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Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: PHYSICAL & DYNAMIC METEOROLOGY | Award Amount: 603.14K | Year: 2016

This study seeks to improve our understanding of the interaction of weak wind flow in the lowest layer of the atmosphere and generation of turbulence in gently sloping terrain. An improved understanding of weak-wind boundary layers could potentially lead to more accurate modeling of the formation of cold pools, damaging frost (including impact to local vineyards), fog formation, and dispersion of contaminants.

This study seeks to investigate weak-wind boundary layers using detailed spatial-temporal measurements. These boundary layers demonstrate non-stationarity and the turbulence in them is generally in a non-equilibrium state with the mean flow. Previous studies of such boundary layers were mostly limited to temporal data at fixed locations, and therefore could not take into account hysteresis when investigating scaling properties. This study analyzes detailed spatial-temporal data to form a more complete picture of boundary layer structures. The evolution of the structures and the impact of the sub-mesoscale motions will be investigated.


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: AERONOMY | Award Amount: 116.23K | Year: 2016

This grant will support an effort to enhance the understanding of the formation processes for ionospheric plasma wave structures seen in regional distributions of Total Electron Content (TEC) events that exhibit circular patterns. These events are believed to be generated by deep convective processes within thunderstorm systems that launch gravity wave structures into the upper atmosphere region of 60 to 100 km where strong viscous dissipation of these wave packets occurs. Part of the wave energy of these primary waves is transformed into the production of secondary waves that are able to propagate higher into the region of atmospheric heights above 200 km. Here, the interaction of these waves with the ionospheric plasma (pushing or pulling plasma along magnetic field lines) would then generate structures called Traveling Ionosphere Disturbances (TIDs) that are so often seen in TEC data. The primary objective of the research is to compare the observed concentric TEC perturbations with those calculated from realistic modeling of the primary and secondary GWs from deep convection in order to strengthen and validate the models for the calculation of these TID structures. A secondary objective would be to utilize the amplitudes and scales of the observed secondary GWs to probe the dynamics of the dark (but highly variable) region near 125-225 km where most of the primary GWs dissipate. A satisfactory explanation of these TID events in terms of gravity wave processes by reference to the successful modeling of the formation of these structures has never been achieved. Thus, the funded research has a significant potential for providing an enhanced understanding of the properties of these circular TID events that relate to the heating and cooling processes associated with the dissipation and transformation of the primary wave structure into the secondary wave output.

Significant societal impact and transformative research outcomes for this award are expected to be achieved as a result of the success in modeling these circular TID events. Because GWs cause scintillation and plasma bubbles that can disrupt satellite communication and GPS signals, this study may lead to better predictions for the occurrence of these phenomena, which is nationally relevant. In order to enhance scientific understanding for the general public, the researcher will disseminate broadly the results via a web site, conference talks, and journal publications. Finally, this project would support the research of a woman scientist (PI).


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: PHYSICAL & DYNAMIC METEOROLOGY | Award Amount: 199.97K | Year: 2016

The goal of the project is to develop, apply, and field-test methodologies to exploit spatiotemporal distortions of dual-telescope, optical image sequences of naturally illuminated, random scenes for the retrieval of range-resolved cross-wind velocities and turbulence statistics. The investigators will use random, natural surfaces with rich optical texture, such as bare mountain faces, hillsides, and canyon walls, which are ubiquitous in the American West. The sun and the moon will serve as light sources by day and by night, respectively. The availability of inexpensive, scalable, multi-purpose techniques and systems for passive optical remote sensing of the atmospheric boundary layer will benefit society in several areas, including weather monitoring and forecasting; air-quality monitoring and forecasting; cross-wind monitoring at highways, airport runways, and rocket launch sites; and wind sensing in support of wind-farm operations. The project will provide resources for mentoring a postdoctoral researcher and a graduate student, contributing to science, technology, engineering and mathematics (STEM) education and educator development.

The study will use pairs of synchronized image sequences collected with two digital cameras mounted at two, laterally spaced, large-aperture telescopes pointing at the same target area. Target distances will range from hundreds of meters to tens of kilometers. Limited-visibility effects due to Rayleigh and non-Rayleigh scatter will be negligible for short ranges but are expected to play an important role for longer ranges. The proposed research will combine observational, computational, and theoretical methodologies from (1) atmospheric turbulence and boundary layer meteorology; (2) wave propagation through atmospheric turbulence; (3) atmospheric radiative transfer of visible light; and (4) imaging physics of coherent and incoherent light. The research will integrate, apply, and test concepts and hypotheses that are traditionally addressed separately in different science and engineering disciplines.


