Simulation Of Cloudiness And Rainfall During The Northeast Monsoon Cold Surge

Rolu P. Encarnacion

A numerical model of the cold surge is developed to simulate cloudiness and rainfall over a warm ocean surface and a land mass with prominent topographic features. The model atmosphere consists of 3 layers: a) surface layer b) mixed layer and c) stable layer. The set of primitive equations is averaged in the mixed layer to yield prediction equations for the horizontal components of the wind, potential temperature and mixing ratio in the layer, and the height of the base of the overlying stable layer. Parameterizations of the interactions between the well-mixed convective layer with both the underlying and overlying layers are employed so that time dependent calculations could be limited to the well-mixed layer.

The model is used to study the dependence of cloudiness and rainfall associated with a cold surge on the prevailing synoptic conditions. A radiosonde observation representing inland conditions is utilized to define the initial state of the atmosphere for a control run. The control run and other numerical integrations (experiments) were used to analyze the cloudiness and rainfall patterns. Two groups of experiments were performed in this study: a) cold surge flow from land mass to warmer ocean surface and b) cold surge flow from the ocean to a warmer land mass with topography.

The results show that the model is capable of simulating the behavior of the atmosphere during cold surge episodes. The predicted variables are found to be reasonable and physically realistic.