How midlevel horizontal humidity gradients affect simulated storm morphology

Of the many problems cloud models have, arguably a crucial one is the braking effect that realistic dry air has on modeled convective storms. In order to better understand how deep moist convection responds to midlevel dry air, simulations of convective storms with simple inhomogeneous environments are conducted. The eastern two-thirds of the domain consists of the familiar Weisman and Klemp sounding with unidirectional westerly shear; the rest of the domain has the same sounding except with progressively drier midlevels from east to west. The dry air is introduced at three different locations along the east—west direction to simulate the effects of drier air at varying times.

Results indicate midlevel dry air is initially inimical to storm intensity; however, the storms subsequently strengthen and display supercellular characteristics in all simulations. The intensity of the supercells in some of the inhomogeneous runs is comparable to that for the moist homogeneous control runs for a variety of microphysical parameterizations. Interestingly, for some of the microphysics schemes the supercells are even stronger and/or better organized in the inhomogeneous runs. This apparent enhancement of storms may be partly related to the convective mode and lack of interference from neighboring cells. Consistent with other modeling studies, the dry air also reduces the size of the storms and the amount of liquid water content. Nevertheless, the influence of midlevel dry air produces relatively isolated storms, thus replicating radar observations of actual storms in dry midlevel environments.