Investigation of GCAPE quasi-equilibrium in the midlatitudes

Abstract

Lorenz (1955, 1978, 1979) developed the concept of the "moist available energy" (MAE) of the atmosphere. This he defined as the portion of non-kinetic energy (NKE) available for conversion to kinetic energy (KE). Randall and Wang (1992) and Wang and Randall (1994) showed that it is possible to consider the component of the MAE that re­ sides in the vertical structure of the atmosphere as a "generalized convective available potential energy" (GCAPE). Using data from the tropics, they tested the GCAPE quasi­ equilibrium hypothesis (Arakawa and Schubert, 1974) which asserts that cumulus convection "consumes" GCAPE as quickly as it is produced by large-scale (non-convective) forcing such that the convectively active atmosphere remains close to a state of conditional neutrality. The main purpose of this study is to also investigate the GCAPE quasi-equilibrium hypothesis, only this time in a midlatitude setting. This is a tougher test of the hypothesis given the significantly larger temperature and moisture fluctuations resulting in stronger large-scale forcing in the midlatitudes, compared with the tropics. Data recently made available by the Atmospheric Radiation Measurement (ARM) program has been used. This new data comes from radiosonde measurements collected at ARM's Cloud and Radiation Testbed (CART) site located in north-central Oklahoma during Intensive Operation Periods (IOPs) run periodically throughout the year.