses increasingly on the issue of matching spatial and temporal scales responsible for ecosystem pattern and dynamics. Benthic coastal communities traditionally were studied at local scales using mostly short-term research, while environmental (oceanographic, climatic) drivers were investigated at large scales (e.g., regional to oceanic, mostly offshore) using combined snapshot and monitoring (time series) research. The comparative-experimental approach combines local-scale studies at multiple sites spanning large-scale environmental gradients in combination with monitoring of inner shelf oceanographic conditions including upwelling/downwelling wind forcing and their consequences (e.g., temperature), and inputs of subsidies (larvae, phytoplankton, detritus). Temporal scale varies depending on the questions, but can extend from years to decades. We discuss two examples of rocky intertidal ecosystem dynamics, one at a regional scale (California Current System, CCS) and one at an interhemispheric scale. In the upwelling-dominated CCS, 52% and 32% of the variance in local community structure (functional group abundances at 13 sites across 725 km) was explained by external factors (ecological subsidies, oceanographic conditions, geographic location), and species interactions, respectively. The interhemispheric study tested the intermittent upwelling hypothesis (IUH), which predicts that key ecological processes will vary unimodally along a persistent downwelling to persistent upwelling gradient. Using 14-22 sites, unimodal relationships between ecological subsidies (phytoplankton, prey recruitment), prey responses (barnacle colonization, mussel growth) and species interactions (competition rate, predation rate and effect) and the Bakun upwelling index calculated at each site accounted for 50% of the variance. Hence, external factors can account for about half of locally-expressed community structure and dynamics.

A Method of Correcting for Tilt From Horizontal in Downwelling Shortwave Irradiance Measurements on Moving Platforms

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

Long, Charles N.; Bucholtz, Anthony; Jonsson, Haf

2010-04-14

Significant errors occur in downwelling shortwave irradiance measurements made on moving platforms due to tilt from horizontal because, when the sun is not completely blocked by overhead cloud, the downwelling shortwave irradiance has a prominent directional component from the direct sun. A-priori knowledge of the partitioning between the direct and diffuse components of the total shortwave irradiance is needed to properly apply a correction for tilt. This partitioning information can be adequately provided using a newly available commercial radiometer that produces reasonable measurements of the total and diffuse shortwave irradiance, and by subtraction the direct shortwave irradiance, with no movingmore » parts and regardless of azimuthal orientation. We have developed methodologies for determining the constant pitch and roll offsets of the radiometers for aircraft applications, and for applying a tilt correction to the total shortwave irradiance data. Results suggest that the methodology is for tilt up to +/-10°, with 90% of the data corrected to within 10 Wm-2 at least for clear-sky data. Without a proper tilt correction, even data limited to 5° of tilt as is typical current practice still exhibits large errors, greater than 100 Wm-2 in some cases. Given the low cost, low weight, and low power consumption of the SPN1 total and diffuse radiometer, opportunities previously excluded for moving platform measurements such as small Unmanned Aerial Vehicles and solar powered buoys now become feasible using our methodology. The increase in measurement accuracy is important, given current concerns over long-term climate variability and change especially over the 70% of the Earth’s surface covered by ocean where long-term records of these measurements are sorely needed and must be made on ships and buoys.« less

One year of downwelling spectral radiance measurements from 100 to 1400 cm-1 at Dome Concordia: Results in clear conditions

NASA Astrophysics Data System (ADS)

Rizzi, R.; Arosio, C.; Maestri, T.; Palchetti, L.; Bianchini, G.; Del Guasta, M.

2016-09-01

The present work examines downwelling radiance spectra measured at the ground during 2013 by a Far Infrared Fourier Transform Spectrometer at Dome C, Antarctica. A tropospheric backscatter and depolarization lidar is also deployed at same site, and a radiosonde system is routinely operative. The measurements allow characterization of the water vapor and clouds infrared properties in Antarctica under all sky conditions. In this paper we specifically discuss cloud detection and the analysis in clear sky condition, required for the discussion of the results obtained in cloudy conditions. First, the paper discusses the procedures adopted for the quality control of spectra acquired automatically. Then it describes the classification procedure used to discriminate spectra measured in clear sky from cloudy conditions. Finally a selection is performed and 66 clear cases, spanning the whole year, are compared to simulations. The computation of layer molecular optical depth is performed with line-by-line techniques and a convolution to simulate the Radiation Explorer in the Far InfraRed-Prototype for Applications and Development (REFIR-PAD) measurements; the downwelling radiance for selected clear cases is computed with a state-of-the-art adding-doubling code. The mean difference over all selected cases between simulated and measured radiance is within experimental error for all the selected microwindows except for the negative residuals found for all microwindows in the range 200 to 400 cm-1, with largest values around 295.1 cm-1. The paper discusses possible reasons for the discrepancy and identifies the incorrect magnitude of the water vapor total absorption coefficient as the cause of such large negative radiance bias below 400 cm-1.

Downwell pump reliability: Geothermal experience update: Final report

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

Ellis, P.F.

1988-01-01

Geothermal resources with temperatures between 250/sup 0/ and 360/sup 0/F (121/sup 0/C and 182/sup 0/C) are prime candidates for binary-cycle power generation, and constitute about 80% of the power-capable resources in the United States. The successful exploitation of these resources requires reliable high-capacity downwell brine production pumps, but earlier experience showed that high-capacity, high-temperature geothermal production pumps had many problems which resulted in a mean time-to-failure (MTTF) of less than 1000 h. However, steady progress has been made since 1981, and a large body of experience has been acquired by three geothermal binary plants. This survey of high-temperature geothermal downwellmore » pump users and manufacturers updates a prior survey (AP-3572) completed in early 1983. This survey traces the development of lineshaft pump technology from the late 1970s to the present (mid-1987), detailing the advances in design, materials selection, and operating practices. Case histories of 72 lineshaft pumps installed at three geothermal binary plants since late 1981 are documented, including some detailed cause of failure reports. In the recent past, pump lives in excess of 7000 h have become common, but a high continuing rate of premature failures resulted in a mean time-to-failure (MTTF) of about 5000 h. Based on recent advances which appear likely to eliminate most premature failures, the estimated near-term MTTF will be on the order of 8000 h. The survey found almost no development of high-temperature geothermal electric submersible pumps (ESP's) or close-coupled downwell hydraulic turbopumps, and concluded that considerable development and demonstration will be needed before these technologies are able to compete with existing high-temperature geothermal lineshaft pump technology. 36 refs., 10 figs., 25 tabs.« less

Seasonal Dynamics of Dissolved Organic Carbon Under Complex Circulation Schemes on a Large Continental Shelf: The Northern South China Sea

NASA Astrophysics Data System (ADS)

Meng, Feifei; Dai, Minhan; Cao, Zhimian; Wu, Kai; Zhao, Xiaozheng; Li, Xiaolin; Chen, Junhui; Gan, Jianping

2017-12-01

We examined the distribution and seasonality of dissolved organic carbon (DOC) based on a large data set collected from the northern South China Sea (NSCS) shelf under complex circulation schemes influenced by river plume, coastal upwelling, and downwelling. The highest surface values of ˜117 μmol L-1 were observed nearshore in summer suggesting high DOC supplies from the river inputs, whereas the lowest surface values of ˜62 μmol L-1 were on the outer shelf in winter due to entrainment of DOC-poor subsurface water under strengthened vertical mixing. While the summer coastal upwelling brought lower DOC from offshore depth to the nearshore surface, the winter coastal downwelling delivered higher surface DOC to the midshelf deep waters from the inner shelf fueled by the China Coastal Current (CCC) transporting relatively high DOC from the East China Sea to the NSCS. The intensified winter downwelling generated a cross-shelf DOC transport of 3.1 × 1012 g C over a large shelf area, which induced a significant depression of the NSCS DOC inventory in winter relative to in autumn. In addition to the variable physical controls, net biological production of DOC was semiquantified in both the river plume (2.8 ± 3.0 μmol L-1) and coastal upwelling (3.1 ± 1.3 μmol L-1) in summer. We demonstrated that the NSCS shelf had various origins of DOC including riverine inputs, inter-shelf transport and in situ production. Via cross-shelf transport, the accumulated DOC would be exported to and stored in the deep ocean, suggesting that continental shelves are a potentially effective carbon sink.

Rapid response to coastal upwelling in a semienclosed bay

NASA Astrophysics Data System (ADS)

Gilcoto, Miguel; Largier, John L.; Barton, Eric D.; Piedracoba, Silvia; Torres, Ricardo; Graña, Rocío.; Alonso-Pérez, Fernando; Villacieros-Robineau, Nicolás.; de la Granda, Francisco

2017-03-01

Bays/estuaries forced by local wind show bidirectional exchange flow. When forced by remote wind, they exhibit unidirectional flow adjustment to coastal sea level. Acoustic Doppler Current Profiler observations over 1 year show that the Ria de Vigo (Iberian Upwelling) responds to coastal wind events with bidirectional exchange flow. The duration of the upwelling and downwelling events, estimated from the current variability, was 3.3 days and 2.6 days, respectively. Vectorial correlations reveal a rapid response to upwelling/downwelling, in which currents lag local wind by <6 h and remote wind by <14 h, less than the Ekman spinup (17.8 h). This rapidity arises from the ria's narrowness (nonrotational local response), equatorward orientation (additive remote and local wind responses), depth greater than the Ekman depth (penetration of shelf circulation into the interior), and vertical stratification (shear reinforcing shelf circulation). Similar rapid responses are expected in other narrow bays where local and remote winds act together and stratification enhances bidirectional flow.

BBAERI vs. BNAERI: A Comparison of Two Hyperspectral Atmospheric Downwelling Radiance Interferometers

NASA Astrophysics Data System (ADS)

Wilson, R.; McMillan, W.; Shaw, J.

2006-12-01

Simultaneous measurements of atmospheric downwelling infrared radiances have been measured at UMBC's Atmospheric Remote sensing Facility (ARF). We present BBAERI and BNAERI spectral comparisons to demonstrate their consistent radiometric calibration and will show examples of retrieval products from each. The atmospheric emitted radiances were measured using two different Atmospheric Emitted Radiance Interferometers' (AERI): the Baltimore Bomem AERI (BBAERI) entirely built by ABB Bomem and the Baltimore NOAA AERI (BNAERI) assembled by research scientists at NOAA. BBAERI previously has been used for field experiments in support of satellite validation, but now will spend most of its time at UMBC. BNAERI was designed for autonomous field operations. Planned upcoming field campaigns for BNAERI include experiments in central Alaska or in the Baltimore-Washington area. AERI devices were originally designed by the University of Madison Wisconsin to retrieve temperature and water vapor profiles up to the boundary layer every eight to ten minutes. In addition to boundary layer temperature and water vapor profiling, we will report retrieved boundary layer abundances of trace gases.

Mantle downwelling and crustal convergence - A model for Ishtar Terra, Venus

NASA Technical Reports Server (NTRS)

Kiefer, Walter S.; Hager, Bradford H.

1991-01-01

Models of viscous crustal flow driven by gradients in topography are presented in order to explore quantitatively the implications of the hypothesis that Ishtar is a crustal convergence zone overlying a downwelling mantle. Assuming a free-slip surface boundary condition, it is found that, if the crustal convergence hypothesis is correct, then the crustal thickness in the plains surrounding Ishtar can be no more than about 25 km thick. If the geothermal gradient is larger or the rheology is weaker, the crust must be even thinner for net crustal convergence to be possible. This upper bound is in good agreement with the several independent estimates of crustal thickness of 15-30 km in the plains of Venus based on modeling of the spacing of tectonic features and of impact crater relaxation. Although Ishtar is treated as a crustal convergence zone, this crustal flow model shows that under some circumstances, near-surface material may actually flow away from Ishtar, providing a possible explanation for the grabenlike structures in Fortuna Tessera.

Uncertainty in Arctic climate projections traced to variability of downwelling longwave radiation

NASA Astrophysics Data System (ADS)

Krikken, Folmer; Bintanja, Richard; Hazeleger, WIlco; van Heerwaarden, Chiel

2017-04-01

The Arctic region has warmed rapidly over the last decades, and this warming is projected to increase. The uncertainty in these projections, i.e. intermodel spread, is however very large and a clear understanding of the sources behind the spread is so far still lacking. Here we use 31 state-of-the-art global climate models to show that variability of May downwelling radiation (DLR) in the models' control climate, primarily located at the land surrounding the Arctic ocean, explains 2/3 of the intermodel spread in projected Arctic warming under the RPC85 scenario. This variability is related to the combined radiative effect of the cloud radiative forcing (CRF) and the albedo response due to snowfall, which varies strongly between the models in these regions. This mechanism dampens or enhances yearly variability of DLR in the control climate but also dampens or enhances the climate response of DLR, sea ice cover and near surface temperature.

A new numerical model of the middle atmosphere. I - Dynamics and transport of tropospheric source gases

NASA Technical Reports Server (NTRS)

Garcia, Rolando R.; Stordal, Frode; Solomon, Susan; Kiehl, Jeffrey T.

1992-01-01

Attention is given to a new model of the middle atmosphere which includes, in addition to the equations governing the zonal mean state, a potential vorticity equation for a single planetary-scale Rossby wave, and an IR radiative transfer code for the stratosphere and lower mesosphere, which replaces the Newtonian cooling parameterization used previously. It is shown that explicit computation of the planetary-scale wave field yields a more realistic representation of the zonal mean dynamics and the distribution of trace chemical species. Wave breaking produces a well-mixed 'surf zone' equatorward of the polar night vortex and drives a meridional circulation with downwelling on the poleward side of the vortex. This combination of mixing and downwelling produces shallow meridional gradients of trace gases in the subtropics and middle latitudes, and very steep gradients at the edge of the polar vortex. Computed distributions of methane and nitrous oxide are shown to agree well with observations.

The Evolution of the Earth's Mantle Structure and Surface and Core-mantle Boundary Heat Flux since the Paleozoic

NASA Astrophysics Data System (ADS)

Zhang, N.; Zhong, S.

2010-12-01

The cause for and time evolution of the seismically observed African and Pacific slow anomalies (i.e., superplumes) are still unclear with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Ma and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma ago) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree-1 structure before the Pangea formation). Here, we construct a plate motion history back to 450 Ma and use it as time-dependent surface boundary conditions in 3-dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure as well as the surface and core-mantle boundary heat flux. Our results for the mantle structures suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ~240 Ma (i.e., ~100 Ma after the assembly of Pangea). The evolution of mantle structure has implications for heat flux at the surface and core-mantle boundary (CMB). Our results show that while the plate motion controls the surface heat flux, the major cold downwellings control the core-mantle boundary heat flux. A notable feature in surface heat flux from our models is that the surface heat flux peaks at ~100 Ma ago but decreases for the last 100 Ma due to the breakup of Pangea and its subsequent plate evolution. The CMB heat flux in the equatorial regions shows two minima during period 320-250 Ma and period 120-84 Ma. The first minimum clearly results from the disappearance of a major cold downwelling above the CMB below the Pangea after the assembly of Pangea ends the subduction and convergence between Gondwana and Laurussia. The second minimum arises because the break-up of Pangea leads to subduction of much smaller and younger oceanic lithosphere in the equatorial regions of the CMB. Considering the recent suggestion that CMB heat flux in the equatorial regions controls the frequency of magnetic polarity reversals (Olson et al., 2010), our results have important implications for the Kaiman Reversal Superchron and Cretaceous Normal Superchron.

Passive margins getting squeezed in the mantle convection vice

NASA Astrophysics Data System (ADS)

Husson, Laurent; Yamato, Philippe; Becker, Thorsten; Pedoja, Kevin

2013-04-01

Quaternary coastal geomorphology reveals that passive margins underwent wholesale uplift at least during the glacial cycle. In addition, these not-so-passive margins often exhibit long term exhumation and tectonic inversion, which suggest that compression and tectonic shortening could be the mechanism that triggers their overall uplift. We speculate that the compression in the lithosphere gradually increased during the Cenozoic. The many mountain belts at active margins that accompany this event readily witness this increase. Less clear is how that compression increase affects passive margins. In order to address this issue, we design minimalist 2D viscous models to quantify the impact of plate collision on the stress regime. In these models, a sluggish plate is disposed on a less viscous mantle. It is driven by a "mantle conveyor belt" alternatively excited by lateral shear stresses that represent a downwelling on one side, an upwelling on the other side, or both simultaneously. The lateral edges of the plate are either free or fixed, respectively representing the cases of free convergence and collision. In practice, it dramatically changes the upper boundary condition for mantle circulation and subsequently, for the stress field. The flow pattern transiently evolves almost between two end-members, starting from a situation close to a Couette flow to a pattern that looks like a Poiseuille flow with an almost null velocity at the surface (though in the models, the horizontal velocity at the surface is not strictly null, as the lithosphere deforms). In the second case, the lithosphere is highly stressed horizontally and deforms. For an equivalent bulk driving force, compression increases drastically at passive margins if upwellings are active because they push plates towards the collision. Conversely, if only downwellings are activated, compression occurs on one half of the plate and extension on the other half, because only the downwelling is pulling the plate. Thus, active upwellings underneath oceanic plates are required to explain compression at passive margins. This conclusion is corroborated by "real-Earth" 3D spherical models, wherein the flow is alternatively driven by density anomalies inferred from seismic tomography -and therefore include both downwellings at subduction zones and upwellings above the superswells- and density anomalies that correspond to subducting slabs only. While the second scenario mostly compresses the active margins of upper plates and leave other areas at rest, the first scenario efficiently compresses passive margins where the geological record reveals their uplift, exhumation, and tectonic inversion.

