MAP IOP 10 South Foehn Event in the Wipp Valley: Verification of High-Resolution Numerical Simulations with Observations A. Gohm*, G. Zängl**, G. J. Mayr* * University of Innsbruck, Austria ** University of Munich, Germany ICAM/MAP 2003 Brig, Switzerland, May 19 to 23, 2003 Gohm, A., G. Zängl, G. J. Mayr, 2003, submitted to Mon. Wea. Rev.

The scientific objective: To assess to what extent the temporal evolution and spatial structure of small-scale orographic flows can be simulated with a state-of-the-art mesoscale model run in a very high- resolution mode. The phenomenon: Deep south foehn in the Wipp Valley on October 1999 The scientific tools: Penn State/NCAR mesoscale model MM5 NOAA/ETL ground-based scanning Doppler lidar (TEACO2) NCAR airborne aerosol backscatter lidar (SABL) ZAMG Doppler sodar radiosoundings and weather stations

MM5 basic setup: 6 domains with  x = 64.8 – km 39 full-sigma levels initialized with operational ECMWF analysis at 23 Oct 18 UTC and 24 Oct 00 UTC Wipp Valley Innsbruck Brenner Pass

Backscatter intensity versus potential temperature, 15 UTC 24 Oct 1999: P1 P2 MM5 00 UTC run  AML top heights & isentropes indicate regions of flow descent and jump-like features  indications for underestimation of flow descent SABL lidar on NCAR Electra InnsbruckBrenner flow

Wind profile at Brenner Pass, 24 Oct 1999: ZAMG PA2 sodar MM5 00 UTC run, D6  simulated wind speed 15 % too high  lower gap area 30% too large in D6  simulated mass flux 50% too high  00 (18) UTC run: RMSE = 5.6 (6.2) m/s ME = +1.5 (+1.6) m/s Alpine crest line lower gap upper gap

Wind speed, 24 Oct 1999: too strong winds

Potential temperature, 24 Oct 1999: -2 K bias

Radial wind velocity, 24 Oct 1999: lidar Doppler lidar 09 UTC MM5 (00 UTC run) ME RMSE 15Z09ZTime abs(radial velocity) 00 UTC run – lidar 15 UTC Doppler lidar MM5 (00 UTC run)

Inversion upstream of the pass, 09 UTC 24 Oct 1999:  upstream inversion 1 km too low early in the event (~09 UTC)  southerly flow too shallow MM5 (00 UTC run): domain 4

Conclusions: The model captured several striking features: foehn break-through in the Inn Valley magnitude of surface wind speed at several weather stations regions of strong descent jump-like features related to deep amplified gravity waves Discrepancies were found between simulations and observations: overestimation of the mass flux through lower Brenner gap (+50%) underestimation of the descent of potentially warm air through upper gap bias of surface pot. temperature in the northern Wipp Valley (-2 K) wrong inversion height upstream of the pass early in the event

ECMWF analysis 12 UTC 24 Oct 1999: 500 hPa geopot. height: Sea level pressure: L H

MM5 flow structure, 15 UTC 24 Oct 1999, 00 UTC run: surface wind speed: wind speed & pot. temperature: BrennerInnsbruck

Pressure gradient, 24 Oct 1999: as function of time as function of wind speed

Doppler lidar rad. vel. 09 UTC Radial wind velocity, 24 Oct 1999: 15 UTC lidar MM5 (00 UTC run) rad.vel. MM5 (00 UTC run)  + wspd ME RMSE 15Z09ZTime abs(radial velocity) 00 UTC run – lidar