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: SOLAR-TERRESTRIAL | Award Amount: 119.94K | Year: 2016

This project science focuses on a fundamental gap in our knowledge of solar energetic events and their potential impact on the heliospheric and interplanetary environment - how to evaluate their potential size in terms of energy release. This project is unique in that it uses as statistics based approach to analyze characteristics of solar active regions. Being able to measure the stored and available energy, and to predict the size of an upcoming event will improve forecasting capability for solar flares and related phenomena such as coronal mass ejections and energetic particle production and propagation. These are the phenomena with direct impacts on human-dependent infrastructure and national security, hence improvements in forecasting eventually benefits large sectors of society. This project supports a postdoctoral researcher and a member of an underrepresented group who will serve as a mentor and Co-PI. Summer inters from the REU program will also be involved.

The objective of this project is to understand the different pathways to the release of stored coronal magnetic energy. When a large amount of free energy is stored, some active regions release it in a few large events, while others release the same amount of energy in many smaller events. Why this occurs is unknown. Two complementary approaches will be used to investigate this: 1) using photospheric proxies for the energy for a large sample of events, and 2) modeling of the coronal magnetic field for a small sample of events. In each case, the energy will be computed for subareas within each active region to estimate the fraction of the total free energy that can be released in a flare. This will be compared to the GOES soft X-ray flux of the events. Verification statistics computed from discriminant analysis will be used to determine whether photospheric proxies for sub-areas of an active region are better then global proxies at distinguishing regions which produce large events versus those which produce only small events. If the analysis indicates that the free energy computed for sub-areas are more closely associated with the energy released, this will indicate that the local configuration of the field is more important than the global configuration. The corona will be modeled using the Minimum Current Corona model and nonlinear force-free field extrapolations. For both models, a detailed comparison will be made of the possible energy release pathways to the flares that occurred, and the location of the flare emission to the currents associated with the stored energy. This will provide insight into the underlying processes governing the production of energetic events.


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: CLIMATE & LARGE-SCALE DYNAMICS | Award Amount: 31.66K | Year: 2017

The tropical upper troposphere and lower stratosphere are home to a variety of wave motions which play key roles in weather, climate, and atmospheric circulation. Waves which are broad (horizontal wavelengths spanning several degrees latitude) but shallow (vertical wavelengths of about one to four kilometers), generated by large areas of tropical convection, are the subject of this investigation. These waves are of interest for three reasons: first, the waves can induce the formation of cirrus clouds in the tropical tropopause layer (TTL), the transition zone between the troposphere and stratosphere that extends from about 14km to 18.5km. TTL cirrus can form as rising air motions associated with the waves depress air temperatures and cause water vapor to freeze out as cirrus ice crystals. The resulting clouds may be too thin to see from the ground or from satellites, yet they have an important climatic effect as they trap outgoing infrared radiation and thus warm the atmosphere. The prevalence of such clouds is difficult to quantify, and the relative importance of wave motions as a source of TTL cirrus, in comparison to cirrus formation due to outflow of ice particles from deep cumulus clouds, is not known.

Second, the freezing out of water vapor by wave-induced temperature depression could be an important constraint on the amount of water vapor entering the stratosphere. The TTL is sometimes referred to as the gateway to the stratosphere, as most of the water vapor in the stratosphere over the entire globe enters through the TTL. The stratosphere is extremely dry compared to the troposphere, but stratospheric water vapor is nevertheless important as it has a relatively strong greenhouse effect and can lead to the formation of the polar stratospheric clouds which are key to the formation of the ozone hole.

Third, waves can transport momentum from the troposphere to the stratosphere, and wave momentum transport is the primary driver of the stratospheric Quasi-Biennial Oscillation (QBO), an alternation between easterly and westerly winds occurring over the global tropics with a cycling time in excess of two years. While the QBO is narrowly confined to the low-latitude stratosphere, it can influence weather and climate worldwide through its effects on prominent modes of climate variability such as the North Atlantic Oscillation. While the theory of wave momentum transport is well established, uncertainties remain as to the relative importance of different wave types in driving the QBO, and current weather and climate models have difficulty in simulating it.