Spatial and temporal variability in coccolithophore abundance and distribution in the NW Iberian coastal upwelling system

NASA Astrophysics Data System (ADS)

Ausín, Blanca; Zúñiga, Diana; Flores, Jose A.; Cavaleiro, Catarina; Froján, María; Villacieros-Robineau, Nicolás; Alonso-Pérez, Fernando; Arbones, Belén; Santos, Celia; de la Granda, Francisco; Castro, Carmen G.; Abrantes, Fátima; Eglinton, Timothy I.; Salgueiro, Emilia

2018-01-01

A systematic investigation of the spatial and temporal variability in coccolithophore abundance and distribution through the water column of the NW Iberian coastal upwelling system was performed. From July 2011 to June 2012, monthly sampling at various water depths was conducted at two parallel stations located at 42° N. Total coccosphere abundance was higher at the outer-shelf station, where warmer, nutrient-depleted waters favoured coccolithophore rather than phytoplanktonic diatom blooms, which are known to dominate the inner-shelf location. In seasonal terms, higher coccosphere and coccolith abundances were registered at both stations during upwelling seasons, coinciding with high irradiance levels. This was typically in conjunction with stratified, nutrient-poor conditions (i.e. relaxing upwelling conditions). However, it also occurred during some upwelling events of colder, nutrient-rich subsurface waters onto the continental shelf. Minimum abundances were generally found during downwelling periods, with unexpectedly high coccolith abundance registered in subsurface waters at the inner-shelf station. This finding can only be explained if strong storms during these downwelling periods favoured resuspension processes, thus remobilizing deposited coccoliths from surface sediments, and hence hampering the identification of autochthonous coccolithophore community structure. At both locations, the major coccolithophore assemblages were dominated by Emiliania huxleyi, small Gephyrocapsa group, Gephyrocapsa oceanica, Florisphaera profunda, Syracosphaera spp., Coronosphaera mediterranea, and Calcidiscus leptoporus. Ecological preferences of the different taxa were assessed by exploring the relationships between environmental conditions and temporal and vertical variability in coccosphere abundance. These findings provide relevant information for the use of fossil coccolith assemblages in marine sediment records, in order to infer past environmental conditions, of particular importance for Paleoceanography. Both E. huxleyi and the small Gephyrocapsa group are proposed as proxies for the upwelling regime with a distinct affinity for different stages of the upwelling event: E. huxleyi was associated with warmer, nutrient-poor and more stable water column (i.e. upwelling relaxation stage) while the small Gephyrocapsa group was linked to colder waters and higher nutrient availability (i.e. early stages of the upwelling event), similarly to G. oceanica. Conversely, F. profunda is suggested as a proxy for the downwelling regime and low-productivity conditions. The assemblage composed by Syracosphaera pulchra, Coronosphaera mediterranea, and Rhabdosphaera clavigera may be a useful indicator of the presence of subtropical waters conveyed northward by the Iberian Poleward Current. Finally, C. leptoporus is proposed as an indicator of warmer, saltier, and oligotrophic waters during the downwelling/winter regime.

Annual and semiannual variations in the ionospheric F2-layer: II. Physical discussion

NASA Astrophysics Data System (ADS)

Rishbeth, H.; Müller-Wodarg, I. C. F.; Zou, L.; Fuller-Rowell, T. J.; Millward, G. H.; Moffett, R. J.; Idenden, D. W.; Aylward, A. D.

2000-08-01

The companion paper by Zou et al. shows that the annual and semiannual variations in the peak F2-layer electron density (NmF2) at midlatitudes can be reproduced by a coupled thermosphere-ionosphere computational model (CTIP), without recourse to external influences such as the solar wind, or waves and tides originating in the lower atmosphere. The present work discusses the physics in greater detail. It shows that noon NmF2 is closely related to the ambient atomic/molecular concentration ratio, and suggests that the variations of NmF2 with geographic and magnetic longitude are largely due to the geometry of the auroral ovals. It also concludes that electric fields play no important part in the dynamics of the midlatitude thermosphere. Our modelling leads to the following picture of the global three-dimensional thermospheric circulation which, as envisaged by Duncan, is the key to explaining the F2-layer variations. At solstice, the almost continuous solar input at high summer latitudes drives a prevailing summer-to-winter wind, with upwelling at low latitudes and throughout most of the summer hemisphere, and a zone of downwelling in the winter hemisphere, just equatorward of the auroral oval. These motions affect thermospheric composition more than do the alternating day/night (up-and-down) motions at equinox. As a result, the thermosphere as a whole is more molecular at solstice than at equinox. Taken in conjunction with the well-known relation of F2-layer electron density to the atomic/molecular ratio in the neutral air, this explains the F2-layer semiannual effect in NmF2 that prevails at low and middle latitudes. At higher midlatitudes, the seasonal behaviour depends on the geographic latitude of the winter downwelling zone, though the effect of the composition changes is modified by the large solar zenith angle at midwinter. The zenith angle effect is especially important in longitudes far from the magnetic poles. Here, the downwelling occurs at high geographic latitudes, where the zenith angle effect becomes overwhelming and causes a midwinter depression of electron density, despite the enhanced atomic/molecular ratio. This leads to a semiannual variation of NmF2. A different situation exists in winter at longitudes near the magnetic poles, where the downwelling occurs at relatively low geographic latitudes so that solar radiation is strong enough to produce large values of NmF2. This circulation-driven mechanism provides a reasonably complete explanation of the observed pattern of F2 layer annual and semiannual quiet-day variations.

Biogeochemical and ecological impacts of boundary currents in the Indian Ocean

NASA Astrophysics Data System (ADS)

Hood, Raleigh R.; Beckley, Lynnath E.; Wiggert, Jerry D.

2017-08-01

Monsoon forcing and the unique geomorphology of the Indian Ocean basin result in complex boundary currents, which are unique in many respects. In the northern Indian Ocean, several boundary current systems reverse seasonally. For example, upwelling coincident with northward-flowing currents along the coast of Oman during the Southwest Monsoon gives rise to high productivity which also alters nutrient stoichiometry and therefore, the species composition of the resulting phytoplankton blooms. During the Northeast Monsoon most of the northern Indian Ocean boundary currents reverse and favor downwelling. Higher trophic level species have evolved behavioral responses to these seasonally changing conditions. Examples from the western Arabian Sea include vertical feeding migrations of a copepod (Calanoides carinatus) and the reproductive cycle of a large pelagic fish (Scomberomorus commerson). The impacts of these seasonal current reversals and changes in upwelling and downwelling circulations are also manifested in West Indian coastal waters, where they influence dissolved oxygen concentrations and have been implicated in massive fish kills. The winds and boundary currents reverse seasonally in the Bay of Bengal, though the associated changes in upwelling and productivity are less pronounced. Nonetheless, their effects are observed on the East Indian shelf as, for example, seasonal changes in copepod abundance and zooplankton community structure. In contrast, south of Sri Lanka seasonal reversals in the boundary currents are associated with dramatic changes in the intensity of coastal upwelling, chlorophyll concentration, and catch per unit effort of fishes. Off the coast of Java, monsoon-driven changes in the currents and upwelling strongly impact chlorophyll concentrations, seasonal vertical migrations of zooplankton, and sardine catch in Bali Strait. In the southern hemisphere the Leeuwin is a downwelling-favorable current that flows southward along western Australia, though local wind forcing can lead to transient near shore current reversals and localized coastal upwelling. The poleward direction of this eastern boundary current is unique. Due to its high kinetic energy the Leeuwin Current sheds anomalous, relatively high chlorophyll, warm-core, downwelling eddies that transport coastal diatom communities westward into open ocean waters. Variations in the Leeuwin transport and eddy generation impact many higher trophic level species including the recruitment and fate of rock lobster (Panulirus cygnus) larvae. In contrast, the transport of the Agulhas Current is very large, with sources derived from the Mozambique Channel, the East Madagascar Current and the southwest Indian Ocean sub-gyre. Dynamically, the Agulhas Current is upwelling favorable; however, the spatial distribution of prominent surface manifestations of upwelling is controlled by local wind and topographic forcing. Meanders and eddies in the Agulhas Current propagate alongshore and interact with seasonal changes in the winds and topographic features. These give rise to seasonally variable localized upwelling and downwelling circulations with commensurate changes in primary production and higher trophic level responses. Due to the strong influence of the Agulhas Current, many neritic fish species in southeast Africa coastal waters have evolved highly selective behaviors and reproductive patterns for successful retention of planktonic eggs and larvae. For example, part of the Southern African sardine (Sardinops sagax) stock undergoes a remarkable northward migration enhanced by transient cyclonic eddies in the shoreward boundary of the Agulhas Current. There is evidence from the paleoceanographic record that these currents and their biogeochemical and ecological impacts have changed significantly over glacial to interglacial timescales. These changes are explored as a means of providing insight into the potential impacts of climate change in the Indian Ocean.

A Climatology of Surface Cloud Radiative Effects at the ARM Tropical Western Pacific Sites

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

McFarlane, Sally A.; Long, Charles N.; Flaherty, Julia E.

Cloud radiative effects on surface downwelling fluxes are investigated using long-term datasets from the three Atmospheric Radiation Measurement (ARM) sites in the Tropical Western Pacific (TWP) region. The Nauru and Darwin sites show significant variability in sky cover, downwelling radiative fluxes, and surface cloud radiative effect (CRE) due to El Niño and the Australian monsoon, respectively, while the Manus site shows little intra-seasonal or interannual variability. Cloud radar measurement of cloud base and top heights are used to define cloud types so that the effect of cloud type on the surface CRE can be examined. Clouds with low bases contributemore » 71-75% of the surface shortwave (SW) CRE and 66-74% of the surface longwave (LW) CRE at the three TWP sites, while clouds with mid-level bases contribute 8-9% of the SW CRE and 12-14% of the LW CRE, and clouds with high bases contribute 16-19% of the SW CRE and 15-21% of the LW CRE.« less

Atmospheric Emitted Radiance Interferometer (AERI) Handbook

DOE Data Explorer

Gero, Jonathan; Hackel, Denny; Garcia, Raymond

2005-01-01

The atmospheric emitted radiance interferometer (AERI) is a ground-based instrument that measures the downwelling infrared radiance from the Earth's atmosphere. The observations have broad spectral content and sufficient spectral resolution to discriminate among gaseous emitters (e.g., carbon dioxide and water vapor) and suspended matter (e.g., aerosols, water droplets, and ice crystals). These upward-looking surface observations can be used to obtain vertical profiles of tropospheric temperature and water vapor, as well as measurements of trace gases (e.g., ozone, carbon monoxide, and methane) and downwelling infrared spectral signatures of clouds and aerosols.The AERI is a passive remote sounding instrument, employing a Fourier transform spectrometer operating in the spectral range 3.3-19.2 μm (520-3020 cm-1) at an unapodized resolution of 0.5 cm-1 (max optical path difference of 1 cm). The extended-range AERI (ER-AERI) deployed in dry climates, like in Alaska, have a spectral range of 3.3-25.0 μm (400-3020 cm-1) that allow measurements in the far-infrared region. Typically, the AERI averages views of the sky over a 16-second interval and operates continuously.

Apparent Optical Properties in Waters Influenced by the Mississippi River

NASA Technical Reports Server (NTRS)

D'Sa, E.; Miller, R. L.; McKee, B. A.; Trzaska, R.

2002-01-01

In-water downwelling irradiance (E(sub d)) and upwelling radiance (L(sub u)) were measured in coastal waters influenced by the Mississippi River at wavelengths corresponding to SeaWiFS spectral bands in April of 2000. Results of derived apparent optical properties (AOP's) such as spectral diffise attenuation coefficient for downwelling irradiance (K(sub d)) suggest that they are mainly influenced by phytoplankton chlorophyll. Large variations in chlorophyll concentrations (0.2 to greater than 10 mg per cubic meters) correspond to variations in K(sub d) at 443 nm ranging from about 0.1 to greater than 1.5 per meter. Attenuation values at 443 nm generally peaked (or were minimal at 555 nm) at depths where chlorophyll concentrations were high. Above water remote sensing reflectance R(sub rs) (443) derived from E(sub d) and L(sub u) shows good agreement to surface chlorophyll. Ratios of remote sensing reflectance, R(sub rs)(443/R(sub rs)(555)versus chlorophyll suggests a potential for obtaining a suitable bio-optical algorithm for the region influenced by the Mississippi River.

Pangea breakup and northward drift of the Indian subcontinent reproduced by a numerical model of mantle convection.

PubMed

Yoshida, Masaki; Hamano, Yozo

2015-02-12

Since around 200 Ma, the most notable event in the process of the breakup of Pangea has been the high speed (up to 20 cm yr(-1)) of the northward drift of the Indian subcontinent. Our numerical simulations of 3-D spherical mantle convection approximately reproduced the process of continental drift from the breakup of Pangea at 200 Ma to the present-day continental distribution. These simulations revealed that a major factor in the northward drift of the Indian subcontinent was the large-scale cold mantle downwelling that developed spontaneously in the North Tethys Ocean, attributed to the overall shape of Pangea. The strong lateral mantle flow caused by the high-temperature anomaly beneath Pangea, due to the thermal insulation effect, enhanced the acceleration of the Indian subcontinent during the early stage of the Pangea breakup. The large-scale hot upwelling plumes from the lower mantle, initially located under Africa, might have contributed to the formation of the large-scale cold mantle downwelling in the North Tethys Ocean.

Pangea breakup and northward drift of the Indian subcontinent reproduced by a numerical model of mantle convection

PubMed Central

Yoshida, Masaki; Hamano, Yozo

2015-01-01

Since around 200 Ma, the most notable event in the process of the breakup of Pangea has been the high speed (up to 20 cm yr−1) of the northward drift of the Indian subcontinent. Our numerical simulations of 3-D spherical mantle convection approximately reproduced the process of continental drift from the breakup of Pangea at 200 Ma to the present-day continental distribution. These simulations revealed that a major factor in the northward drift of the Indian subcontinent was the large-scale cold mantle downwelling that developed spontaneously in the North Tethys Ocean, attributed to the overall shape of Pangea. The strong lateral mantle flow caused by the high-temperature anomaly beneath Pangea, due to the thermal insulation effect, enhanced the acceleration of the Indian subcontinent during the early stage of the Pangea breakup. The large-scale hot upwelling plumes from the lower mantle, initially located under Africa, might have contributed to the formation of the large-scale cold mantle downwelling in the North Tethys Ocean. PMID:25673102

Multivariate Analysis of Solar Spectral Irradiance Measurements

NASA Technical Reports Server (NTRS)

Pilewskie, P.; Rabbette, M.

2001-01-01

Principal component analysis is used to characterize approximately 7000 downwelling solar irradiance spectra retrieved at the Southern Great Plains site during an Atmospheric Radiation Measurement (ARM) shortwave intensive operating period. This analysis technique has proven to be very effective in reducing a large set of variables into a much smaller set of independent variables while retaining the information content. It is used to determine the minimum number of parameters necessary to characterize atmospheric spectral irradiance or the dimensionality of atmospheric variability. It was found that well over 99% of the spectral information was contained in the first six mutually orthogonal linear combinations of the observed variables (flux at various wavelengths). Rotation of the principal components was effective in separating various components by their independent physical influences. The majority of the variability in the downwelling solar irradiance (380-1000 nm) was explained by the following fundamental atmospheric parameters (in order of their importance): cloud scattering, water vapor absorption, molecular scattering, and ozone absorption. In contrast to what has been proposed as a resolution to a clear-sky absorption anomaly, no unexpected gaseous absorption signature was found in any of the significant components.

The Impact of Cloud Properties on Young Sea Ice during Three Winter Storms at N-ICE2015

NASA Astrophysics Data System (ADS)

Murphy, S. Y.; Walden, V. P.; Cohen, L.; Hudson, S. R.

