Adiabatic lapse rates in tornadic environments

Recently, attention has turned to the interactions between tornadic thunderstorms and their environments. One interesting aspect of this is that many tornadic environments possess adiabatic vertical temperature lapse rates through some depth. In addition to the straightforward effects of steep lapse rates upon updraft strength, another important consideration is the effect they may have upon gravity wave propagation. Such impacts appear to have received little attention to this point.

Gravity waves are fundamental in dispersing thunderstorms' local heating via propagating “compensating” subsidence. However, because gravity waves cannot propagate in adiabatic environments, in such regimes the convection's heating can be accumulated in the convective column, at least until the convection produces a sufficiently strong divergent wind field to advect it away. This advection by the perturbation wind is considerably slower and less efficient at dispersing the heating than is gravity wave propagation. Idealized simulations with simple convective heating profiles reveal that a compact, large-magnitude pressure minimum can accumulate below cloud base in an adiabatic environment, with a significant attending cyclostrophic flow field. However, such compact pressure minima do not occur in nearly adiabatic environments because gravity waves rapidly disperse the heating from the column. Owing to the lack of gravity waves, it appears that adiabatic lapse rates may uniquely favor rapid generation of low-level vortices, especially in environments with appreciable background vorticity.