ATMOSPHERIC CONTRIBUTION TO HYDROLOGIC VARIATIONS IN THE ARCTIC

High-latitude rawinsonde data for 18 years (1973-1990) are used to compute the atmospheric moisture flux convergence over two regions: the Arctic Ocean and the Mackenzie River drainage basin. The primary objectives are to assess the interannual variability and to compare the macroscale hydrologic regimes of the two regions. The moisture flux convergence is positive in all months over the Arctic Ocean, but is occasionally negative during summer over the Mackenzie Basin. The climatological seasonal cycle of the moisture convergence contains a late-summer (August-September) maximum over the Arctic Ocean but a late-summer minimum over the Mackenzie Basin. Evaporation, deduced from the moisture inflow and independent data on precipitation, makes a much greater contribution to the atmospheric moisture budget of the Mackenzie domain, especially during summer. The respective equivalent area averages of the 18-year annual mean moisture flux convergence, precipitation and derived evaporation are 17.3, 19.5 and 2.2 cm a-1 for the Arctic Ocean and 24.9, 33.6 and 8.7 cm a-1 for the Mackenzie domain. However, the range of interannual variations of the flux convergence is about +/-50% of the annual means and more than twice the monthly means. The annual totals of the flux convergence are correlated with station-derived precipitation over the Mackenzie domain and with yearly variations of the Mackenzie discharge. The moisture flux convergence over the Mackenzie domain suggests that station reports underestimate precipitation during the winter months by amounts equivalent to several centimetres per annum.