2017-12-01

The impact of clouds on sea ice varies significantly as cloud properties change. Instruments deployed during the Norwegian Young Sea Ice field campaign (N-ICE2015) are used to study how differing cloud properties influence the cloud radiative forcing at the sea ice surface. N-ICE2015 was the first campaign in the Arctic winter since SHEBA (1997/1998) to study the surface energy budget of sea ice and the associated effects of cloud properties. Cloud characteristics, surface radiative and turbulent fluxes, and meteorological properties were measured throughout the field campaign. Here we explore how cloud macrophysical and microphysical properties affect young, thin sea ice during three winter storms from 31 January to 15 February 2015. This time period is of interest due to the varying surface and atmospheric conditions, which showcase the variety of conditions the newly-formed sea ice can experience during the winter. This period was characterized by large variations in the ice surface and near-surface air temperatures, with highs near 0°C when warm, moist air was advected into the area and lows reaching -40°C during clear, calm periods between storms. The advection of warm, moist air into the area influenced the cloud properties and enhanced the downwelling longwave flux. For most of the period, downwelling longwave flux correlates closely with the air temperature. However, at the end of the first storm, a drop in downwelling longwave flux of about 50 Wm-2 was observed, independent of any change in surface or air temperature or cloud fraction, indicating a change in cloud properties. Lidar data show an increase in cloud height during this period and a potential shift in cloud phase from ice to mixed-phase. This study will describe the cloud properties during the three winter storms and discuss their impacts on surface energy budget.

Formation of mantle "lone plumes" in the global downwelling zone - A multiscale modelling of subduction-controlled plume generation beneath the South China Sea

NASA Astrophysics Data System (ADS)

Zhang, Nan; Li, Zheng-Xiang

2018-01-01

It has been established that almost all known mantle plumes since the Mesozoic formed above the two lower mantle large low shear velocity provinces (LLSVPs). The Hainan plume is one of the rare exceptions in that instead of rising above the LLSVPs, it is located within the broad global mantle downwelling zone, therefore classified as a "lone plume". Here, we use the Hainan plume example to investigate the feasibility of such lone plumes being generated by subducting slabs in the mantle downwelling zone using 3D geodynamic modelling. Our geodynamic model has a high-resolution regional domain embedded in a relatively low resolution global domain, which is set up in an adaptive-mesh-refined, 3D mantle convection code ASPECT (Advanced Solver for Problems in Earth's ConvecTion). We use a recently published plate motion model to define the top mechanical boundary condition. Our modelling results suggest that cold slabs under the present-day Eurasia, formed from the Mesozoic subduction and closure of the Tethys oceans, have prevented deep mantle hot materials from moving to the South China Sea from regions north or west of the South China Sea. From the east side, the Western Pacific subduction systems started to promote the formation of a lower-mantle thermal-chemical pile in the vicinity of the future South China Sea region since 70 Ma ago. As the top of this lower-mantle thermal-chemical pile rises, it first moved to the west, and finally rested beneath the South China Sea. The presence of a thermochemical layer (possible the D″ layer) in the model helps stabilizing the plume root. Our modelling is the first implementation of multi-scale mesh in the regional model. It has been proved to be an effective way of modelling regional dynamics within a global plate motion and mantle dynamics background.

Completion of spectral rotating shadowband radiometers and analysis of ARM spectral short-wave data. Technical progress report, November 1, 1994--October 31, 1995

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

Michalsky, J.; Harrison, L.

1995-04-26

The authors goal in the ARM program is the improvement of radiation models used in GCMs, especially in the shortwave, (1) by providing improved shortwave radiometric measurements for the testing of models and (2) by developing methods for retrieving climatologically sensitive parameters that serve as input to shortwave and longwave models. They are acquiring downwelling direct and diffuse spectral irradiance, at six wavelengths, plus downwelling broadband longwave, and upwelling and downwelling broadband shortwave irradiances that they combined with surface and upper air data from the Albany airport as a test data set for ARM modelers. They have also developed algorithmsmore » to improve shortwave measurements made at the Southern Great Plains (SGP) ARM site by standard thermopile instruments and by the multifolter rotating shadowband radiometer (MFRSR). However, the major objective of the program has been the development of two spectral versions of the rotating shadowband radiometer. The MFRSR, has become a workhose at the CART site in Oklahoma and Kansas, and it is widely deployed in other climate programs. They have spent most of their effort this year developing techniques to retrieve column aerosol, water vapor, and ozone from direct beam spectral measurements of the MFRSR. Additionally, they have had success in calculating shortwave surface albedo and aerosol optical depth from the ratio of direct to diffuse spectral irradiance. Using the surface albedo and the global irradiance, they have calculated cloud optical depths. From cloud optical depth and liquid water measured with the microwave radiometer, they have calculated effective liquid cloud particle radii. In each case the authors have attempted to validate the approach using independent measurements or retrievals of the parameters under investigation. With the exception of the ozone intercomparison, the corroborative measurements have been made at the SGP CART site. This report highlights these results.« less

Comparison of tracer methods to quantify hydrodynamic exchange within the hyporheic zone

NASA Astrophysics Data System (ADS)

Engelhardt, I.; Piepenbrink, M.; Trauth, N.; Stadler, S.; Kludt, C.; Schulz, M.; Schüth, C.; Ternes, T. A.

2011-03-01

SummaryHydrodynamic exchange between surface-water and groundwater was studied at a river located within the Rhine Valley in Germany. Piezometric pressure heads and environmental tracers such as temperature, stable isotopes, chloride, X-ray contrast media, and artificial sweetener were investigated within the hyporheic zone and river water plume. Vertical profiles of environmental tracers were collected using multi-level wells within the neutral up-gradient zone, beneath the river bed, and within the horizontal proximal and distal down-gradient zone. Infiltration velocities were calculated from pressure heads, temperature fluctuations and gradients. The amount of river water within groundwater was estimated from vertical profiles of chloride, stable isotopes, and persistent pharmaceuticals. Profiles of stable isotopes and chloride reveal the existence of down-welling within the shallow hyporheic zone that is generated by river bed irregularities. Due to down-welling an above-average migration of river water into the hyporheic zone establishes even under upward hydraulic pressure gradients. The investigated environmental tracers could not distinctively display short-time-infiltration velocities representative for flood waves, while average infiltration velocities calculated over several months are uniform displayed. Based on vertical temperature profiles the down-gradient migration of the river water plume could be observed even after long periods of effluent conditions and over a distance of 200 m from the river bank. X-ray contrast media and artificial sweeteners were observed in high concentrations within the proximal zone, but were not detected at a distance of 200 m from the river bank. Using temperature as environmental tracer within the hyporheic zone may result in overestimating the migration of pollutants within the river water plume as the process of natural attenuation will be neglected. Furthermore, temperature was not able to display the effect of down-welling. Stable isotopes and chloride were found to be suitable environmental tracers to forecast the release and fate of organic contaminants within the hyporheic zone.

Particulate organic matter fluxes and hydrodynamics at the Tisler cold-water coral reef

NASA Astrophysics Data System (ADS)

Wagner, Hannes; Purser, Autun; Thomsen, Laurenz; Jesus, Carlos César; Lundälv, Tomas

2011-03-01

Cold-water coral reefs occur in many regions of the world's oceans. Fundamental questions regarding their functioning remain unanswered. These include the biogeochemical influence of reefs on their environment ("reef effects") and the influence of hydrodynamic processes on reef nutrition. In a succession of field campaigns in 2007 and 2008, these questions were addressed at the Tisler cold-water coral reef, which is centered on a sill peak in the Norwegian Skagerrak. A variety of methodological approaches were used. These consisted of the collection of CTD and chlorophyll profiles, current measurements, sampling of particulate organic matter (POM) in the benthic boundary layer (BBL) across the reef with subsequent chemical analyses, and the chemical analysis of freshly released Lophelia pertusa mucus. CTD and chlorophyll profiles indicated that downstream of the sill crest, downwelling delivered warmer, fresher and chlorophyll richer water masses down to the BBL. Both sides of the reef received downwelling nutrition delivery, as flow direction over the reef reversed periodically. Several chemical composition indicators revealed that suspended POM was significantly fresher on the downstream side of the reef than on the upstream side. L. pertusa mucus from the Tisler Reef was labile in composition, as indicated by a low C/N ratio and a high amino acid degradation index (DI) value. Particulate organic carbon (POC) content in the BBL was significantly depleted across the reef. Lateral depositional fluxes were calculated to be 18-1485 mg POC m -2 d -1, with a mean of 459 mg POC m -2 d -1. We propose that the combination of fresh, downwelling POM with mucus released from the reef was the cause of the greater lability of the downstream POM. Our data on POC depletion across the reef suggest that cold-water coral reefs could play an important role in carbon cycling along continental margins.

The Influence of Photoreceptor Size and Distribution on Optical Sensitivity in the Eyes of Lanternfishes (Myctophidae)

PubMed Central

de Busserolles, Fanny; Fitzpatrick, John L.; Marshall, N. Justin; Collin, Shaun P.

2014-01-01

The mesopelagic zone of the deep-sea (200-1000 m) is characterised by exponentially diminishing levels of downwelling sunlight and by the predominance of bioluminescence emissions. The ability of mesopelagic organisms to detect and behaviourally react to downwelling sunlight and/or bioluminescence will depend on the visual task and ultimately on the eyes and their capacity for detecting low levels of illumination and intermittent point sources of bioluminescent light. In this study, we investigate the diversity of the visual system of the lanternfish (Myctophidae). We focus specifically on the photoreceptor cells by examining their size, arrangement, topographic distribution and contribution to optical sensitivity in 53 different species from 18 genera. We also examine the influence(s) of both phylogeny and ecology on these photoreceptor variables using phylogenetic comparative analyses in order to understand the constraints placed on the visual systems of this large group of mesopelagic fishes at the first stage of retinal processing. We report great diversity in the visual system of the Myctophidae at the level of the photoreceptors. Photoreceptor distribution reveals clear interspecific differences in visual specialisations (areas of high rod photoreceptor density), indicating potential interspecific differences in interactions with prey, predators and/or mates. A great diversity in photoreceptor design (length and diameter) and density is also present. Overall, the myctophid eye is very sensitive compared to other teleosts and each species seems to be specialised for the detection of a specific signal (downwelling light or bioluminescence), potentially reflecting different visual demands for survival. Phylogenetic comparative analyses highlight several relationships between photoreceptor characteristics and the ecological variables tested (depth distribution and luminous tissue patterns). Depth distribution at night was a significant factor in most of the models tested, indicating that vision at night is of great importance for lanternfishes and may drive the evolution of their photoreceptor design. PMID:24927016

Interaction Between Downwelling Flow and the Laterally-Varying Thickness of the North American Lithosphere Inferred from Seismic Anisotropy

NASA Astrophysics Data System (ADS)

Behn, M. D.; Conrad, C. P.; Silver, P. G.

2005-12-01

Shear flow in the asthenosphere tends to align olivine crystals in the direction of shear, producing a seismically anisotropic asthenosphere that can be detected using a number of seismic techniques (e.g., shear-wave splitting (SWS) and surface waves). In the ocean basins, where the asthenosphere has a relatively uniform thickness and lithospheric anisotropy appears to be small, observed azimuthal anisotropy is well fit by asthenospheric shear flow in global flow models driven by a combination of plate motions and mantle density heterogeneity. In contrast, beneath the continents both the lithospheric ceiling and asthenospheric thickness may vary considerably across cratonic regions and ocean-continent boundaries. To examine the influence of a continental lithosphere with variable thickness on predictions of continental seismic anisotropy, we impose lateral variations in lithospheric viscosity in global models of mantle flow driven by plate motions and mantle density heterogeneity. For the North American continent, the Farallon slab descends beneath a deep cratonic root, producing downwelling flow in the upper mantle and convergent flow beneath the cratonic lithosphere. We evaluate both the orientation of the predicted azimuthal anisotropy and the depth dependence of radial anisotropy for this downwelling flow and find that the inclusion of a strong continental root provides an improved fit to observed SWS observations beneath the North American craton. Thus, we hypothesize that at least some continental anisotropy is associated with sub-lithospheric viscous shear, although fossil anisotropy in the lithospheric layer may also contribute significantly. Although we do not observe significant variations in the direction of predicted anisotropy with depth, we do find that the inclusion of deep continental roots pushes the depth of the anisotropy layer deeper into the upper mantle. We test several different models of laterally-varying lithosphere and asthenosphere viscosity. These models can be used to separate the contributions of asthenospheric flow and lithospheric fossil fabric in observations of continental anisotropy.

The Surface Radiation Budget over Oceans and Continents.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Prata, A. J.; Rotstayn, L. D.; McAvaney, B. J.; Cusack, S.

1998-08-01

An updated evaluation of the surface radiation budget in climate models (1994-96 versions; seven datasets available, with and without aerosols) and in two new satellite-based global datasets (with aerosols) is presented. All nine datasets capture the broad mean monthly zonal variations in the flux components and in the net radiation, with maximum differences of some 100 W m2 occurring in the downwelling fluxes at specific latitudes. Using long-term surface observations, both from land stations and the Pacific warm pool (with typical uncertainties in the annual values varying between ±5 and 20 W m2), excess net radiation (RN) and downwelling shortwave flux density (So) are found in all datasets, consistent with results from earlier studies [for global land, excesses of 15%-20% (12 W m2) in RN and about 12% (20 W m2) in So]. For the nine datasets combined, the spread in annual fluxes is significant: for RN, it is 15 (50) W m2 over global land (Pacific warm pool) in an observed annual mean of 65 (135) W m2; for So, it is 25 (60) W m2 over land (warm pool) in an annual mean of 176 (197) W m2.The effects of aerosols are included in three of the authors' datasets, based on simple aerosol climatologies and assumptions regarding aerosol optical properties. They offer guidance on the broad impact of aerosols on climate, suggesting that the inclusion of aerosols in models would reduce the annual So by 15-20 W m2 over land and 5-10 W m2 over the oceans. Model differences in cloud cover contribute to differences in So between datasets; for global land, this is most clearly demonstrated through the effects of cloud cover on the surface shortwave cloud forcing. The tendency for most datasets to underestimate cloudiness, particularly over global land, and possibly to underestimate atmospheric water vapor absorption, probably contributes to the excess downwelling shortwave flux at the surface.

Impacts of Advection Fog on the Surface Radiation Budget in coastal California

NASA Astrophysics Data System (ADS)

Oliphant, A. J.; Baguskas, S. A.

2016-12-01

Clouds and other aerosols alter the nature of the surface radiation budget (SRB) by reducing the quantity and changing the quality of solar radiation incident upon the surface as well as enhancing down-welling thermal infrared radiation (TIR) and suppressing upwelling TIR during daytime. Our study aimed to characterize the impact of advection fog on SRB components in coastal California, and develop methods to identify and characterize fog events using surface-mounted radiometers. First, we generated a climatology of summertime SRB components based on observations from south-western San Francisco, CA (2005-2008). From this we drew clear distinctions in characteristic surface radiation regimes between foggy and clear-sky days using atmospheric transmission indices during the day and down-welling TIR at any time of day. Secondly, we applied these empirical models to a dataset gathered in 2016 on a coastal strawberry farm located in the fog-belt in the Salinas Valley, California. From this we investigated methods to improve the models to distinguish fog events that cause surface deposition from those when the stratocumulus deck is slightly elevated, i.e., overcast conditions. On average, coastal fog was found to decrease incident solar radiation by about 50% and increase the diffuse fraction by 81%. There was a mean difference of about 70 W m-2 in down-welling TIR between clear-sky and foggy conditions throughout the diurnal cycle, with a standard deviation of less than 10 W m-2, which allows robust 24-hr estimates of fog presence using simple thresholds. As the cloud base lowers in elevation during fog events, the differences in temperature between the cloud base and surface is reduced; therefore, the ratio of opposing TIR fluxes is related to cloud base heights and should help disentangle `fog' events to better inform environmental drivers of coastal ecosystems.

Formation and evolution of Lakshmi Planum, Venus: Assessment of models using observations from geological mapping

NASA Astrophysics Data System (ADS)

Ivanov, M. A.; Head, J. W.

