The discernment of an association between stratospheric warmings in winter and tropospheric blocking is made difficult by two factors: (1) the multiple occurrence of both features within a winter, complicating the determination of leads and lags, and (2) the choice of criteria for defining blocking and warmings. Criteria which take actual flow conditions into account, in distinction to the use of persistent height anomalies, were employed to monitor blocking in the Northern hemisphere since 1981. Major and minor warmings were identified with criteria consistent with the World Meteorological Organization definition. Broad and case-by-casse comparisons were made of warming and blocking activity during November-March of 1981-1982 to 1984-1985. The broad comparison suggests a relation between the date of zonal flow reversal in major warmings and the number of blocking days in each winter. Te detailed comparison, which included consideration of the thermal phase structure rom 700 to 10 mbar, gave a demonstrable link between 500-mbar blocking and 10-mbar warming episodes in 85% of the cases examined with blocks leading warmings by an average of 3.5 days. In the spectacular major warming of December-January 1984-1985 a tropospheric lead of 15 days was observed. |