Radiative influence of Antarctica on the polar-night vortex

Temperatures over the Antarctic plateau are sharply colder than those over its maritime surroundings. The sharp temperature contrast due to Antarctica is conveyed upward through 9.6-μm absorption by ozone, which shapes the thermal structure in the stratosphere. The radiative impact of Antarctica on the polar stratosphere is investigated in three-dimensional integrations of the nonlinear primitive equations, coupled to a full radiative-transfer calculation that is performed with and without clouds. Cooling associated with Antarctica depresses radiative-equilibrium temperatures by as much as 10 K. This direct radiative influence emerges clearly at high latitudes of the lowermost stratosphere. It is accompanied elsewhere by temperature changes of opposite sign, which result indirectly through adiabatic warming by the induced residual meridional circulation. Collectively, these influences reinforce the polar-night vortex, shift the jet axis poleward, and intensify downward transport over the polar cap by the residual circulation. In this way, radiative forcing from below contributes significantly to the features that distinguish the Antarctic vortex from the Arctic vortex.