Abstract
The next-generation global climate model from the NASA Goddard Institute
for Space Studies, GISS-E3, contains many improvements to resolution and
physics that allow for improved representation of tropical cyclones
(TCs) in the model. This study examines the properties of TCs in two
different versions of E3 at different points in its development cycle,
run for 20 years at 0.5 degree resolution, and compares these TCs with
observations, the previous generation GISS model, E2, and other climate
models. E3 shares many TC biases common to global climate models, such
as having too few tropical cyclones, but is much improved from E2. E3
produces strong enough TCs that observation-based wind speed thresholds
can now be used to detect and track them, and some storms now reach
hurricane intensity; neither of these was true of E2. Model development
between the first and second versions of E3 further increased the number
and intensity of TCs and reduced TC count biases globally and in most
regions. One-year sensitivity tests to changes in various microphysical
and dynamical tuning parameters are also examined. Increasing the
entrainment rate for the more strongly entraining plume in the
convection scheme increases the number of TCs (though also affecting
other climate variables, and in some cases increasing biases).
Variations in divergence damping did not have a strong effect on
simulated TC properties, contrary to expectations based on previous
studies. Overall, the improvements in E3 make it more credible for
studies of TC activity and its relationship to climate.