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Preliminary results of assimilation of ASAR wave spectra level 2b products in WAM

Preliminary results of assimilation of ASAR wave spectra level 2b products in WAM. L. Aouf (1) , J.M. Lefevre (1) and D. Hauser (2) (1) Meteo France; (2) CETP/CNRS. 1. Introduction. Assimilation of directional spectra in wave model in Meteo France. Better estimate of the wave parameters

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Preliminary results of assimilation of ASAR wave spectra level 2b products in WAM

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  1. Preliminary results of assimilation of ASAR wave spectra level 2b products in WAM L. Aouf (1), J.M. Lefevre (1) and D. Hauser (2) (1) Meteo France; (2) CETP/CNRS 1. Introduction Assimilation of directional spectra in wave model in Meteo France Better estimate of the wave parameters (Synthetic directional spectra) 2. Description of the assimilation scheme Partitioning of the wave spectrum (first guess and observed) Cross-assignement between equivalent wave systems (fg and obs) Optimal interpolation for the selected partitions Reconstitution of the analysed wave spectrum

  2. 3. Case studies ASAR-ENVISAT wave spectra Data set 1 data set 2 data set 3 data set 4 May 3 at 6:00 may 3 at 12:00 may 4 at 0:00 may 8 at 12:00 Wave model WAM (global scale 1x1 degrees) Discretization 24 frequency (0.044-0.22 Hz) and 36 directions 4. Limitation for the observed ASAR wave spectrum Two versions of the assimilation scheme : 1- all wave spectrum 2- limited wave spectrum (cut-off fc=0.1 Hz)

  3. Comparison between wave spectra: Without limitation in the scheme (may 3 at 6:00) Long=282 deg; lat=-26 deg

  4. Comparison between wave spectra: Without limitation in the scheme (f=0.1 Hz) Long=282 deg;lat=-26 deg

  5. Comparison between wave spectra: Without limitation in the scheme Long=278 deg; lat=-11 deg

  6. Comparison between wave spectra: Without limitation in the scheme (f=0.1 Hz) Long=278 deg; lat=-11 deg

  7. Bias(m) RMS(m) STD(m) Assi total spectrum -0.102 0.292 0.277 0.037 0.243 0.245 -0.369 0.648 0.539 Assi spectrum cut-off 0.1 Hz Statistic analysis for low frequency wave height Hs>10s(set 1) Date : may 3 at 6:00 Without assim

  8. Bias(m) RMS(m) STD(m) -0.057 0.475 0.475 -0.092 0.341 0.329 -0.461 0.688 0.513 Assi total spectrum Assi spectrum cut-off 0.1 Hz Statistic analysis for low frequency wave height Hs>10s(set 2) Date : may 3 at 12:00 Without assim

  9. Bias(m) RMS(m) STD(m) Assi total spectrum 0.010 0.592 0.596 -0.077 0.349 0.342 -0.438 0.7 0.548 Assi spectrum cut-off 0.1 Hz Statistic analysis for low frequency wave height Hs>10s (set 3) Date : may 4 at 0:00 Without assim

  10. Comparison to ERS2 Altimeter significant wave height Bias (m) RMS (m) ERS2alti-asar-level2 1.18 1.35 ERS2alti-wam 0.28 0.89 ERS2alti-assi-cutoff 0.47 0.87 Results on significant Wave height may 3 at 6:00

  11. Comparison to ERS2 Altimeter significant wave height Bias (m) RMS (m) Ers2alti-asar-level2 0.58 1.24 Ers2alti-wam -0.75 1.37 Ers2alti-assi-cutoff -0.42 1.25 Results on significant Wave height may 3 at 12:00

  12. Comparison to ERS2 Altimeter significant wave height Bias (m) RMS (m) Ers2alti-asar-level2 0.62 0.73 Ers2alti-wam -0.66 0.68 Ers2alti-assi-cutoff -0.52 0.55 Results on significant Wave height may 4 at 0:00

  13. Assimilation impact on SWH may 3 at 12:00 Assimilation impact on mean Frequency may 3 at 12:00

  14. Assimilation impact on SWH may 8 at 12:00 Assimilation index : (%) SWH 53 mean period 41.6 mean direction 51.3 RMS with assi without assi SWH (m) 0.385 0.817 Period (s) 1.56 2.6 Direction(deg) 32.7 49.4

  15. Assimilation mpact on mean frequency may 8 at 12:00

  16. Concluding remarks and future works Assimilation scheme in wave model is efficient and works correctly performance will be improved The limitation of the spectral information (frequency cut-off) is very important for the wave forecast otherwise the analysed wave parameters will be deteriorated Long period assimilation for validation and analyse of the Impact on the wave forecast (one week complete data, if Nick can provide us) Combined assimilation ASAR and RA2 Financial support to continue this study and to have more conclusive Interpretations (ESA, CNES)

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