Thermodynamics and Microphysics Relation During CAIPEEX-I

Abstract

Influence of the environmental thermodynamics on the microphysics of deep cumulus clouds over different parts of India is studied using in situ airborne observations from the Cloud Aerosol Interaction and Precipitation Enhancement EXperiment (CAIPEEX) during 2009. This study provides an understanding of the thermodynamics–microphysics relation over the Indian summer-monsoon region. Relatively stronger updraft and turbulence are noted in the pre-monsoon cloud base layers compared to that of the monsoon clouds. It is illustrated from the in situ observations as well as from a microphysical parcel model that the vertical variation of cloud droplet number concentration (CDNC) has a well-defined peak at a certain height above the cloud base. This elevated CDNC peak is found to be connected with the cloud parcel buoyancy and cumulative convective available potential energy (cCAPE). Higher parcel buoyancy above the cloud base of dry pre-monsoon clouds is associated with stronger in-cloud updraft velocity, higher supersaturation and higher droplet number concentration (in addition to aerosol effect). Higher adiabatic fraction and lower entrainment rate are observed in polluted clouds where boundary layer moisture is low, compared to clean clouds. Relative dispersion of droplet size distribution is found to vary concurrently with air mass characteristics and aerosol number concentration observed over different locations during the experiment. Aerosol–precipitation relationships are also investigated from the observation. Maximum reflectivity and rain rates showed a direct link with boundary layer water vapor content rather than with subcloud aerosol number concentration.