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MAP IOP 10 South Foehn Event in the Wipp Valley: Verification of High-Resolution Numerical

ICAM/MAP 2003 Brig, Switzerland, May 19 to 23, 2003. 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.

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MAP IOP 10 South Foehn Event in the Wipp Valley: Verification of High-Resolution Numerical

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  1. ICAM/MAP 2003 Brig, Switzerland, May 19 to 23, 2003 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 Gohm, A., G. Zängl, G. J. Mayr, 2003, submitted to Mon. Wea. Rev.

  2. The scientific objective: To assess to what extent the temporal evolution and spatial structure of small-scale orographic flows can be simulatedwith a state-of-the-art mesoscale model run in a very high-resolution mode. The phenomenon: Deep south foehn in the Wipp Valley on 24-25 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

  3. Wipp Valley Innsbruck • MM5 basic setup: • 6 domains withx = 64.8 – 0.267 km • 39 full-sigma levels • initialized with operational ECMWF analysis at 23 Oct 18 UTC and 24 Oct 00 UTC Brenner Pass

  4.  AML top heights &isentropes indicateregions of flow descentand jump-like features •  indications forunderestimation offlow descent P2 P1 SABL lidar on NCAR Electra flow MM5 00 UTC run Brenner Innsbruck Backscatter intensityversus potentialtemperature,15 UTC 24 Oct 1999:

  5. Alpine crest line upper gap lower gap ZAMG PA2 sodar MM5 00 UTC run, D6 Wind profile at Brenner Pass, 24 Oct 1999: •  simulated windspeed 15 % too high •  lower gap area30% too large in D6 • simulated massflux 50% too high • 00 (18) UTC run: RMSE = 5.6 (6.2) m/sME = +1.5 (+1.6) m/s

  6. too strong winds Wind speed, 24 Oct 1999:

  7. -2 K bias Potential temperature, 24 Oct 1999:

  8. 09 UTC 15 UTC lidar Doppler lidar Doppler lidar abs(radial velocity) 00 UTC run – lidar MM5 (00 UTC run) MM5 (00 UTC run) Time 09Z 15Z RMSE 6.9 5.3 ME -3.1 -1.6 Radial windvelocity,24 Oct 1999:

  9.  upstream inversion1 km too low early inthe event (~09 UTC) •  southerly flow tooshallow MM5 (00 UTC run): domain 4 Inversion upstream of the pass, 09 UTC 24 Oct 1999:

  10. 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

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

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

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

  14. 09 UTC 15 UTC Doppler lidar rad. vel. lidar MM5 (00 UTC run) rad.vel. abs(radial velocity) 00 UTC run – lidar Time 09Z 15Z RMSE 6.9 5.3 ME -3.1 -1.6 MM5 (00 UTC run)  + wspd Radial windvelocity,24 Oct 1999:

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