Published in

American Meteorological Society, Journal of Climate, 5(27), p. 1999-2013, 2014

DOI: 10.1175/jcli-d-13-00287.1

Links

Tools

Export citation

Search in Google Scholar

How Fast Are the Tropics Expanding?

Journal article published in 2014 by Xiao-Wei Quan, Martin P. Hoerling, Judith Perlwitz, Henry F. Diaz, Taiyi Xu
This paper is available in a repository.
This paper is available in a repository.

Full text: Download

Green circle
Preprint: archiving allowed
Green circle
Postprint: archiving allowed
Orange circle
Published version: archiving restricted
Data provided by SHERPA/RoMEO

Abstract

Diagnosing the sensitivity of the tropical belt provides one framework for understanding how global precipitation patterns may change in a warming world. This paper seeks to understand boreal winter rates of subtropical dry zone expansion since 1979, and explores physical mechanisms. Various reanalysis estimates based on the latitude where zonal mean precipitation P exceeds evaporation E and the zero crossing latitude for the zonal mean meridional streamfunction () yield tropical width expansion rates in each hemisphere ranging from near zero to over 1 degrees latitude decade(-1). Comparisons with 30-yr trends computed from unforced climate model simulations indicate that the range among reanalyses is nearly an order of magnitude greater than the standard deviation of internal climate variability. Furthermore, comparisons with forced climate models indicate that this range is an order of magnitude greater than the forced change signal since 1979. Rapid widening rates during 1979-2009 derived from some reanalyses are thus viewed to be unreliable. The intercomparison of models and reanalyses supports the prevailing view of a tropical widening, but the forced component of tropical widening has likely been only about 0.1 degrees-0.2 degrees latitude decade(-1), considerably less than has generally been assumed based on inferences drawn from observations and reanalyses. Climate model diagnosis indicates that the principal mechanism for forced tropical widening since 1979 has been atmospheric sensitivity to warming oceans. The magnitude of this widening and its potential detectability has been greater in the Southern Hemisphere than in the Northern Hemisphere during boreal winter, in part owing to Antarctic stratospheric ozone depletion.