Browsing by Department "Atmospheric Sciences"

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Assessing the Impact of TTL Cirrus on the Climate System - CloudSat and CALIPSO Science Team Recompete/ROSES-2015
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/636; NASA-Langley Research Center
We use a forward Lagrangian trajectory model to diagnose mechanisms that produce the water vapor seasonal cycle observed by the Microwave Limb Sounder (MLS) and reproduced by the Goddard Earth Observing System Chemistry-Climate Model (GEOSCCM) in the tropical tropopause layer (TTL). We confirm in both the MLS and GEOSCCM that the seasonal cycle of water vapor entering the stratosphere is primarily determined by the seasonal cycle of TTL temperatures. However, we find that the seasonal cycle of temperature predicts a smaller seasonal cycle of TTL water vapor between 10 and 40? N than observed by MLS or simulated by the GEOSCCM. Our analysis of the GEOSCCM shows that including evaporation of convective ice in the trajectory model increases both the simulated maximum value of the 100 hPa 10–40? N water vapor seasonal cycle and the seasonal-cycle amplitude. We conclude that the moistening effect from convective ice evaporation in the TTL plays a key role in regulating and maintaining the seasonal cycle of water vapor in the TTL. Most of the convective moistening in the 10–40? N range comes from convective ice evaporation occurring at the same latitudes. A small contribution to the moistening comes from convective ice evaporation occurring between 10? S and 10? N. Within the 10–40? N band, the Asian monsoon region is the most important region for convective moistening by ice evaporation during boreal summer and autumn.
Assessing the influence of background state and climate variability on tropical cyclones using initialized ensembles and mesh refinement in E3SM
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/227; DOE-Office Of Science
The scientific goal of this project is to assess the influence of the background state and horizontal resolution of climate models on the simulation of extreme events like intense precipitation, tropical cyclones, atmospheric rivers, and heatwaves. The main results are: - Initialized ensembles of 4-week forecasts using a climate model (E3SM) show that dynamic (flow) and thermodynamic (moisture) biases asymptote to their climatological values at different rates—dynamic bias grows rapidly and approaches its climatological value within about 2 weeks whereas the thermodynamic bias takes about 4 weeks. - Moisture bias has a bigger impact on extreme events like tropical cyclones and intense precipitation than flow bias, and this impact is non-monotonic over bias evolution time. - Climate models are capable of simulating the flow features associated with unprecedented extreme events like the Western North America heatwave of June 2021, but moisture biases can weaken the surface manifestation of extreme heatwaves. Reducing model bias may be more important than increasing model resolution in improving the fidelity of heatwave simulations in climate models. - Climate models are capable of simulating weather patterns associated with “power droughts”, i.e., periods with low solar and wind power generation, provided model biases in the simulation of the background state can be corrected. - Regional mesh refinement can improve the simulation of extreme weather events but model biases may still persist.
Assessing the influence of background state and climate variability on tropical cyclones using initialized ensembles and mesh refinement in E3SM
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/227; DOE-Office Of Science
One of the important applications of global climate models is to predict anticipated changes in the statistical properties of extreme events. Tropical cyclones are among the extreme events with the greatest socioeconomic impacts in the United States and other regions of the world. Landfalling hurricanes cause significant loss of property and life along the Atlantic and Pacific coasts of North America. Although coarse-resolution global climate models are incapable of simulating individual hurricanes accurately, they do exhibit significant skill in simulating the interannual and decadal variations in the aggregate statistics of hurricanes in the Atlantic basin, when provided the observed sea surface temperature as the boundary condition. We propose to analyze and validate simulated tropical cyclone activity in the Energy Exascale Earth System Model (E3SM), with a focus on tropical cyclones in the Northern Hemisphere. As global climate models approach horizontal spatial resolutions of 25km, their ability to simulate the statistical properties of tropical cyclones becomes an important validation metric. The U.S. CLIVAR Hurricane Working Group recently carried out an intercomparison of tropical cyclone characteristics as simulated by climate models and found that models are indeed able to reproduce the gross features of the geographical distribution of observed global tropical cyclone frequency. However, most models are not able to reproduce the detailed spatial structure of tropical cyclone tracks over the North Atlantic and other regions. In general, regionally-aggregated measures of tropical cyclone activity turn out to be much more predictable than local tropical cyclone occurrences. One of the challenges in simulating the spatial distribution of tropical cyclone track density in global climate models is the effect of climate bias. The genesis and evolution of tropical cyclones is quite sensitive to the large-scale background flow. For example, excessive vertical wind shear can inhibit the development of tropical cyclones. Since atmospheric flow biases can develop within a few weeks from the start of a simulation, it becomes difficult to distinguish between the flow bias effect and other possible deficiencies in the climate model, such as errors in subgrid parameterizations or poor spatial resolution. To address this problem, we propose to use an initialized ensembles approach, where a series of 14-day hindcasts is carried out using the atmospheric component of E3SM. The integrations will be initialized from atmospheric reanalyses every 3 days over the decadal period 2000-2009. By construction, the background flow in these hindcasts will be close to observations. Comparing the statistics of tropical cyclone simulations in the initialized ensemble to that in the control runs will allow us to isolate the impact of mean flow biases. Errors in the representation of fine-scale orographic features in certain areas, such as the Central American Gap Wind region, can also lead to biases in the simulation of tropical cyclones. We propose to use a mesh-refinement approach to better represent orographic features in this region and study its impact on tropical cyclone activity.
Collaborative Research: Cirrus Cloud Formation and Microphysical Properties from In-situ Observed Characteristics to Global Climate Impacts
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/600; National Science Foundation
This study will investigate the determinant factors behind cirrus cloud formation and evolution based on in-situ observations at various geographical locations. In addition, the global radiative forcing of observation-constrained aerosol impacts on cirrus microphysical properties will be quantified by using a climate model. The project will focus on three critical scientific issues: (1) Hemispheric differences in cirrus cloud macroscopic and microphysical properties under similar dynamical conditions; (2) Multi-scale dynamical forcings driving ice nucleation and their impacts on cirrus simulations in a climate model; and (3) Impacts of anthropogenic aerosol emissions on cirrus microphysical properties and the subsequent influences on global radiation. To address these scientific issues, The research team will: (1) extract cirrus cloud samples from a composite in-situ dataset covering various geographical locations, and compare the formation and evolution of cirrus clouds between two hemispheres; (2) examine the micro- to mesoscale (~0.1-10 km) variabilities of water vapor and temperature, and improve the NCAR Community Atmosphere Model version 5 (CAM5) by including these observed variabilities; (3) compare the in-situ measured cirrus microphysical properties between polluted and pristine regions, and use CAM5 to quantify the consequent perturbations on global radiation balance. Intellectual Merit: Cirrus clouds are one of the main modulators of Earth's climate system. However, due to their large spatial heterogeneity and temporal variability, cirrus clouds remain one of the poorly-represented components in current general circulation models (GCMs). This project will improve our understanding of cirrus microphysical properties in relation to dynamical conditions and aerosol backgrounds, by analyzing in-situ aircraft data obtained from both the Northern and Southern Hemispheres, polluted and pristine regions. Furthermore, the research team will use the observed characteristics to evaluate the simulations of relative humidity and cirrus clouds in CAM5 in terms of their occurrence, spatial coverage and microphysical properties. In addition, a "best-observation-matched" ice microphysics configuration will be implemented into CAM5. Overall, using micro- to mesoscale observations of cirrus formation and evolution, the research will improve cirrus cloud simulations in CAM5 and provide a new estimation on cirrus clouds' adjustments due to anthropogenic aerosol emissions (i.e., aerosol indirect forcing through perturbations of cirrus microphysical properties). Broader Impacts: Both the observational dataset and the new model parameterization will be released to the community, including a synthesized in-situ observation dataset (a total of 8 campaigns from NSF, NASA and European Union), and a sub-grid scale parameterization of relative humidity variability for GCMs. The improved estimation of anthropogenic aerosol impact on cirrus cloud radiative forcing can contribute to uncertainty reduction in the next IPCC report. The project will greatly benefit teaching and mentoring of undergraduate and graduate students at University of Wyoming and San Jose State University. The project will also recruit and train undergraduate students for presenting their research at the local K-12 schools via San Jose State University's undergraduate Ambassador Program.