This project seeks to improve understanding of waves in the TTL by building and launching a balloon-borne instrument which receives positioning signals from satellites of the Global Navigation Satellite System (GNSS, which includes the GPS satellites launched by the US). The GNSS signals are refracted as they pass through the atmosphere, and the amount of refraction can be used to infer air temperature in the upper troposphere. Because the profiles are retrieved from the rising and setting, or occultation, of the GNSS satellites relative to the receiver, the balloon-borne instrument has the acronym ROC, for Radio OCcultation.

ROC is developed for use on balloons flow as part of the Strateole-2 field campaign organized by the Centre National dEtudes Spatiales (CNES), the French Space Agency, and the Laboratoire de Meteorologie Dynamic (LMD) of the University of Paris-Saclay. Strateole-2 is a five-year campaign, with a small validation deployment in 2018 and full science deployments in 2020-2021 and 2022-2023. Balloons are launched from the Seychelles (about 5S in the Indian Ocean), with the expectation that each balloon will circle the earth for up to 90 days and observe the TTL between 20S and 15N. This award supports US participation in the validation campaign and the first full science deployment, along with post-campaign analysis. It is one of three awards made to US PIs for participation in Strateole-2, the full set being AGS-1643022, AGS-1642277/1642246, and AGS-1642650/1653644.

ROC is oriented to retrieve signals from GNSS satellites on either side of the balloon flight path, with observations taken between 8km and the flight level of about 20km and a vertical resolution between 200m and 250m. The observing geometry is such that observations at lower levels are farther away from the balloon, so that observations at 18, 15, and 12km altitude correspond to distances of roughly 100, 200, and 300km on either side of the balloon. The waves of interest have periods from hours to days and ROC can record two to three occultations per hour. Thus the three-dimensional structure of the waves is captured by the ROC measurements as the balloon advances along its trajectory.

ROC is accompanied by two other instruments which provide complementary observations. One is the Balloonborne Cloud Overshoot Observation Lidar (BeCOOL), provided by the Laboratoire Atmospheres, Milieux, Observations Spatiales (LATMOS, a laboratory of the Institut Pierre Simon Laplace) in collaboration with CNES. The lidar provides measurements of cirrus clouds which can be combined with ROC observations to examine the role of wave motions in generating cirrus clouds. The other is the Temperature SENsor (TSEN), an instrument from LMD which records atmospheric temperature and pressure at the gondola. Gondola displacements are precisely determined by ROC, and TSEN observations are used to factor out gondola movement relative to the ambient wave motion (these are super-pressure balloons which fly at a level of constant density). The displacement data are then used to estimate the wave momentum flux at flight level associated with the large-scale waves observed by ROC.

The work has scientific broader impacts due to the value of the observations for addressing a variety of questions regarding the effect of wave motions on TTL clouds, stratospheric humidity, and the QBO. Observations collected in this project will be made available to the research community from servers at the Laboratory for Atmospheric and Space Physics at the University of Colorado so that they can be freely examined by the research community. The project also engages undergraduate students through a research class, offered simultaneously at the University of California San Diego, the University of Arizona (UA), and the Autonomous University of Mexico (UNAM), in which students design a research project based on a test flight of ROC. The class is followed by undergraduate research internships at UCSD, UA, the Research Experiences in Solid Earth Sciences for Students (RESESS) program at UNAVCO (the University NAVSTAR Consortium, dedicated to applying GNSS technology to earth science), and the Significant Opportunities in Atmospheric Research and Science (SOARS) program of the University Corporation for Atmospheric Research. Beyond these broader impacts, the project supports two graduate students.


