Date of this Version
Zhifeng Yang, 2013, Mesoscale modeling and satellite observation of transport and mixing of smoke and dust particles over Northern Sub-Saharan African Region, M.S. Thesis, University of Nebraska-Lincoln
The transport and vertical distribution of smoke and mineral dust aerosols over the Northern Sub-Saharan African (NSSA) region have important implications for regional and global air quality and climate. This study employs ground-based and satellite observations, and numerical simulations conducted with a fully-coupled meteorology-chemistry-aerosol model, Weather Research and Forecasting model with Chemistry (WRF-Chem). The WRF-Chem simulation is for February 2008 and uses hourly dynamic smoke emissions from the Fire Locating and Modeling of Burning Emissions (FLAMBE) database derived from Moderate Resolution Imaging Spectroradiometer (MODIS) fire products. Model performance of smoke and dust simulation is evaluated using numerous satellite and ground-based datasets: MODIS true color images, ground-based Aerosol Optical Depth (AOD) measurements from AERONET, MODIS AOD retrievals, and Cloud-Aerosol Lidar data with Orthogonal Polarization (CALIOP) atmospheric backscattering and extinction products. Specification of smoke injection height of 650 m in WRF-Chem yields aerosol vertical profiles that are most consistent with CALIOP observations of aerosol layer height. Consistent with past field campaigns, CALIOP data and WRF-Chem simulations show that Saharan dust is often mixed with smoke near the surface in a well-confined belt between the Equator and 10°N, and together they are transported over the Atlantic Ocean. Aerosol transport patterns near the surface manifest the interplay of trade winds, subtropical highs, precipitation associated with the Intertropical Convergence Zone (ITCZ), and the high mountains located near the Great Rift Valley region. In contrast, at the 700 hPa level and above, smoke layers spread farther to the north and south, and are often above the dust layers over the Sahel region, which is consistent with past field data. In some cases, transported smoke can also be mixed with dust over the Saharan region. Statistically, 5% of the CALIPSO valid measurements of aerosols in February 2007-2011 show aerosol layers either above the cloud layers or between the cloud layers, reinforcing the importance of the aerosol vertical distribution for quantifying aerosol impact on climate in the Sahel region.
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