\centerline {\bf Role of Stratospheric Air in a Severe Weather Event

The Role of Stratospheric Air in a Severe Weather Event: Analysis of PV and Total Ozone

Melissa A. Goering (1), William A. Gallus, Jr.(1), Mark A. Olsen and John L. Stanford

(1) Department of Geological & Atmospheric Sciences, Iowa State University, Ames, Iowa 50011

J. Geophys. Rev., 106, 11,813-11,823 (2001)


The role of dry stratospheric air descending to low and middle tropospheric levels in a severe weather outbreak in the Midwestern United States is examined using NCEP Eta model output, Rapid Update Cycle (RUC) analyses, and Earth Probe Total Ozone Mapping Spectrometer (EP/TOMS) total ozone data. Backward trajectories show stratospheric air descended to 800 hPa just west of the severe convection in the region. Damaging surface winds not associated with thunderstorms also occurred in the region of greatest stratospheric descent. Small-scale features in the high-resolution total ozone data compare favorably with geopotential heights and potential vorticity fields, supporting the notion that stratospheric air descended to near the surface. Detailed vertical structure in the potential vorticity appears to be captured by the small-scale total ozone variations. The capability of the total ozone to identify mesoscale features assists model verification. The total ozone data suggest biases in the RUC analysis and Eta forecast of this event. The total ozone is also useful in determining whether potential vorticity is of stratospheric origin or is diabatically generated in the troposphere.