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


The scientific objective: 2003

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


Wipp Valley 2003

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


  •  AML top heights & 2003isentropes 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:


Alpine crest line 2003

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


too strong winds 2003

Wind speed, 24 Oct 1999:


-2 K bias 2003

Potential temperature, 24 Oct 1999:


09 UTC 2003

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:


MM5 (00 UTC run): domain 4

Inversion upstream

of the pass,

09 UTC 24 Oct 1999:


  • Conclusions: 2003

  • 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


L 2003

Sea level pressure:

H

ECMWF analysis

12 UTC 24 Oct 1999:

500 hPa geopot. height:


wind speed & 2003

pot. temperature:

Brenner

Innsbruck

MM5 flow structure,

15 UTC 24 Oct 1999,

00 UTC run:

surface wind speed:


as function of time 2003

as function of wind speed

Pressure gradient, 24 Oct 1999:


09 UTC 2003

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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