UMD Theses and Dissertations
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Item Identification and Quantification of Regional Aerosol Trends and Impact on Clouds over the North Atlantic Ocean(2017) Jongeward, Andrew; Li, Zhanqing; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols and clouds contribute to atmospheric variability and Earth’s radiative balance across local, regional, and global scales. Originating from both natural and anthropogenic sources, aerosols can cause adverse health effects and can interact directly with solar radiation as well as indirectly through complex interactions with clouds. Aerosol optical depth (AOD) has been observed from satellite platforms for over 30 years. During this time, regional changes in emissions, arising from air quality policies and socioeconomic factors, have been suggested as causes for some observed AOD trends. In the United States, the Clean Air Act and amendments have produced improvements in air quality. In this work the impacts of improved air quality on the aerosol loading and aerosol direct and indirect effects over the North Atlantic Ocean are explored using satellite, ground, and model datasets on the monthly timescale during 2002 to 2012. It is established that two trends exist in the total AOD observed by MODIS over the North Atlantic. A decreasing AOD trend between −0.02 and −0.04 per decade is observed over the mid-latitude region. Using the GOCART aerosol model it is shown that this trend results from decreases in anthropogenic species. Ground based aerosol networks (AERONET and IMPROVE) support a decreasing trend in AOD and further strengthen links to anthropogenic aerosol species, particularly sulfate species. This anthropogenic decrease occurs primarily during spring and summer. During the same time period, MODIS also observes an increasing AOD trend of 0.02 per decade located in the sub-tropical region. This trend is shown to occur during summer and is the result of natural dust aerosol. Changes in the North African environment seen in the MERRA reanalysis suggest an accelerated warming over the Saharan Desert leads to changes in the African Easterly Jet, related Easterly Waves, and baroclinicity playing a role in an increase and northward shift in African dust. Both the direct and indirect impacts of the aerosol trends are investigated. Using the SBDART radiative transfer model, estimates of the shortwave direct radiative forcing are calculated. The decrease in anthropogenic AOD produces an increase of 2.0 ± 0.3 W/m2 per decade in the Earth-system absorbance over the mid-latitude site (37.5ºN, −68.5ºE). The increase in natural AOD results in a decrease of −1.1 ± 0.2 W/m2 per decade in the Earth-system absorbance over the sub-tropical site (23.5ºN, −55.5ºE). Evaluation of the first indirect effect demonstrates agreement with Twomey theory when considering the North Atlantic domain on the whole. A regional analysis reveals the existence of counter-Twomey behavior along the U.S. Atlantic coast. Using a daily dataset during summertime with focus on warm, non-precipitating clouds, it is found that aerosol-cloud interaction in this coastal region is sensitive to vertical velocity and aerosol size. Cases experiencing updrafts (ω < 0 Pa/s) and cases of mainly coarse-mode aerosol demonstrate good agreement with Twomey theory. Additionally, cases with low specific humidity near the cloud base show non-Twomey behavior for clouds with low liquid water path.Item Influence of weekdays, weekends, bandhas and weather conditions on particulate matter (PM10) concentrations in the Kathmandu Valley in Nepal(2011) Fransen, Michelle Julia; Sapkota, Amir; Maryland Institute for Applied Environmental Health; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Particulate matter (PM) exposure has been associated with a variety of adverse health effects. Quantifying the relative source contribution of PM is important as it provides policymakers critical information needed to formulate successful pollution reduction programs. The aim of this study was to evaluate the effects of bandhas (general strikes) and meteorological parameters on PM10 concentrations in the Kathmandu Valley. Within station seasonal differences in PM10 concentrations were compared using t-tests. Linear mixed effects regression models were used to examine the effects of weekends or bandh days on PM10 concentrations. Results showed significant (p<0.001) seasonal variability across all stations. In the urban high traffic (UHT) and urban residential (UR) areas, there were statistically significant (p<0.05) lower PM10 concentrations on weekends. In the UHT, PM10 concentrations were significantly lower on bandh days (p<0.05). These results suggest that a reduction in vehicular emissions may alleviate the PM10 pollution problem in the valley.Item