Tropical Cyclones and Equatorial Waves in a Convection-Permitting
Aquaplanet Simulation with Off-Equatorial SST Maximum
Abstract
Tropical cyclogenesis can be influenced by convectively coupled
equatorial waves; yet, existing datasets prevent a complete analysis of
the multi-scale processes governing both tropical cyclones (TCs) and
equatorial waves. This study introduces a convection-permitting
aquaplanet simulation that can be used as a laboratory to study TCs,
equatorial waves, and their interactions. The simulation was produced
with the Model for Prediction Across Scales-Atmosphere (MPAS-A) using a
variable resolution mesh with convection-permitting resolution (i.e.,
3-km cell spacing) between 10oS–30oN. The underlying sea-surface
temperature is given by a zonally symmetric profile with a peak at 10oN,
which allows for the formation of TCs. A comparison between the
simulation and satellite, reanalysis, and airborne dropsonde data is
presented to determine the realism of the simulated phenomena. The
simulation captures a realistic TC intensity distribution, including
major hurricanes, but their lifetime maximum intensities may be limited
by the stronger vertical wind shear in the simulation compared to the
observed tropical Pacific region. The simulation also captures
convectively coupled equatorial waves, including Kelvin waves and
easterly waves. Despite the idealization of the aquaplanet setup, the
simulated three-dimensional structure of both groups of waves is
consistent with their observed structure as deduced from satellite and
reanalysis data. Easterly waves, however, have peak rotation and
meridional winds at a slightly higher altitude than in the reanalysis.
Future studies may use this simulation to understand how convectively
coupled equatorial waves influence the multi-scale processes leading to
tropical cyclogenesis.