Abstract
Abstract. The representation of the Tropical Tropopause Layer (TTL) in 13 different Chemistry Climate Models (CCMs) designed to represent the stratosphere is analyzed. Simulations for 1960–2005 and 1980–2100 are analyzed. Simulations for 1960–2005 are compared to reanalysis model output. CCMs are able to reproduce the basic structure of the TTL. There is a large (10 K) spread in annual mean tropical cold point tropopause temperatures. CCMs are able to reproduce historical trends in tropopause pressure obtained from reanalysis products. Simulated historical trends in cold point tropopause temperatures are not consistent across models or reanalyses. The pressure of both the tropical tropopause and the level of main convective outflow appear to have decreased (increased altitude) in historical runs as well as in reanalyses. Decreasing pressure trends in the tropical tropopause and level of main convective outflow are also seen in the future. Models consistently predict decreasing tropopause and convective outflow pressure, by several hPa/decade. Tropical cold point temperatures are projected to increase by 0.09 K/decade. Tropopause anomalies are highly correlated with tropical surface temperature anomalies and with tropopause level ozone anomalies, less so with stratospheric temperature anomalies. Simulated stratospheric water vapor at 90 hPa increases by up to 0.5–1 ppmv by 2100. The result is consistent with the simulated increase in temperature, highlighting the correlation of tropopause temperatures with stratospheric water vapor.
Highlights
The Tropical Tropopause Layer (TTL), the region in the tropics within which air has characteristics of both the troposphere and the stratosphere, is a critical part of the atmosphere
The TTL is the layer in the tropics between the level of main convective outflow and the cold point, about 12–18 km (Gettelman and Forster, 2002)
We focus discussion on three questions: (1) Do tropospheric or stratospheric changes dominate at the cold point? (2) Does ozone significantly affect TTL structure? (3) What will happen to stratospheric water vapor?
Summary
The Tropical Tropopause Layer (TTL), the region in the tropics within which air has characteristics of both the troposphere and the stratosphere, is a critical part of the atmosphere. Gettelman and Forster (2002) described a climatology of the TTL, and looked at changes over the observed record from radiosondes, finding decreases in tropopause pressure (increasing height) with little significant change in the bottom of the TTL (see below). Dameris et al (2005) looked at simulations from 1960–1999 in a global model and found no consistent trend in thermal tropopause pressure or water vapor. We will compare the models to observations over the observed record, and examine model predictions for the evolution of the TTL in the 21st Century These simulations have been used to assess future trends in stratospheric ozone in Eyring et al (2007) and World Meteorological Organization (2007), Chapter 6.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
