On the definition and persistence of blocking

Abstract

In this paper, we have investigated under what conditions positive geopotential height anomalies can be interpreted as blocking structures. Furthermore, we have studied the persistence of blocking. The data used here are the observed daily 500 hPa geopotential heights for 10 winter seasons from 1982/83 to 1991/92. The objective blocking criteria of Dole (1978) have been compared with the subjective blocking criteria established by Rex (1950a, b). Our study indicates that if we want to relate positive geopotential height anomalies to blocking as defined by Rex, not only the amplitude, but also the latitudinal position of the anomalies is important. We conclude that blocking is not more persistent than other atmospheric anomalies of the same geographical scale. This is in agreement with Lindzen (1986). -from Author