Abstract
This study explores effects of the nontraditional Coriolis terms (NCTs)
on convective system propagation in radiative-convective equilibrium
(RCE). NCTs are restored to the System for Atmospheric Modeling (SAM) to
explicitly simulate the temporal evolution of convective systems in a
zonal vertical domain rotating about a meridional axis. The system
rotation rate is tested over a wide range. The results are transformed
into space-time spectra to analyze the overall propagation
characteristics. The raw spectra show local power maxima in bands
associated with self-aggregated convection and convectively coupled
gravity waves. Changes in the spectra due to the inclusion of NCTs can
mostly be explained by the compressional beta effect (CBE), which speeds
up the eastward propagation and slows down the westward propagation of
zonal vertical circulation. For example, given the power spectra red in
frequency, the power increases in the band of eastward propagating
convective clusters and decreases in the band of westward ones.
Furthermore, the speed changes of convectively coupled gravity waves are
measured from the spectra. The magnitude of the speed changes increases
with the system rotation rate, and this increase agrees with the
theoretical speed change due to the CBE. These results suggest that the
dry CBE theory can explain the effect of NCTs on the propagation of
convective systems. This study recommends the restoration of NCTs to
model dynamical cores because NCTs meaningfully correct the propagation
speed of convectively coupled circulations and computationally costs
little. SIGNIFICANCE STATEMENT The rotation of Earth turns eastward
motion upward and upward motion westward, and vice versa. This effect is
called the nontraditional Coriolis effect and is omitted in most of the
current atmospheric models for predicting weather and climate. Using an
idealized model with cloud physics, this study suggests that the
inclusion of the nontraditional Coriolis effect speeds up eastward
moving rainy systems and slows down westward moving ones. The speed
change agrees with a theory without cloud physics. This study encourages
restoring the nontraditional Coriolis effect to the atmospheric models
since it increases the accuracy of tropical large-scale weather
prediction while the cost is low.