To investigate the maintenance mechanism of the blocking flow, we performed a numerical experiment using a barotropic spectral model on the sphere. The model is linearized about two types of realistic basic flows. One is a blocking flow near Alaska (blocking flow case) and the other is a zonal flow in the North Pacific (zonal flow case).

The model is integrated in time with prescribed high-frequency eddies which are generated in the Far East and propagate eastward along the northern flank of the jet stream. After several days of time integration, time mean vorticity flux divergence is calculated. Then, the resulting vorticity flux divergence field is used as the eddy vorticity forcing to compute the second-order flow induced by eddies. It is found that the induced second-order flow intensifies the blocking for the blocking flow case, and that this is not the case for the zonal flow case.