Computations of Vertical Motion and Vorticity Budget in a Blocking Situation

The synoptic situation under study is a blocking situation over Western Europe and the North-Eastern Atlantic. Barotropic tendency computations for the 500 mb surface are carried out and compared with the 12 hour observed height change. Tendency computations are also carried out for the mean height (averaged along the vertical with respect to pressure). The vertical motion compatible with the observed local vorticity changes is computed from the vorticity equation at several levels. The result is in fair agreement with the observed distribution of precipitation and cloudiness. The computations indicate that horizontal divergence and horizontal vorticity advection are of about equal importance in the vorticity budget at 500 mb, whereas the vertical vorticity transport seems to be less important.