Pollution, dust and smoke aerosols have a significant influence on the properties of stratocumulus and cumulus clouds over significant portions of the world�s oceans. Through a combination of indirect effects, whereby aerosols modify the microphysical properties of the clouds, and the semi-direct effect, whereby absorption of sunlight by aerosols reduces cloud cover, aerosols influence the water content of clouds, the horizontal extent of clouds, and their radiative properties. In this project we build on our previous analyses of aerosol-cloud interactions in A-Train observations to understand how factors such as the meteorological environment and the vertical profile of aerosols modulate the response of cloud cover and liquid water path to aerosols in low subtropical cumulus and stratocumulus clouds. We will test specific hypotheses derived from large-eddy simulation studies. These studies suggest that the humidity above clouds determines whether LWP increases or decreases with aerosol amount; that the vertical distribution of aerosols determines LWP increases or decreases in response to the semi-direct effect; and that the size distribution clouds changes with pollution owing to changes in drop size and entrainment. AIRS humidity and temperature profiles, in addition to CALIPSO aerosol and cloud profiles, will be integrated into our published strategies for assessing aerosol-cloud interactions in MODIS and AMSR-E data in order to objectively test for evidence of the processes described above in real cloud fields. The addition of the AIRS data will also help us unravel the role of the meteorological environment in determining low cloud cover and liquid water path from the effects of aerosols. By testing specific hypotheses of factors influencing aerosol-cloud interactions, we aim to gain a deeper understanding of the response of cloud fields to aerosol indirect forcing, and reduce uncertainties in deductions about aerosol-cloud interaction derived from regional- to global-scale statistical analyses of satellite imagery.
