Tropospheric Response in the Antarctic Circumpolar Wave along the Sea Ice Edge around Antarctica

Abstract

The Antarctic circumpolar wave (ACW) signal of a 3.7-yr period occurs along the sea ice edge forming around Antarctic each fall?winter?spring from 1982 to 2001. It was larger during the first decade than the second and has retracted sea ice extent (SIE) anomalies coinciding with warmer sea surface temperature, greater upward latent heat flux, and higher precipitation, driving deep convection in the troposphere associated with low-level convergence and upper-level divergence. Lower sea level pressure is displaced ?90° of phase to the west of retracted SIE anomalies, coinciding with increased extratropical cyclone density and intensity. The authors diagnose tropospheric thermal and potential vorticity budgets of this ACW signal using NCEP?NCAR reanalysis datasets, which show retracted SIE anomalies driving upper-level diabatic heating and low-level cooling, the former (latter) balanced mainly by vertical heat advection (poleward heat advection). This explains the anomalous poleward surface winds and deep convection observed over retracted SIE anomalies in this ACW signal. Thus, the vertical gradient of diabatic heating is balanced mainly by horizontal vortex tube advection at the low level and horizontal absolute vorticity advection at the upper level, together yielding the anomalous equivalently barotropic poleward wind response to the retracted SIE anomaly. Anomalous SIE-induced deep convection at the sea ice edge drives anomalous zonal (Walker-like) cells that teleconnect opposite phases in the ACW signal. It also drives anomalous Ferrell cells that teleconnect the ACW signal along the sea ice edge to that along the Subtropical Front near 35°S.