Structure of the wake north of the Alps

Six PV banner missions were flown during the Special Observation Period (SOP) of MAP in Sept-Nov 1999. In this study we investigate structure of the wake and dynamics of potential vorticity banners north of the Alps, employing comparison of field data with high-resolution simulations carried out with the Naval Research Laboratory's Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS).

The wake north of the Alps was investigated during MAP IOP 8 in a single-aircraft mission flown by NCAR Electra over the Bavarian plane, north of the east-west oriented portion of the main ridge of the Alps during an episode of deep south Foehn. The Electra carried out multiple transverses within a single Alps-parallel vertical plane, which was covered additionally by a dense curtain of dropsondes. The wind speed variation along the flown tracks, in both model-generated and the observed data, reveals a strong variation of the strength of the southerly wind along the Alps and existence of multiple narrow shearlines and associated PV banners. The position of two major documented jets correlates well with two large gaps in the terrain, representing exit regions of the Inn and the Rhine Valleys. The presentation will also examine the generation mechanism of PV and the sensitivity of the simulated wake structure to the model horizontal resolution.