CLIMATE ASSESSMENT FOR 1995

The El Nino-Southern Oscillation (ENSO) phenomenon is a major contribu tor to the observed year-to-year variability in the Pacific Ocean and in the global atmospheric circulation. The short-term climate system w itnessed the return to the mature phase of warm ENSO conditions (commo nly referred to as the El Nino) during early 1995 for the third time i n four years. This frequency of occurrence is unprecedented in the las t 50 years and is comparable to that observed during the prolonged 191 1-15 ENSO episode. These warm ENSO conditions contributed to a large-s cale disruption of the normal patterns of wind, rainfall, and temperat ure over much of the tropics and middle latitudes, particularly during the December 1994-February 1995 period. This period was followed by a dramatic decrease in sea surface temperatures in the tropical Pacific , resulting in a complete disappearance of all warm episode conditions during June-August and in the development of weak cold-episode condit ions during September-November. Changes in the tropical Pacific were a ccompanied by pronounced, large-scale changes in the atmospheric circu lation patterns from those that had prevailed during much of the early 1990s. Particular examples of these changes include 1) a dramatic ret urn to a very active hurricane season over the North Atlantic, followi ng four consecutive years of significantly below-normal hurricane acti vity; 2) the return to above-normal rainfall throughout Indonesia, nor thern Australia, and southern Africa, following a prolonged period of below-normal rainfall and periodic drought; and 3) a northward shift o f the jet stream and storm track position over the eastern half of the North Pacific during the latter part of the year, following several w inter seasons (three in the last four) characterized by a significant strengthening, southward shift, and eastward extension of these featur es toward the southwestern United States. Other regional climate anoma lies during 1995 included extreme warmth throughout western and centra l Asia during January-May and colder than normal conditions in this re gion during November-December, severe flooding in the midwestern Unite d States (April-May), abnormally wet conditions in California and the southwestern United States (December-February) combined with near-reco rd warmth over eastern North America, deadly heat waves in the central United States (mid-July) and India (first three weeks of June), droug ht in the northeastern United States (August), a drier-than-normal rai ny season in central Brazil (September-December), and an intensificati on of drier-than-normal conditions over southern Brazil, Uruguay, and northeastern Argentina at the end of the year. The global annual mean surface temperature for land and marine areas during 1995 averaged 0.4 0 degrees C above the 1961-90 mean. This value exceeds the previous wa rmest year in the record (1990) by 0.04 degrees C. The Northern Hemisp here also recorded its warmest year on record during 1995, with a mean departure from normal of 0.55 degrees C. The global annual mean surfa ce temperature for land areas only during 1995 was the second warmest since 1951. The year also witnessed near-record low ozone amounts in t he Southern Hemisphere stratosphere, with minimum values only slightly higher than the record low values observed in 1993. The areal extent of very low ozone values during 1995 was as widespread over Antarctica as in the record low year of 1993.