1(of 11)EMS - Reading - 10/9/2013
The added value of scatterometer ocean surface wind
for the limited area model HARMONIE in extreme weather events
Gert-Jan MarseilleKNMI – The Netherlands
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Motivation
• EU-funded MyWave project (mywave.eu)• What is the additional value of scatterometer (SCAT) ocean surface winds for
ocean wave and storm surge forecasting?– Verification– Direct assimilation of SCAT winds in wave/surge models– Indirect: model wind (with assimilated SCAT) used as input for wave/surge models
• Focus on extreme weather events– 2006/10/28 – 2006/11/03 - NW-W storm. "The storm is marked as a surge- and
SWL record in Delfzijl and well known as Allerheiligenvloed or the “Horses storm”, because 227 horses were isolated due to flood in Marrum, 25 horses drowned, the rest was saved in a spectacular rescue operation.“
– 2007/11/05 - 2007/11/11 - NW storm. "The first storm since the building of the Nieuwe Waterweg and the Maeslantkering that was closed due to the exceeding the threshold water levels in Hoek van Holland“
– 2011/07/11 – 2011/07/17 - NE storm. Not very common but interesting, one of the periods used in the assessment of the operational SWAN model for the North Sea.
– 2011/12/06 – 2012/01/06 - A 1 month period that includes Ulli (Rapid development over UK 2012-01-03 Storm Ulli).
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Satellite Scatterometers
ASCAT
www.knmi.nl/scatterometer
In this study we use:• ASCAT (METOP-A)• QuikSCAT• Oceansat-2
• Ocean surface wind speed and direction
• global coverage
• Increasing spatial and temporal resolution
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• Non-hydrostatic
• 800x800 grid
• 2.5 km grid size
• 3D-var assimilatie– 4/8 times per day
– 36-hour forecast
• ECMWF boundaries
• Available since 1/1/2012
Harmonie model(Hirlam ALADIN Research on Meso-scale Operational NWP in Euromed)
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Scatterometer assimilation in Harmonie
• Works technically!• First experiments in Harmonie using ASCAT and
QuikSCAT18:52
18:52
20:22
20:22
Harmonie DA default settings• 6-hour assimilation window; too large
for fast moving weather systems
• Scatterometer usage based on ECMWF SCAT usage
• ASCAT thinning: factor 4 in both directions => ~94% not used
• QSCAT: no thinning
AN: 18UTCQuikSCAT
TEMP, AIREP, SYNOP, ASCAT, SCAT locations
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Analysis increment
• Red circles: analysis increment mainly from assimilation of scatterometer
• Scatterometer corrects model winds in the order of a couple of ms-1
Model 10-m wind+
assimilated ASCAT
model 10-manalysis increment
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Learning how to use observations in Harmonie DA
• Four experiments to address questions like– What does data assimilation add to HARMONIE forecast improvement?– What is the optimal assimilation window length: 6/3/1/… hour?– What is the optimal density/weight given to observations?– Apply averaging or thinning of dense observations (Mode-S/radar
wind/SCAT/…)?– How well is quality control?
1. NoDA: No data assimilation2. Conv: Assimilation of conventional observations
(TEMP/Aircraft/SYNOP) only3. Conv + ASCAT/QSCAT (default settings)4. Conv + ASCAT – no thinning
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Case study: closure Maeslantkering
• Part of the Dutch Delta Works plan (initiated after the 1953 flooding disaster) to protect the South-Western part of the Netherlands for high sea levels
• Closed for the first time:– 9 November 2007
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surface wind speed
AN: 2007110900FC+6
VT: 2007110906
ECMWF underestimates
wind overNorth Sea
121110987
654321
no assim ECMWF
Closure Maeslantkering
verifying qscat
assim: conv + ascat + qscat
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surface wind speed
AN: 2007110900FC+6
VT: 2007110906
Note the maximumwind speed in
South-West Netherlands for
conv+scat experiment
121110987
654321
no assim
conv + ascat + qscat
ECMWF
verifying qscat
Closure Maeslantkering… zooming in to The Netherlands
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Harmonie DA• Does improve analysis• does not improve
250hPa-T forecast• does improve 850hPa-
T forecast
• does not improve 850hPa-u/v forecast
• Scat impact on model wind at 850 hPa, not at 250hPa (deviation green/blue/cyan)
Forecast verification using aircraft observations
No assimConvConv+ascat+qscatConv+ascat – no thinnECMWF
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Status and plans
• Status– Analyzing the results from the experiments– First conclusion: added value of DA in HARMONIE is a bit disappointing
based on standard bias/RMSE scores but some issues encountered:• Too large weight is given to observations• QC not strict enough; poor quality observations are still accepted for
DA
• Plans– Recommendations on how to optimally use observations in HARMONIE
(weights, thinning, averaging, quality control, …..)– Make HARMONIE ready for the assimilation of the Indian scatterometer
Oceansat-2– Run the other selected cases– Disseminate HARMONIE model fields to project partners as input for
wave/surge models.