DATA ASSIMILATION OF THE GLOBAL OCEAN USING THE 4D LOCAL ENSEMBLE TRANSFORM KALMAN FILTER (4D-LETKF) AND THE MODULAR OCEAN MODEL (MOM2)(2011) Penny, Stephen G.; Kalnay, Eugenia; Carton, Jim; Applied Mathematics and Scientific Computation; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The 4D Local Ensemble Transform Kalman Filter (4D-LETKF), originally designed for atmospheric applications, has been adapted and applied to the Geophysical Fluid Dynamics Laboratory's (GFDL) Modular Ocean Model (MOM2). This new ocean assimilation system provides an estimation of the evolving errors in the global oceanic domain for all state variables. Multiple configurations of LETKF have been designed to manage observation coverage that is sparse relative to the model resolution. An Optimal Interpolation (OI) method, implemented through the Simple Ocean Data Assimilation (SODA) system, has also been applied to MOM2 for use as a benchmark. Retrospective 7-year analyses using the two systems are compared for validation. The oceanic 4D-LETKF assimilation system is demonstrated to be an effective method for data assimilation of the global ocean as determined by comparisons of global and regional `observation minus forecast' RMS, as well as comparisons with temperature/salinity relationships and independent observations of altimetry and velocity.Item An evaluation of a severe smog episode in the Eastern U.S. using regional modeling and satellite measurements(2011) Yegorova, Elena Andreyevna; Dickerson, Russell R; Allen, Dale J; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)An ensemble of regional chemical modeling (WRF/Chem with RADM2) simulations, satellite, ozonesonde, and surface observations during July 7-11, 2007 was used to examine the horizontal and vertical signature of one of the worst smog events in the eastern U.S. in the past decade. The general features of this event -- a broad area of high pressure, weak winds and heavy pollution, terminated by the passage of a cold front -- were well simulated by the model. Average 8-hr maximum O3 has a mean (±Σ) bias of 0.59 (±11.0) ppbv and a root mean square error of 11.0 ppbv. WRF/Chem performed the best on poor air quality days, simulating correctly the spatial pattern of surface O3. Yet the model underpredicted O3 maxima by 5-7 ppbv in the Northeast and overpredicted by 8-11 ppbv in the Southeast. High O3 biases in the Southeast are explained by overpredicted temperatures in the model (>1.5°C). Sensitivity simulations with 1) accelerated O3 dry deposition velocity and 2) suppressed multiphase nitric acid formation pushed the model closer to observations. Simulated O3 vertical profiles over Beltsville, MD showed good agreement with ozonesonde measurements, but the modeled boundary layer depth was overpredicted on July 9, contributing to the low bias over this region. During this severe smog episode, space-borne TES detected high total tropospheric column ozone (TCO) over the Western Atlantic Ocean off the coast near North and South Carolina. The standard product (OMI/MLS) missed the magnitude of these local maxima, but the level-2 ozone profile (OMI) confirmed the TES observations. HYSPLIT back trajectories from these O3 maxima intersected regions of strong convection over the Southeast and Great Lakes regions. When lightning NO emissions were implemented in WRF/Chem, the high concentrations of NOx and O3 off the coast were well reproduced, showing that the exported O3 was produced by a combination of natural NO and pollutants lofted from the lower atmosphere. Lastly, WINTER MONEX O3 data from 1978 are presented for the first time here in discussion of open cell convection over Indonesia.Item Strategies for Coupling Global and Limited-Area Ensemble Kalman Filter Assimilation(2011) Merkova, Dagmar; Szunyogh, Istvan; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis compares the forecast performance of four strategies for coupling global and limited area data assimilation: three strategies propagate information from the global to the limited area process, while the fourth strategy feeds back information from the limited area to the global process. All four strategies are formulated in the Local Ensemble Transform Kalman Filter (LETKF) framework. Numerical experiments are carried out with the model component of the National Centers for Environmental Prediction (NCEP) Global Forecast System (GFS) and the NCEP Regional Spectral Model (RSM). The limited area domain is an extended North-America region that includes part of the north-east Pacific. The GFS is integrated at horizontal resolution T62 (about 150 km in the middle latitudes), while the RSM is integrated at horizontal resolution 48 km. Experiments are carried out both under the perfect model hypothesis and in a realistic setting. The coupling strategies are