Enhancement of Asian Subtropical Front due to Thermodynamic Effect of Cumulus Convections

Real Data Forecast Experiment Using Coarse-Mesh Primitive Model

Abstract

Several observational studies indicate enhancement of the Asian subtropical front (Baiu front) in the vicinity of the Japan Islands due to the thermodynamic influence of cumulus ensemble. In the present real data forecast experiments, we demonstrate the influence through comparisons among predictions by a coarse-mesh primitive equation model without condensation (NO CND model), a model with large-scale condensation (LG CND model) and a model including both large-scale condensation and convective adjustment (AJS model), for two typical cases of Baiu front.
The Baiu front is remarkably enhanced in AJS model as compared with the front in NO CND and LG CND model. An important fact found by the experiment is that the generation of thermal instability due to large-scale advection process is restricted within the zone along the northern periphery of the tropical marine air mass. The release of instability and the concomitant enhancement of Baiu front are consequently restricted in the aforementioned periphery zone.