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The added value of scatterometer ocean surface wind for the limited area model HARMONIE

Explore the additional value of scatterometer ocean wind data for storm forecasting in extreme weather events. Learn the benefits of assimilating scatterometer winds into the HARMONIE model and its impact on improving forecast accuracy.

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The added value of scatterometer ocean surface wind for the limited area model HARMONIE

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  1. The added value of scatterometer ocean surface wind for the limited area model HARMONIE in extreme weather events Gert-Jan Marseille KNMI – The Netherlands Gert-Jan.Marseille@knmi.nl

  2. 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).

  3. Satellite Scatterometers • Ocean surface wind speed and direction • global coverage • Increasing spatial and temporal resolution ASCAT www.knmi.nl/scatterometer • In this study we use: • ASCAT (METOP-A) • QuikSCAT • Oceansat-2

  4. Harmonie model(Hirlam ALADIN Research on Meso-scale Operational NWP in Euromed) • 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

  5. 20:22 18:52 18:52 20:22 Scatterometer assimilation in Harmonie • Works technically! • First experiments in Harmonie using ASCAT and QuikSCAT AN: 18UTC QuikSCAT 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 TEMP, AIREP, SYNOP, ASCAT, SCAT locations

  6. 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-m analysis increment

  7. 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? • NoDA: No data assimilation • Conv: Assimilation of conventional observations (TEMP/Aircraft/SYNOP) only • Conv + ASCAT/QSCAT (default settings) • Conv + ASCAT – no thinning

  8. 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

  9. 12 11 10 9 8 7 6 5 4 3 2 1 Closure Maeslantkering ECMWF no assim surface wind speed AN: 2007110900 FC+6 VT: 2007110906 ECMWF underestimates wind over North Sea verifying qscat assim: conv + ascat + qscat

  10. 12 11 10 9 8 7 6 5 4 3 2 1 Closure Maeslantkering … zooming in to The Netherlands ECMWF no assim surface wind speed AN: 2007110900 FC+6 VT: 2007110906 Note the maximum wind speed in South-West Netherlands for conv+scat experiment verifying qscat conv + ascat + qscat

  11. No assim Conv Conv+ascat+qscat Conv+ascat – no thinn ECMWF Forecast verification using aircraft observations 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)

  12. 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.

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