貿易風帯の逆転層のモデル

Abstract

A one dimensional semi-empirical model of the trade-wind inversion in a steady state is developed to predict the height of the inversion in terms of the external parameters such as the heat and moisture fluxes at the ocean surface, the large-scale subsidence and the radiative cooling rate. The cumulus cloud effects on the heat and moisture budgets are explicitely incorporated into the model using a simple entrainment cloud model. The atmosphere is divided into five layers with distinctively different characteristics: a mixed layer, a transition layer, a cloud layer, the trade-wind inversion and a layer above it. Both transition and inversion layers are assumed to be infinitesimally thin and only the vertically integrated properties in the cloud layer are considered. The lapse rates of static energy and moisture in the cloud layer are assumed to be linear and prescribed. All layers interact with each other through the vertical transports of heat and moisture due to cumulus clouds and condensation and evaporation processes. Thus the cloud mass flux at the cloud base is an important parameter to be determined internally by the model.Theoretical values of the characteristics of the trade-wind inversion, such as the height of the inversion and jumps of static energy and moisture across the inversion, are computed using observed values of the external parameters for the BOMEX region. Reasonal agreement is obtained between these theoretical values and the observed values. However, the sensitivity test of the model reveals some limitations of the applicability of the model.