On the regulation of minimum mid-tropospheric temperatures in the Arctic

Observations indicate a minimum mid-tropospheric Arctic winter temperature of about -45°C at 500 hPa. This minimum temperature coincides with that predicted for moist adiabatic ascent over a sea surface near its salinity-adjusted freezing point. NCAR/NCEP Reanalysis data show that convective heating maxima averaged over the 50-70°N latitude band coincide both in longitude and altitude with total horizontal energy flux maxima entering the Arctic, indicating the significance of convection over open water on the winter Arctic energy budget. NCAR CCM single column model experiments simulating convective warming of a cold airmass moving over open water and radiative cooling as it moves again over cold land/sea ice support the hypothesis that the -45°C threshold can be maintained for 10-14 days after convective warming occurs. We speculate on the implications of this regulatory mechanism on surface temperatures.