The ECMWF prototype for coupled reanalysis. Patrick Laloyaux

Transcription

1 The ECMWF prototype for coupled reanalysis Patrick Laloyaux ECMWF July 10, 2015

2 Outline Current status and future plans for ECMWF operational reanalyses Extended climate reanalyses Coupled atmosphere-ocean reanalysis

3 Current status and future plans for ECMWF operational reanalyses Atmospheric and ocean reanalyses are produced separately Current atmospheric reanalysis: ERA-Interim Period: 1979 to present Analysis: atmosphere, land surface and ocean waves Model: IFS model (2006 version) Resolution: 80 km with 60 vertical levels Boundary conditions: SST and SIC IFS relies on external estimates (currently prescribed to OSTIA analysis product) Surface air temperature anomaly for 2010 for ERA-Interim and CRUTEM4 relative to

4 Current status and future plans for ECMWF operational reanalyses Atmospheric and ocean reanalyses are produced separately Next atmospheric reanalysis: ERA-5 Period: 1979 to present Analysis: atmosphere, land surface and ocean waves Model: IFS model (2015 version) Resolution: 32 km with 137 vertical levels Large effort devoted to the acquisition of new observational datasets the reprocessing of observational datasets used in operations

5 Current status and future plans for ECMWF operational reanalyses Atmospheric and ocean reanalyses are produced separately Current ocean reanalysis: ORAS4 Period: 1957 to present Analysis: ocean Model: NEMO model (V3.0) Resolution: ORCA1 with 42 vertical levels Boundary conditions: SST and SIC no prognostic sea-ice model, SIC is prescribed no SST observational data, a strong relaxation is applied 12-m running mean for SST anomaly in Eastern Pacific ( climate)

6 Current status and future plans for ECMWF operational reanalyses Atmospheric and ocean reanalyses are produced separately Next ocean reanalysis: ORAS5 Period: 1975 to present Analysis: ocean and sea-ice Model: NEMO model (V3.4) and LIM2 model Resolution: ORCA025 with 75 vertical levels Boundary condition: SST and SIC Assimilation of SIC measurements no SST observational data, a strong relaxation is applied

7 Extended climate reanalyses Focus on consistency and low-frequency climate variability (~ years) ECMWF atmospheric 20 th century reanalysis: ERA-20C Assimilate surface pressure and ocean surface winds from conventional instruments Safe approach to avoid the introduction of biases due to changes in the observing system 12-m running mean for precipitation anomaly averaged over Europe ( climate) ERA-20C represents well the inter-annual fluctuations for the whole century, especially from 1945 onwards

8 Coupled atmosphere-ocean assimilation ECMWF develops a coupled earth model for the Ensemble Prediction System (ENS) atmosphere IFS wave WAM land CHTESSEL ocean NEMO sea-ice LIM2 CERA is an assimilation system for the ECMWF coupled earth model assimilate simultaneously observations in atmosphere and ocean components based on an incremental variational approach with a common 24-hour window CERA-20C is a coupled 20th century reanalysis based on the CERA system Low-resolution model: 120km and ORCA1 A subset of observations: surface pressure and winds (ICOADS/ISPD) temperature and salinity (EN4) sea surface temperature (monthly HADISST2)

9 Positive impact of the coupled assimilation - Tropics Uncoupled and coupled assimilation systems compared for September 2010 over Tropics Negative values means that background temperature RMSE is smaller in the coupled assimilation system (with respect to conventional observations) Coupled assimilation produces estimates closer to near-surface observations

10 Positive impact of the coupled assimilation - cyclone Phailin Argo probe with high frequency measurements Ocean temperature analysis at 40-meter depth Uncoupled assimilation Coupled assimilation Coupled analysis has a stronger cold wake (closer to observations) October 29, 2014

11 Conclusions Replacement of the current ocean and atmospheric operational reanalyses at ECMWF is ongoing A coupled atmosphere-ocean assimilation system (CERA) has been developed: preliminary results are promising the production of a coupled 20 th century reanalysis will start this summer Works started on: sea-ice thickness validation using SMOS data investigation of SMOS assimilation with LIM3 model