Meridional Patterns of Surface Warming and the Underlying Mechanisms in Dry and Moist AGCMS

LI Juan1,2, XIA Yan1, YANG Jun1,†

1. Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871; 2. 96941 PLA Troops, Beijing 102208; † Corresponding author, E-mail: junyang@pku.edu.cn

Abstract Using an atmospheric general circulation model (AGCM) coupled to a slab ocean, the mechanisms for producing the PWA (polar warming amplification) in idealized conditions are investigated. In the simulations, both ice albedo feedback and cloud radiative effects are turned off, but realistic radiative transfer of greenhouse gases (such as CO2) and atmospheric heat transport are included. Surface albedo is fixed and meridional oceanic heat transport is set to zero everywhere. Through turning on or off surface evaporation, the model is a moist AGCM or becomes a dry AGCM. Results show that under doubling atmospheric CO2 concentration, PWA occurs in the moist AGCM but not in the dry AGCM. In the dry AGCM, the increases of surface temperatures are nearly uniform from the equator to the poles. The radiative forcing of increased CO2 and water vapor feedback are stronger in the tropics than those in the polar region, so that the only mechanism for driving the PWA in the moist AGCM is an enhanced meridional heat transport. In the dry AGCM, the poleward heat transport also increases with a much smaller magnitude, so that it is not able to support a PWA. This study emphasizes that water vapor and its associated meridional heat transport are necessary for the PWA on Earth, and PWA may not occur in a dry atmosphere such as Martian atmosphere. Key words polar warming amplification; dry AGCM; moist AGCM; meridional heat transport; Planck effect