Wind shear effects in convection-permitting models
influence MCS rainfall and forcing of tropical circulation
Abstract
Mesoscale Convective Systems (MCSs) play a critical role in tropical
rainfall patterns and circulations. To reduce persistent biases and
improve understanding of the climate system, international groups have
called for unprecedented investment in global convection-permitting (CP)
climate models. It is essential such models accurately represent MCSs,
and in particular environmental interactions such as dynamical control
by wind shear. We show that in representative current generation CP
simulations, MCS updraft entrainment decreases with shear, leading to a
realistic increase of extreme rainfall. We find the control of
environmental shear extends to mean storm rainfall and anvil heights.
The simulation of these effects depends strongly on model physics in
both CP and parameterised models. We show that in West Africa, MCS shear response
influences the zonal distribution of storm diabatic heating, modifying
upscale impacts of convection. Our results demonstrate key tests for
focused process-based assessment of CP model fidelity.