A Preliminary Analysis of MAP Sounding Data Collected in the Wipp Valley

One of the objectives of the Mesoscale Alpine Programme (MAP) was a study of gap flow in the Wipp Valley (the Wipptal). In this work the radiosonde and dropsonde data gathered during the Föhn events in the Wipptal is used to examine the extent, to which a reduced-gravity shallow-water theory correctly describes the flow. We also survey unusual and notable atmospheric features contained in the sounding data.

As a first step, we examine the entire sounding dataset to determine the frequency with which the observed atmospheric structure is reasonably consistent with that of idealized reduced-gravity shallow-water theory. Cases with a relatively uniform wind and stability between the ground and a capping inversion are further analyzed for quantitative and qualitative consistency with the theory. We found that the strongest cases of Föhn flow in the Wipptal can not necessarily be characterized as supercritical using the Froude number criterion F > 1. In fact, there is the least quantitative agreement between the theory and data when we expect the dynamics to be most strongly driven by interface displacement.