Collaborative Research: Contrasting the Effects of Aerosols on MBL Cloud-precipitation Properties and Processes in Boreal and Austral Mid-latitude Regions
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/243; National Science Foundation
The project is to investigate formation of marine-boundary-layer clouds, which are clouds that are directly influenced by the ocean. Particularly, how tiny suspended particles or aerosols contribute to clouds and how clouds interact with aerosols. Aerosols are generated from atmospheric, land, and oceanic processes such as urban/industrial activity, dust storms, burning vegetation, biological activity, sea spray, wind currents, and volcanoes. Certain aerosol types can initiate marine-boundary-layer cloud development more easily than others. This adds to the complexity and uncertainty of marine-boundary-layer cloud impacts on weather variations. Marine-boundary-layer clouds have significant climatological effects on the hydrological cycle and the Earth?s radiation balance. For example, varying distributions of marine-boundary-layer clouds around the globe contribute to areas of deficits and surpluses in solar energy and rainfall. Many studies have been conducted on aerosol-cloud interactions in the Northern Hemisphere where most of the global population and landmasses are located. Not much is known over the vast area of remote land and oceanic regions in the Southern Hemisphere. This study will investigate differences and similarities of aerosol-cloud interactions between the Northern and Southern Hemispheres by analyzing recent field observations and utilizing numerical model simulations. The project involves undergraduate and graduate students to participate in the research project and train them to be the next generation of scientists. This study employs long-term ground-based observations and remote sensing retrievals from a dedicated observation site in the Eastern North Atlantic Ocean and aircraft in situ measurements from two intensive field campaigns in 2018: 1) the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA), and 2) the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES). The research team utilizes a synergistic measurement/modeling approach in conjunction with meteorological patterns to compare the characteristics of marine-boundary-layer aerosol, cloud, and drizzle properties over the two hemispheres through answering three scientific questions. Those are: 1) what are the relative roles of surface cloud condensation nuclei and updrafts in aerosol-cloud interactions over the marine boundary layer and warm rain processes? 2) what are the characteristics of marine-boundary-layer aerosol, cloud and drizzle properties and their interactions during two field campaigns? 3) what are the characteristics of marine-boundary-layer aerosol, cloud, and drizzle properties, their interactions over the Southern Ocean, and their similarities and differences compared with those in the Eastern North Atlantic Ocean? Comparisons of precipitation processes and aerosol-cloud interactions at the two sites with significantly different environmental conditions will shed light on the controlling factors in aerosol-cloud interactions and eventually lead to a generalized parameterization for aerosol-cloud interactions applicable for the global climate models. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Contrasting the Effects of Aerosols on MBL Cloud-precipitation Properties and Processes in Boreal and Austral Mid-latitude Regions
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/243; National Science Foundation
The project is to investigate formation of marine-boundary-layer clouds, which are clouds that are directly influenced by the ocean. Particularly, how tiny suspended particles or aerosols contribute to clouds and how clouds interact with aerosols. Aerosols are generated from atmospheric, land, and oceanic processes such as urban/industrial activity, dust storms, burning vegetation, biological activity, sea spray, wind currents, and volcanoes. Certain aerosol types can initiate marine-boundary-layer cloud development more easily than others. This adds to the complexity and uncertainty of marine-boundary-layer cloud impacts on weather variations. Marine-boundary-layer clouds have significant climatological effects on the hydrological cycle and the Earth?s radiation balance. For example, varying distributions of marine-boundary-layer clouds around the globe contribute to areas of deficits and surpluses in solar energy and rainfall. Many studies have been conducted on aerosol-cloud interactions in the Northern Hemisphere where most of the global population and landmasses are located. Not much is known over the vast area of remote land and oceanic regions in the Southern Hemisphere. This study will investigate differences and similarities of aerosol-cloud interactions between the Northern and Southern Hemispheres by analyzing recent field observations and utilizing numerical model simulations. The project involves undergraduate and graduate students to participate in the research project and train them to be the next generation of scientists. This study employs long-term ground-based observations and remote sensing retrievals from a dedicated observation site in the Eastern North Atlantic Ocean and aircraft in situ measurements from two intensive field campaigns in 2018: 1) the Aerosol and Cloud Experiments in the Eastern North Atlantic (ACE-ENA), and 2) the Southern Ocean Clouds, Radiation, Aerosol Transport Experimental Study (SOCRATES). The research team utilizes a synergistic measurement/modeling approach in conjunction with meteorological patterns to compare the characteristics of marine-boundary-layer aerosol, cloud, and drizzle properties over the two hemispheres through answering three scientific questions. Those are: 1) what are the relative roles of surface cloud condensation nuclei and updrafts in aerosol-cloud interactions over the marine boundary layer and warm rain processes? 2) what are the characteristics of marine-boundary-layer aerosol, cloud and drizzle properties and their interactions during two field campaigns? 3) what are the characteristics of marine-boundary-layer aerosol, cloud, and drizzle properties, their interactions over the Southern Ocean, and their similarities and differences compared with those in the Eastern North Atlantic Ocean? Comparisons of precipitation processes and aerosol-cloud interactions at the two sites with significantly different environmental conditions will shed light on the controlling factors in aerosol-cloud interactions and eventually lead to a generalized parameterization for aerosol-cloud interactions applicable for the global climate models.