2008-12-01

Detailed geological analysis of the Lakshmi Planum region of western Ishtar Terra results in the establishment of the sequence of major events during the formation and evolution of western Ishtar Terra, an important and somewhat unique area on Venus characterized by a raised volcanic plateau surrounded by distinctive folded mountain belts, such as Maxwell Montes. These mapping results and the stratigraphic and structural relationships provide a basis for addressing the complicated problem of Lakshmi Planum formation and for testing the suite of models previously proposed to explain this structure. We review and classify previous models of formation for western Ishtar Terra into "downwelling" models (generally involving convergence and underthrusting) and "upwelling" models (generally involving plume-like upwelling and divergence). The interpreted nature of units and the sequence of events derived from geological mapping are in contrast to the predictions of the divergent models. The major contradictions are as follows: (1) The very likely presence of an ancient (craton-like) tessera massif in the core of Lakshmi, which is inconsistent with the model of formation of Lakshmi due to rise and collapse of a mantle diapir; (2) The absence of rift zones in the interior of Lakshmi that are predicted by the divergent models; (3) The apparent migration of volcanic activity toward the center of Lakshmi, whereas divergent models predict the opposite trend; (4) The abrupt cessation of ridges of the mountain ranges at the edge of Lakshmi Planum and propagation of these ridges over hundreds of kilometers outside Lakshmi; the divergent models predict the opposite progression in the development of major contractional features. In contrast, convergent models of formation and evolution of Lakshmi Planum appear to be more consistent with the observations and explain this structure by collision and underthrusting/subduction of lower-lying plains with the elevated and rigid block of tessera. These models are capable of explaining formation of the major features of western Ishtar (for example, the mountain belts), the sequences of events, and principal volcanic and tectonic trends during the evolution of Lakshmi. To explain the pronounced north-south asymmetry of Lakshmi these models need to consider the likelihood that the major focal points of collision are at the north and north-west margins of the plateau. We note that pure downwelling models, however, face three important difficulties: (1) The possibly unrealistically long time span that appears to be required to produce the major features of Lakshmi; (2) The strong north-south asymmetry of the Planum; the pure downwelling models predict the formation of a more symmetrical structure; and (3) The absence of radial contractional structures (arches and ridges) in the interior of Lakshmi that would represent the predictions of the downwelling models.

Upwelling Response to Hurricane Isaac in Geostrophic Oceanic Vortices

NASA Astrophysics Data System (ADS)

Jaimes, B.; Shay, L. K.; Brewster, J. K.; Schuster, R.

2013-05-01

As a tropical cyclone (TC) moves over the ocean, the cyclonic curl of the wind stress produces a region of upwelling waters under the TC center that is compensated by downwelling waters at regions outside the center. Direct measurements conducted during hurricane Rita and recent numerical studies indicate that this is not necessarily the case when TCs move over geostrophic oceanic features, where its background relative vorticity impacts wind-driven horizontal current divergence and the upwelling velocity. Modulation of the upwelling response in these energetic oceanic regimes impacts vertical mixing across the oceanic mixed layer base, air-sea fluxes into the atmosphere, and ultimately storm intensity. As part of NOAA Intensity Forecasting Experiment, an experiment was conducted during the passage of TC Isaac over the energetic geostrophic eddy field in the Gulf of Mexico in August 2012. Expendable bathythermographs, current profilers, and conductivity-temperature-depth probes were deployed in Isaac from NOAA WP-3D aircraft during four in-storm flights to measure oceanic variability and its impact on TC-driven upwelling and surface fluxes of heat and momentum. During intensification to hurricane, the cyclonic curl of the wind stress of Isaac extended over a region of more than 300 km in diameter (4 to 5 times the radius of maximum winds). Isaac's center moved over a cold cyclonic feature, while its right and left sides moved over warm anticyclones. Contrasting upwelling and downwelling regimes developed inside the region of cyclonic curl of the wind stress. Both positive (upwelling) and negative (downwelling) vertical displacements of 40 and 60 m, respectively, were measured inside the region of cyclonic curl of the wind stress, which are between 3 to 4 times larger than predicted vertical displacements for a quiescent ocean based on scaling arguments. Oceanic mixed layer (OML) currents of 0.2 to 0.7 m s-1 were measured, which are about 50% smaller than the expected velocity response under quiescent oceanic conditions. Although OML currents were measured inside the core of cyclonic curl of the wind stress, their orientation is not consistent with horizontally divergent flows typically found in upwelling regimes under TC centers. Theoretical predictions that consider background relative vorticity effects on the upwelling response mimic the contrasting upwelling/downwelling regimes inside the region of cyclonic curl of the wind stress. These results point to an important modulation of the OML current and upwelling response by background oceanic flows, where the upwelling velocity is a function of the curl of wind-intensified pre-storm geostrophic currents, rather than just a function of the curl of the wind stress. Thus, properly initializing temperature and salinity fields in numerical models is needed to accurately represent these oceanic processes in coupled forecast models.

Assessment of the effect of air pollution controls on trends in shortwave radiation over the United States from 1995 through 2010 from multiple observation networks

EPA Science Inventory

Long-term data sets of all-sky and clear-sky downwelling shortwave (SW) radiation, cloud cover fraction, and aerosol optical depth (AOD) were analyzed together with surface concentrations from several networks (e.g., Surface Radiation Budget Network (SURFRAD), Clean Air Status an...

TEMPORAL AND SPATIAL VARIATION IN SOLAR RADIATION AND PHOTO-ENHANCED TOXICITY RISKS OF SPILLED OIL IN PRINCE WILLIAM SOUND, ALASKA

EPA Science Inventory

Solar irradiance (W/m2) and downwelling diffuse attenuation coefficients (Kd; m-1) were determined in several locations in Prince William Sound, Alaska, USA, between April 2003 and December 2005 to assess temporal and spatial variation in solar radiation and the risks of photoenh...

A toy model linking atmospheric thermal radiation and sea ice growth

NASA Technical Reports Server (NTRS)

Thorndike, A. S.

1992-01-01

A simplified analytical model of sea ice growth is presented where the atmosphere is in thermal radiative equilibrium with the ice. This makes the downwelling longwave radiation reaching the ice surface an internal variable rather than a specified forcing. Analytical results demonstrate how the ice state depends on properties of the ice and on the externally specified climate.

Bio-physical changes in the coastal ocean triggered by typhoon: A case of Typhoon Meari in summer 2011

NASA Astrophysics Data System (ADS)

Wu, Xiao; Wang, Houjie; Bi, Naishuang; Song, Zhenjie; Zang, Zhengchen; Kineke, Gail C.

2016-12-01

Based on the combination of synchronous satellite and in-situ observations, we here, for the first time, provide the compelling evidence of bio-physical response of coastal environment in the Bohai Sea (China) to the passage of Typhoon Meari over the northern Yellow Sea on June 26, 2011. Strong sustained winds induced a tongue-like intrusion of cool water from the northern Yellow Sea into the Bohai Sea, resulting in significant surface cooling and an anomalous increase in sea surface height along the coast of the western Bohai Sea. This, in return, produced downwelling and transport of the warm and nutrient-rich coastal water from the western coast to the central Bohai Sea, as driven by the barotropic pressure gradient force. In-situ observational data confirmed the cooling of both surface and bottom layers with salinity increase; however, the measured temperature increase by 2-3 °C, concomitant salinity decrease by 0.3 PSU and two-fold increase in chlorophyll-a in the middle layers suggested an influence from coastal downwelling. Ekman transport and typhoon-enhanced mixing redistributed the nutrients and thus resulted in higher chlorophyll-a concentrations in the upper layers.

Can lower mantle slab-like seismic anomalies be explained by thermal coupling between the upper and lower mantles?

NASA Astrophysics Data System (ADS)

Čížková, Hana; Čadek, Ondřej; van den Berg, Arie P.; Vlaar, Nicolaas J.

Below subduction zones, high resolution seismic tomographic models resolve fast anomalies that often extend into the deep lower mantle. These anomalies are generally interpreted as slabs penetrating through the 660-km seismic discontinuity, evidence in support of whole-mantle convection. However, thermal coupling between two flow systems separated by an impermeable interface might provide an alternative explanation of the tomographic results. We have tested this hypothesis within the context of an axisymmetric model of mantle convection in which an impermeable boundary is imposed at a depth of 660 km. When an increase in viscosity alone is imposed across the impermeable interface, our results demonstrate the dominant role of mechanical coupling between shells, producing lower mantle upwellings (downwellings) below upper mantle downwellings (upwellings). However, we find that the effect of mechanical coupling can be significantly weakened if a narrow low viscosity zone exists beneath the 660-km discontinuity. In such a case, both thermally induced ‘slabs’ in the lower mantle and thermally activated plumes that rise from the upper/lower mantle boundary are observed even though mass transfer between the shells does not exist.

The Characteristics of Marine Environment around the Ieodo in Aug. 2016

NASA Astrophysics Data System (ADS)

Choi, E.; KIM, S. H.; KIM, E.; KIM, B. N.; CHOI, B. K.

2017-12-01

The sea area around Ieodo is analyzed from the CTD data and the S-ADCP data observed in 23 Aug. 2016. Ieodo, an underwater reef, is located 149 km southwest of Marado in Republic of Korea. It has 4 peaks and is about 4.6 meter below sea level. It stretches about 600m north to south and 750m east to west from its top. It has the same geographical characteristics as the seamount. In the sea area around Ieodo, the northward flow appeared during the ebb tide, the southward flow appeared during the flood tide. The strong stratification formed in summer seems to change the depth depending on the sea water current. The thermocline depth becomes deeper at the north of the Ieodo when the northward current flows and the upwelling flow occurs. And the thermocline depth becomes shallower at the south when the southward current flows and the downwelling flow occurs. In this way, the upwelling and downwelling seems to be according to the tide's direction. Acknowledgements This research was a part of the projects entitled "Construction of Ocean Research Stations and their application Studies, Phase 2", funded by the Ministry of Oceans and Fisheries, Korea.

Direct nutritional link between 600-m deep cold-water corals and surface productivity

NASA Astrophysics Data System (ADS)

Soetaert, Karline; Mohn, Christian; Rengstorff, Anna; Grehan, Anthony; van Oevelen, Dick

2016-04-01

Cold-water corals (CWC) form deep-sea reefs that are found in all of the world's oceans, with an areal extent at par with that of tropical coral reefs, and are recognised hotspots of biodiversity and metabolic activity. Yet, it remains largely enigmatic how these rich CWC reefs can thrive in a cold and dark environment that is considered to be strongly food-limited. Here, we use a novel benthic-pelagic modeling approach, which involves coupling models of hydrodynamics, biogeochemistry and habitat suitability, to unravel organic matter delivery to reef mounds at a water depth of 600 m that are capped with a thriving CWC reef community at Rockall Bank (NE Atlantic). Model simulations show that the interaction between 300-m high reef mounds and spring tidal currents induces episodic downwelling events that establish a vertical coupling between 600-m deep CWC with surface productivity. We therefore conclude that there is a positive feedback between CWC mound growth and organic matter supply. This episodic downwelling strongly enhances carbon sequestration to the deep ocean and the ubiquitous occurrence of topographic rises along the ocean margins suggests that a topographically-induced benthic-pelagic carbon pump could be of global importance.

The Rossby Centre Regional Atmospheric Climate Model part II: application to the Arctic climate.

PubMed

Jones, Colin G; Wyser, Klaus; Ullerstig, Anders; Willén, Ulrika

2004-06-01

The Rossby Centre regional climate model (RCA2) has been integrated over the Arctic Ocean as part of the international ARCMIP project. Results have been compared to observations derived from the SHEBA data set. The standard RCA2 model overpredicts cloud cover and downwelling longwave radiation, during the Arctic winter. This error was improved by introducing a new cloud parameterization, which significantly improves the annual cycle of cloud cover. Compensating biases between clear sky downwelling longwave radiation and longwave radiation emitted from cloud base were identified. Modifications have been introduced to the model radiation scheme that more accurately treat solar radiation interaction with ice crystals. This leads to a more realistic representation of cloud-solar radiation interaction. The clear sky portion of the model radiation code transmits too much solar radiation through the atmosphere, producing a positive bias at the top of the frequent boundary layer clouds. A realistic treatment of the temporally evolving albedo, of both sea-ice and snow, appears crucial for an accurate simulation of the net surface energy budget. Likewise, inclusion of a prognostic snow-surface temperature seems necessary, to accurately simulate near-surface thermodynamic processes in the Arctic.

Evolution of high-temperature geothermal brine production pumps

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

Ellis, P.F. II

1989-01-01

Geothermal resources with temperatures between 250{degrees} and 360{degrees}F (121{degrees} and 182{degrees}C) are prime candidates for binary-cycle power generation in the United States and abroad, and constitute about 80% of the known power-capable resources in the United States. Initially there were many technological obstacles to exploitation of these resources, with one of the greatest being the absence of reliable high-capacity downwell brine production pumps to supply the required amounts of brine from an economically small group of wells. Early experience revealed many problems with downwell pumps, resulting in a mean-time-to-failure (MTTF) in 1981 of less than 1000 hours for the bestmore » available technology. This paper reports how evolutionary advances in pump design and materials selection have resolved most of the early problems, producing third- generation pumps which have run as long as 20,000 hours. Pump life extension practices - greatly enhanced component and assembly quality control, increased care in pump installation, and continuous monitoring of pump performance with swift intervention at the first signs of distress - have essentially eliminated premature failure where implemented, leading to estimated near-term MTTFs of 8000 hours.« less

Local effects of partly cloudy skies on solar and emitted radiations

NASA Technical Reports Server (NTRS)

Whitney, D. A.; Venable, D. D.

1981-01-01

Solar radiation measurements are made on a routine basis. Global solar, atmospheric emitted, downwelled diffuse solar, and direct solar radiation measurement systems are fully operational with the first two in continuous operation. Fractional cloud cover measurements are made from GOES imagery or from ground based whole sky photographs. Normalized global solar irradiance values for partly cloudy skies were correlated to fractional cloud cover.

Numerical study of turbulent channel flow perturbed by spanwise topographic heterogeneity: Amplitude and frequency modulation within low- and high-momentum pathways

NASA Astrophysics Data System (ADS)

Awasthi, Ankit; Anderson, William

2018-04-01

We have studied the effects of topographically driven secondary flows on inner-outer interaction in turbulent channel flow. Recent studies have revealed that large-scale motions in the logarithmic region impose an amplitude and frequency modulation on the dynamics of small-scale structures near the wall. This led to development of a predictive model for near-wall dynamics, which has practical relevance for large-eddy simulations. Existing work on amplitude modulation has focused on smooth-wall flows; however, Anderson [J. Fluid Mech. 789, 567 (2016), 10.1017/jfm.2015.744] addressed the problem of rough-wall turbulent channel flow in which the correlation profiles for amplitude modulation showed trends similar to those reported by Mathis et al. [Phys. Fluids 21, 111703 (2009), 10.1063/1.3267726]. For the present study, we considered flow over surfaces with a prominent spanwise heterogeneity, such that domain-scale turbulent secondary flows in the form of counter-rotating vortices are sustained within the flow. (We also show results for flow over a homogeneous roughness, which serves as a benchmark against the spanwise-perturbed cases.) The vortices are anchored to the topography such that prominent upwelling and downwelling occur above the low and high roughness, respectively. We have quantified the extent to which such secondary flows disrupt the distribution of spectral density across constituent wavelengths throughout the depth of the flow, which has direct implications for the existence of amplitude and frequency modulation. We find that the distinct outer peak associated with large-scale motions—the "modulators"—is preserved within the upwelling zone but vanishes in the downwelling zone. Within the downwelling zones, structures are steeper and shorter. Single- and two-point correlations for inner-outer amplitude and frequency modulation demonstrate insensitivity to resolution across cases. We also show a pronounced crossover between the single- and two-point correlations, a product of modulation quantification based upon Parseval's theorem (i.e., spectral density, but not the wavelength at which energy resides, defines the strength of modulation).

Evidence of Boundary Reflection of Kelvin and First-Mode Rossby Waves from Topex/Poseidon Sea Level Data

NASA Technical Reports Server (NTRS)

Boulanger, Jean-Philippe; Fu, Lee-Lueng

1996-01-01

The TOPEX/POSEIDON sea level data lead to new opportunities to investigate some theoretical mechanisms suggested to be involved in the El Nino-Southern Oscillation phenomenon in the tropical Pacific ocean. In particular, we are interested in studying the western boundary reflection, a process crucial for the delayed action oscillator theory, by using the TOPEX/POSEIDON data from November 1992 to May 1995. We first projected the sea level data onto Kelvin and first-mode Ross waves. Then we estimated the contribution of wind forcing to these waves by using a single baroclinic mode simple wave model forced by the ERS-1 wind data. Wave propagation was clearly observed with amplitudes well explained by the wind forcing in the ocean interior. Evidence of wave reflection was detected at both the western and eastern boundaries of the tropical Pacific ocean. At the eastern boundary, Kelvin waves were seen to reflect as first-mode Rossby waves during the entire period. The reflection efficiency (in terms of wave amplitude) of the South American coasts was estimated to be 80% of that of an infinite meridional wall. At the western boundary, reflection was observed in April-August 1993, in January-June 1994, and, later, in December 1994 to February 1995. Although the general roles of these reflection events in the variability observed in the equatorial Pacific ocean are not clear, the data suggest that the reflections in January-June 1994 have played a role in the onset of the warm conditions observed in late 1994 to early 1995. Indeed, during the January-June 1994 period, as strong downwelling first-mode Rossby waves reflected into downwelling Kelvin waves, easterly wind and cold sea surface temperature anomalies located near the date line weakened and eventually reversed in June-July 1994. The presence of the warm anomalies near the date line then favored convection and westerly wind anomalies that triggered strong downwelling Kelvin waves propagating throughout the basin simultaneously with the beginning of the 1994-1995 warm conditions.

