Effective Factors in the Development of Deep Convective Clouds over the Wet Region of Eastern China during the Summer Monsoon Season.

Abstract

A two-dimensional cloud-resolving model, including a supply of sensible and latent heat fluxes from the surface, is used to study the development of deep convective clouds over a southern region far from the Meiyu front (wet region) of eastern China. Some deep convective clouds were observed during the latter half of the GAME/HUBEX IOP (GEWEX Asian Monsoon Experiment/Huaihe River Basin Experiment Intensive Observation Periods, GEWEX: Global Energy and Water Cycle Experiment) 1998, although there is less large-scale convergence over this region. Numerical simulations reproduce the development of deep convective clouds, and their generating/decaying time. The development process of a convective mixing layer and generation of shallow convective clouds around the top of this layer are also simulated. The results of sensitivity tests on the surface land-use (i.e., the supply of the sensible and latent heat fluxes) and the relative humidity in the middle troposphere, indicate that there are two effective factors in the development of deep convective clouds over this region. One is the large amount of latent heat flux from the surface, and the other is the moist environment in the middle troposphere. The latent heat flux from the surface supplies water vapor to generate convective clouds. Paddy fields can supply a large amount of latent heat flux into the lower atmosphere and are widely distributed over this region. On the other hand, the moist environment in the middle troposphere can cause shallow convective clouds to become deep because the positive buoyancy in the shallow convective clouds is not lost by the evaporation cooling of the entrained air mass. Additionally, this moist environment in the middle troposphere is formed by the development of shallow convective clouds, which transport water vapor from the convective mixing layer.