ON THE MAINTENANCE OF BLOCKING ANTICYCLONES OF NORTHERN HEMISPHERE-PARTⅠ:QUASI-GEOSTROPHIC POTENTIAL VORTICITY ANALYSIS

Four observed blocking anticyclones in different regions of the Northern Hemisphere are investigated.Analyses show that there exist distinct differences in the maintenance of the time-mean quasi-geostrophic potential vorticity(PV) low in 300 hPa within blocking areas.In two Pacific blocking cases,the PV advection by time-mean flow tends to flow the PV low to northwestern part of the blocking highs,and thus is beneficial to the maintenance of the blockings'strength.The transfer by transient eddies acts to balance the effect of the time-mean flow.In the Atlantic and Alaska blocking cases,however,the advection of mean flow tends to flow the PV low eastward.The PV transfer by transient eddies acts to flow potential vorticity low to the western part of the blocking ridges and also to balance the time-mean flow's effect.Thus,in the latter two cases,it is the transfer by the transient eddies that acts to maintain the blockings.