Thermodynamic impact of the heated landmass on the nocturnal evolution of a cloud cluster over a Meiyu-Baiu front

摘要

Numerical simulations of a cloud cluster over a Meiyu-Baiu front were conducted using a cloud-resolving non-hydrostatic model. The purpose was to demonstrate thermodynamic impact of the diurnal heating of the mainland China upon the nocturnal evolution of the cluster. Simulations were conducted within a domain covering eastern and southern China to reproduce land-surface heating on the southern side of the front. The case simulated was a rainband associated with the cluster, which formed on the late afternoon of 22 June 2003. The environment is characterized by a synoptic-scale southerly inflow of warm and moist air in the lower troposphere. A control simulation reproduced the rainband successfully, and showed that the evolution resulted from the strong latent instability over the frontal convergence zone, due to the southerly inflow of the warm and moist air. The origin of this air was the surface heat flux over a cloud-free area to the south of the front. The importance of the heating was proved by a sensitivity simulation without insolation, which failed to reproduce deep convective updrafts. The water budget analysis demonstrated that the evaporation from the ground, rather than the moisture convergence, contributed to the increase in the precipitable water before the rainband evolution. This study, thus, indicates that the continental surface, heated by insolation, has a significant impact upon the nocturnal evolution of a cloud cluster over a Meiyu-Baiu front.