Difference in Seasonal Variation of net Precipitation between the Arctic and Antarctic Regions

The difference in the climatological seasonal variation of the net precipitation (precipitation minus evaporation) between the Arctic and the Antarctic was evaluated using ECMWF reanalysis data. Evaluated for simplified polar caps (the regions poleward of 70N and 67.5S), over the Arctic, the net precipitation is large in the boreal summer, while, over the Antarctic, it is large in the austral winter. The net precipitation depends strongly on the poleward transient moisture flux into the region, which is affected by both the meridional moisture gradient and eddy activity. Thus, the seasonal variation of the poleward transient moisture flux is determined by the relative amplitude of the moisture and eddy factors, that is, by the ratio of the amplitude of the seasonal variation to the annual mean. While both regions have similar relative amplitudes of the eddy factor, the moisture factor in the Arctic is much larger than in the Antarctic. The moisture factor explains the difference in the seasonal variation of the net precipitation.