Grant
Agency: NSF | Branch: Continuing grant | Program: | Phase: SOLAR-TERRESTRIAL | Award Amount: 119.76K | Year: 2017

The survey to be produced as part of this 3-year project will considerably increase our knowledge about the physics of subsurface flows inside the Sun, allowing their variation with magnetic region properties, and with time, to be ascertained. The research program seeks to understand how these flows affect larger circulation patterns, particularly the meridional and zonal flow components of global circulation. The meridional flow is involved critically in the process that leads to Suns polar field polarity reversals and the ability to predict properties of subsequent solar cycles. It is not clear how it is modulated in time by the contribution of active-region related inflows. A quantitative assessment of this contribution, provided by this research project, will allow critical improvements to be made in predictive models. Theories regarding the physics of the flows have been put forward, with predictions about their variation with depth. These predictions will be tested by the inverse modeling efforts as part of this project. Using artificial data available from numerical MHD simulations, the research activities will also aim to develop and validate methods to infer subsurface flows reliably and which avoid artifacts caused by the influence of surface magnetic fields on the seismic waves. These methods will be invaluable for improving and validating other models of flows and structures inferred through helioseismology.

The main purpose of this 3-year project is to perform a comprehensive, high-spatial-resolution helioseismic survey of subsurface flows around solar magnetic regions in order to improve models of solar dynamo. The research project has four main objectives. The first objective is to characterize, using helioseismic holography applied to Dopplergrams from the Helioseismic Imager onboard the SDO mission, the near-surface flows observed around solar active regions. This characterization will include examining the dependence of the flow properties with magnetic flux. The time dependence of the flows as regions evolve will also be examined. The second objective is to establish and quantify the contribution of the near-surface flows surrounding active regions to the latitudinal- and temporal-variation of the global meridional and zonal flow patterns. This will be achieved by comparing monthly time and longitude averages of active-region related flows with meridional and zonal flow measurements. The third objective is to determine, through helioseismic inverse modeling, the depth dependence of active-region related flows, in order to provide a physical understanding of the flows. The fourth objective is to validate the reliability of the flow determination around active regions. This will be achieved using existing synthetic data derived from state-of-the-art numerical MHD simulations of waves in the vicinity of magnetic structures.

An understanding of the contribution of active-region-related flows in Suns interior to the larger-scale dynamics is required for improving surface-flux-transport models of the solar dynamo. The outcome of this project is expected to improve general knowledge of solar and stellar dynamos and the evolution of magnetic fields. The expected results will allow improvements in predicting the solar-cycles of the Sun. The project team will broadly disseminate data products for their use in these types of models as part of this program. This project will facilitate continued involvement of the team in the REU Program in Solar and Space Physics hosted by the University of Colorado at Boulder. A considerable portion of this research is being carried out by a postdoctoral research scientist who will take the lead on several of the project tasks. The research and EPO agenda of this project supports the Strategic Goals of the AGS Division in discovery, learning, diversity, and interdisciplinary research.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: PHYSICAL OCEANOGRAPHY | Award Amount: 434.29K | Year: 2015

The Lagrangian drift associated with ocean surface waves, known as Stokes Drift, plays an important role in the ocean surface boundary layer dynamics and in particular the small-scale (nominally a few kilometers) diffusion of passive tracers. Thus it is important for the break-up and dispersion of oil spills or sewage outflow, and transport of material in the upper ocean and near the coast in general. Considerable theoretical advances have been made over the last few decades, but the lack of direct observations hampers progress on the role of Stokes Drift in material transport in the upper ocean. The collection of new observations and development of theoretical and numerical models will advance the current understanding of these dynamics in realistic wave conditions in both the open ocean and the coastal environment. The nonlinear Lagrangian theory and sea surface kinematics simulations developed in this project will provide a general framework for the analysis and interpretation of measurements of surface-following moored buoys, drifters, and remote sensing systems. The findings from this study will provide a framework towards understanding and predicting wave-driven material transport processes, including the break-up of surface slicks and transport of larvae, and will contribute to more effective disaster mitigation and coastal ecology protection programs. The development of small, low-power, inexpensive drifters with satellite communication and sustainable energy sources, which can resolve both surface waves and surface drift fluctuations, is an important step toward more ambitious, global applications. Large arrays of these types of instruments can be used to monitor ocean waves, surf zone motions, mean surface currents, and surface temperature and salinity. A post-doctoral fellow will be trained in both observational and modeling techniques in the upper ocean and summer undergraduate interns will be exposed to the research process.

