Three Dimensional Assimilation of Tropical Wind Field by MASCON Model

Abstract

Assimilation of tropical wind fields was developed using the three-dimensional Mass Consistent Atmospheric Flux (MASCON) model based on Sasaki's variational method. Variational calculus techniques are used to adjust the spatially sparse wind data set of satellite cloud and rawinsonde, satisfying the continuity equation. Three-dimensional wind fields (u, v, w) are provided over the whole troposphere using the p coordinate, which is a hybrid of the p and σ- coordinates. This model can give us a three-dimensional wind field in the tropical region for the analysis of synoptic scale phenomena. Reanalysis of the tropical wind field surrounding tropical disturbances reveals characteristics similar to the previous two-dimensional MASCON model (Heta). Moreover vertical velocity can be calculated directly in the three-dimensional model. As a result, an upward motion area is recognized around a pre-typhoon disturbance with upward velocity increasing with the development of the disturbance.