Circulation patterns in active lava lakes

NASA Astrophysics Data System (ADS)

Redmond, T. C.; Lev, E.

2014-12-01

Active lava lakes provide a unique window into magmatic conduit processes. We investigated circulation patterns of 4 active lava lakes: Kilauea's Halemaumau crater, Mount Erebus, Erta Ale and Nyiragongo, and in an artificial "lava lake" constructed at the Syracuse University Lava Lab. We employed visual and thermal video recordings collected at these volcanoes and use computer vision techniques to extract time-dependent, two-dimensional surface velocity maps. The large amount of data available from Halemaumau enabled us to identify several characteristic circulation patterns. One such pattern is a rapid acceleration followed by rapid deceleration, often to a level lower than the pre-acceleration level, and then a slow recovery. Another pattern is periodic asymmetric peaks of gradual acceleration and rapid deceleration, or vice versa, previously explained by gas pistoning. Using spectral analysis, we find that the dominant period of circulation cycles at approximately 30 minutes, 3 times longer than the dominant period identified previously for Mount Erebus. Measuring a complete surface velocity field allowed us to map and follow locations of divergence and convergence, therefore upwelling and downwelling, thus connecting the surface flow with that at depth. At Nyiragongo, the location of main upwelling shifts gradually, yet is usually at the interior of the lake, for Erebus it is usually along the perimeter yet often there is catastrophic downwelling at the interior; For Halemaumau upwelling/downwelling position is almost always on the perimeter. In addition to velocity fields, we developed an automated tool for counting crustal plates at the surface of the lava lakes, and found a correlation, and a lag time, between changes if circulation vigor and the average size of crustal plates. Circulation in the artificial basaltic lava "lake" was limited by its size and degree of foaming, yet we measured surface velocities and identify patterns. Maximum surface velocity showed symmetrical peaks of acceleration and deceleration. In summary, extended observations at lava lakes reveal patterns of circulations at different time scales, yielding insight into different processes controlling the exchange of gas and fluids between the magma chamber and conduit, and the surface and atmosphere.

Evolution of the Marginal Ice Zone: Adaptive Sampling with Autonomous Gliders

DTIC Science & Technology

2015-09-30

kinetic energy (ε). Gliders also sampled dissolved oxygen, optical backscatter ( chlorophyll and CDOM fluorescence) and multi-spectral downwelling...Fig. 2). In the pack, Pacific Summer Water and a deep chlorophyll maximum form distinct layers at roughly 60 m and 80 m, respectively, which become...Sections across the ice edge just prior to recovery, during freeze-up, reveal elevated chlorophyll fluorescence throughout the mixed layer (Fig. 4

Physical Processes in Coastal Stratocumulus Clouds from Aircraft Measurements During UPPEF 2012

DTIC Science & Technology

2013-09-01

pressure, dew point, water vapor, absolute humidity, and carbon dioxide concentration. There were various upward and downward looking pyranometers ...Meteorological parameters IR Temperature -50 to +20 °C Up-looking modified Kipp & Zonen CM-22 pyranometer (CIRPAS/NRL) Meteorological parameters Down...welling Solar Irradiance 0-1400 W m -2 Down-looking modified Kipp & Zonen CM-22 pyranometer (CIRPAS/NRL) Meteorological parameters Up-welling Solar

Effects of Greenhouse Gas Increase and Stratospheric Ozone Depletion on Stratospheric Mean Age of Air in 1960-2010

NASA Technical Reports Server (NTRS)

Li, Feng; Newman, Paul; Pawson, Steven; Perlwitz, Judith

2018-01-01

The relative impacts of greenhouse gas (GHG) increase and stratospheric ozone depletion on stratospheric mean age of air in the 1960-2010 period are quantified using the Goddard Earth Observing System Chemistry-�Climate Model. The experiment compares controlled simulations using a coupled atmosphere-�ocean version of the Goddard Earth Observing System Chemistry-�Climate Model, in which either GHGs or ozone depleting substances, or both factors evolve over time. The model results show that GHGs and ozone-depleting substances have about equal contributions to the simulated mean age decrease, but GHG increases account for about two thirds of the enhanced strength of the lower stratospheric residual circulation. It is also found that both the acceleration of the diabatic circulation and the decrease of the mean age difference between downwelling and upwelling regions are mainly caused by GHG forcing. The results show that ozone depletion causes an increase in the mean age of air in the Antarctic summer lower stratosphere through two processes: (1) a seasonal delay in the Antarctic polar vortex breakup that inhibits young midlatitude air from mixing with the older air inside the vortex, and (2) enhanced Antarctic downwelling that brings older air from middle and upper stratosphere into the lower stratosphere.

Visual Sensitivity of Deepwater Fishes in Lake Superior

PubMed Central

Harrington, Kelly A.; Hrabik, Thomas R.; Mensinger, Allen F.

2015-01-01

The predator-prey interactions in the offshore food web of Lake Superior have been well documented, but the sensory systems mediating these interactions remain unknown. The deepwater sculpin, (Myoxocephalus thompsoni), siscowet (Salvelinus namaycush siscowet), and kiyi (Coregonus kiyi) inhabit low light level environments. To investigate the potential role of vision in predator-prey interactions, electroretinography was used to determine visual sensitivity for each species. Spectral sensitivity curves revealed peak sensitivity at 525 nm for each species which closely corresponds to the prevalent downwelling light spectrum at depth. To determine if sufficient light was available to mediate predator-prey interactions, visual sensitivity was correlated with the intensity of downwelling light in Lake Superior to construct visual depth profiles for each species. Sufficient daytime irradiance exists for visual interactions to approximately 325 m for siscowet and kiyi and 355 m for the deepwater sculpin during summer months. Under full moon conditions, sufficient irradiance exists to elicit ERG response to light available at approximately 30 m for the siscowet and kiyi and 45 m for the deepwater sculpin. Visual interactions are therefore possible at the depths and times when these organisms overlap in the water column indicating that vision may play a far greater role at depth in deep freshwater lakes than had been previously documented. PMID:25646781

Diffuse attenuation coefficient for downwelling irradiance at 490 nm and its spectral characteristics in the Black Sea upper layer: modeling, in situ measurements and ocean color data

NASA Astrophysics Data System (ADS)

Suslin, V. V.; Slabakova, V. K.; Churilova, T. Ya.

2017-11-01

Vertical diffuse attenuation coefficient, Kd(490), is one of the key parameter required for water quality modeling, hydrodynamic and biological processes in the sea. We showed that standard level-2 product of Kd(490) was underestimated in comparison with Kd(490) values simulated by the regional model during the diatom bloom in the Black Sea. Using data of SeaWiFS, MERIS and MODIS color scanners, a regional relationship between the model value of Kd(490) and the ratio of remote sensing reflectances has been obtained. Based on the bulgarian argo-bio-buoy dataset, the relationship between the attenuation coefficient of photosynthetically active radiation and attenuation coefficient at a wavelength of 490 nm is obtained. The simplified model, below as the S-model, of the diffuse attenuation coefficient spectrum for downwelling irradiance in the Black Sea upper layer is described. As a consequence of the S-model, the link between the depth of the euphotic zone and Kd(490) has been obtained. It is shown that the Kd(490) values, retrieved from ocean color data with using the regional link and from argo-bio-buoy measurements at depths between 6-20 m, are close to each other.

On the relative role of meridional convergence and downwelling motion during the heat buildup leading to El Niño events

NASA Astrophysics Data System (ADS)

Ballester, Joan; Bordoni, Simona; Petrova, Desislava; Rodó, Xavier

2015-04-01

Despite steady progress in the understanding of El Niño-Southern Oscillation (ENSO) in the past decades, questions remain on the exact mechanisms leading to the onset of El Niño (EN) events. Several authors have highlighted how the subsurface heat buildup in the western tropical Pacific and the recharged phase in equatorial heat content are intrinsic elements of ENSO variability, leading to those changes in zonal wind stress, sea surface temperature and thermocline tilt that characterize the growing and mature phases of EN. Here we use an ensemble of ocean and atmosphere assimilation products to identify the mechanisms contributing to the heat buildup that precedes EN events by about 18-24 months on average. Anomalous equatorward subsurface mass convergence due to meridional Sverdrup transport is found to be an important mechanism of thermocline deepening near and to the east of the dateline. In the warm pool, instead, surface horizontal convergence and downwelling motion have a leading role in subsurface warming, since equatorward mass convergence is weaker and counterbalanced by subsurface zonal divergence. The picture emerging from our results highlights the complexity of the three dimensional dynamic and thermodynamic structure of the tropical Pacific during the heat buildup leading to EN events.

Coldspots or hotspots? The origin of plateau-shaped highlands on Venus

NASA Technical Reports Server (NTRS)

Bindschadler, D. L.

1992-01-01

A compelling question for the terrestrial planets is the origin of the highland regions on Venus. Data on the topography, gravity signature, and surface morphology returned by the Pioneer Venus, Venera 15/16, and Magellan spacecraft represent a basis for dividing these highlands into two distinct groups: volcanic rises and plateau-shaped highlands. Volcanic rises are generally thought to be due to mantle upwellings in the form of large mantle plumes and are thus similar in origin to terrestrial hotspots. There is less agreement as to the origin of plateau-shaped highlands (PSH). Coldspot mantle downwelling can lead to the formation of a highland region under Venus conditions, and previous to Magellan some PSH (particularly W. Ishtar Terra and Ovda and Thetis Regiones) were suggested to be compressionally deformed regions of thickened crust created by mantle downwelling. A hotspot model proposes that such regions are formed by magmatism and tectonism related to the near-surface ascent of either the diapir-shaped large mantle plume or a solitary disturbance propagating up a plume conduit. The characteristics of both volcanic rises and plateau-shaped highlands on Venus and the models for their formation are briefly reviewed, and tests that may help to make clear which model best explains the plateau-shaped highlands are considered.

Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo

NASA Astrophysics Data System (ADS)

Takahashi, F.

2011-12-01

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.

Ockham's Razorblade Shaving Wind-Induced Circulation

NASA Astrophysics Data System (ADS)

Bergmann, Juan Carlos

2010-05-01

Terrestrial physical oceanography is fortunate because of the existence of the continents that divide the low-latitude oceans into basins. At first glance, the previous statement appears to be not obvious because an ocean-planet should be much simpler to describe. Simple-case explanation is the central aspect of Ockham's Razorblade: If a theory fails to describe the most-simple case properly, the theory is, at least, ‘not good'. Also Descartes' methodical rules take the most-simple case as starting point. The analysis of wind-induced circulation on an ocean-planet will support the initial statement. Earth's south hemisphere is dominated by the oceans. The continents' influence on the zonal-average zonal-wind climate is relatively small. Therefore, South Hemisphere's zonal wind pattern is a relatively good proxy for that of an ocean planet. Application of this wind-stress pattern to an ocean planet yields reasonable meridional mass-flow results from the polar-regions down to the high-pressure belts: Down-welling and up-welling of water-mass are approximately balanced. However, the entire tropical circulation can in principle not be closed because there is only down-welling - even if the extreme down-welling in the equatorial belt (± 8°, with a singularity at the equator) is disregarded. The only input to the calculations is the observed terrestrial south-hemisphere zonal wind-stress pattern. Meridional stress is irrelevant because it produces a closed zonal Ekman-transport around the ocean planet (sic!). Vertical mass-transport is calculated from the divergence of the wind-induced meridional Ekman-mass-transport, which in its turn is a necessary consequence of angular-momentum conservation. No assumptions are made on how the return-flows at depth are forced because the wind-force equations cannot contribute hereto. This circumstance expresses a fundamental difference to atmospheric circulation, where mechanical forcing is caused by the pressure-fields that result from differential heating/cooling and therefore ‘automatically' comprise the entire circulation system. Wind-caused oceanic flow is exclusively generated by frictional wind-forces at the surface, and other processes in the ocean are not causally connected hereto. In absence of continents it is quite difficult to ‘find' the corresponding forcing for the meridional return-flows - and it can definitely not be wind-force-caused - very strange! The fact that the wind-induced circulation can only be closed by the action of other processes, which are not causally connected to wind-forces, demonstrates that something must be fundamentally wrong. The singularity at the equator and the extreme down-welling in the equatorial belt indicate an additional severe problem that can only be avoided if zonal wind-stress is completely excluded. Escape to additional assumptions is similar to the introduction of the epicycles in order to explain the planets' retrograde motion in maintaining geocentric cosmology. Should the previous analysis be ignored in favour of maintaining the ‘established' ideas of wind-induced circulation or should there be an effort to formulate new ideas that provide closed and balanced circulation without employing other processes than wind-forces?

Quantum phases and phase transitions in disordered low-dimensional systems: thin film superconductors, bilayer two-dimensional electron systems, and one-dimensional optical lattices

NASA Astrophysics Data System (ADS)

Zhang, Nan

Understanding the Earth's evolution is a fundamental goal of geophysics. The mantle plays the key role in understanding the Earth's evolution. The convective planform of the mantle influences the energy exchange of the core on the core-mantle boundary (CMB) and hence the geodynamo process, determines the heat release and hence the thermal evolution of the Earth, and shapes the long wavelength topography on the surface of the Earth. Given the observationally constrained mantle viscosity structure, and realistic convective vigor and internal heating rate, the numerical modeling of mantle convection shows that the mobile-lid mantle convection is characterized by either a spherical harmonic degree-1 planform with a major upwelling in one hemisphere and a major downwelling in the other hemisphere when continents are absent, or a degree-2 planform with two antipodal major upwellings when a supercontinent is present. The Earth's mantle evolves from one to the other of these two modes due to modulation of continents, causing the cyclic processes of assembly and breakup of supercontinents. However, to constrain the realistically temporal evolution of mantle convection, other observations such as the time-dependent plate motion and geological records are needed. I reconstruct a proxy model for global plate motion for the last 450 Myr. Using the proxy plate motion model as time dependent boundary conditions, I reproduce well the basic features of the present-day mantle structure including the African and Pacific superplumes and chemical piles, and a predominantly degree 2 structure throughout the lower mantle. I further demonstrate that the mantle in the African hemisphere around the Pangea time is predominated by cold downwellings resulting from the convergence between Gondwana and Laurussia, consistent with the 1-2-1 cyclic model from the numerical modeling of mantle convection. Based on the evolution of the three-dimensional mantle structures, I reconstruct tempo-spatial evolutions of the surface and CMB heat fluxes, and the dynamic topography since the Paleozoic. My result shows that the surface heat flux increases by ~16% from 200 to 120 Ma ago as a result of Pangea breakup and the equatorial CMB heat flux has two minima that coincide with the Kiaman (316-262 Ma) and Cretaceous (118-83 Ma) Superchrons, respectively, and may be responsible for the Superchrons. My results of the dynamic topography show that the Slave Craton subsided when the major downwelling occupied the mantle beneath North America, while Sao Francisco Craton, Kaapvaal Craton, and Yilgarn Craton were supported by the large scale upwellings in the mantle beneath the very south of Pangea around 330 Ma during Pangea formation. After Pangea formed, Slave Craton started to uplift as the major downwelling heated up with time and were controlled by the subductions close to it. Sao Francisco Craton and Kaapvaal Craton kept uplifting due to the returning African Superplume. My reconstructed dynamic topography history compares well with the vertical motion history of Slave Craton indicated by the thermochronometry study.

Surface radiation budget for climate applications

NASA Technical Reports Server (NTRS)

Suttles, J. T. (Editor); Ohring, G. (Editor)

1986-01-01

The Surface Radiation Budget (SRB) consists of the upwelling and downwelling radiation fluxes at the surface, separately determined for the broadband shortwave (SW) (0 to 5 micron) and longwave (LW) (greater than 5 microns) spectral regions plus certain key parameters that control these fluxes, specifically, SW albedo, LW emissivity, and surface temperature. The uses and requirements for SRB data, critical assessment of current capabilities for producing these data, and directions for future research are presented.

Analysis of the In-Water and Sky Radiance Distribution Data Acquired During the Radyo Project

DTIC Science & Technology

2013-09-30

radiative transfer to model the BRDF of particulate surfaces. OBJECTIVES The major objective of this research is to understand the downwelling...of image and radiative transfer models used in the ocean. My near term ocean optics objectives have been: 1) to improve the measurement capability...directional Reflectance Distribution Function ( BRDF ) of benthic surfaces in the ocean, and 4) to understand the capabilities and limitations of using

Coastal and Submesoscale Process Studies for ASIRI and Data Serving for ASIRI Participants

DTIC Science & Technology

2014-09-30

spatial distributions of Chlorophyll fluorescence, colored dissolved organic matter (CDOM), and apparent oxygen utilization (AOU). It is evident that...Vertical section of tem perature (left) and salinity (right) w ith density in black contours, from 4 long tracks surveyed in Leg 2 (N ovem ber 2013) from...vertical derivative of the downwelling light is proportional to the radiant heating rate at depth. This figure shows that deeply penetrating blue

Downwelled longwave surface irradiance data from five sites for the FIRE/SRB Wisconsin Experiment from October 12 through November 2, 1986

NASA Technical Reports Server (NTRS)

Whitlock, Charles H.; Cox, Stephen K.; Lecroy, Stuart R.

