AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Can Meteorology Obfuscate Aerosol Indirect Effects in Stratocumulus?
Jonathan Petters, Hongli Jiang, Graham Feingold, Dione Rossiter, Djamal Khelif, Lisa Sloan, PATRICK CHUANG, University of California, Santa Cruz
Abstract Number: 642 Working Group: Aerosols, Clouds, and Climate
Abstract The impact of changes in aerosol and cloud droplet concentration on the radiative forcing of stratocumulus-topped boundary layers has been widely studied. However, how these impacts compare to those due to variations in meteorological context has not been investigated in a systematic fashion for non-drizzling overcast stratocumulus. In this study we examine the impact of observed variations in meteorological context and aerosol state on daytime, non-drizzling overcast stratiform evolution, and determine how resulting changes in cloud properties compare. Using large-eddy simulation we create a model base case of daytime southeast Pacific coastal stratocumulus, spanning a portion of the diurnal cycle (early morning to near noon) that is constrained by observations taken during the VOCALS (VAMOS Ocean-Atmosphere-Land Study) field campaign. We perturb aerosol and meteorological properties around this base case to investigate the stratocumulus response, specifically changes in cloud liquid water path, bulk optical depth and cloud radiative forcing (CRF). We find that realistic variations in meteorological context can elicit responses in radiative forcing that are on the same order of magnitude as, and at times larger than, the responses due to factor of two changes in drop concentration. We estimate that cloud top jumps of potential temperature and total water must be constrained to within 0.1 to 1 K and 0.1 to 1 g/kg, respectively, for accurate observation of aerosol radiative impacts on stratocumulus, depending on time of day. These constraints suggest that accurately observing aerosol radiative impacts in stratocumulus may be challenging as co-variation of meteorological properties may obfuscate aerosol-cloud interactions.