evaluated by comparing their deterministic forecast performance at 12-hr and 48-hr lead times. The results suggest that the limited area data assimilation system has the potential to enhance the forecasts at 12-hr lead time in the limited area domain at the synoptic and sub-synoptic scales (in the global wave number range of about 10 to 40). There is a clear indication that between the forecast performance of the different coupling strategies those that cycle the limited area assimilation process produce the most accurate forecasts. In the realistic setting, at 12-hr forecast time the limited area systems produce more modest improvements compared to the global system than under the perfect model hypothesis, and at 48-hr forecast time the global forecasts are more accurate than the limited area forecasts.Item Investigating Aerosol Effects on Clouds, Precipitation and Regional Climate in US and China by Means of Ground-based and Satellite Observations and a Global Climate Model(2011) Niu, Feng; Li, Zhanqing; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols affect climate by scattering/absorbing radiation and by acting as cloud condensation nuclei (CCN) or ice nuclei (IN). One of the least understood but most significant aspects of climate change is the aerosol effect on cloud and precipitation. A hypothesis has recently been proposed that, in addition to reducing cloud effective radius and suppressing precipitation, aerosols may also modify the thermodynamic structure of deep convective clouds and lead to enhanced precipitation when complex thermodynamic processes are involved. Taking advantage of the long-term and extensive ground-based observations at the US Department of Energy's Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site, we thoroughly tested such a hypothesis and provide direct evidence of it. Moreover, the hypothesis is also supported by analysis of satellite-based observations over tropical regions from multiple sensors in the A-Train satellites constellation. Extensive analyses of the long-term ground-based and large-scale data reveal significant increases in rain rate or frequency and cloud top heights with increasing aerosol loading for mix-phase deep convective clouds, decreases rain frequency for low liquid clouds, but little impact on cloud height for liquid clouds. Rigorous tests are conducted to investigate any potential artifacts and influences of meteorological conditions. Large-scale circulation patterns and monsoon systems can be changed by scattering and absorption of solar radiation by aerosols. By means of model simulations with the National Center for Atmospheric Research Community Climate Model (NCAR/CCM3), we found that the increase of aerosol loading in China contributes to circulation changes, leading to more frequent occurrence of fog events in winter as observed from meteorological records. The increase in atmospheric aerosols over China heats the atmosphere and generates a cyclonic circulation anomaly over eastern-central China. This circulation anomaly leads to a reduction in the influx of dry and cold air over that area during winter. Weakening of the East Asian winter monsoon system may also contribute to these changes. All these changes favor the formation and maintenance of fog over this region. The MODerate resolution Imaging Spectroradiometer (MODIS) aerosol products used in the above studies are validated using ground-based measurements from the Chinese Sun Hazemeter Network (CSHNET). Overall, substantial improvement was found in the current version of aerosol products relative to the previous one. At individual sites, the improvement varies with surface and atmospheric conditions.Item On the interaction of wind energy with climate and weather(2010) Barrie, Daniel; Kirk-Davidoff, Daniel B; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This study focuses on the interaction of large-scale wind energy with the atmosphere; namely, the impact that a substantial development of the wind resource may have on climate and weather as well as the impact that anthropogenic global warming (AGW) may have on the amount of available energy in the wind. A large downstream climate response to wind turbines distributed throughout the central United States is shown in model results from the Community Atmosphere Model (CAM). The mean response takes the form of a stationary Rossby wave. Furthermore, a case study is shown where the wind turbines altered a storm system over the North Atlantic. The resulting magnitude of the anomalous 500 hPa geopotential height field is comparable to the range of forecast uncertainty, which indicates that impacts induced in weather systems may be forecastable Building on this work, a thorough examination of wind farm and atmospheric parameters, including wind farm size, position, and parameterization