THE DISTRIBUTION AND TRANSPORT OF ATMOSPHERIC WATER-VAPOR OVER THE ARCTIC BASIN

A comprehensive rawinsonde archive, comprising atmospheric soundings f rom fixed stations, ships, and the former Soviet Union 'North Pole' se ries of drifting ice stations, is used to examine features of the dist ribution and transport of Arctic water vapour. Results are based on an alysis of climatological, gridded seasonal and monthly fields north of 65 degrees N of precipitable water, vertically integrated vapour flux es, and profiles of specific humidity, vapour fluxes, temperature, and winds, compiled from objective interpolation of the quality controlle d soundings. Emphasis is placed on contrasting conditions for winter a nd summer, with due attention paid to the potential effects of uncerta inties in the rawinsonde humidity data. For zonal means, specific humi dity for all seasons typically displays a surface maximum, decreasing poleward at all levels. Precipitable water (surface-300 hPa), has wint er values ranging from 3 . 8 mm for 65 degrees-70 degrees N and 1 . 8 mm for 80 degrees-90 degrees N, with annual maxima in July of 18 . 2 a nd 12 . 5 mm, respectively. These zonal means, however, mask large spa tial variations; precipitable water for winter, spring, and autumn sho ws a marked equatorward increase towards the Atlantic side of the Arct ic only. Minima are found over north-east Canada during spring, summer , and autumn. Vapour fluxes tend to peak in the lower troposphere at a bout 850 hPa in winter, but over a broader layer in summer. During win ter, the largest vertically integrated (surface-300 hPa) zonal and mer idional vapour transports are found between Iceland and Scandinavia. T he Beaufort Sea and western Canada are the only regions where vertical ly integrated meridional fluxes are equatorward. During summer, the ve rtically integrated total flux (zonal plus meridional components) incr eases sharply over the Beaufort Sea. Equatorward meridional fluxes are again found over western Canada, with strong poleward meridional tran sports over the Atlantic sector.