Stratocumulus-to-Cumulus Cloud Transition: A case study from the MAGIC field campaign

 

Authors

Virendra Prakash Ghate — Argonne National Laboratory
Michael Christian Schwartz — Space Dynamics Laboratory

Category

General Topics – Cloud

Description

MWACR radar reflectivity factor for MAGIC Leg 15A (7/20/13-7/25/13, LA to Hawaii). Cloud base as determined by ceilometer is plotted in purple, and Lifting Condensation Level as computed from surface meteorological observations is plotted in pink. Three regions are marked: stratocumulus-capped boundary layer, cumulus-capped boundary layer, and a middle region where transition between the other two may be occurring.
Marine boundary layer cumulus and stratocumulus clouds are a significant component of the Earth’s climate system and hence need to be accurately represented in Global Climate Model (GCM) simulations aimed at predicting the future climate and energy needs. One feature germane to these clouds, and where GCMs encounter difficulty, is the transition from stratocumulus- to cumulus-capped marine boundary layers. This transition is climatologically important due to the large decreases in cloud cover and to the significant changes in boundary layer structure that accompany it. In order to increase understanding of these transitions, many ship-based measurements of eastern Pacific marine cloud systems were made during the Marine ARM GPCI Investigations of Clouds (MAGIC) field campaign. Here we present a case study of a well-defined transition from marine stratocumulus to cumulus cloud system observed during one of the MAGIC ship transits that spanned about 5 days. Three distinct regions that were characterized by stratocumulus, transition and cumulus cloud regimes were identified from the 5-day period. Ship based in situ and remote measurements, along with radiative transfer modeling and reanalysis data are used to characterize the cloud macro- and micro-physical structure, boundary layer radiative structure, in-cloud vertical air motion, and other relevant meteorological variables. Similarities and differences in the parameters between the three regimes will illuminate the processes responsible for causing the transition and their relative importance.