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. Data set 1data set 2data set 3data set 4 May 3 at 6:00may 3 at 12:00may 4 at 0:00may 8 at 12:00 3. Case studies ASAR-ENVISAT wave spectra 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 Assi spectrum cut-off 0.1 Hz Without assim -0.1020.2920.277 0.0370.2430.245 -0.3690.6480.539 Statistic analysis for low frequency wave height Hs>10s(set 1) Date : may 3 at 6:00

8. Statistic analysis for low frequency wave height Hs>10s(set 2) Date : may 3 at 12:00 Assi total spectrum Assi spectrum cut-off 0.1 Hz Without assim -0.0570.4750.475 -0.0920.3410.329 -0.4610.6880.513 Bias(m) RMS(m) STD(m)

9. Statistic analysis for low frequency wave height Hs>10s (set 3) Date : may 4 at 0:00 Assi total spectrum Assi spectrum cut-off 0.1 Hz Without assim 0.0100.5920.596 -0.0770.3490.342 -0.4380.70.548 Bias(m) RMS(m) STD(m)

10. Bias (m)RMS (m) ERS2alti-asar-level21.181.35 ERS2alti-wam0.280.89 ERS2alti-assi-cutoff0.470.87 Results on significant Wave height may 3 at 6:00 Comparison to ERS2 Altimeter significant wave height

11. Bias (m)RMS (m) Ers2alti-asar-level20.581.24 Ers2alti-wam-0.751.37 Ers2alti-assi-cutoff-0.421.25 Results on significant Wave height may 3 at 12:00 Comparison to ERS2 Altimeter significant wave height

12. Bias (m)RMS (m) Ers2alti-asar-level20.620.73 Ers2alti-wam-0.660.68 Ers2alti-assi-cutoff-0.520.55 Results on significant Wave height may 4 at 0:00 Comparison to ERS2 Altimeter significant wave height

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

14. Assimilation index : (%) SWH 53 mean period 41.6 mean direction 51.3 RMS with assiwithout assi SWH (m) 0.385 0.817 Period (s) 1.562.6 Direction(deg) 32.7 49.4 Assimilation impact on SWH may 8 at 12:00

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)