1990-01-01

Tables are presented which show data from five sites in the First ISCCP (International Satellite Cloud Climatology Project) Regional Experiment (FIRE)/Surface Radiation Budget (SRB) Wisconsin experiment regional from October 12 through November 2, 1986. A discussion of intercomparison results is also included. The field experiment was conducted for the purposes of both intensive cirrus-cloud measurements and SRB algorithm validation activities.

Summary of Temperature Data Collected to Improve Emergence Timing Estimates for Chum and Fall Chinook Salmon in the Lower Columbia River, 1998-2004 Progress Report.

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

Arntzen, E.; Geist, D.; Hanrahan, T.

2005-10-01

From 1999 through 2004, Pacific Northwest National Laboratory collected temperature data from within chum and fall Chinook salmon spawning gravels and the overlying river at 21 locations in the Ives Island area approximately 5 km downstream from Bonneville Dam. Sample locations included areas where riverbed temperatures were elevated, potentially influencing alevin development and emergence timing. The study objectives were to (1) collect riverbed and river temperature data each year from the onset of spawning (October) to the end of emergence (June) and (2) provide those data in-season to fisheries management agencies to assist with fall Chinook and chum salmon emergencemore » timing estimates. Three systems were used over the life of the study. The first consisted of temperature sensors deployed inside piezometers that were screened to the riverbed or the river within chum and fall Chinook salmon spawning areas. These sensors required direct access by staff to download data and were difficult to recover during high river discharge. The second system consisted of a similar arrangement but with a wire connecting the thermistor to a data logger attached to a buoy at the water surface. This system allowed for data retrieval at high river discharge but proved relatively unreliable. The third system consisted of temperature sensors installed in piezometers such that real-time data could be downloaded remotely via radio telemetry. After being downloaded, data were posted hourly on the Internet. Several times during the emergence season of each year, temperature data were downloaded manually and provided to management agencies. During 2003 and 2004, the real-time data were made available on the Internet to assist with emergence timing estimates. Examination of temperature data reveals several important patterns. Piezometer sites differ in the direction of vertical flow between surface and subsurface water. Bed temperatures in upwelling areas are more stable during salmon spawning and incubation than they are in downwelling areas. Bed temperatures in downwelling areas generally reflect river temperatures. Chum and fall Chinook salmon spawning is spatially segregated, with chum salmon in upwelling areas and fall Chinook salmon in downwelling areas. Although these general patterns remain similar among the years during which data were collected, differences also exist that are dependent on interannual flow characteristics.« less

Ten-year global distribution of downwelling longwave radiation

NASA Astrophysics Data System (ADS)

Pavlakis, K. G.; Hatzidimitriou, D.; Matsoukas, C.; Drakakis, E.; Hatzianastassiou, N.; Vardavas, I.

2003-10-01

Downwelling longwave fluxes, DLFs, have been derived for each month over a ten year period (1984-1993), on a global scale with a resolution of 2.5° × 2.5°. The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles. The cloud climatologies were taken from the latest released and improved International Satellite Climatology Project D2 series. Specific humidity and temperature vertical profiles were taken from three different reanalysis datasets; NCEP/NCAR, GEOS, and ECMWF (acronyms explained in main text). DLFs were computed for each reanalysis dataset, with differences reaching values as high as 30 Wm-2 in specific regions, particularly over high altitude areas and deserts. However, globally, the agreement is good, with the rms of the difference between the DLFs derived from the different reanalysis datasets ranging from 5 to 7 Wm-2. The results are presented as geographical distributions and as time series of hemispheric and global averages. The DLF time series based on the different reanalysis datasets show similar seasonal and inter-annual variations, and similar anomalies related to the 86/87 El Niño and 89/90 La Niña events. The global ten-year average of the DLF was found to be between 342.2 Wm-2 and 344.3 Wm-2, depending on the dataset. We also conducted a detailed sensitivity analysis of the calculated DLFs to the key input data. Plots are given that can be used to obtain a quick assessment of the sensitivity of the DLF to each of the three key climatic quantities, for specific climatic conditions corresponding to different regions of the globe. Our model downwelling fluxes are validated against available data from ground-based stations distributed over the globe, as given by the Baseline Surface Radiation Network. There is a negative bias of the model fluxes when compared against BSRN fluxes, ranging from -7 to -9 Wm-2, mostly caused by low cloud amount differences between the station and satellite measurements, particularly in cold climates. Finally, we compare our model results with those of other deterministic models and general circulation models.

Ten-year global distribution of downwelling longwave radiation

NASA Astrophysics Data System (ADS)

Pavlakis, K. G.; Hatzidimitriou, D.; Matsoukas, C.; Drakakis, E.; Hatzianastassiou, N.; Vardavas, I.

2004-01-01

Downwelling longwave fluxes, DLFs, have been derived for each month over a ten year period (1984-1993), on a global scale with a spatial resolution of 2.5x2.5 degrees and a monthly temporal resolution. The fluxes were computed using a deterministic model for atmospheric radiation transfer, along with satellite and reanalysis data for the key atmospheric input parameters, i.e. cloud properties, and specific humidity and temperature profiles. The cloud climatologies were taken from the latest released and improved International Satellite Climatology Project D2 series. Specific humidity and temperature vertical profiles were taken from three different reanalysis datasets; NCEP/NCAR, GEOS, and ECMWF (acronyms explained in main text). DLFs were computed for each reanalysis dataset, with differences reaching values as high as 30 Wm-2 in specific regions, particularly over high altitude areas and deserts. However, globally, the agreement is good, with the rms of the difference between the DLFs derived from the different reanalysis datasets ranging from 5 to 7 Wm-2. The results are presented as geographical distributions and as time series of hemispheric and global averages. The DLF time series based on the different reanalysis datasets show similar seasonal and inter-annual variations, and similar anomalies related to the 86/87 El Niño and 89/90 La Niña events. The global ten-year average of the DLF was found to be between 342.2 Wm-2 and 344.3 Wm-2, depending on the dataset. We also conducted a detailed sensitivity analysis of the calculated DLFs to the key input data. Plots are given that can be used to obtain a quick assessment of the sensitivity of the DLF to each of the three key climatic quantities, for specific climatic conditions corresponding to different regions of the globe. Our model downwelling fluxes are validated against available data from ground-based stations distributed over the globe, as given by the Baseline Surface Radiation Network. There is a negative bias of the model fluxes when compared against BSRN fluxes, ranging from -7 to -9 Wm-2, mostly caused by low cloud amount differences between the station and satellite measurements, particularly in cold climates. Finally, we compare our model results with those of other deterministic models and general circulation models.

Constraints on the Geophysical Detection of Brine within the Europa Ice Shell From a Synthesis of Dielectric Spectroscopy Measurements

NASA Astrophysics Data System (ADS)

Stillman, D. E.; Grimm, R. E.; MacGregor, J. A.; Sander-Olhoeft, M.; Brown, J.

2016-12-01

The numerous chaos regions, lenticulae and double layer ridges on Europa's surface suggest that pockets of liquid currently exist or did exist. Here we investigate the sensitivity of ice-penetrating radar (IPR) and magnetotelluric (MT) methods to the putative electrical properties of Europa's ice shell, based on a set of plausible ice-shell scenarios and a synthesis of laboratory dielectric spectroscopy measurements of hundreds of ice samples. We evaluate models of the electrical conductivity of the ice shell as a function of impurity content, temperature and liquid vein network tortuosity. Europa's ice shell is estimated to be 5-30 km thick. If its thickness exceeds 10 km, the shell likely convects within its bottom 70%, while the upper part is thermally conductive. These convective downwellings and upwellings are estimated to have core temperatures of 235 K and 253 K, respectively. Downwellings are so cold that they are below of eutectic temperature of most Europa-relevant salts, but not below that of Europa-relevant acids. Given the low temperature of downwelling ice, IPR is expected to penetrate through it. Warmer upwellings may possess significant amounts of unfrozen water if the shell is acid- or salt-rich. The injection of liquid or the melting of acid- or salt-rich ice will eventually lead to refreezing, as the shell conducts away this excess heat. As liquid freezes, impurities are rejected and concentrated in a liquid vein network surrounding relatively pure ice crystals. These vein networks remain liquid as long as the temperature is greater than that of the eutectic of the bulk impurities. Therefore, in upwellings, vein networks should be briny and hence more electrically conductive. The electrical conductivity of these vein networks depends on the initial impurity concentration of the liquid, impurity type, temperature and the tortuosity of any vein networks. The latter property decreases with increasing ice recrystallization. We conclude that IPR will likely be able to map the top of the unfrozen zone, assuming typical marine ice salt concentrations, but not penetrate through it. MT measurements could complement IPR effectively, because they could measure a conductivity depth profile within the unfrozen part of the ice shell, where the electrical conductivity exceeds 0.1 mS/m.

An 1-2-1 Cyclic Model for the Evolution of Mantle Structure

NASA Astrophysics Data System (ADS)

Zhong, S.; Zhang, N.

2006-12-01

The present-day Earth`s mantle is predominated by long-wavelength structures including circum-Pacific subducted slabs and Africa and Pacific super-plumes. These long-wavelength structures are largely controlled by the history of plate tectonic motion. Although it dictates the evolution of mantle structure, global plate tectonic history prior to 120 Ma is poorly constrained except for continental motions that can be reliably traced back to >1 Ga. An important observation of continental motions in the last 1 Ga is the two episodes of formation and breakup of super-continents Pangea and Rodinia. We formulated 3D global models of mantle convection with temperature- and depth-dependent viscosity to study the formation of mantle structure. We found that for the upper mantle with 30 times smaller viscosity than the lower mantle, in the absence of continents, mantle convection is characterized by a hemispherically asymmetric structure in which one hemisphere is largely upwellings, while the other hemisphere contains downwellings (i.e., degree-1 convection). This is the first study in which degree-1 mantle convection is observed in mobile-lid/plate-tectonic convection regime at high Rayleigh number. This result suggests that degree-1 convection is a dynamically preferred state for the Earth`s mantle. We suggest that the evolution of mantle structure is controlled by a cyclic process of formation and breakdown of degree-1 convection modulated strongly by continents. The formation and breakup of supercontinents are surface manifestation of this cyclic process. During the degree-1 convection state, the upwellings in one hemisphere push all continents into the other hemisphere with the downwellings to form a supercontinent. The non-subducting nature of continents dictates that subduction in the downwelling hemisphere occurs along the edge of the supercontinent upon its formation. The insulating effect of a supercontinent and return flow from the circum-supercontinent subduction should heat up sub-continental mantle and lead to formation of another upwelling system below the supercontinent and eventually to breakup of the supercontinent. After the breakup of a supercontinent, the mantle with two large upwellings, similar to that for the present-day Earth, is then evolved back to degree-1 convection state. We will also discuss the geological and geophysical consequences of our proposed model.

Global Ocean Vertical Velocity From a Dynamically Consistent Ocean State Estimate

NASA Astrophysics Data System (ADS)

Liang, Xinfeng; Spall, Michael; Wunsch, Carl

2017-10-01

Estimates of the global ocean vertical velocities (Eulerian, eddy-induced, and residual) from a dynamically consistent and data-constrained ocean state estimate are presented and analyzed. Conventional patterns of vertical velocity, Ekman pumping, appear in the upper ocean, with topographic dominance at depth. Intense and vertically coherent upwelling and downwelling occur in the Southern Ocean, which are likely due to the interaction of the Antarctic Circumpolar Current and large-scale topographic features and are generally canceled out in the conventional zonally averaged results. These "elevators" at high latitudes connect the upper to the deep and abyssal oceans and working together with isopycnal mixing are likely a mechanism, in addition to the formation of deep and abyssal waters, for fast responses of the deep and abyssal oceans to the changing climate. Also, Eulerian and parameterized eddy-induced components are of opposite signs in numerous regions around the global ocean, particularly in the ocean interior away from surface and bottom. Nevertheless, residual vertical velocity is primarily determined by the Eulerian component, and related to winds and large-scale topographic features. The current estimates of vertical velocities can serve as a useful reference for investigating the vertical exchange of ocean properties and tracers, and its complex spatial structure ultimately permits regional tests of basic oceanographic concepts such as Sverdrup balance and coastal upwelling/downwelling.

Seismic evidence for water transport out of the mantle transition zone beneath the European Alps

NASA Astrophysics Data System (ADS)

Liu, Zhen; Park, Jeffrey; Karato, Shun-ichiro

2018-01-01

The mantle transition zone has been considered a major water reservoir in the deep Earth. Mass transfer across the transition-zone boundaries may transport water-rich minerals from the transition zone into the water-poor upper or lower mantle. Water release in the mantle surrounding the transition zone could cause dehydration melting and produce seismic low-velocity anomalies if some conditions are met. Therefore, seismic observations of low-velocity layers surrounding the transition zone could provide clues of water circulation at mid-mantle depths. Below the Alpine orogen, a depressed 660-km discontinuity has been imaged clearly using seismic tomography and receiver functions, suggesting downwellings of materials from the transition zone. Multitaper-correlation receiver functions show prominent ∼0.5-1.5% velocity reductions at ∼750-800-km depths, possibly caused by partial melting in the upper part of lower mantle. The gap between the depressed 660-km discontinuity and the low-velocity layers is consistent with metallic iron as a minor phase in the topmost lower mantle reported by laboratory studies. Velocity drops atop the 410-km discontinuity are observed surrounding the Alpine orogeny, suggesting upwelling of water-rich rock from the transition zone in response to the downwelled materials below the orogeny. Our results provide evidence that convective penetration of the mantle transition zone pushes hydrated minerals both upward and downward to add hydrogen to the surrounding mantle.

Steady induction effects in geomagnetism. Part 1A: Steady motional induction of geomagnetic chaos

NASA Technical Reports Server (NTRS)

Voorhies, Coerte V.

1992-01-01

Geomagnetic effects of magnetic induction by hypothetically steady fluid motion and steady magnetic flux diffusion near the top of Earth's core are investigated using electromagnetic theory, simple magnetic earth models, and numerical experiments with geomagnetic field models. The problem of estimating a steady fluid velocity field near the top of Earth's core which induces the secular variation indicated by broad-scale models of the observed geomagnetic field is examined and solved. In Part 1, the steady surficial core flow estimation problem is solved in the context of the source-free mantle/frozen-flux core model. In the first paper (IA), the theory underlying such estimates is reviewed and some consequences of various kinematic and dynamic flow hypotheses are derived. For a frozen-flux core, fluid downwelling is required to change the mean square normal magnetic flux density averaged over the core-mantle boundary. For surficially geostrophic flow, downwelling implies poleward flow. The solution of the forward steady motional induction problem at the surface of a frozen-flux core is derived and found to be a fine, easily visualized example of deterministic chaos. Geomagnetic effects of statistically steady core surface flow may well dominate secular variation over several decades. Indeed, effects of persistent, if not steady, surficially geostrophic core flow are described which may help explain certain features of the present broad-scale geomagnetic field and perhaps paleomagnetic secular variation.

Deep water characteristics and circulation in the South China Sea

NASA Astrophysics Data System (ADS)

Wang, Aimei; Du, Yan; Peng, Shiqiu; Liu, Kexiu; Huang, Rui Xin

2018-04-01

This study investigates the deep circulation in the South China Sea (SCS) using oceanographic observations combined with results from a bottom layer reduced gravity model. The SCS water, 2000 m below the surface, is quite different from that in the adjacent Pacific Ocean, and it is characterized by its low dissolved oxygen (DO), high temperature and low salinity. The horizontal distribution of deep water properties indicates a basin-scale cyclonic circulation driven by the Luzon overflow. The results of the bottom layer reduced gravity model are consistent with the existence of the cyclonic circulation in the deep SCS. The circulation is stronger at the northern/western boundary. After overflowing the sill of the Luzon Strait, the deep water moves broadly southwestward, constrained by the 3500 m isobath. The broadening of the southward flow is induced by the downwelling velocity in the interior of the deep basin. The main deep circulation bifurcates into two branches after the Zhongsha Islands. The southward branch continues flowing along the 3500 m isobath, and the eastward branch forms the sub-basin scale cyclonic circulation around the seamounts in the central deep SCS. The returning flow along the east boundary is fairly weak. The numerical experiments of the bottom layer reduced gravity model reveal the important roles of topography, bottom friction, and the upwelling/downwelling pattern in controlling the spatial structure, particularly the strong, deep western boundary current.

