SEASONAL AND REGIONAL VARIATIONS OF TROPOSPHERIC TEMPERATURES IN THE NORTHERN-HEMISPHERE 1976-1990

The 300-1000 hPa monthly average thickness data for the Northern Hemis phere (NH) published by the synoptic climatology group of the Free Uni versity of Berlin are analysed on a seasonally aggregated basis and wi th respect to regional variations. It is shown that the rise in tropos pheric temperatures between 1976 and 1990 began over the tropical ocea ns-when temperatures in the mid-latitudes were still falling-continued over continental areas of the mid-latitudes in the late 1970s, fell i n 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 slo wly in the late 1970s, fell in the early 1980s and rose strongly in th e late 1980s. High-latitude tropospheric temperatures showed no signif icant change throughout the period. In terms of seasonal variations, t he largest warming relative to the late 1970s occurred over mid-latitu de continents in winter. However, compared with the base period used h ere, 1951-1960, the largest warming in absolute terms occurred over th e low-latitude oceans in summer and autumn and over mid-latitude conti nents in spring. Low-latitude warming was particularly strong over the Pacific Ocean. There was some significant warming over mid-latitude c ontinents in summer in the 1980s, which was of the same magnitude as t he 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-degrees-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-latit udes it is of comparable magnitude and in the higher latitudes it is s maller than surface warming.