Tellus, in press.
Suzana J. Camargo
IRI, Lamont-Doherty Earth Observatory
of Columbia University, Palisades, NY
Adam H. Sobel
Department of Applied Physics and Applied Mathematics and Department of Earth and Environmental Sciences,
Columbia University, New York, NY.
Anthony G. Barnston
IRI, Lamont-Doherty Earth Observatory
of Columbia University, Palisades, NY
Kerry A. Emanuel
Department of Earth, Atmospheric and Planetary Sciences,
Massachusetts Institute of Technology, Cambridge, MA.
Abstract
The potential for tropical cyclogenesis in a given ocean basin during its active season has
been represented by a genesis potential index (GPI) that contains several large-scale environmental
variables demonstrated to relate to tropical cyclone (TC) genesis. Here we examine the
ability of some of today’s atmospheric climate models, forced with historical observed SST
over a multidecadal hindcast period, to reproduce observed values and patterns of the GPI, as
well as the expected implications for their TC number. The evaluation is done toward the goal
of being able to rely on climate models to predict anomalies in TC behavior, including activity
level and preferred location, on time-scales from interannual through multidecadal and longer.
The effect of the horizontal resolution of a climate model on its GPI is explored.
The five analyzed models are found capable of reproducing the observed seasonal phasing
of GPI in a given region, but most of them them have a higher GPI than observed. Additionally,
each model has its own unique relationship between mean GPI and mean TC number. The
interannual correlation of GPI and number of TCs in a given basin differs significantly among
models.
Experiments using different horizontal resolutions of the ECHAM5 model indicate that as
resolution is increased, model GPI also increases for many of the ocean basins during their
peak TC seasons. Most of this increase is realized between resolution T42 and T63, with
much smaller increases for further resolution increases up to T159. Increases in model GPI
with increasing resolution implies a more favorable large-scale environment for model TC
genesis.
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