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Improved Water Vapour and Wind Initialisation for Precipitation Forecasts: Impact Studies with the ECMWF IFS. Martin Weissmann, Andreas Dörnbrack, Gerhard Ehret, Christoph Kiemle, Stephan Rahm, Oliver Reitebuch Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany - PowerPoint PPT Presentation
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Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Improved Water Vapour and Wind Initialisation for Precipitation Forecasts: Impact Studies with the ECMWF IFS
Martin Weissmann, Andreas Dörnbrack, Gerhard Ehret, Christoph Kiemle, Stephan Rahm, Oliver Reitebuch
Institut für Physik der Atmosphäre, DLR Oberpfaffenhofen, Germany
Carla Cardinali, Elias HolmEuropean Centre for Medium-Range Weather Forecasts (ECMWF), Reading, UK
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Motivation
above oceans:hardly any radiosondesaircraft at cruise level height errors of AMVslow accuracy of passive instruments low vertical and horizontal resolution
lidars can measure various atmospheric quantities in remoteregions with high accuracy and highresolution either from satellites or aircraft
goal: estimate benefit with impact studies
AMSU-A:50-55 GHz
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
DLR lidar instruments
Doppler lidardropsondes,u, v, t, rh, p
scanning coherent 2 µm Doppler lidarconical scans with 24 azimuth positions vertical profile of 3-D wind vectorhoriz. resolution 5 - 40 kmvert. resolution 100 m
Differential Absorption Lidar (DIAL) nadir or zenith pointingprofile of water vapour molecule numberhoriz. resolution: 2 - 40 kmvert. resolution: 500 - 2000 m
DIAL lidar
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
4 flights in "sensitive areas" (targeting)1 flight for Greenland Tip Jet1 flight for intercomparison ASAR and lidar2 transfer flights=======================================8 flights, 1600 wind profiles, 40 000 lidar measurements, 49 dropsondes
Wind data - Atlantic THORPEX Regional Campaign (A-TReC)
5 million operational measurements used per daylidar = 0.005% additional measurements
DLR Falcon:14 - 28 Nov. 2003
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Iceland
Ireland
ECMWF sensitivity plot and 500 hPa
http://www.sat.dundee.ac.uk/
Observations on 25 November 2003
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Dropsonde(2000 times enlarged)
Error lidar1-1.5 m/s
Error drops/raso2-3 m/s
Instrumental and representativeness errors
Error AMV2-5 m/s
Background departures:(Std(bg-dep))2 = (Stdobs)2 + (Stdbg)2
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
observation influence (Cardinali et al. 2004):0 --> no influence of observations1 --> no influence of backgroundmean global observation influence = 0.15
Observation influence (22 November 2003)
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
(gpd
m)
Reduction of forecast error at 500 hPa - 72 h
area: 17 x 10-6 km2
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Mean reduction over Europe, averaged over 29 forecasts (~2 weeks)black: experiments with lidar, gray: experiment with 100 dropsondes
Reduction of forecast error - 500 hPa
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Reduction of forecast error of 500 hPa geopotential height:Lidar 72 h: ~ 1 m (3.5%)
Simmons and Hollingsworth 2002:72 h: 10 m in 10 years
Comparison to mean reduction of NWP error
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Reduction of forecast error - 48, 72, 96 h
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Reduction of u, v, z, rh, and t forecast errors
Relative reduction of RH forecast error - 48, 72, 96 h
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
NOAA
DLR
20031115 at 18 Step42 20031120 at 18 Step54
20031122 at 18 Step66 20031125 at 18 Step30
Cut off low; heavy precipitation in SE-Spain
Heavy rain/strong wind in Portugaland NW-Spain
Strong winds –northwest Europe Heavy rain, Scotland and Norway
A-TReC targeting campaigns
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
The influence of targeted observations
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
Airep Lidar Temp Drop
ATReC 200112018
Contribution to FCE Obs Rel Num
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
Airep Lidar Temp Drop
ATReC 2003112218
Contribution to FCE ObsRel Num
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
Airep Lidar Temp Drop
ATRec 2003112518
Contribution to FCE Obs Rel Num
-1.2
-0.8
-0.4
0
0.4
0.8
1.2
1.6
Airep Lidar Temp Drop
ATReC 2003111518
Contribution to FCE Obs Rel Num
+
+ statistical problem --> larger sample63 - 90% of total impact outside of verification area --> larger areasimproved sensitivity predictionsbetter structure functionspractical restrictions --> better planning
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
DIAL lidar water vapour observations
Transfer flights to 4 field campaigns during 2002 - 2005
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Impact of lidar H2O-observations (preliminary)
Longitude
La
titu
de
60 W 20 E20 W
Reduction of TCWV first guess error (lidar - control)
WV
mixing ratio [m
g/kg]
Kick-Off-Treffen SPP, Bonn 23-24 October 2006
Conclusions
first assimilation of "real" Doppler lidar measurements in global NWP model lidar measurements have a smaller error than all other operational wind observations --> high analysis influence and information content
lidar wind measurements reduce the average forecast error of u, v, z, rh, and t over Europeaverage reduction of the 48 - 96h forecast error over Europe ~3%
limitations of targeted observations:need for more cases, larger verification area, systematic decisions, better structure functions...
ongoing water vapour studies
emphasizes the potential of airborne and spaceborne lidars (ADM-Aeolus, possible future water vapour DIAL satellite)
future campaigns: COPS 2007, IPY 2008, T-PARC 2008
www.pa.op.dlr.de/na-trec/