as well as atmospheric static stability and jet strength is carried out using an idealized version of the Weather Research and Forecasting (WRF) model. Downstream impacts were found to grow in magnitude as wind farm size and the value of damping used to parameterize the wind turbines was increased. Altering the position of the wind farm with respect to the westerlies and synoptic disturbances revealed that the interaction between baroclinic instabilities and the wind farm enables downstream propagation and growth of the wind farm impacts. However, far downstream impacts were observed to be somewhat independent of the wind farm position, i.e., similar downstream effects were noted for model runs initialized with wind farms 20° of longitude from each other. By increasing atmospheric static stability, a fast saturation of wind farm-induced anomalies was observed throughout the atmosphere. This observation is surprising in light of the increased phasing between surface and upper atmospheric anomalies when static stability is low. Anomalies were able to propagate farther downstream over a shorter period of time when jet strength was increased. To study projected climate change impacts on the wind resource, data from the third phase of the Coupled Model Intercomparison Project (CMIP3) and the North American Regional Climate Change Assessment Project (NARCCAP) were studied. The results are dominated by substantial intermodel variability; however, many of the models project an increase in wind speeds and energy over the central United States. This increase in wind energy is related to an increase in low-frequency, high-speed transient wind speeds, which have a high power density due to the cubic relationship between wind speed and power.Item IMPACT OF LAND SURFACE VEGETATION CHANGE OVER THE LA PLATA BASIN ON THE REGIONAL CLIMATIC ENVIRONMENT: A STUDY USING CONVENTIONAL LAND-COVER/LAND-USE AND NEWLY DEVELOPED ECOSYSTEM FUNCTIONAL TYPES(2010) Lee, Seung-Jae; Berbery, Ernesto H; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Naturally occurring or human induced changes in land surface vegetation have been recognized as one of the important factors influencing climate change. The La Plata Basin in South America has experienced significant changes in structural land-cover/land-use types, and those changes can involve changes in the surface physical properties such as albedo and roughness length, evapotranspiration, infiltration, and water storage eventually affecting the development of precipita-tion and the hydroclimate of the basin. In this study, the Weather Research and Forecast (WRF) modeling system was employed to investigate the role of changing land surface conditions in the La Plata Basin. For this purpose, ensembles of seasonal simulations were prepared for a control case and two extreme land cover scenarios: the first one assumes an expansion of the agricultural activities and the second one assumes a "natural" vegetation cover where no croplands are present. An extreme anthropogenic land-cover change -simulating an extensive agricultural practice- implies that the northern part of the basin, where croplands replace forests and savannah, would experience an overall increase in albedo and reduced surface friction. The two changes lead to a reduction of sensible heat and surface temperature, and a somewhat higher evapotranspiration due to decreased stomatal resistance and stronger near-surface winds. The effect on sensible heat seems to dominate and leads to a reduction in convective instability. The stronger low level winds due to reduced friction also imply a larger amount of moisture advected out of the basin, and thus resulting in reduced moisture flux convergence (MFC) within the basin. The two effects, increased stability and reduced MFC, result in a reduction of precipitation. On the other hand, the southern part of the basin exhibits the opposite behavior, as crops would replace grasslands, resulting in reduced albedo, a slight increase of surface temperature and increased precipitation. Notably, the results are not strictly local, as advective processes tend to modify the circulation and precipitation patterns downstream over the South Atlantic Ocean. A newly developed land surface classification, so-called Ecosystem Functional Types (EFTs, systems that share homogeneous energy and mass exchanges with the atmosphere), is implemented in the WRF model to explore its usefulness in regional climate simulations of surface and atmospheric variables. Results show that use of the EFT data improves the climate simulation of 2-m temperature and precipitation, making EFTs a good alternative to land cover types in numerical climate models. An additional advantage of EFTs is that they can be calculated on a yearly basis, thus representing the interannual