Atmospheric moisture budget in the Arctic based on the ERA-40 reanalysis

The atmospheric moisture budget in the Arctic in 1979-2001 was analysed on the basis of the ERA-40 reanalysis. Zonal variations in the profiles of specific humidity mainly occur at altitudes below 5 km. The moisture transport peaks at altitudes lower than previously suggested; the median peak level of meridional moisture flux (MMF) across 70 degrees N is in winter at 930 hPa pressure level and in other seasons at 970-990 hPa level. Mean precipitable water for the polar cap (70-90 degrees N) ranges from 2.4 mm in winter to 12.3 mm in summer. Transient eddies (TE) are responsible for most of the water vapour transport across 70 degrees N by providing from 81% of MMF in winter to 92% of MMF in summer. The contribution by stationary eddies (SE) ranges from 5 to 9%, whereas the contribution of mean meridional circulation (MMC) ranges from 1% in summer to 12% in winter. Relative inter-annual variation in MMF components is highest for SE (standard deviation/mean = 133%), second highest for the MMC (61%) and smallest for TE (4%). The MMF across 70 degrees N accounts for 59% of the annual precipitation. Averaged for the polar cap, the mean annual moisture flux convergence (192 mm) and net precipitation (179 mm) are close to each other, but local differences exceeding 200 mm occur at several places. Over the open ocean, the moisture flux convergence is considered more reliable. The Arctic Oscillation (AO) index correlates with MMF in spring and winter (correlation coefficient r = 0.75) and with net precipitation in spring (r = 0.61) and winter (r = 0.50). The AO and precipitable water correlate in Canada and Greenland in winter and spring (r = -0.7) and in Europe in winter (r = 0.8). Copyright (C) 2009 Royal Meteorological Society