Seasonal and regional variations of tropospheric temperatures in the Northern Hemisphere 1976–1990

Abstract The 300–1000 hPa monthly average thickness data for the Northern Hemisphere (NH) published by the synoptic climatology group of the Free University of Berlin are analysed on a seasonally aggregated basis and with respect to regional variations. It is shown that the rise in tropospheric temperatures between 1976 and 1990 began over the tropical oceans—when temperatures in the mid‐latitudes were still falling—continued over continental areas of the mid‐latitudes in the late 1970s, fell in the of the first half of the 1980s and continued again in the second half of the 1980s. Temperatures over the mid‐latitude oceans rose slowly in the late 1970s, fell in the early 1980s and rose strongly in the late 1980s. High‐latitude tropospheric temperatures showed no significant change throughout the period. In terms of seasonal variations, the largest warming relative to the late 1970s occurred over mid‐latitude continents in winter. However, compared with the base period used here, 1951–1960, the largest warming in absolute terms occurred over the low‐latitude oceans in summer and autumn and over mid‐latitude continents in spring. Low‐latitude warming was particularly strong over the Pacific Ocean. There was some significant warming over mid‐latitude continents in summer in the 1980s, which was of the same magnitude as the cooling in previous decades. The high latitudes are generally still colder than during the 1950s even though there has been some warming there as well since the 1970s. Around latitude 35°N, a ring of minimum warming appears in all seasons except winter. In the tropics, tropospheric warming is larger than surface warming; in the mid‐latitudes it is of comparable magnitude and in the higher latitudes it is smaller than surface warming.