Collaborative Research: Evaluating the Influences of Aerosols on Low-level Cloud-precipitation Properties over Land and Ocean Using Long-term Ground-based-Observations and WRF Simulations
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/243; National Science Foundation
Aerosol generation resulting from natural and anthropogenic activities is expected to have considerable, far-reaching effects on cloud development and the hydrologic cycle. Though the aerosol direct effect can simply be thought of as a reduction of incoming solar radiation reaching the Earth's surface, the aerosol indirect effect (AIE) involves a complex set of aerosol-cloud-precipitation interactions. These indirect effects include the alteration of cloud microphysical properties such as cloud lifetime, droplet size distribution, liquid water content and path, optical depth, and albedo. Precipitation processes will certainly be affected in numerous and at times, detrimental ways. Hence, there is a major impact to society as a whole due to a heavy dependence on the distribution of available water over a given region for public consumption, agriculture, and industrial purposes. Intellectual Merit: This research adopts a synergistic approach that uses the long-term ground-based observations and retrievals from the Southern Great Plains of the United States and Eastern North Atlantic Ocean regions to investigate the seasonal and diurnal variations of aerosol and clouds under the continental and maritime conditions, as well as compare their similarities and differences. Air parcel trajectory modeling will be conducted to identify the sources of air masses for the selected cases to investigate the AIEs over these two regions with additional WRF simulations. This study is important because it will aid to improve aerosol and cloud parameterizations as well as provide an in-depth understanding of aerosol-cloud-precipitation interactions in typical maritime and continental conditions. The following three scientific questions (SQs) will be investigated. SQ1: What are the similarities and differences of aerosol-cloud properties, as well as their interactions over ocean and land? SQ2: What are the indirect effects of aerosols on cloud microphysical properties? SQ3: How does wind shear enhance turbulent mixing and stimulate drizzle formation? Broader Impacts: This research will benefit society by helping to provide better support for the modeling of aerosol-cloud-precipitation interactions which will aid in researching the long-term distribution of available water by clouds and precipitation processes. The far-reaching goal of this project is to further reduce uncertainties in the climate modeling community by providing better constraints for seasonal and regional aerosol and cloud properties. Moreover, there will be plenty of opportunities to introduce aerosol-cloud interactions as "real world" examples in undergraduate and graduate geoscience courses where the students can not only investigate these examples as interdisciplinary class projects, but also improve upon current research techniques and develop their own theses and dissertation areas of focus.
Collaborative Research: Quantifying the Role of Pollen in Cloud Formation through Measurements and Modeling
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/214; National Science Foundation
While pollen is emitted from the Earth's surface in large quantities from vegetation, these emissions are typically excluded from inventories due to the large size of pollen grains. However, recent studies have shown that pollen grains easily rupture when wet, forming smaller sub pollen particles (SPP); these SPP have not been well-studied. The central goal of this study is to accurately establish the amount of SPP produced by pollen rupture and to determine its cloud formation properties. This study will include a series of experiments utilizing a plant chamber and atmospheric modeling simulations. The laboratory measurements will (1) Quantify the number of SPP emitted from a single pollen grain and from a plant under atmospheric conditions, (2) Determine the supersaturation required for cloud condensation nuclei (CCN) activation, and (3) Determine the temperatures and relative humidities required for ice nucleating particles (INP) activation. These results will provide critical input for an online pollen emissions model that will be used with the Weather Research and Forecasting model coupled with Chemistry model (WRF-Chem) to (1) Implement the pollen emission rupture mechanism in WRF-Chem, (2) Utilize measured rupture data to improve simulations of pollen rupture, and (3) Conduct new simulations that account for the indirect effects from both warm and cold clouds using CCN and INP activation measurements. This interdisciplinary project uses laboratory and modeling components to maximize the value of the measurements for improving model estimates of pollen effects on cloud formation. The work will also be integrated in an undergraduate course that will introduce pollen sampling equipment and instruct students on the basics of aerosol and climate modeling. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Collaborative Research: Systematic Evaluation and Further Improvement of Present Broadband Radiative Transfer Modeling Capabilities
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/202; National Science Foundation
