Exploring Western North Pacific Tropical Cyclone Activity in the
High-Resolution Community Atmosphere Model
Abstract
High-resolution climate models (~28 km grid spacing) can
permit realistic simulations of tropical cyclones (TCs), thus enabling
their investigation in relation to the climate system. On the global
scale, previous works have demonstrated that the Community Atmosphere
Model (CAM) version 5 presents a reasonable TC climatology under
prescribed present-day (1980-2005) forcing. However, for the Western
North Pacific (WNP) region, known biases in simulated TC genesis
frequency and location under-represent the basin’s dominant share in
observation. This study addresses these model biases in WNP by
evaluating WNP TCs in a decadal simulation, and exploring potential
improvements through nudging experiments. Among the major environmental
controls of TC genesis, the lack of mid-level moisture is identified as
the leading cause of the deficit in simulated WNP TC genesis over the
Pacific Warm Pool. Subsequent seasonal experiments explore the effect of
constraining the large-scale environment on TC development by nudging
WNP temperature field towards reanalysis at various strengths.
Temperature nudging elicits significant response in TC genesis and
intensity development, as well as in moisture and convection over the
Warm Pool. These responses are sensitive to the choice of nudging
timescale. Overall, the nudging experiments demonstrate that
improvements in the large-scale environment can lead to improvements in
simulated TCs. The verification of the environmental controls for
simulated TC genesis suggests future model developments in relation to
model physics. The potential improvements will contribute to the
understanding of how the mean state of current or future climates may
give rise to extremes such as TCs.