Vorticity of vector change of wind during 24 hours related to spatial distribution of rainfall during the next 24 hours.

Abstract

From the study of wind changes at various levels over Indian area during the monsoon period, it is seen that the stream-lines of 24-ho.ur wind changes contain cyclonic and anti-cyclonic vortices, which are not indicated in the stream-line analysis of the actual wind flow at these levels on the day of forecast. The regions of these vortices are sometimes associated with rainfall over that area during the subsequent 24 hours. However, it is not too often that well defined cyclonic or anti-cyclonic circulation of wind changes which obviously indicate large positive or negative vorticity changes occur. Thus, in order to know the vorticity changes in the area concerned, the actual value of the change is calculated.

Vector wind changes at 00 GMT on the day of forecast with respect to its previous day are calculated at 850 mb for all PB/RW stations. The area is divided: into a number of triangles by joining these stations suitably taking care' that the triangles so formed are more or less equilateral.Vorticity of these triangular areas are calculated with the help of Bellamy's grid. The vertical component of the vorticity in the area is related to the rainfall which occurs during the next 24 hours. A forecast scheme is suggested for prediction of spatial distribution of rainfall during the next 24 hours.