The Role of Inertial Instability in Stratosphere-Troposphere Exchange in Midlatitude Cyclones

A unique dynamical relationship is found between regions of inertial instability (negative equivalent potential vorticity, EPV) and stratosphere – troposphere exchange (STE) near midlatitude westerly jets. Convection along a cold front can lead to enhancement of inertial instability on the anticyclonic shear side of the jet in the upper troposphere and lower stratosphere (UTLS). Turbulent entrainment results from these areas of negative EPV, disrupting the base of the stratosphere. This inertial instability enhances a waterfall effect over the jet, as a poleward and downward surge of mixed statospheric-tropospheric air enters the troposphere. Inertial instability in this quadrant of the jet also leads to a momentum surge within the jet.

Examples from several midlatitude storms are analyzed according to their proximity to the westerly jet using the University of Wisconsin Non-Hydrostatic Modeling System (UWNMS) simulations and structure as seen in ETA/NAM analysis. In each case distinct eruptions of inertial instability adhere to the anticyclonic shear side of the jet in direct relationship with intense convective processes along a surface cold front. These areas of negative EPV disrupt the UTLS, resulting in a poleward and downward surge of stratospheric high PV air into the troposphere. Initial results will also be included to apply this idea to tropical cyclones with respect to the effects of inertial instability and resulting STE.