The dependence of aerosol-cloud interactions in shallow cumuli on source region

Aerosol-cloud interactions in shallow cumuli over Southern Great Plain (SGP) region are investigated by examining how cloud properties vary with aerosol concentration and meteorological conditions. During the 2009 Routine AAF Clouds with Low Optical Water Depths (CLOWD) Optical Radiative Observations (RACORO) field campaign, a total of 260 hours of in-situ airborne cloud and aerosol measurements were made over a period of 6 months, with 85 hours of data collected on days when shallow cumuli were present in varying meteorological regimes. Meteorological conditions during RACORO were examined using a multi-scale comprehensive dataset: weather maps, satellite images, radar images, and rawinsonde data.

It is difficult to isolate aerosol effects on clouds because of the complicated microphysical, dynamical, and chemical feedbacks that occur. Cloud kinematics (particularly, updraft velocity) have been previously used to represent meteorological effects on clouds, but their impact is poorly understood. To avoid complications and ambiguity, the synoptic meteorology of the Great Plain regions was investigated here. The RACORO fair weather cumuli days were grouped into five different categories according to the airmass source regions and meteorological characteristics. The relationship between aerosol and cloud properties was separately investigated for each category. Therefore, the influence of the synoptic / mesoscale meteorological conditions on the cloud macrophysical / microphysical properties was examined by assessing the relative importance of the effect of varying aerosol concentrations.