Melting energy sources in rainfall conditions over Pine Island Bay, Antarctica.

The case of a strong heat anomaly around Pine Island Bay is examined. This region of west Antarctica is well known for its rapidly thinning and accelerating marine-terminating glaciers. Polar-WRF model simulations were used to investigate the atmospheric structure, dynamic and energy fluxes of this event at high spatial resolution. The modeling discovered a hot spot that formed due to the development of relatively large-scale foehn phenomena at the basin of Pine Island Glacier (PIG). The thickness of the positive temperature layer over this region can exceed 1 km with a maximum of +8ºC. The layering of several warm air masses, accompanied by atmospheric rivers, causes significant liquid precipitation over coastal glaciers and ice shelves.  In such rare cases precipitation makes the main contribution to heat flux directed from atmosphere to the surface. The flux can reach up to 400 W m^-2 in the form of latent heat (which may release later). Direct heat transfer is also contributing to surface warming as a negligible part of the heat balance. We also tried to estimate a nonlinear dependence of precipitation heat fluxes in relation to atmosphere warming.  Finally, Noah LSM used in WRF model has some simplicities that make it not an ideal instrument for estimation of precipitation heat fluxes in polar regions. Although precipitation distribution and local wind patterns are sensitive to topography representation and demand high model resolution for estimation accuracy.