variability of the surface states. During dry years the 2-m temperature and 10-m wind are more sensitive to changes in EFTs, while during wet years the sensitivity is larger for the 2-m water vapor mixing ratio, convective available potential energy, vertically-integrated moisture fluxes and surface precipitation. This indicates that the impact of land-cover and land-use changes on the climate of the LPB is dependent not only on the wetness of the year, but also on the meteorological or climate variables. Comparisons with observations show that the simulated precipitation difference induced by EFT changes resembles the overall pattern of observed precipitation changes for those same years over the LPB. In the case of the 2-m temperature, the simulated changes due to EFT changes are similar to the observed changes in the eastern part and the southern part of the basin (especially in Uruguay), where t he strongest EFT changes occurred.Item Computational Fluid Dynamic Solutions of Optimized Heat Shields Designed for Earth Entry(2010) Meeroff, Jamie Gabriel; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Computational fluid dynamic solutions are obtained for heat shields optimized aerothermodynamically using Newtonian impact theory. Aerodynamically, the low-order approach matches computational simulations within 10%. Benchmark Apollo 4 solutions show that predicted heat fluxes under-predict convective heating by 30% and over-predict radiative heating by 16% compared to computational results. Parametric studies display a power law reliance of convective heat flux on edge radius. A slender heat shield optimized for a single design point produces heat fluxes 1.8 times what was predicted using the Newtonian approach. Here, maximum heating decreases with the inverse cube of the base sharpness. Coupled vehicle/trajectory optimized designs are examined for lunar return (11 km/s) and Mars return (12.5 km/s) and show possible discrepancies for eccentric shapes using low-order empirical correlations. Ultimately, gains suggested by the low-order approach using complex geometries are not reflected in high-fidelity simulations. In some respects, the simpler shape is the ideal oneItem SURFACE AND AEROSOL EFFECTS ON THE SOUTH ASIAN MONSOON HYDROCLIMATE(2010) Bollasina, Massimo A.; Nigam, Sumant; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work targets important couplings in the South Asian monsoon system at interannual or longer time-scales and associated processes and mechanisms: aerosol-hydroclimate, atmosphere-ocean, and land-atmosphere. Anomalous springtime absorbing aerosols loading over the Indo-Gangetic Plain (IGP) leads to large-scale variations of the monsoon: cloudiness reduction associated with increased aerosols is suggested to play an important role in triggering surface heating over India, which strengthens the monsoon. Indeed, a closer analysis with high resolution data depicts a complex interplay between aerosols, dynamics and precipitation. Interestingly, observations do not provide any evidence for the Elevated Heat Pump hypothesis, a mechanism proposed for the aerosol-monsoon link. Current coupled climate models, which have been extensively used to study aerosol-monsoon interactions, are shown to have large, systematic, and coherent biases in precipitation, evaporation, sea-surface temperature (SST) over the Indian Ocean during the monsoon. Models are also found to deficiently portray local and non-local air-sea interactions. For example, they tend to emphasize local oceanic forcing on precipitation or to poorly simulate the relationship between SST and evaporation. The Indian monsoon rainfall-SST link is also spuriously misrepresented, suggesting caution when interpreting model-based findings. Both regional and remote forcings modulate the annual cycle of the heat-low over the desert areas (including the Thar Desert) between Pakistan and northwestern India, source of most of the dust loading over India. Land-surface heating has a limited role in the development of the low. Regional orography and monsoon summertime deep-convection over the Bay of Bengal, with its upstream descent to the west and related northerlies, contribute to the strengthening of the low, indicating a monsoon modulation on desert processes, including dust emission. The Thar Desert is expanding westward and the potential impact of land-cover change (without consideration of the additional aerosol loading) on summer monsoon hydroclimate and circulation is found to be significant. Locally, the atmospheric water cycle weakens, air temperature cools and subsidence prevails. An anomalous northwesterly flow over the IGP weakens the monsoon circulation over eastern India, causing precipitation to decrease. Orographic enhanced precipitation occurs over the Eastern Himalayas and southern China.