The terrestrial climate system is sensitive to the radiation budget. Thus, accurate knowledge about the solar and thermal infrared radiation in the coupled atmosphere-ocean system is critical to robust climate study. An example of this sensitivity is the suggestion that a 1% decrease in the solar constant could lead to an ice age. The effect of doubling CO2 on radiative forcing is approximately 4 Wm-2, whereas uncertainties in radiation simulations due to, for example, insufficient knowledge about the optical properties of clouds, may be larger than this value. During the 1980s and 1990s, many researchers made substantial progress in developing and improving radiative transfer schemes used in general climate models (GCMs), and various intercomparisons of GCM radiation codes were published. Since that time, significant progress has been made in light scattering computational methods, in-situ measurements and laboratory studies of the optical and microphysical properties of clouds and aerosols, gaseous absorption line parameters and the water vapor continuum absorption, optical properties of various oceanic constituents, and the efficiency of numerical schemes for solving radiative transfer equations. There is a pressing need to incorporate the aforesaid progress into radiative transfer modeling capabilities. Moreover, the ocean and atmosphere are not coupled in many existing radiative transfer models. The scattering and absorption of radiation by oceanic water, dissolved organic matter (the so-called yellow substance), and phytoplankton have an influence in heating the uppermost water layers, and consequently affect thermal and dynamic properties such as the sea surface temperature and depth of the mixed atmosphere-ocean layer. The reflection of radiation by the oceans, including the effects of a wavy air-water interface and whitecap, can also affect the spectral characteristics and magnitude of radiation and, thus, the radiative heating and cooling rates in the atmosphere. The overarching goal is to systematically evaluate and further improve current radiative transfer modeling capabilities. Intellectual Merit: The outcomes of the study will include 1) systematic quantification of the potential errors/inaccuracies of the aforesaid radiative transfer models, 2) extension of the current radiative transfer modeling capabilities to an atmosphere-ocean coupled system, 3) implementation of spectrally consistent parameterizations of ice clouds and dust aerosols, and 4) development and implementation of a computationally efficient radiative transfer solver. Broader Impacts: The research effort will improve the radiative transfer package currently used in climate models, and be a valuable contribution to the atmospheric radiative transfer and climate study communities. Furthermore, the light scattering modeling and parameterization capabilities can find potential applications in other areas such as remote sensing of dust aerosol and ice cloud properties. The associated educational pursuits will focus on mentoring a postdoc researcher, training a graduate student, and developing teaching materials. This effort will contribute to training young researchers in the discipline of radiative transfer and light scattering that is a quite unique branch of atmospheric physics. Furthermore, the integration of RRTMG into classroom teaching will directly benefit the educational program in atmospheric sciences, particularly, in hands-on experience in atmospheric radiative transfer simulation.
CONSTRAINING THE MODELING OF DUST AEROSOL AND CLIMATE IMPACTS USING CALIPSO, CLOUDSAT, AND OTHER A-TRAIN SATELLITE MEASUREMENTS
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/600; National Aeronautics And Space Administration
1. Abstract As the science community seeks to get a better handle on the energy budget of Earth’s atmosphere, ice clouds continue to be a source of significant uncertainty. Ice cloud microphysical and optical properties (i.e. effective radius and optical depth) are among the most uncertain components in our understanding of cloud-climate forcings and feedbacks. Reduction in cloud feedback uncertainty was recommended as a most important endeavor by the decadal survey (National Academy of Sciences, 2017). The Climate Absolute Radiance and Reflectivity Observatory Pathfinder (CLARREO-PF), while not specifically designed for cloud research, will provide hyperspectral measurements of the solar reflected radiance over the range of 320 – 2300 nm. Such a complete measurement of the reflected solar spectrum provides an impressive platform to study microphysical and optical properties of ice clouds in an effort to increase information, reduce noise, and analyze spectral consistency of the retrievals. With this proposal, we seek to leverage recent advancements in ice particle radiative modeling and CLARREO-Pathfinder’s unique accuracy, spectrally resolved reflectances, and Shannon information content for retrieval of ice cloud optical depth and effective radius in order to reduce uncertainty in global distributions of cloud optical properties. Finally, using NASA’s proposed CLARREO-Infrared (CLARREO-IR) and Polar Radiant Energy in the Far-Infared Experiment (PREFIRE) as inspiration, we will investigate the expansion of our study into the far-infrared.
Convective multi-scale interactions over the Maritime Continent during the propagation of the MJO
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/651; DOC-NOAA-Climate Program Office
There are strong convective variations over the land and ocean regions of the MC. These land/ocean differences lead to strong diurnal variability in wind, clouds, and precipitation that also vary during the propagation of the MJO. Figure 1 (left panel) shows that the MC islands show a strong evening maximum with offshore propagation in the early morning. Figure 1 (right panel) shows that the diurnal cycle over land decreases sharply once the MJO begins traversing the MC (i.e., after phase 3), whereas the diurnal cycle over ocean shows less variation during the MJO propagation. The hypothesis of this work is that the diurnal cycle over land disrupts the convective evolution in the MJO envelope and that the MJO has to overcome this strong diurnal signal to make it through the MC unscathed.
