Rawinsonde data collected from the Atlantic Stratocumulus Transition Experiment (ASTEX) are used to investigate the mean and temporal characteristics of large-scale heat and moisture budgets for a two week period in June 1992. During this period a large apparent heat sink and apparent moisture source are observed near inversion base which resulted from evaporation of cloud droplets which detrained near this level. Analyses from other budget studies show that similar convective signatures (i.e., low-level apparent moistening and cooling) occur in a wide variety of regimes when trade-wind type inversions are present. The vertical eddy flux of moist static energy over the ASTEX domain (centered at 33N with an average sea-surface temperature of 19.4 C) is about half that observed in the undisturbed trade-wind regime of BOMEX (centered at 15N with an average sea-surface temperature of 28.1 C).
The apparent heat source, apparent moisture sink and convective flux of moist static energy over ASTEX are strongly modulated on a synoptic time scale by the passage of fronts and by fluctuations in the subsidence rate associated with changes in the strength and position of the subtropical high. The influence of midlatitude disturbances on convection over ASTEX further distinguishes this region from trade-wind and tropical regimes. We will also examine the diurnal variability of large-scale motion fields over ASTEX and compare these results to other regions in order to deepen our understanding of why regional phase and amplitude differences exist in the diurnal cycle.