Evaluation of a mesoscale coupled ocean-atmosphere configuration for
tropical cyclone forecasting in the South West Indian Ocean basin
Abstract
The performance in term of tropical cyclone track and intensity
prediction of the new coupled ocean-atmosphere system based on the
operational atmospheric model AROME-Indian Ocean and the ocean model
NEMO is assessed against that of the current operational configuration
in the case of seven recent tropical cyclones. Five different
configurations of the forecast system are evaluated: two with the
coupled system, two with an ocean mixed layer parameterization and one
with a constant sea surface temperature. For each ocean-atmosphere
coupling option, one is initialized directly with the MERCATOR-Ocean
PSY4 product as in the current operational configuration and the other
with the ocean state that is cycled in the AROME-NEMO coupled suite
since a few days before the cyclone intensification. The results show
that the coupling with NEMO improves the intensity of cyclones in
AROME-IO, especially when they encounter a slow propagation phase. For
short-term forecasts (less than 36 hours), the presence of a cooling in
the initial state that has been triggered by the AROME high-resolution
cyclonic winds in a previous coupled forecast already improves the
tropical cyclone intensity for all coupled or uncoupled configurations.
However, the simplification of the ocean-atmosphere interactions in the
configurations using the ocean mixed layer parameterization is not the
only reason for the overestimation of the intensity of already
well-developed TC in AROME-IO. The impact of other model components,
such as the air-sea flux parameterization and the cloud microphysics
scheme will need to be further investigated.