Antarctic Sea Ice and a West Pacific Teleconnection in the NCAR Community Atmosphere Model

A teleconnection between the Northern Hemisphere and high latitudes of the Southern Hemisphere has been found during August in observations. A very similar teleconnection was also found during September in simulations with the National Center for Atmospheric Research (NCAR) Community Climate Model version 2 (CCM2) with forcing resulting from removal of Antarctic sea ice. The teleconnection in monthly-average surface pressure fields displays three primary anomalies: (i) a high Southern latitude component including Wilkes Land, Antarctica, the nearby Southern Ocean and the Ross Sea, (ii) a mid-latitude component near Australia and New Zealand, and (iii) a Northern Hemisphere subtropical component over the extreme western Pacific Ocean. Surface pressure for the high-latitude anomaly is negatively correlated to the other two primary anomalies which are positively correlated. Intraseasonal variations in tropical convection are highly linked to the phenomenon. For both the observed and modeled teleconnection, significant local increases in East Asian monsoon precipitation are found during the phase with increased pressure near Australia. The teleconnection, however, is not clearly displayed in simulations with the NCAR CCM3, which has the Zhang-McFarlane scheme that poorly simulates tropical instraseasonal variability. The new NCAR Community Atmosphere Model version 2 (CAM2) also has the Zhang-McFarlane scheme as its standard convection parameterization. Eric Maloney of NCAR, however, has adapted the relaxed Arakawa-Schubert convection scheme for the NCAR climate models, resulting in a much improved simulation of tropical instraseasonal variability. A series of CAM2 simulations employing the relaxed Arakawa-Schubert scheme are run with different specifications of Antarctic sea ice in order to explore the development of the teleconnection. While the observations suggest a tropical forcing, the earlier CCM2 results, on the other hand, suggest a forcing in high southern latitudes. The new simulations help to resolve the questions raised by the earlier model results and observations.