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Quality Assessment of a 1985-2007 Mediterranean Sea Reanalysis

This study evaluates the quality of a Mediterranean Sea reanalysis spanning 1985-2007 using assimilation schemes, atmospheric and hydrological forcings, and observational data. Results show insights into ocean circulation, variability, and water mass formation, highlighting the importance of reanalysis datasets.

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Quality Assessment of a 1985-2007 Mediterranean Sea Reanalysis

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  1. Quality Assessment of a 1985-2007 Mediterranean Sea Reanalysis M. Adani, G. Coppini, C.Fratianni, P.Oddo, M.Tonani, GNOO, INGV Sez Bologna N. Pinardi, M. Zavatarelli, Univ. of Bologna V. Lyubartsev, S. Dobricic, CMCC, Bologna

  2. Assimilation schemes: • OceanVar (Dobricic, S., and N., Pinardi, 2007) • SOFA (De Mey, P., and M. Benkiran, 2002) Experimental set-up Atmospheric and hydrological forcing: ➔ ECMWF operational analysis + ERA15 ➔ Monthly mean climatological NCEP precipitation ➔ Monthly mean climatological river runoff (GRDC) Daily Mean output: • Temperature • Salinity • Velocities • Wind Stress • Sea Surface Height • Heat Flux • Water Flux • Shortwave Radiation Ocean General Circulation Model: OPA code (Tonani et al., 2008) 1/16 x 1/16 and 71 unevenly spaced levels Assimilation schemes: RELAXATION Observations: • T/S in situ profiles (MedAtlas, MFS) • SLA along track (T/P,ERS1,ERS2, ENVISAT,J1) Observations: • OI-SST

  3. Experimental set-up cont. Examples of spatial distribution of in situ and satellite observations in one day. Data Distribution

  4. Experimental set-up cont. • Multivariate part of the error background covariance matrix (B) is common to both assimilation schemeand the observational error matrix (R) is identical. • Major difference between the two implementations is that OceanVar uses a barotropic model to estimates the corrections on SLA and SOFA uses formula of level of no-motion. In the latter case the SLA data can be assimilated only in area deeper then 1000 meters resulting in 12% less satellite observations assimilated for SO-RE.

  5. Results • Mediterranean Volume Temperature • Gibraltar advective/diffusive part • Solar radiation • Relaxation term relaxation data assimilation

  6. Results cont. TEMPERATURE SALINITY RMSE BIAS

  7. Results cont. SLA RMSE

  8. Large scale low frequency ocean variability

  9. Mean circulation at 15 m

  10. Mean circulation in the 200-300m Eddy driven areas Pathway of the LIW ‘barotropic flow’ The interpretation

  11. 1987-1996 1997-2006 Decadal variability Ionian reversal Strengthening of the Levantine circulation

  12. The mean vs Eddy Kinetic Energy (EKE) 0-150 m: 0,07 m s-1 0-bot: 0,03 m s-1 EKE is 70-90%of TKE

  13. Water mass formation rates: results WMDW EMDW • Four major events: • 1987 for WMDW • 2) 1992-1993 for LIW, CDW and EMDW • 3) 1999-2000 for WMDW and EMDW • 4) 2005-2006 WMDW, EMDW and LIW CDW LIW Eastern Med Transient Sv

  14. Conclusions • Two re-analysis and a simulation has been carried out for the Mediterranean Sea from 1985 to 2007 . • All available in situ and satellite information for the past 23 years have been used with two assimilation schemes, a Reduced Order Optimal Interpolation scheme, so-called SOFA, and a three-dimensional variational scheme, so-called OceanVar. • OV-RE gives better results for abundant data such as SLA, improving by about 10% the RMSE with respect to SO-RE, but giving the same RMSE of SO-RE for sparse data sets, such as temperature and salinity profiles. • Reanalysis is a useful dataset to study the low frequency variability of the ocean References: M. Adani, S. Dobricic, N. Pinardi, 2011: Quality Assessment of a 1985–2007 Mediterranean Sea Reanalysis. J. Atmos. Oceanic Technol., 28, 569–589. doi: 10.1175/2010JTECHO798.1 N. Pinardi, M. Adani, G. Coppini, C. Fratianni, P. Oddo, M. Tonani, V. Lyubartsev, S. Dobricic, M. Zavatarelli.. The Mediterranean Sea large scale low frequency ocean variability from 1987 to 2007: a retrospective analysis., in preparation.

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