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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. - PowerPoint PPT Presentation
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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 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
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
Wipp Valley Innsbruck
Brenner Pass
Backscatter intensityversus potentialtemperature,15 UTC 24 Oct 1999:
P1
P2
MM5 00 UTC run
AML top heights &isentropes indicateregions of flow descentand jump-like features
indications forunderestimation offlow 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 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
Alpine crest line
lower gap
upper gap
Wind speed, 24 Oct 1999:
too strong winds
Potential temperature, 24 Oct 1999:
-2 K bias
Radial windvelocity,24 Oct 1999:
lidar Doppler lidar
09 UTC
MM5 (00 UTC run)
-1.6-3.1ME
5.36.9RMSE
15Z09ZTime
abs(radial velocity)00 UTC run – lidar
15 UTC
Doppler lidar
MM5 (00 UTC run)
Inversion upstreamof the pass,09 UTC 24 Oct 1999:
upstream inversion1 km too low early inthe event (~09 UTC)
southerly flow tooshallow
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 analysis12 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:
Brenner Innsbruck
Pressure gradient, 24 Oct 1999:
as function of time
as function of wind speed
Doppler lidar rad. vel.
09 UTCRadial windvelocity,24 Oct 1999:
15 UTC
lidar
MM5 (00 UTC run) rad.vel.
MM5 (00 UTC run) + wspd-1.6-3.1ME
5.36.9RMSE
15Z09ZTime
abs(radial velocity)00 UTC run – lidar