Tropically Excited Arctic warMing mechanism (TEAM): A Theory based on a General Circulation Perspective

Sukyoung Lee

Department of Meteorology and Atmospheric Science, Pennsylvania State University

Wednesday, Feb 22, 2017, 2:00 pm
DSRC Room 1D403

Abstract

Records of the past climates show a wide range of values of the equator-to-pole temperature gradient, with an apparent universal relationship between the temperature gradient and the global-mean temperature: relative to a reference climate, if the global-mean temperature is higher (lower), the greatest warming (cooling) occurs at polar regions. Understanding this equator-to-pole temperature gradient is fundamental to climate and the general circulation. Here, a general circulation-based theory for polar amplification is presented. Recognizing the fact that most of the zonal available potential energy (ZAPE) in the atmosphere is untapped, this theory invokes that La-Niña-like tropical heating can help tap ZAPE and warm the Arctic by exciting poleward and upward propagating Rossby waves that reinforce the climatological planetary-scale waves.

This theory is supported by observation-based data and idealized model experiments. The theory is also supported by the ongoing multi-decadal trend in the convective precipitation which shows a steady increase over the western tropical Pacific. In contrast, most of the climate models predict an El-Nino-like response to greenhouse-gas warming. Discrepancies between climate model ensemble means and the observations are often attributed to internal variability. However, evidence will be presented wherein the models are predicting El-Nino-like response to warming at least in part because the convective parameterizations in climate models over-stabilize the tropical troposphere.