Downwelling Far-Infrared Emission Spectra Measured By First at Cerro Toco, Chile and Table Mountain, California

NASA Astrophysics Data System (ADS)

Mast, J. C.; Mlynczak, M. G.; Cageao, R.; Kratz, D. P.; Johnson, D. G.; Mlawer, E. J.; Turner, D. D.

2014-12-01

The Far-Infrared Spectroscopy of the Troposphere (FIRST) instrument is a Fourier transform spectrometer developed to measure the important far-infrared spectrum between 100 and 650 cm-1. Presented here are measurements made by FIRST during two successful deployments in a ground-based configuration to measure downwelling longwave radiation at Earth's surface. The initial deployment was to Cerro Toco, Chile, where FIRST operated from August to October, 2009 as part of the Radiative Heating in Underexplored Bands Campaign (RHUBC-II) campaign. After recalibration, FIRST was deployed to the Table Mountain Facility from September through October, 2012. Spectra observed at each location are substantially different, due in large part to the order of magnitude difference in integrated precipitable water vapor (0.3 cm at Table Mountain, 0.03 cm at Cerro Toco). Dry days for both campaigns are chosen for analysis - 09/24/2009 and 10/19/2012. Also available during both deployments are coincident radiosonde temperature and water vapor vertical profiles which are used as inputs a line-by-line radiative transfer program. Comparisons between measured and modeled spectra are presented over the 200 to 800 cm-1 range. An extensive error analysis of both the measured and modeled spectra is presented. In general, the differences between the measured and modeled spectra are within their combined uncertainties.

Ocean-atmosphere interface: its influence on radiation.

PubMed

Plass, G N; Humphreys, T J; Kattawar, G W

1981-03-15

The influence of the ocean-atmosphere interface on the radiance distribution in both the ocean and atmosphere is investigated. At visible wavelengths in the real ocean just below the surface, the downwelling radiance is a maximum within the critical angle and drops off by 1 or 2 orders of magnitude toward the horizon. The usual explanation that this is due to the sky radiation concentrated within the critical angle and the total internal reflection of the weak upward radiance at the ocean surface at angles outside the critical angle is too simplistic. There are two other important factors: (1) the atmosphere must have sufficient optical thickness so that appreciable sky (multiple scattered) radiation develops at all angles in the downward direction; (2) the water must have appreciable absorption so that the upwelling radiance just below the ocean surface is only a small fraction of the downwelling radiance entering the ocean. Examples show that, if either one of these conditions is not satisfied, an entirely different radiance distribution develops. The variation of the following quantities with depth is studied: radiance; vector and scalar irradiance; distribution function; reflectance; and heating rate. The radiance distribution in a homogeneous medium is compared with that in the same medium with an atmosphere-ocean interface at various depths within the medium. Most of the calculations are done for Rayleigh scattering centers, but some results are given for Mie-type scattering.

Short-term meso-scale variability of mesozooplankton communities in a coastal upwelling system (NW Spain)

NASA Astrophysics Data System (ADS)

Roura, Álvaro; Álvarez-Salgado, Xosé A.; González, Ángel F.; Gregori, María; Rosón, Gabriel; Guerra, Ángel

2013-02-01

The short-term, meso-scale variability of the mesozooplankton community present in the coastal upwelling system of the Ría de Vigo (NW Spain) has been analysed. Three well-defined communities were identified: coastal, frontal and oceanic, according to their holoplankton-meroplankton ratio, richness, and total abundance. These communities changed from summer to autumn due to a shift from downwelling to upwelling-favourable conditions coupled with taxa dependent changes in life strategies. Relationships between the resemblance matrix of mesozooplankton and the resemblance matrices of meteorologic, hydrographic and community-derived biotic variables were determined with distance-based linear models (DistLM, 18 variables), showing an increasing amount of explained variability of 6%, 16.1% and 54.5%, respectively. A simplified model revealed that the variability found in the resemblance matrix of mesozooplankton was mainly described by the holoplankton-meroplankton ratio, the total abundance, the influence of lunar cycles, the upwelling index and the richness; altogether accounting for 64% of the total variability. The largest variability of the mesozooplankton resemblance matrix (39.6%) is accounted by the holoplankton-meroplankton ratio, a simple index that describes appropriately the coastal-ocean gradient. The communities described herein kept their integrity in the studied upwelling and downwelling episodes in spite of the highly advective environment off the Ría de Vigo, presumably due to behavioural changes in the vertical position of the zooplankton.

Can a coupled meteorology–chemistry model reproduce the ...

EPA Pesticide Factsheets

The ability of a coupled meteorology–chemistry model, i.e., Weather Research and Forecast and Community Multiscale Air Quality (WRF-CMAQ), to reproduce the historical trend in aerosol optical depth (AOD) and clear-sky shortwave radiation (SWR) over the Northern Hemisphere has been evaluated through a comparison of 21-year simulated results with observation-derived records from 1990 to 2010. Six satellite-retrieved AOD products including AVHRR, TOMS, SeaWiFS, MISR, MODIS-Terra and MODIS-Aqua as well as long-term historical records from 11 AERONET sites were used for the comparison of AOD trends. Clear-sky SWR products derived by CERES at both the top of atmosphere (TOA) and surface as well as surface SWR data derived from seven SURFRAD sites were used for the comparison of trends in SWR. The model successfully captured increasing AOD trends along with the corresponding increased TOA SWR (upwelling) and decreased surface SWR (downwelling) in both eastern China and the northern Pacific. The model also captured declining AOD trends along with the corresponding decreased TOA SWR (upwelling) and increased surface SWR (downwelling) in the eastern US, Europe and the northern Atlantic for the period of 2000–2010. However, the model underestimated the AOD over regions with substantial natural dust aerosol contributions, such as the Sahara Desert, Arabian Desert, central Atlantic and northern Indian Ocean. Estimates of the aerosol direct radiative effect (DRE) at TOA a

The impact of the diurnal cycle on the propagation of Madden-Julian Oscillation convection across the Maritime Continent

DOE PAGES

Hagos, Samson M.; Zhang, Chidong; Feng, Zhe; ...

2016-09-19

Influences of the diurnal cycle of convection on the propagation of the Madden-Julian Oscillation (MJO) across the Maritime Continent (MC) are examined using cloud-permitting regional model simulations and observations. A pair of ensembles of control (CONTROL) and no-diurnal cycle (NODC) simulations of the November 2011 MJO episode are performed. In the CONTROL simulations, the MJO signal is weakened as it propagates across the MC, with much of the convection stalling over the large islands of Sumatra and Borneo. In the NODC simulations, where the incoming shortwave radiation at the top of the atmosphere is maintained at its daily mean value,more » the MJO signal propagating across the MC is enhanced. Examination of the surface energy fluxes in the simulations indicates that in the presence of the diurnal cycle, surface downwelling shortwave radiation in CONTROL simulations is larger because clouds preferentially form in the afternoon. Furthermore, the diurnal co-variability of surface wind speed and skin temperature results in a larger sensible heat flux and a cooler land surface in CONTROL compared to NODC simulations. Here, an analysis of observations indicates that the modulation of the downwelling shortwave radiation at the surface by the diurnal cycle of cloudiness negatively projects on the MJO intraseasonal cycle and therefore disrupts the propagation of the MJO across the MC.« less

Mantle transition zone structure beneath the Canadian Shield

NASA Astrophysics Data System (ADS)

Thompson, D. A.; Helffrich, G. R.; Bastow, I. D.; Kendall, J. M.; Wookey, J.; Eaton, D. W.; Snyder, D. B.

2010-12-01

The Canadian Shield is underlain by one of the deepest and most laterally extensive continental roots on the planet. Seismological constraints on the mantle structure beneath the region are presently lacking due to the paucity of stations in this remote area. Presented here is a receiver function study on transition zone structure using data from recently deployed seismic networks from the Hudson Bay region. High resolution images based on high signal-to-noise ratio data show clear arrivals from the 410 km and 660 km discontinuities, revealing remarkably little variation in transition zone structure. Transition zone thickness is close to the global average (averaging 245 km across the study area), and any deviations in Pds arrival time from reference Earth models can be readily explained by upper-mantle velocity structure. The 520 km discontinuity is not a ubiquitous feature, and is only weakly observed in localised areas. These results imply that the Laurentian root is likely confined to the upper-mantle and if any mantle downwelling exists, possibly explaining the existence of Hudson Bay, it is also confined to the upper 400 km. Any thermal perturbations at transition zone depths associated with the existence of the root, whether they be cold downwellings or elevated temperatures due to the insulating effect of the root, are thus either non-existent or below the resolution of the study.

Response of near-surface currents in the Indian Ocean to the anomalous atmospheric condition in 2015

NASA Astrophysics Data System (ADS)

Utari, P. A.; Nurkhakim, M. Y.; Setiabudidaya, D.; Iskandar, I.

2018-05-01

Anomalous ocean-atmosphere conditions were detected in the tropical Indian Ocean during boreal spring to boreal winter 2015. It was suggested that the anomalous conditions were characteristics of the positive Indian Ocean Dipole (pIOD) event. The purpose of this investigation was to investigate the response of near-surface currents in the tropical Indian Ocean to the anomalous atmospheric condition in 2015. Near-surface current from OSCAR (Ocean Surface Current Analyses Real Time) reanalysis data combined with the sea surface temperature (SST) data from OISST – NOAA, sea surface height (SSH) and surface winds from the ECMWF were used in this investigation. The analysis showed that the evolution of 2015 pIOD started in June/July, peaked in the September and terminated in late November 2015. Correlated with the evolution of the pIOD, easterly winds anomalies were detected along the equator. As the oceanic response to these easterly wind anomalies, the surface currents anomalously westward during the peak of the pIOD. It was interesting to note that the evolution of 2015 pIOD event was closely related to the ocean wave dynamics as revealed by the SSH data. Downwelling westward propagating Rossby waves were detected in the southwestern tropical Indian Ocean. Once reached the western boundary of the Indian Ocean, they were redirected back into interior Indian Ocean and propagating eastward as the downwelling Kelvin waves.

Direct radiative effects induced by intense desert dust outbreaks over the broader Mediterranean basin

NASA Astrophysics Data System (ADS)

Gkikas, Antonis; Obiso, Vincenzo; Vendrell, Lluis; Basart, Sara; Jorba, Oriol; Pérez Garcia-Pando, Carlos; Hatzianastassiou, Nikos; Gassó, Santiago; Baldasano, Jose Maria

2016-04-01

Throughout the year, under favorable conditions, massive loads of mineral particles originating in the northern African and Middle East deserts are transported over the Mediterranean basin. Due to their composition and size, dust aerosols perturb the Earth-Atmosphere system's energy budget interacting directly with the shortwave (SW) and longwave (LW) radiation. The present study aims to compute the Mediterranean dust outbreaks' direct radiative effects (DREs) as well as to assess the effect of including dust DREs in numerical simulations of a regional model. To this aim, 20 intense dust outbreaks have been selected based on their spatial coverage and intensity. Their identification, over the period 2000-2013, has been achieved through an objective and dynamic algorithm which utilizes as inputs daily satellite retrievals derived by the MODIS-Terra, EP-TOMS and OMI-Aura sensors. For each outbreak, two simulations of the NMMB/BSC-Dust model were made for a forecast period of 84 hours, with the model initialized at 00 UTC of the day when the dust outbreak was ignited, activating (RADON) and deactivating (RADOFF) dust-radiation interactions. The simulation domain covers the northern Africa, the Middle East and Europe at 0.25° x 0.25° horizontal resolution, for 40 hybrid sigma pressure levels up to 50 hPa. The instantaneous and regional DREs have been calculated at the top of the atmosphere (TOA), into the atmosphere (ATMAB), and at surface, for the downwelling (SURF) and the absorbed (NETSURF) radiation, for the SW, LW and NET (SW+LW) radiation. The interaction between dust aerosols and NET radiation, locally leads to an atmospheric warming (DREATMAB) by up to 150 Wm-2, a surface cooling (DRENETSURF) by up to 250 Wm-2 and a reduction of the downwelling radiation at the surface (DRESURF) by up to 300 Wm-2. At TOA, DREs are mainly negative (down to -150 Wm-2) indicating a cooling of the Earth-Atmosphere system, although positive values (up to 50 Wm-2) are encountered over desert areas. The mean regional NET DREs, under clear-sky conditions, vary between -10 to 2, -3 to 25, -35 to 3 and -22 to 3 Wm-2 for TOA, ATMAB, SURF and NETSURF, respectively. According to our results, dust outbreaks can cause a decrease of temperature at 2 meters by 4 °C during daytime while an increase of a similar magnitude is found at night. Moreover, negative feedbacks on dust emissions and aerosol optical depth are observed when dust-radiation interactions are activated. Our analysis clearly shows that taking into account the dust radiative effects in numerical simulations (RADON) the model's ability to reproduce the temperature fields as well as the downwelling radiation fluxes at the surface is improved. The former is confirmed by the evaluation of the model's outputs against ERA-Interim reanalyses datasets and weather stations observations (Integrated Surface Database, ISD) while the latter is justified through the comparison of model's downwelling SW/LW radiation fluxes at the surface with ground measurements from 6 Baseline Surface Radiation Network (BSRN) stations. A similar analysis is also attempted for the dust aerosol optical depth at 550 nm using the AERONET ground retrievals as reference measurements.

On the Unsteady Response of an Oceanic Front to Local Atmospheric Forcing.

DTIC Science & Technology

1983-06-01

fluxes, mass and momentum transport, inertial-internal wave activity and mix- ing all can occur. Oceanic frontal areas are areas of sound 11 speed...in the Sargasso Sea in May. He found the front to be a separaticn cf two distinct water masses , with a tran- sitin zone cf only a few meters in the...presence of an eddy. If the water masses had been of similar types, it would have been indicative cf downwelling. With regard tc one-dimensional mixing

Observed Circulation and Inferred Sediment Transport in Hudson Submarine Canyon.

DTIC Science & Technology

1982-06-01

included in a regional survey conducted on September 24-27, following a week of westward (downwelling-favorable) winds (at JFK Airport ) which reached a...Figure 3-9. Vector plots of low-pass filtered velocity data. Horizontal scale is marked at weekly intervals. (a) Wind at JFK Airport , New York City...figure 3-12. winds rose at JFK airport about noon on January 8, blowing ini- tially from the southeast but shifting to the west as they reached their

Analysis of the In-Water and Sky Radiance Distribution Data Acquired During the RaDyO Project

DTIC Science & Technology

2011-09-30

radiative transfer to model the BRDF of particulate surfaces. OBJECTIVES The major objective of this research is to understand the downwelling spectral...in the water, was also used by the two major modeling groups in RaDyO, to successfully validate their radiative transfer models . This work is...image and radiative transfer models used in the ocean. My near term ocean optics objectives have been: 1) to improve the measurement capability of

Bio-optical profile data report: Southern California Bight Study (SCB2-29) R/V Robert G. Sproul, 20-25 August 1988

NASA Technical Reports Server (NTRS)

Collins, Donald J.; Tran, An Van

1990-01-01

Time series measurements of the incident surface downwelling irradiance and vertical profiles of the bio-optical properties of the ocean were studied during the 29th cruise of the Southern California Bight Study (SCBS) during the period of August 20-25, 1988. A summary of these data is presented to permit investigators an overview of the data collected. The data are available in digital form for scientific investigators.

Mapping the downwelling atmospheric radiation at the Earth's surface: A research strategy

NASA Technical Reports Server (NTRS)

Raschke, E.

1986-01-01

A strategy is presented along with background material for determining downward atmospheric radiation at the Earth's surface on a regional scale but over the entire globe, using available information on the temperature and humidity of the air near the ground and at cloud base altitudes. Most of these parameters can be inferred from satellite radiance measurements. Careful validation of the derived radiances will be required using ground-based direct measurements of radiances, to avoid systematic biases of these derived field quantities.

Diurnal Variability of the inner-shelf circulation in the lee of a cape under upwelling conditions

NASA Astrophysics Data System (ADS)

Lamas, Luisa; Peliz, Álvaro; Marchesiello, Patrick

2013-04-01

The circulation over the inner-shelf is a key component of shelf dynamics and an important mechanism for cross-shore exchange on most shelves. Yet our understanding of the cross-shore circulation and how it depends on different forcing conditions, bathymetry and stratification remains poor due in part to sparse observations and the difficulty of resolving spatial and temporal scales within the inner-shelf. Most studies of cross-shore transport on the inner-shelf consider only a 2D circulation, due to coastal upwelling or downwelling and assume along-shore uniformity. However, divergence in the along-shore and cross-shore flows may occur with the presence of complex coastline topography or subtle bathymetric features, and can drive substantial horizontal cross-shore exchange, with same order of magnitude as coastal upwelling and downwelling. A recent study using observational data collected near cape Sines, Portugal, showed that not only wind, waves and tides are important forcing mechanisms of the inner-shelf circulation, but also that the along-shore pressure gradient plays a major role on driving cross-shore exchange. A modeling study was conducted in order to study the complexity of the inner-shelf dynamics, in the presence of a cape. A simplified configuration was used in order to isolate the effects of individual processes: wind, heat fluxes, tides and waves. The preliminary results of the effects of these processes on the inner-shelf circulation will be presented.