Convective-Environmental Interactions in the Tropics
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/651; DOE-Office Of Science
During the four years of this grant performance, the PI and her research group have made a number of significant contributions toward better understanding convective processes over the Amazon. First, she made available to the broader community a two-year data set of convective storm metrics based on SIPAM radar data from the central Amazon that has been utilized widely. Second, her students analyzed cold pool and heating characteristics of Amazonian convection and showed in heretofore unknown ways how both can impact new convective initiation (e.g., through multiple cold pool interactions and gravity waves formed via pulsed heating). Finally, her group more broadly showed how Amazonian and Indian Ocean convection interacts with the large-scale environment, especially low-level winds (e.g., the nocturnal Amazonian low-level jet) and deeper tropospheric moisture, to help it organize and how this interaction is represented in climate models.
Development of Community Light Scattering Computational Capabilities
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/202; National Science Foundation
This study seeks to develop theoretical and computational methods to improve simulations of optical properties of non-spherical particles over a broad range of size parameters. Applications of the theoretical/computational work span many broad areas of physics, chemistry, and engineering; with specific importance in atmospheric and oceanic sciences, combustion science, astrophysics, bio-optics, manufacturing diagnostics and control, and many other fields. This study will train graduate students and post-doctoral scholars. After testing and optimization, this research group plans to release the computational programs as open-source codes to the research community. This study seeks to expand previous NSF-funded research to develop advanced capabilities based on the invariant imbedding T-matrix method (II-TM) for simulating the optical properties of non-spherical, inhomogeneous particles with small to moderate size parameters. This study seeks to further improve the II-TM from both theoretical and numerical perspectives. This group recently developed a preliminary version of a physical geometric optics model (PGOM) based on either an electromagnetic volume- or a surface-integral relation for large size parameters. The suite of PGOM and II-TM will represent state-of-the-art light scattering computational capabilities, with a wide range of applications in atmospheric/oceanic radiative transfer and remote sensing. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
Development of Ice Cloud and Snow Optical Property Models in Support of CERES Science Team
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/202; NASA-Langley Research Center
1. Synopsis Surface snow and ice clouds have important impacts on the earth’s radiation budget. The single-scattering properties, namely, the phase function, single-scattering albedo, and extinction efficiency, of ice crystals are fundamental to the radiative transfer and remote sensing of ice clouds and snow. Ice crystals in clouds and snow particles are extremely complicated. Their optical properties are significantly different from “equivalent” ice spheres. It is necessary to use appropriate optical properties of ice crystal and snow particles in radiative transfer simulations and remote sensing concerning ice clouds and snow. Our research group at Texas A&M University has developed unique capabilities for simulating the optical properties of ice crystals and has been leading in this specific research area. For this project, we propose, building on existing on research, to simulate the optical properties of ice/snow particles in support of the NASA CERES (Clouds and the Earth’s Radiant Energy System) Science Team. Specifically, we propose the following three major tasks: 1) Improve and validate a new ice cloud bulk radiative property model; furthermore, generate look-up tables (LUTs) in support of the cloud property retrievals by the CERES Science Team using the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Visible and Infrared Imaging Radiometer Suite (VIIRS) observations. 2) Develop a novel snow albedo model in support of the radiative transfer model used by the CERES team for flux calculations. 3) Document and deliver the optical property and LUT data; furthermore, publish the research findings in peer-reviewed scientific journals.
Dynamics and Kinematics of the Monsoon Anticyclones
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/392; National Science Foundation
The Asian monsoon is one of the most important weather and climate systems on Earth. During the summer, warm moist air from the tropical oceans moves onto the southern and eastern parts of the Asian continent. This leads to convective storms, which provide critical precipitation and water supplies for a region that is home to several billion people. A similar but weaker monsoon circulation exists over North America. Monsoon storms also transport water and human-produced pollutants to great altitudes. These pollutants can have major effects on the chemistry of the atmosphere, including the stratospheric ozone layer, which protects living things from harmful solar radiation. Using computer simulations and atmospheric observations, this research will investigate the physical processes responsible for the Asian and North American monsoons and how they transport pollutants from near the Earth's surface throughout the atmosphere. The monsoons directly affect billions of people around the globe and have important indirect effects on the Earth's climate and the composition of the atmosphere. Changes in the circulation and composition of the atmosphere have the potential to disrupt physical, economic, social, and political systems around the globe. By improving our understanding of the physical processes responsible for the monsoon circulations, this study will advance our understanding of the present climate and reduce uncertainties in predictions of future climate change. This will lead to better guidance for social and economic policymakers. In addition, this project will train graduate students for careers in science and related fields.
