An unusual Saharan dust outbreak into central Europe and heavy
precipitation at the southern side of the Alps in May 2008:A TIGGE case study
Lars Wiegand1,2, Arwen Twitchett2, Conny Schwierz3 & Peter Knippertz2
Third THORPEX International Science Symposium, Monterey: 14-18 Sept. 2009
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Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Outline
Motivation
Upper-Level Development RMSE/SPREAD
analysis errors
position of forecasted streamers
High Impact Weather Saharan dust storm
heavy precipitation in Southern Switzerland
Conclusions
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Motivation
2008/05/27 10UTC 2008/05/27 13UTC
article in newspaper „Süddeutsche“ 2008/05/29: „Die Sahara über Deutschland“
Gornergletscher 08/2008, dust from 05/2008
albedo increase ablation increase mass balance decrease
Motivation
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Motivation
widespread heavy precipitation caused: flooding on the Alpine south side of Switzerland and Italy
Lake Maggiore rised by 10 cm in just 24 hours
Motivation
4-day sumof precipitation
(26th – 29th of May 2008)
mm
data: ENSEMBLE (gridded data set from rain gauges)
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Analysis End of May 2008 (21st-26th)
Upper-Level Development
upper level PV
operational analysis ECMWF
region of interest (29-55N, 15W-2E)
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
RMSE of all models (Box: 29-55N, 15W-2E)
ECMWF_europe
BoM_australia
CMA_china
CMC_canada
CPTEC_brazil
JMA_japan
KMA_korea
NCEP_usa
UKMO_uk
RMSE calculated with Analysis from ECMWF
RMSE calculated with every Centers own Analysis
Upper-Level Development
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
0,22
(USA,
Interpolation)
0,44
(Korea,
3Dvar)
0,59
(China,
Interpolation)
0,23
(Brazil,
USA Interpolation)
0,26
(Japan,
4Dvar)
0,41
(Australia,
Interpolation)
0,23
(UK,
4Dvar)
0,25
(Canada,
4Dvar)
RMSE in box
-0.5 1.0 1.5-1.0-1.5 0.5
Upper-Level Development
(4Dvar)
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
“non-dispersive”
CMA_china
CMC_canada
ECMWF_europe
JMA_japan
RMSE & SPREAD
RMSE
SPREAD
(slightly) overdispersiveunderdispersive
BoM_australia
CPTEC_brazil
NCEP_usa
UKMO_uk
KMA_korea
Upper-Level Development
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Position of Streamer (center of mass)
Upper-Level Development
48h forecast
position of ECMWF analysis
envelope of member positions
ECMWF_europeBoM_australiaCMA_chinaCMC_canadaCPTEC_brazilJMA_japanKMA_koreaNCEP_usaUKMO_uk
96h forecast120h forecast168h forecast
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Saharan dust outbreak RGB composite: purple color = dust from 2008/05/26: 09UTC – 23UTC
needed for dust mobilization: u925hPa > 10 m/s
High Impact Weather
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Region of interest (5W-10E & 23N-35N)
number of grid points in box: 208
number of gp, wind > 10m/s: 113
High Impact Weather
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Grid points where wind > 10m/s
ECMWF_europe
BoM_australia
CMA_china
CMC_canada
CPTEC_brazil
JMA_japan
KMA_korea
NCEP_usa
UKMO_uk
High Impact Weather
median of centres forecasts
ECMWF analysis
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Precipitation forecast (box average)
High Impact Weather
ECMWF_europeBoM_australiaCMA_chinaCMC_canadaCPTEC_brazilJMA_japanKMA_koreaNCEP_usaUKMO_uk
median of centres forecasts
observed precipitation
(ENSEMBLE data set)
Third THORPEX International Science Symposium, Monterey: 14-18 September 2009
Motivation Upper-Level Development High Impact Weather Conclusion
Conclusions
Open question: which analysis is the “best” one to use? RMSE smaller with own analysis
Upper-level development increase of RMSE with lead time
SPREAD of similar magnitude as RMSE in 4 models, 4 models are
underdispersive and 1 model is slightly overdispersive
forecasted positions of streamers are mostly too far north
Wind for dust mobilization over Sahara winds systematically too weak
Precipitation at southern side of Alps systematically too high in medium-range
mostly too low in short-range
Conclusion