The Lagrangian near-surface drift of ocean surface waves (Stokes Drift) is still poorly understood and no direct measurements have been reported. In particular, very little is known about random fluctuations in the Stokes Drift that are believed to be important to upper ocean diffusion processes. Detailed observations of the fluctuating surface drift in the upper ocean due to surface waves will be obtained, building on the investigators recent development of small, wave-resolving drifters. Approximately 25 drifters will be deployed in homogeneous, open ocean conditions and in a more complex coastal environment with variable depth and currents, to observe the near surface kinematics and particle dispersion. To interpret the drifter data and develop a better understanding of the effects of nonlinearity and directional spreading on the surface drift and diffusion statistics, a Lagrangian theory for the surface kinematics in a random wave field will be developed. The theory will be extended to include random, small-scale medium variations (e.g. bottom topography and ambient currents), and augmented with direct numerical integration of the surface momentum balance to simulate more complex conditions with strong nonlinearity and/or rapid medium variations. Then, observations will be compared to theory and numerical simulations, and the relative contribution of Stokes Drift fluctuations to the observed particle diffusion will be evaluated to gain a better understanding of the role of waves in material transport and diffusion, both offshore and near the coast.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: PHYSICAL OCEANOGRAPHY | Award Amount: 658.99K | Year: 2015

Lateral stirring is among the fundamental processes, along with advection and diapycnal (vertical) mixing that determines the distribution and fate of water-mass properties, nutrients and dissolved gases in the ocean. Ocean general circulation models (OGCMs) resolve stirring on scales larger than ~30 km, and regional models on scales ~1 km, but isopycnal (lateral) stirring by submesoscale (1 to 10 km) and finescale (10 m to 1 km) processes must be parameterized. Tracer-release experiments consistently find isopycnal diffusivities at scales of 1-10 km to be an order of magnitude larger than predictions for internal-wave shear dispersion. This project will provide a more complete and accurate assessment of the roles of internal waves and vortical mode in lateral stirring at the submesoscale of order 10 m to 10 km), and the cascade of energy to dissipative vertical scales, to resolve this paradox. Internal waves and vortical mode are difficult to distinguish observationally. However, judicious use of a numerical model can tease apart their influences by isolating different physics. A major advantage of the approach of this project is that all of the above processes/dynamics can be explored in the context of a single model, allowing us to seamlessly explore the internal-wave cascade and lateral dispersion by the different mechanisms across a wide range of parameter regimes and forcing conditions. The proposed simulations will elucidate the underlying physics and inform our understanding of how these processes work in the ocean so as to provide an order-one parameterization of submesoscale isopycnal diffusivities for OGCMs. Parameterizations developed in this study will be made available through peer-reviewed publications and conference presentations. Two graduate students will be trained in high resolution numerical modeling and data analysis techniques. A public project website will also be maintained, with initial conditions and parameters for our simulations archived and shared on request with other investigators interested in collaboration.

The proposed approach will use a Boussinesq pseudo-spectral model to investigate lateral dispersion and the internal-wave energy cascade. Specific goals are to determine the roles of (1) wave/wave and wave/vortex interactions in the internal-wave cascade to small vertical scales and turbulence production, (2) wave/wave and wave/vortex de-phasing of the internal wave field in isopycnal stirring, (3) turbulent intermittency in internal-wave shear dispersion, and (4) vortical-mode shear dispersion and stirring. Model results will also be used to examine (5) the physics of the finescale roll-off and (6) the statistics of unstable shear events (Richardson number less than a quarter). Simulations with and without finescale potential vorticity production by internal-wave breaking will be used to isolate the roles of the vortical-mode inverse cascade. Passive tracers subject to diapycnal mixing and non-diffusive Lagrangian particles will be used to distinguish between shear dispersion and stirring. The simulations will be run with varying buoyancy frequency, Coriolis frequency, internal-wave spectral energy level and frequency spectral shapes to explore fundamental parameter dependences of the cascade, finescale roll-off, Richardson Number statistics, diapycnal diffusion and isopycnal diffusion. First-order submesoscale horizontal diffusivities for OGCMs and regional models will result. Different forcings (surface wind, tidal) for maintaining the internal-wave field in a statistically steady state will be tested. Profiling float and dye data collected in the Sargasso Sea during summer will be used to guide model initialization and assess the realism of the results. Where possible, differences in modelled dispersion characteristics will be identified and used to identify stirring mechanisms in the observational data sets.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: CLIMATE & LARGE-SCALE DYNAMICS | Award Amount: 489.85K | Year: 2015

