Net Precipitation of Antarctica: Thermodynamical and Dynamical Parts of the Climate Change Signal

This study investigates mechanisms leading to climate change signals of Antarctic net precipitation (E-P) simulated by three members of one CMIP3 and an multi-model ensemble of CMIP5 coupled atmosphere-ocean general circulation models (AOGCM). We present an approach to distinguish between thermodynamical and dynamical influences on climate change signals. Net precipitation is calculated with the divergence of vertically integrated moisture flux. A physical interpretation of the changing flux signal due to dynamics is given by decomposing transient atmospheric waves into different length scales and temporal variations. Concerning the spatial scale we distinguish between transient long waves (wavenumber less equal 6) and synoptic scale waves. To decompose temporal variations an 8-day low-pass filter is used. Climate change of moisture transport is compared with fluctuations of geopotential height fields as well as climate signals of extra-tropical cyclones.In the recent paper it is shown that moisture flux changes are generally dominated by increased humidity in the atmosphere due to temperature increase in the future climate projections. This leads to increasing net precipitation inside a spherical cap around the Antarctic continent due to the thermodynamical part of climate change. The dynamical component of the signal shows a decrease which is mainly due to the low variability component of synoptic scale waves. It shows a decreasing climate change signal especially off-coast of West Antarctica. This is discussed to be connected to changing variability of the Amundsen Sea Low. The climate change signal of the Southern Hemisphere stormtrack, which shows a distinctive poleward shift in the future projection, can be assigned to synoptic scale moisture flux with temporal variations less than 8 days. Spatial patterns of this moisture flux component can be understood by means of an analysis of the most intensive extra-tropical cyclones, which increase especially on the Eastern Hemisphere. Concerning the climate change signal of net precipitation inside the polar cap, the influence of changing extra-tropical cyclone activity is minor.