Diurnal variation of aerosol effects on cloud and radiative forcing over the DOE ARM SGP site

Description

Aerosols can modify cloud particle size, fraction and height, all of which change cloud radiative forcing. For convective clouds, these changes in the shortwave and longwave may be very large in magnitude and opposite in sign, leading to an uncertain net effect that depends highly on the diurnal variation of deep convective clouds and their interaction with aerosols. In this study, we will use high temporal resolution data from ground-based instruments, a geostationary satellite, and a reanalysis dataset to study diurnal variations of various aerosol effects, especially the aerosol invigoration effect (AIV) and its radiative forcing at the Southern Great Plains site. We present preliminary results showing a consistent AIV present at the site. We show that the fraction of the core of a DCC first increases with CN concentration when CN is less than 2000 cm-3, and then decreases. However, the cloud fraction increases with increasing CN concentration when the CN concentration is greater than 5000 cm-3. The areal coverage of the cloud anvil monotonously increases with CN concentration. Whatever the vertical velocity, the cloud-top height increases with CN concentration. We will also estimate aerosol induced changes in cloud radiative forcing obtained from combining radiative fluxes retrieved from both GOES observations and model calculations for DCCs present at different levels of CN concentration.