Seminar

Towards an improved understanding of tropical widening

DSRC entrance

Sean Davis, NOAA ESRL CSD & CU CIRES

Wednesday, September 28, 2011, 3:30 pm Mountain Time
DSRC 2A305

Abstract

Poleward migration of the latitudinal edge of the tropics of ~0.25 - 3° decade-1 has been reported in several recent studies based on reanalysis, satellite, and radiosonde data covering the past ~30 years. Currently, this large spread of tropical widening estimates has made it difficult to assess climate model performance or rigorously evaluate proposed tropical widening mechanisms that relate to thermal changes induced by changes in the concentrations of ozone and well-mixed greenhouse gases. It is not clear to what extent this large range of observational estimates reflects inherent differences in various aspects of the circulation, versus the use of different datasets, time periods, and details of the tropical edge definitions. Furthermore, most of these estimates have been based on reanalysis output, whose trends have the potential to be biased by inhomogeneities in the assimilated data and underlying forecast models, and may not be suitable for climate trend detection studies.

In this presentation, I will give an overview of recent tropical widening research, and present new findings regarding the robustness of tropical widening estimates and potential widening mechanisms. In particular, I will focus on the extent to which this large range of trends can be explained by the use of different data sources, time periods, and edge definitions by analyzing a suite of tropical edge latitude diagnostics based on tropopause height, winds, precipitation/evaporation, and outgoing longwave radiation (OLR) from several reanalyses and satellite data sets. I will also briefly discuss ongoing work related to new observational-based diagnostics of widening from satellite water vapor and ozone measurements, and idealized climate modeling for evaluating the impact of stratospheric water vapor changes on the tropical belt width.

ALL Seminar attendees agree not to cite, quote, copy, or distribute material presented without the explicit written consent of the seminar presenter. Any opinions expressed in this seminar are those of the speaker alone and do not necessarily reflect the opinions of NOAA or CSL.