Recent changes in the summer monsoon circulation and their impact on dynamics and thermodynamics of the Arabian Sea

NASA Astrophysics Data System (ADS)

Pratik, Kad; Parekh, Anant; Karmakar, Ananya; Chowdary, Jasti S.; Gnanaseelan, C.

2018-05-01

The present study examines changes in the low-level summer monsoon circulation over the Arabian Sea and their impact on the ocean dynamics using reanalysis data. The study confirms intensification and northward migration of low-level jet during 1979 to 2015. Further during the study period, an increase in the Arabian Sea upper ocean heat content is found in spite of a decreasing trend in the net surface heat flux, indicating the possible role of ocean dynamics in the upper ocean warming. Increase in the anti-cyclonic wind stress curl associated with the change in the monsoon circulation induces downwelling over the central Arabian Sea, favoring upper ocean warming. The decreasing trend of southward Ekman transport, a mechanism transporting heat from the land-locked north Indian Ocean to southern latitudes, also supports increasing trend of the upper ocean heat content. To reinstate and quantify the role of changing monsoon circulation in increasing the heat content over the Arabian Sea, sensitivity experiment is carried out using ocean general circulation model. In this experiment, the model is forced by inter-annual momentum forcing while rest of the forcing is climatological. Experiment reveals that the changing monsoon circulation increases the upper ocean heat content, effectively by enhancing downwelling processes and reducing southward heat transport, which strongly endorses our hypothesis that changing ocean dynamics associated with low-level monsoon circulation is causing the increasing trend in the heat content of the Arabian Sea.

Evolution of Gases and Particles from a Savanna Fire in South Africa

NASA Technical Reports Server (NTRS)

Hobbs, Peter V.; Sinha, Parikhit; Yokelson, Robert J.; Christian, Ted J.; Blake, Donald R.; Gao, Song; Kirchstetter, Thomas W.; Novakov, Tica; Pilewskie, Peter

2003-01-01

Airborne measurements of particles and gases fiom a 1000-ha savanna fire in South Africa are presented. These measurements represent the most extensive data set reported on the aging of biomass smoke. The measurements include total concentrations of particles (CN), particle sizes, particulate organic carbon and black carbon, light-scattering coefficients, downwelling UV fluxes, and mixing ratios for 42 trace gases and 7 particulate species. The ratios of excess nitrate, ozone, and gaseous acetic acid to excess CO increased significantly as the smoke aged over approximately 40-45 min, indicating that these species were formed by photochemistry in the plume. For 17 other species, the excess mixing ratio normalized by the excess mixing ratio of CO decreased significantly with ' smoke age. The relative rates of decrease for a number of chemical species imply that the average OH concentration in the plume was approximately 1.7 x l0(exp 7) molecules /cubic centimeter. Excess CN, normalized by excess CO, decreased rapidly during the first approximately 5 min of aging, probably due to coagulation, and then increased, probably due to gas-to-particle conversion. The CO-normalized concentrations of particles < 1.5 microns in diameter decreased, and particles >1.5 micron diameter increased, with smoke age. The spectral depletion of solar radiation by the smoke is depicted. The downwelling UV flux near the vertical center of the plume was about two-thirds of that near the top of the plume.

Implications of the nonlinear equation of state for upwelling in the ocean interior

NASA Astrophysics Data System (ADS)

McDougall, Trevor J.; You, Yuzhu

1990-08-01

The nonlinear nature of the in situ density of seawater as a function of the potential temperature, pressure and salinity causes two vertical advection processes (thermobaricity and cabbeling) and also complicates the use of microstructure data to deduce upwelling velocities. Cabbeling and thermobaricity are evaluated and mapped on some neutral surfaces in each of the world's oceans by taking the lateral flux of scalars to be parameterized by a lateral diffusivity. In most of the ocean, these two processes are weak, but where there is a significant epineutral gradient of potential temperature, the downwelling due to cabbeling is quite large. In the Southern ocean, where there is a large slope of the neutral surfaces, thermobaricity causes a larger downwelling velocity than cabbeling, and the two processes together cause a dianeutral velocity of about -2×10-7 m s-1. The complementary roles of vertical mixing and vertical advection in achieving water-mass conversion are demonstrated, since maps of the dianeutral motion caused by vertical mixing are quite different to maps of water-mass conversion caused by the same process. This emphasizes the need to include both vertical advection and vertical mixing in ocean models. The method that is used to infer the upwelling velocity from microstructure dissipation measurements is also significantly affected by the nonlinear nature of the equation of state. The extra term that needs to be included in this method is a strong function of depth, changing sign at a depth of about 1500m.

Characterizing energy budget variability at a Sahelian site: a test of NWP model behaviour

NASA Astrophysics Data System (ADS)

Mackie, Anna; Palmer, Paul I.; Brindley, Helen

2017-12-01

We use observations of surface and top-of-the-atmosphere (TOA) broadband radiation fluxes determined from the Atmospheric Radiation Measurement programme mobile facility, the Geostationary Earth Radiation Budget (GERB) and Spinning Enhanced Visible and Infrared Imager (SEVIRI) instruments and a range of meteorological variables at a site in the Sahel to test the ability of the ECMWF Integrated Forecasting System cycle 43r1 to describe energy budget variability. The model has daily average biases of -12 and 18 W m-2 for outgoing longwave and reflected shortwave TOA radiation fluxes, respectively. At the surface, the daily average bias is 12(13) W m-2 for the longwave downwelling (upwelling) radiation flux and -21(-13) W m-2 for the shortwave downwelling (upwelling) radiation flux. Using multivariate linear models of observation-model differences, we attribute radiation flux discrepancies to physical processes, and link surface and TOA fluxes. We find that model biases in surface radiation fluxes are mainly due to a low bias in ice water path (IWP), poor description of surface albedo and model-observation differences in surface temperature. We also attribute observed discrepancies in the radiation fluxes, particularly during the dry season, to the misrepresentation of aerosol fields in the model from use of a climatology instead of a dynamic approach. At the TOA, the low IWP impacts the amount of reflected shortwave radiation while biases in outgoing longwave radiation are additionally coupled to discrepancies in the surface upwelling longwave flux and atmospheric humidity.

Highlights from 40 Years of Satellite UV Measurements

NASA Technical Reports Server (NTRS)

Bhartia, Pawan K.

2010-01-01

This year we are celebrating the 40th anniversary of the launch of the Backscatter Ultraviolet (BUV) instrument on NASA's Nimbus-4 satellite. The purpose of this instrument was to demonstrate the capability to measure total column ozone and its vertical distribution from space. The success of this instrument led to about a dozen instruments of this type on various NASA and NOAA satellites. These instruments used a single photomultiplier tube (PMT) that restricted the measurements to 6-12 discrete wavelengths in the 250-380 nm range. With the availability of solid-state detector arrays in the past decade it has been possible to make similar measurements but with hyperspectral (contiguous in wavelength) sampling and enhanced spectral resolution. This has allowed global mapping of several weakly-absorbing trace gases including S0 2, NO2, BrO, HCHO, and CIIOCHO. Since these measurements are affected by clouds and aerosols, a great deal of effort has gone into understanding their effect on ultraviolet radiation- both upwelling and downwelling. The downwelling UV radiation is chemically and biologically active and has both negative (genetic damage, air pollution) and positive (production of vitamin D and OH radical) environmental effects. I will discuss how the interaction of Rayleigh-scattered UV radiation with clouds and aerosols produce a variety of interesting effects that are leading to new methods of remote sensing of their properties. The UV measurements can greatly enhance the information that one derives from more traditional methods that use infrared and visible part of the solar spectrum.

Passive margins getting squeezed in the mantle convection vice

NASA Astrophysics Data System (ADS)

Yamato, Philippe; Husson, Laurent; Becker, Thorsten W.; Pedoja, Kevin

2013-12-01

margins often exhibit uplift, exhumation, and tectonic inversion. We speculate that the compression in the lithosphere gradually increased during the Cenozoic, as seen in the number of mountain belts found at active margins during that period. Less clear is how that compression increase affects passive margins. In order to address this issue, we design a 2-D viscous numerical model wherein a lithospheric plate rests above a weaker mantle. It is driven by a mantle conveyor belt, alternatively excited by a lateral downwelling on one side, an upwelling on the other side, or both simultaneously. The lateral edges of the plate are either free or fixed, representing the cases of free convergence, and collision (or slab anchoring), respectively. This distinction changes the upper mechanical boundary condition for mantle circulation and thus, the stress field. Between these two regimes, the flow pattern transiently evolves from a free-slip convection mode toward a no-slip boundary condition above the upper mantle. In the second case, the lithosphere is highly stressed horizontally and deforms. For a constant total driving force, compression increases drastically at passive margins if upwellings are active. Conversely, if downwellings alone are activated, compression occurs at short distances from the trench and extension prevails elsewhere. These results are supported by Earth-like models that reveal the same pattern, where active upwellings are required to excite passive margins compression. Our results substantiate the idea that compression at passive margins is in response to the underlying mantle flow that is increasingly resisted by the Cenozoic collisions.

Impact of Equatorial Waves on the Variability of Upwelling Process Along West Coast of India

NASA Astrophysics Data System (ADS)

Prakash, K. R.; Nigam, T.; Pant, V.

2017-12-01

Coastal upwelling is a seasonal phenomenon along the south eastern Arabian Sea (SEAS) due to favourable wind setup during Indian Summer Monsoon Season (June-September). This upwelling brings subsurface cold and nutrient rich water to the surface layers. The cold water transported northward by the altered along shore current of west coast of India in the post-monsoon season. The different climatological forcing of positive Indian Ocean Dipole (IOD) and normal years were utilised to simulate the upwelling off the west coast of India using a three dimensional Regional Ocean Modelling System (ROMS). Strength of upwelling and the northward transport were found to be weaken for positive IOD simulations as compared to normal years. Analysis suggests that the meridional wind stress weakening resulted into a decrease in strength of West India Coastal Current (WICC) and, therefore, reduced magnitude of offshore Ekman transport. The mixed layer heat budget calculation also supports the findings by showing dominated vertical process in comparison to net heat flux effect. The post-monsoon northward transport of cold water was found to be correlated with the coastally trapped downwelling Kelvin waves. These waves are the only remote forcing from the Bay of Bengal that reaches to the south-eastern Arabian Sea during the months of October-December. The composite of sea surface height anomalies for the positive IOD and normal years shows that the downwelling Kelwin wave was absent during October-December.

The Impact of Moisture Intrusions from Lower Latitudes on Arctic Net Surface Radiative Fluxes and Sea Ice Growth in Fall and Winter

NASA Astrophysics Data System (ADS)

Hegyi, B. M.; Taylor, P. C.

2017-12-01

The fall and winter seasons mark an important period in the evolution of Arctic sea ice, where energy is transferred away from the surface to facilitate the cooling of the surface and the growth of Arctic sea ice extent and thickness. Climatologically, these seasons are characterized by distinct periods of increased and reduced surface cooling and sea ice growth. Periods of reduced sea ice growth and surface cooling are associated with cloudy conditions and the transport of warm and moist air from lower latitudes, termed moisture intrusions. In the research presented, we explore the regional and Arctic-wide impact of moisture intrusions on the surface net radiative fluxes and sea ice growth for each fall and winter season from 2000/01-2015/16, utilizing MERRA2 reanalysis data, PIOMAS sea ice thickness data, and daily CERES radiative flux data. Consistent with previous studies, we find that positive anomalies in downwelling longwave surface flux are associated with increased temperature and water vapor content in the atmospheric column contained within the moisture intrusions. Interestingly, there are periods of increased downwelling LW flux anomalies that persist for one week or longer (i.e. longer than synoptic timescales) that are associated with persistent poleward flux of warm, moist air from lower latitudes. These persistent anomalies significantly reduce the regional growth of Arctic sea ice, and may in part explain the interannual variability of fall and winter Arctic sea ice growth.

An Improved Algorithm for Retrieving Surface Downwelling Longwave Radiation from Satellite Measurements

NASA Technical Reports Server (NTRS)

Zhou, Yaping; Kratz, David P.; Wilber, Anne C.; Gupta, Shashi K.; Cess, Robert D.

2007-01-01

Zhou and Cess [2001] developed an algorithm for retrieving surface downwelling longwave radiation (SDLW) based upon detailed studies using radiative transfer model calculations and surface radiometric measurements. Their algorithm linked clear sky SDLW with surface upwelling longwave flux and column precipitable water vapor. For cloudy sky cases, they used cloud liquid water path as an additional parameter to account for the effects of clouds. Despite the simplicity of their algorithm, it performed very well for most geographical regions except for those regions where the atmospheric conditions near the surface tend to be extremely cold and dry. Systematic errors were also found for scenes that were covered with ice clouds. An improved version of the algorithm prevents the large errors in the SDLW at low water vapor amounts by taking into account that under such conditions the SDLW and water vapor amount are nearly linear in their relationship. The new algorithm also utilizes cloud fraction and cloud liquid and ice water paths available from the Cloud and the Earth's Radiant Energy System (CERES) single scanner footprint (SSF) product to separately compute the clear and cloudy portions of the fluxes. The new algorithm has been validated against surface measurements at 29 stations around the globe for Terra and Aqua satellites. The results show significant improvement over the original version. The revised Zhou-Cess algorithm is also slightly better or comparable to more sophisticated algorithms currently implemented in the CERES processing and will be incorporated as one of the CERES empirical surface radiation algorithms.

Using Heat as a Tracer to Estimate Streambed Water Exchanges beneath the Losing Disconnected Stream

NASA Astrophysics Data System (ADS)

Chiu, Yung-Chia; Lee, Tsung-Yu; Hsu, Shao-Yu; Liao, Lin-Yan

2017-04-01

Streambed water exchanges is the movement of water from a river into the beneath sediments and then back into the river. This interaction between river and streambed is considered as a fundamental role in the functioning of riparian ecosystems. Chichiawan Watershed located in central Taiwan is the only habitat for the endangered species of formosan land-locked salmon and such dynamics of downwelling/upwelling flow within the streambed can affect the survival of salmon. In order to investigate the interaction between river and streambed, heat is used as an environmental tracer to determine the water exchanges within the streambed and estimate the hydraulic conductivity of sediments. The detailed hydrographs, thermographs, and vertical temperature profiles obtained along the Yusheng Creek, a tributary at the upstream of Chichiawan Creek, were presented and used to estimate the streambed water exchanges. Results showed that the Yusheng Creek along the monitoring section is a losing stream and its downwelling flux increases from up- to down-stream. Partial monitoring sections changed from perennial to intermittence when the consecutive dry days over a period of time increase significantly and an unsaturated zone between the creek and the groundwater existed. According to the measured temperature and water level data, the numerical model of VS2DH was used to quantify the vertical fluxes and hydraulic conductivities of streamed. The potential mechanisms causing the creek transited from perennial to intermittence and becoming a losing disconnected system need further study.

Reverse Estuarine Circulation Due to Local and Remote Wind Forcing, Enhanced by the Presence of Along-Coast Estuaries

NASA Astrophysics Data System (ADS)

Giddings, S. N.; MacCready, P.

2017-12-01

Estuarine exchange flow governs the interaction between oceans and estuaries and thus plays a large role in their biogeochemical processes. This study investigates the variability in estuarine exchange flow due to offshore oceanic conditions including upwelling/downwelling, and the presence of a river plume offshore (from a neighboring estuary). We address these processes via numerical simulations at the mouth of the Salish Sea, a large estuarine system in the Northeast Pacific. An analysis of the Total Exchange Flow indicates that during the upwelling season, the exchange flow is fairly consistent in magnitude and oriented in a positive (into the estuary at depth and out at the surface) direction. However, during periods of downwelling favorable winds, the exchange flow shows significantly more variability including multiple reversals, consistent with observations, and surface intrusions of the Columbia River plume which originates 250 km to the south. Numerical along-strait momentum budgets show that the exchange flow is forced dominantly by the pressure gradients, particularly the baroclinic. The pressure gradient is modified by Coriolis and sometimes advection, highlighting the importance of geostrophy and local adjustments. In experiments conducted without the offshore river plume, reversals still occur but are weaker, and the baroclinic pressure gradient plays a reduced role. These results suggest that estuaries along strong upwelling coastlines should experience significant modulation in the exchange flow during upwelling versus downwelling conditions. Additionally, they highlight the importance of nearby estuaries impacting one-another, not only in terms of connectivity, but also altering the exchange flow.