Waves in which buoyancy is the restoring force are referred to as gravity waves, and such waves are ubiquitous in the atmosphere. They occur over a broad range of spatial scales but are generally smaller than the frontal weather systems seen on weather maps. They can be generated by a variety of mechanisms including air flow over mountains, the formation of frontal systems, and the vertical motions that accompany convection. Despite their relatively small size, they are thought to play an important role in the atmospheric circulation due to their vertical flux of horizontal momentum, through which they drive the quasi-biennial oscillation in the equatorial stratosphere, modulate the strength of the midlatitude jet streams, and alter the strength of the stratospheric polar vortices, thereby playing a role in the seasonal evolution of the Southern Hemisphere ozone hole. But the small size of the waves and their relatively rapid propagation make it difficult to observe them and examine their generation, propagation, and impacts on the mean flow. Moreover, the waves cannot generally be simulated by global weather and climate models due to their small size, and instead they must represented through parameterizations which estimate their aggregate effects as a function of the resolved flow. While these parameterizations have become quite sophisticated, their validity is difficult to establish, and common circulation biases in models are often ascribed to inadequacies of the gravity wave parameterizations.

Work under this award specifically addresses gravity waves generated by convection, motivated by recent observations from balloons and satellites suggesting that that large amplitude gravity waves, of the sort that come from vigorous, small-scale deep convection, account for a larger fraction of the gravity wave momentum flux than previously assumed. Further motivation comes from the availability of the record of tropical convection from the Tropical Rainfall Measurement Mission (TRMM), a satellite record which is now over a dozen years long and can be used to estimate the generation of gravity waves by tropical and subtropical convection. The data is used in conjunction with the gravity wave parameterization from the Community Atmosphere Model, along with observational wind and atmospheric stability data, to estimate the generation, propagation, and momentum flux of convectively generated gravity wave activity. The momentum flux is then compared with estimates calculated from the satellite record of atmospheric temperature from the satellite record of the Atmospheric Infrared Sounder (AIRS). The goal of this effort is to reconcile the large-scale patterns in gravity wave activity observed in the tropics and subtropics with existing knowledge of their convective sources, based on a theoretical understanding of their propagation and mean flow interaction. The reconciliation is expected to require some ad hoc adjustment of free parameters in the parameterization scheme, and the PIs will conduct further experiments to determine how this tuning of the parameterization affects the large-scale atmospheric simulation produced by the model. Some work will also consider the generation of gravity waves by convection occurring in the storm tracks of the middle latitudes, using other data sources to estimate convection.

The work has broader impacts due to the need for accurate gravity wave parameterizations in weather and climate models. These models are widely used as research tools for a variety of applications, and are also used to provide information to first responders, decision makers, and the general public. In addition, the project supports and trains a graduate student, thereby providing for the future workforce in this research area.


Grant
Agency: NSF | Branch: Standard Grant | Program: | Phase: ANTARCTIC OCEAN & ATMOSPH SCI | Award Amount: 185.90K | Year: 2016

Despite their importance to radiative transfer, the amount of supercooled liquid water in polar clouds may be uncertain. This underestimation in turn results in significant radiation biases at the surface and TOA (top of the atmosphere) and misrepresentation of polar aerosol-cloud interactions. Recent work involving tuning a climate model to match mixed phase cloud distributions with observations resulted in an increase in net cloud radiative effects over Antarctica. A crucial component of understanding Antarctic climate, therefore, is a more accurate representation of the abundance of supercooled liquid in clouds and of corresponding cloud-radiative interactions.

Leveraging down-welling radiance measurement data previously collected with FT-IR instruments (Atmospheric Emitted Radiance Interferometers; AERIs) at South Pole Station - (2000) , Dome C - (2003) and to be made at McMurdo Station (planned for Nov. 2015-Nov. 2016) will be used to assess the seasonal dependence of cloud properties and cloud impacts on the local surface radiative budget. Two hypotheses will be considered:
1) The Antarctic radiation budget is highly sensitive to cloud properties, particularly thermodynamic phase.
2) The radiative impact of supercooled liquid in Antarctic clouds is significantly influenced by the temperature dependence of the complex refractive index of water (CRI)

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