Aerosols optical depth enhancement in presence of clouds
Abstract
Moderate Resolution Imaging Spectrometer (MODIS) observations at 550 nm are used to estimate aerosol optical depth (AOD) enhancement in presence of clouds. Daily 10x10 km observations from eleven years of MODIS-Terra (MOD04_L2) are processed to determine the enhancement defined as the difference between AOD at high (0.8-0.9) and low (0.1-0.2) cloud fraction (CF). The analysis is performed globally over the oceans at 2.5degx2.5deg resolution. First results indicate that the enhancement in AOD is observed in the presence of higher cloud fraction. The elevated AOD at higher CF is not distributed uniformly but shows regional and latitudinal patterns in different seasons. The highest enhancement in AOD is observed near the aerosol source regions indicating that the source of this enhancement is less likely due to cloud contamination. The spring (MAM) and summer (JJA) seasons show higher enhancement in AOD over the northern hemisphere. The normalized enhancement in AOD at these CF is highest in the tropics and subtropics. We hypothesize that the most of the enhancement in AOD is a result of the hygroscopic swelling of the aerosol in the relatively more humid air accompanying partially cloudy conditions. Since the MODIS AOD observations are widely used for climate research and other applications, a consideration of these cloud-dependent enhancements can help improve our understanding on aerosol-cloud interactions. Seasonal and geographical variations in AOD in the presence of low and high CFs will be studied and possible explanations using models will be discussed.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.A11B0072C
- Keywords:
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- 0305 ATMOSPHERIC COMPOSITION AND STRUCTURE / Aerosols and particles;
- 3311 ATMOSPHERIC PROCESSES / Clouds and aerosols;
- 3337 ATMOSPHERIC PROCESSES / Global climate models;
- 3360 ATMOSPHERIC PROCESSES / Remote sensing