ENSO Indices For a Changing Climate
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/453; DOC-National Oceanic and Atmospheric Administration
Many years before a basic dynamical understanding of the El Niño-Southern Oscillation (ENSO) was available, ENSO was monitored using the Southern Oscillation Index, which was based on differences of air pressure across the offequatorial Pacific. Later, as the fundamental role of equatorial ocean temperatures was realized, ENSO monitoring and quantification focused on the ocean surface. At present, the most commonly used ENSO indices are based on sea surface temperature (SST) anomalies in fixed regions of the tropical ocean. NOAA’s operational definition of ENSO is based on the Optimal Niño Index (ONI), a running mean of anomalies in the NINO 3.4 region. Many other indices are in use, including those that attempt to quantify different variants of ENSO or those that combine atmospheric and oceanic information. There are at least two problems with this situation. First, the research community presently does not have a standard definition for the intensity of ENSO. Even a researcher who chooses to use a common index, such as NINO 3.4, must decide on the base period from which anomalies are calculated. NOAA has attempted to keep up with climate change by updating its 30-year reference period every five years, but this is a patch rather than a cure. Researchers working with climate model output have chosen to take anomalies relative to fixed periods, to linearly detrended SSTs, to quadratically detrended SSTs, and so forth. The second problem is a more fundamental one. ENSO’s atmospheric impact involves a shift in the location of tropical convection across the tropical Pacific basin. This shift is driven by a reduction or reversal of the zonal sea surface temperature (SST) gradient. The atmospheric response is nonlinear, as a large horizontal displacement of tropical convection is possible once the SST gradient becomes flat or reverses. In a changing climate, the mean zonal SST gradient is likely to change, and so is the magnitude of the NINO 3.4 SST anomaly needed to cause an SST gradient reversal. And in climate models with different tropical SST climatologies, the threshold for SST gradient reversal is model-dependent. A regional anomaly index is only weakly related to the SST variations that control the response of the atmosphere in different climates, be they model climates, paleoclimates, or future climates. NOAA CPO FY17 COM 1 2 Nielsen-Gammon Statement of Work This sort of problem is not unique to ENSO. The Atlantic Multidecadal Oscillation is also defined in terms of temperature departures, in this case from a long-term linear trend. While the AMO is strongly correlated to Atlantic hurricane activity, it has been noted that a more physical correlation might be to the difference between tropical Atlantic temperatures and global tropical temperatures. So, in the Atlantic, the scientific community is already moving in the direction of a difference index as a replacement for the AMO index for some applications. (Third problem: relative vs. absolute indices) Motivated by the problems described above, and building on the work of Chiodi and Harrison, we propose to develop an ENSO index based on SST differences in the two tropical regions where convective activity (as measured by outgoing long wave radiation, or OLR) exhibits the largest ENSO-related variability. These regions are the NINO 3.4 region and the Maritime Continent (MC) region. The difference between these two regionally-averaged SSTs (3.4 – MC) reflects the extent to which SST variations act to keep tropical convection confined to the MC or allow it to spread eastward along the equator. Preliminary testing shows that such an index shares the advantage of an OLR-based index in being able to distinguish the dichotomy between weak and strong El Niño events and more precisely indicate extratropical teleconnections, but our SST-based index can also be applied to the pre-satellite era or to any ocean model simulations. It takes advantage of community familiarity with NINO 3.4 and related indices but does not require establishing a reference period from which anomalies should be calculated. The value of such an index is affected by the background modeled climate state or climate change, but in a good way, because it still quantifies the most physically relevant aspect of oceanic drivers of atmospheric response.
Evaluation of Climate Model Precipitation Processes using a TRMM/GPM Radar Simulator
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/651; NASA-Goddard Space Flight Center
The Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) will be adapted for Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and Global Precipitation Measurement (GPM) dual-frequency precipitation radar (DPR) observations and applied to NASA GISS Model-E and other Coupled Model Intercomparison Project Phase 6 (CMIP6) general circulation model (GCM) grid-box output. The COSP sub-grid scale algorithm will be improved to align better with observations. We will comprehensively compare model-simulated observations to satellite-based radar reflectivity of precipitating cloud systems using the above radar simulator. Specifically, we aim to evaluate model fidelity at representing convective and stratiform precipitation processes and pinpoint possible causes for model-observation discrepancies. This research satisfies Section 2.3.2 Methodologies for Climate Model Improvement under Section 2.3 Data and Methodology for Climate Projection Assessment desire for “novel strategies and methodologies to compare results from Earth system models with NASA observations and reanalysis” and the goal to “identify any model systematic errors, associate the errors with model algorithm deficiencies, and pinpoint the necessary model improvements.”
