Observed Enhancements in Aerosol Optical Depth in the Vicinity of Cumulus Clouds during DISCOVER-AQ
Abstract
During the DISCOVER-AQ field experiment in Maryland USA in July 2011 large increases in fine mode Aerosol Optical Depth (AOD) were observed adjacent to larger Cu cloud cells in afternoon from AERONET direct sun observations on some days. Increases in AOD at 500 nm as high as ~0.3 to 0.5 in only 15 minutes to an hour were measured for sites adjacent to relatively large cumulus cells while sites in relatively cloud-free areas showed little AOD increase. Additionally, Micro-Pulse Lidar (MPL) from the ground and High Spectral Resolution Lidar (HSRL) from high altitude aircraft both measured enhanced aerosol backscatter at the cloud altitudes for the same afternoon cumulus cloud cases. Possible reasons for AOD increases near to clouds include rapid conversion of sulfur dioxide to sulfate aerosol in cloud droplets and/or aerosol hygroscopic growth in-cloud and near-cloud enhanced RH environments. In situ aircraft data showed higher sulfate concentrations in afternoon on some days suggesting some of the AOD increase was due to oxidation of sulfur dioxide. High-resolution modeling also suggests significant sulfate formation in fair weather Cu clouds in afternoon in the Baltimore-Washington DC region. An analysis of the multi-year climatology at the Goddard Space Flight Center Maryland site of diurnal fine mode AOD for July (1997-2011) shows increases in AOD consistent with the timing of late morning early afternoon cumulus cloud formation. HSRL data will be analyzed to investigate the spatial extent of AOD increases as a function of distance from cloud on specific dates in July 2011. Satellite retrievals of AOD from the MODIS sensors on Terra and Aqua will be analyzed at high resolution (3km for standard retrievals and 1 km from MAIAC) for cases with afternoon AOD increases associated with cumulus cloud formation.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.A13K0328E
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 0345 ATMOSPHERIC COMPOSITION AND STRUCTURE / Pollution: urban and regional;
- 0360 ATMOSPHERIC COMPOSITION AND STRUCTURE / Radiation: transmission and scattering;
- 0394 ATMOSPHERIC COMPOSITION AND STRUCTURE / Instruments and techniques