Frédéric Vitart and Francisco J. Doblas-Reyes
ECMWF, Shinfield Park
RG2 9AX, Reading, UK
The impact of using realistic varying instead of fixed greenhouse gas concentrations
is investigated in an ensemble of 6-month integrations from 1958 to 2001. Results suggest
that an increase of greenhouse gas concentration is conducive to a decrease of tropical storm
activity over all basins except the western North Atlantic and the eastern North Pacific. This
result seems consistent with the impact of an increase of greenhouse gas concentration on
the thermodynamical and dynamical variables that have an impact on the tropical cyclone
activity.
The interdecadal variability of tropical storm frequency is more realistic when using
realistic varying GHG concentration than when using constant GHG. Therefore, it is important
for seasonal forecasting systems to take account of the variation of GHG in the hindcast
period used to calibrate the system.