Improved Community Radiative Transfer Model (CRTM CRTM for Ultra-Violet (UV) and Passive Microwave Hydrometeor Simulation
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/202; DOC-National Oceanic and Atmospheric Administration
In support of CRTM, it is important to develop robust graupel and snowflake optical property models, which will achieve spectral consistency (i.e., the data will be spectrally consistent across from ultraviolet to microwave spectral regimes). In far-infrared to microwave regimes, the ice refractive index has dependence on temperature and is critical to remote sensing applications and radiative flux estimations. The goal of this work is to use a synergy of a suit of light-scattering modeling capabilities (specifically, the invariant-imbedding T-matrix model (II-TM) and the improved geometric optics model (IGOM)] to compute the single-scattering properties of realistic graupel and snowflake particles, and to develop the bulk single-scattering properties of these hydrometeors with various particle size distributions. We will leverage particle geometry of graupel and snowflakes with considering various ice density and hollow structures inside these hydrometeors. The proposed research effort will be directed towards answering the question: “how do realistic graupel and snowflake models improve forward radiative transfer simulations based on CRTM for remote sensing and data assimilation applications?” To address the question, requested efforts will be focused on the followings.
Improving the Drought Monitoring Capabilities of Land Surface Models by Integrating Bias-Corrected, Gridded Precipitation Estimates
Atmospheric Sciences; TAMU; https://hdl.handle.net/20.500.14641/453; DOC-National Oceanic and Atmospheric Administration
The “SPoRT-LIS” product is used by the NWS forecast offices in situational awareness (e.g., drought monitoring; White and Case 2015) as well as in local numerical modeling applications for enhanced initialization of land surface fields (Medlin et al. 2012). One of the limitations of the SPoRT-LIS accuracy is the input atmospheric forcing that drives the offline Noah land surface model simulation. The quality of the land surface model output is dependent on the input forcing fields, particularly the quantitative precipitation estimate (QPE). The current configuration of the SPoRT-LIS relies on long-term input forcing from the North American Land Data Assimilation System – Phase II product (NLDAS-2; Xia et al. 2012a; Xia et al. 2012b). The NLDAS-2 is the top choice for forcing due to its long duration (30+ years) and hourly output frequency. Due to real-time latency of 4 days in NLDAS-2, SPoRT-LIS bridges the gap for real-time output with supplemental hourly QPE from the Multi-Radar Multi-Sensor high-resolution radar/gauge blended product (Zhang et al. 2016) and global analyses from the National Centers for Environmental Prediction (NCEP)/Environmental Modeling Center (EMC). The limitations of NLDAS-2 forcing include real-time latency, coarse resolution grid (~15 km grid spacing), periodic quality issues arising from gauge quality control, and improper blending with the North American Regional Reanalysis (NARR). The primary limiting factors of implementing higher-resolution Multi-Radar/Multi-sensor (MRMS) QPE in a longer-term SPoRT-LIS are radar gaps and blending challenges on the peripheries of data coverage. Meanwhile, satellite QPE often introduces large biases due to inherent uncertainties in retrievals (e.g., Prat and Nelson 2015). SPoRT documented each of these QPE limitations and impacts on the soil moisture solution in a series of offline LIS simulations (Case et al. 2013). Problems with grid coverage and radar gaps are evident in the Stage IV and NMQ (currently MRMS) products, and the large over-estimation of satellite QPE was evident with the GOES-based algorithm. In order to provide an adequate spin-up of land surface model features, improved and bias-corrected QPE inputs are needed to preserve high spatial resolution features while offering seamless continuity in both space and time over a long duration simulation.
Investigation and Forecast Improvements of Tornadoes in Landfalling Tropical Cyclones
Atmospheric Sciences; TAMU; DOC-National Oceanic and Atmospheric Administration
The two major goals of this project are: (1) Advance our understanding of tropical cyclone tornado (TCTOR) cell attributes and environments, focusing on differences between verified tornado warnings and false alarms. (2) Improve the operational forecasting and warning decision process through integration of observed cell attributes and near-cell environments. The specific objectives to accomplish these goals are as follows: (O1) Build a database of all tornadoes and tornado warnings in TCs in the United States since the NEXRAD dual-polarization upgrade that includes radar-based storm attributes and near-storm environment information from model analyses. (O2) Assess the skill of high-resolution model analyses and forecasts in depicting the low-level, near-cell environment for convective cells in TCs and forecast proxies for low-level rotation. (O3) Compare near-cell environment and storm attribute information between verified warnings and false alarms in the climatology to determine differences that may be leveraged to reduce false alarms. (O4) In partnership with NWS collaborators, assess the performance of current radar, high-resolution NWP, and storm-environment based TCTOR forecasting practices and heuristics. (O5) In partnership with NWS collaborators, improve and streamline TCTOR warning practices using information gained from the climatology, including development and evaluation of probabilistic hazard information (PHI) produced by a statistical model trained on data produced in our climatological database.