Optimal nonlinear wind analysis over the Indian region by iterative correction scheme

The development of satellite observing systems (asynoptic observations) has led to the idea that dynamical evolution of atmospheric flow should be explicitly taken into account while defining the initial conditions of the forecast. In view of this, objective analysis of wind field over the Indian region has been made by applying an iterative analysis correction scheme proposed by Lorenc Lorenc A C, Q J R Meteorol Soc (UK), 112 (1986) 1177. The most likely analysis of wind field for a given set of observations is obtained. In this process, at each iteration, the height values are estimated from wind field by nonlinear balance equation. Their partial derivatives with reference to wind field are used in modifying the weights and to obtain the convergence. The solution of the iteration is the most likely analysis of wind field. The scheme has been tested for two cases of monsoon depressions, 2-5 August 1988 and 28-30 July 1991. The analysis has been compared with the conventional linear optimum interpolation analysis. Divergence and vorticity computed from both the analysed wind fields have been examined. Synoptic features depicted in both the analyses are similar and agree with cloud pictures, suggesting that the scheme has performed well and also it is possible to introduce the information on approximate geostrophic balance in assimilation process.