Atmospheric & Oceanic Science
Permanent URI for this communityhttp://hdl.handle.net/1903/2264
Formerly known as the Department of Meteorology.
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Item A STUDY OF REMOTELY SENSED AEROSOL PROPERTIES FROM GROUND-BASED SUN AND SKY SCANNING RADIOMETERS(2012) Giles, David Matthew; Dickerson, Russell R; Thompson, Anne M.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosol particles impact human health by degrading air quality and affect climate by heating or cooling the atmosphere. The Indo-Gangetic Plain (IGP) of Northern India, one of the most populous regions in the world, produces and is impacted by a variety of aerosols including pollution, smoke, dust, and mixtures of them. The NASA Aerosol Robotic Network (AERONET) mesoscale distribution of Sun and sky-pointing instruments in India was established to measure aerosol characteristics at sites across the IGP and around Kanpur, India, a large urban and industrial center in the IGP, during the 2008 pre-monsoon (April-June). This study focused on detecting spatial and temporal variability of aerosols, validating satellite retrievals, and classifying the dominant aerosol mixing states and origins. The Kanpur region typically experiences high aerosol loading due to pollution and smoke during the winter and high aerosol loading due to the addition of dust to the pollution and smoke mixture during the pre-monsoon. Aerosol emissions in Kanpur likely contribute up to 20% of the aerosol loading during the pre-monsoon over the IGP. Aerosol absorption also increases significantly downwind of Kanpur indicating the possibility of the black carbon emissions from aerosol sources such as coal-fired power plants and brick kilns. Aerosol retrievals from satellite show a high bias when compared to the mesoscale distributed instruments around Kanpur during the pre-monsoon with few high quality retrievals due to imperfect aerosol type and land surface characteristic assumptions. Aerosol type classification using the aerosol absorption, size, and shape properties can identify dominant aerosol mixing states of absorbing dust and black carbon particles. Using 19 long-term AERONET sites near various aerosol source regions (Dust, Mixed, Urban/Industrial, and Biomass Burning), aerosol absorption property statistics are expanded upon and show significant differences when compared to previous work. The sensitivity of absorption properties is evaluated and quantified with respect to aerosol retrieval uncertainty. Using clustering analysis, aerosol absorption and size relationships provide a simple method to classify aerosol mixing states and origins and potentially improve aerosol retrievals from ground-based and satellite-based instrumentation.Item Inferring Radiative Fluxes from a New Generation of Satellites: Model Updates(2007-08-05) Wang, Hengmao; Pinker, Rachel T.; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this study an inference scheme is developed to derive surface, Top of the Atmosphere (TOA), and atmospheric spectral shortwave (SW) radiative fluxes for implementation with observations from the Moderate Resolution Imaging Spectroradiometer (MODIS) type of sensors. The model takes into account all atmospheric constituents and addresses the characteristics of water and ice clouds and the variation of cloud particle effective radius. The near infrared spectrum is divided into three bands to better represent the spectral variation of cloud optical properties and water vapor absorption. A multi-layered structure allows for the treatment of surface elevation effects and for the representation of the vertical distribution of the radiative fluxes. Spectral fluxes such as Photosynthetically Active Radiation (PAR) and near-infrared radiation (NIR) are also estimated. The new inference scheme is implemented with MODIS one degree products as well as with the 5 km swath products. The derived fluxes are evaluated against the globally distributed Baseline Radiation Network (BSRN) measurements and compared with products from independent satellites. It was demonstrated that the MODIS products are in good agreement with ground observations and provide improved estimates of radiative fluxes than the other evaluated satellite products. In problematic areas for most satellite retrievals, such as the Tibet Plateau and Antarctica, the MODIS results have shown a substantial improvement. Availability of the high resolution swath based estimates of surface radiative fluxes allow, for the first time, to address unique space-time coupling issues.Item RETRIEVAL OF TROPOSPHERIC AEROSOL PROPERTIES OVER LAND FROM INVERSION OF VISIBLE AND NEAR-INFRARED SPECTRAL REFLECTANCE: APPLICATION OVER MARYLAND(2007-04-26) Levy, Robert; Dickerson, Russell R.; Remer, Lorraine A; Atmospheric and Oceanic Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerosols are major components of the Earth's global climate system, affecting the radiation budget and cloud processes of the atmosphere. When located near the surface, high concentrations lead to lowered visibility, increased health problems and generally reduced quality of life for the human population. Over the United States mid-Atlantic region, aerosol pollution is a problem mainly during the summer. Satellites, such as the MODerate Imaging Spectrometer (MODIS), from their vantage point above the atmosphere, provide unprecedented coverage of global and regional aerosols over land. During MODIS' eight-year operation, exhaustive data validation and analyses have shown how the algorithm should be improved. This dissertation describes the development of the 'second-generation' operational algorithm for retrieval of global tropospheric aerosol properties over dark land surfaces, from MODIS -observed spectral reflectance. New understanding about global aerosol properties, land surface reflectance characteristics, and radiative transfer properties were learned in the process. This new operational algorithm performs a simultaneous inversion of reflectance in two visible channels (0.47 and 0.66 μm) and one shortwave infrared channel (2.12 μm), thereby having increased sensitivity to coarse aerosol. Inversion of the three channels retrieves the aerosol optical depth (τ) at 0.55 μm, the percentage of non-dust (fine model) aerosol (η) and the surface reflectance. This algorithm is applied globally, and retrieves τ that is highly correlated (y = 0.02 + 1.0x, R=0.9) with ground-based sunphotometer measurements. The new algorithm estimates the global, over-land, long-term averaged τ ~ 0.21, a 25% reduction from previous MODIS estimates. This leads to reducing estimates of global, non-desert, over-land aerosol direct radiative effect (all aerosols) by 1.7 W·m-2 (0.5 W·m-2 over the entire globe), which significantly impacts assessment of aerosol direct radiative forcing (contribution from anthropogenic aerosols only). Over the U.S. mid-Atlantic region, validated retrievals of τ (an integrated column property) can help to estimate surface PM2.5 concentration, a monitored criteria air quality property. The 3-dimensional aerosol loading in the region is characterized using aircraft measurements and the Community Multi-scale Air Quality Model (CMAQ) model, leading to some convergence of observed quantities and modeled processes.