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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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slide1

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.

slide2

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
slide3

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

slide4

 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:

slide5

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
slide6

too strong winds

Wind speed, 24 Oct 1999:

slide7

-2 K bias

Potential temperature, 24 Oct 1999:

slide8

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:

slide9

 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:

slide10

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
slide11

L

Sea level pressure:

H

ECMWF analysis

12 UTC 24 Oct 1999:

500 hPa geopot. height:

slide12

wind speed &

pot. temperature:

Brenner

Innsbruck

MM5 flow structure,

15 UTC 24 Oct 1999,

00 UTC run:

surface wind speed:

slide13

as function of time

as function of wind speed

Pressure gradient, 24 Oct 1999:

slide14

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: