A GCM Study on the Maintenance of the June 1982 Blocking in the Southern Hemisphere

Abstract

Abstract General Circulation Model (GCM) experiments have been performed to determine mechanisms that maintained the blocking episode in the Australian-New Zealand region during the period 8–22 June 1982. A control forecast reproduces the persistent ridge. Several mechanistic experiments lead to the following conclusions. (i) The block was not due to orographic forcing, which has only a small local influence on the winter atmospheric circulation in the Southern Hemisphere. (ii) The block was not produced by the sea surface temperature anomalies (SST). By comparing the relative location of low-level atmospheric vorticity and SST anomalies, we are able to show that during June 1982 the atmospheric blocking was the cause of the SST anomalies in the Pacific. (iii) The block was not a response to tropical heating or the Asian Monsoon. There are only weak effects on the block when the tropical heating or heating in the Pacific region is suppressed. (iv) The most important boundary forcing maintaining this block...