Vertical Mixing and the Temperature and Wind Structure of the Tropical Tropopause Layer

Abstract

Vertical mixing may lead to significant momentum and heat fluxes in the tropical tropopause layer (TTL) and these momentum and heat fluxes can force large climatological temperature and zonal wind changes in the TTL. The climatology of vertical mixing and associated momentum and heat fluxes as parameterized in the Interim ECMWF Re-Analysis (ERA-Interim) and as parameterized by the mixing scheme currently used in the ECMWF operational analyses are presented. Each scheme produces a very different climatology showing that the momentum and heat fluxes arising from vertical mixing are highly dependent on the scheme used. A dry GCM is then forced with momentum and heat fluxes similar to those seen in ERA-Interim to assess the potential impact of such momentum and heat fluxes. A significant response in the TTL is found, leading to a temperature perturbation of approximately 4 K and a zonal wind perturbation of approximately 12 m s−1. These temperature and zonal wind perturbations are approximately zonally symmetric, are approximately linear perturbations to the unforced climatology, and are confined to the TTL between approximately 10°N and 10°S. There is also a smaller-amplitude tropospheric component to the response. The results presented herein indicate that vertical mixing can have a large but uncertain effect on the TTL and that the choice and impact of the vertical mixing scheme should be an important consideration when modeling the TTL.