mistralanditssiblingsinrcms - goethe university frankfurt · 2014-07-01 ·...
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Mistral and its Siblings in RCMsANIKA OBERMANN, BODO AHRENS
IAU, Goethe University Frankfurt
Presented at COSMO/CLM/ART User Seminar 2014 in Offenbach
DAILY MEAN WIND SPEED DATA
• Buoy data daily mean wind speed from hourly measurementsat Côte d’Azur and Gulf of Lion [1].
• QuikSCAT gridded 0.25◦ scatterometer data of wind speedover sea (measurements ≈ 6 a.m and 6 p.m. local time) [2] fittedto buoy measurements at Gulf of Lion [3].
• SAFRAN gridded daily mean wind speed over France usingoptimal interpolation method [4].
• ERA-Interim daily mean windspeed [5].
MODELS
ERA-Interim driven runs on Med-CORDEX domain:
• COSMO-CLM [6] with 0.44◦ and 0.088◦ resolution.• ALADIN-climate [7] with 0.44◦ and 0.11◦ resolution.
ESTIMATING FETCHDistance the wind travelled overwater before reaching grid cellestimated on QuikSCAT grid:
1. Distance to coastal cells ineach direction (black cir-cles).
2. Line of Sight: Shading offar away cells by closercells (red line).
3. Avaraging due to uncer-tainties in wind direction:Fetch in φ ± 90◦ intervalweighted with a cos2 func-tion (blue line).
Fetch at Gulf of Lion buoy.
MISTRAL & SIBLINGS
• Mistral: Regional cold anddry north to northwest-erly wind following thelower Rhône Valley. Itcauses deep water forma-tion in the MediterraneanSea. Therefore it is im-portant for modeling of thecirculation in the Mediter-ranean Sea.
• Tramontane: In valley be-tween Pyrenees and MassifCentral.
• Cierzo: Along Ebro Valleysouth of Pyrenees.
Terrain height (m) of COSMO-CLM0.088◦ Med-CORDEX run. Circles:buoys, triangles: surface stations.
WIND TIME SERIESGusts ≥ 16m
s and gust directionat 13 stations in France [8].
• Mistral (≈ 19%): At leastone station in the valley,one at its exit, and oneclose to sea show gusts.
• Tramontane (≈ 43%): Atleast one inland stationand one station close to seashow gusts.
FETCH DEPENDENCE OF ERRORS
Fetch (0.25◦ pixels) on 09.02.2000.
Mistral Days Tramontane Days Other Days
Rel
.Bia
sR
MSE
Red: COSMO-CLM 0.44◦, orange: COSMO-CLM 0.088◦, blue: ALADIN0.44◦, light blue: ALADIN 0.11◦, yellow: ERA-Interim.
Relative bias and RMSE 2000-2008 in Mistral and Tramontanearea (black square).
• Negative relative bias de-creases with increasingfetch (except for COSMO-CLM 0.088◦).
• RMSE decreases with in-creasing fetch and shows adrop at about 12 pixels onwindy days.
WIND SPEED
Mean wind speed 2000-2008 fol-lowing Mistral and Tramontanetracks (black lines in right fig-ure).
• Rhône Valley (blue ar-rows): Increase in windspeed during Mistral days.
• Coast (black arrows): Lo-cation, shape and amountof wind speed gain in mod-els differ from observationsfor Mistral and Tramon-tane days.
Observed wind speed (m/s) on09.02.2000.
Mistral Days Tramontane Days Other Days
Mis
tral
Tram
onta
ne
Black: Observations, red: COSMO-CLM 0.44◦, orange: COSMO-CLM 0.088◦,blue: ALADIN 0.44◦, light blue: ALADIN 0.11◦, yellow: ERA-Interim.
OUTLOOKModels work fine for non-windy days but underestimatewind speed in the Gulf of Lionon windy days.
• Possible modifications ofCharnock formula forhigh winds and fetch?
• Error propagation fromland to sea?
– Funneling in valley?– Deceleration at valley
exit?– Other effects?
• Effects in other winds:Bora, Cierzo, ...
REFERENCES[1] provided by S. Belamari, Meteo France
[2] Physical Oceanography DAAC (2001): SeaWinds onQuikSCAT Level 3 Daily, Gridded Ocean Wind Vectors (JPLSeaWinds Project): Guide Document
[3] P. M. Ruti et Al. (2008): Comparison of analyzed and mea-sured wind speeds in the perspective of oceanic simulationsover the Mediterranean basin: Analyses, QuikSCAT andbuoy data, Journal of Marine Systems 70: 33-48
[4] J. P. Vidal et Al. (2010): A 50-Year High-Resolution Atmo-spheric Reanalysis Over France with the Safran System, INTJ CLIMATOL 30 (11): 1627-1644
[5] D. P. Dee et Al. (2011): The ERA-Interim reanalysis: config-uration and performance of the data assimilation system, QJ ROY METEOR SOC 137 (656): 553-597, April 2011 Part A
[6] G. Doms et Al. (2011): A Description of the NonhydrostaticRegional COSMO Model, Part II: Physical Parameterization
[7] M. Herrmann et Al. (2011): Representation of daily windspeed spatial and temporal variability and intense windevents over the Mediterranean Sea using dynamical down-scaling: impact of the regional climate model configuration,Nat. Hazards Earth Syst. Sci. 11: 1983-2001
[8] V. Jacq (2011): personal communication