ON THE HYPOTHESIS OF EQUIPRESSURE BETWEEN PASSIVE CLOUDS CELLS AND THEIR SURROUNDING ENVIRONMENT

Emile Danho (Ivory Coast) and Roger N’dri Djue (Ivory Coast)

Received December 24, 2008

Abstract

The complexity of cloudy media leads very often to the adoption of some simplified hypotheses that facilitate their modelling. One of these hypotheses sometimes used consists in the identification of the pressure inside the cloud cell to that of the surrounding environment of the cloud. This hypothesis leads to the decoupling of the dynamic and the thermodynamic problems. However, never has been estimated the magnitude of error done by adopting this hypothesis nor had been tested the validity of the driven results. In this paper, we focus on the direct simulation of the cloudy media dynamics and compute the magnitude of error done by adopting the equipressure hypothesis. The study shows that the magnitude of error depends on the altitude, and it varies from 2.7% at 1000m to 8.3% at 2500m and the model cannot simulate the entrainment effects driven by the surrounding environment.

Keywords and phrases: clouds, droplets, microphysics, dynamics, thermodynamics, mixing ratio, equipressure.