Tropical Cyclones in High-Resolution Community Atmosphere Model version
5: Evaluation for Western North Pacific
Abstract
Climate models at high resolution (~25 km horizontal
grid spacing) can permit realistic simulations of tropical cyclones
(TCs), thus promising the investigation of these high-impact extreme
events under present and future climates. On the global scale,
simulations with the Community Atmosphere Model version 5 (CAM5) present
a reasonable TC climatology under prescribed present-day (1980-2005) sea
surface temperature (SST) and greenhouse gas (GHG) forcing. However, for
the disaster-prone western North Pacific (WNP) region, biases in TC
genesis frequency and location persist across various configurations.
The biases under-represent the basin’s share in global TC climatology,
complicating the fidelity of future projections. This study addresses
these model biases in WNP by evaluating the large-scale environmental
controls of TC genesis in CAM5 with two aerosol configurations. Across
the two configurations, the lack of mid-level moisture is consistently
identified as the leading cause of the deficit in simulated WNP TC
genesis. This lack of mid-level moisture in WNP TC main develop region
is potentially linked to previously identified deficits in Pacific warm
pool precipitation at high horizontal resolution in CAM5, as well as
biases in the East Asian Summer Monsoon circulation and moisture
transport. Additional CAM5 simulation experiments will explore the
effect of moisture nudging on the large-scale environment and subsequent
TC genesis, tracks, and intensity development. For a chosen year,
simulations covering WNP peak TC season (July - October) under otherwise
identical forcing (SST, GHG etc.) will be run with and without nudging
the specific humidity field towards MERRA-2 reanalysis. The insight into
the biases of basin-scale TC simulation under the present climate and
potential improvements will help reduce the uncertainty in
future-climate projections, in the interest of disaster risk management.