Numerical study of slantwise circulations in a strongly sheared prefrontal environment

The simultaneous presence of convective, symmetric and inertial instability in a prefrontal region of strong vertical wind shear was simulated with the non-hydrostatic model MOLOCH. Model diagnostics of absolute vorticity, pseudo-angular momentum, saturated equivalent potential temperature and vorticity reveal a sequence of events that includes "deltaM-adjustment", followed by slanted ascent in symmetrically unstable regions, becoming saturated in the later stages. An idealized experiment without orography was performed to isolate the presence and role of instabilities characterizing the development. The diagnosed circulation is reminiscent of a wavenumber-two normal mode of dry symmetric instability, while moist symmetric instability is confined to a very limited region, despite the appearance of wider areas of negative moist potential vorticity. The evaluation of moist thermodynamic quantities which give proper account of condensate loading is suggested as a possible resolution of this apparent inconsistency. Copyright © 2011 Royal Meteorological Society