Global Ocean Freshwater Flux Components from Satellite, Re-analysis and In-Situ Climatologies

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1 Global Ocean Freshwater Flux Components from Satellite, Re-analysis and In-Situ Climatologies Axel Andersson1, Christian Klepp2, Stephan Bakan1, Karsten Fennig3, Jörg Schulz4 1 Max-Planck-Institut für Meteorologie, Hamburg 2 Universität Hamburg, KlimaCampus, Hamburg 3 Deutscher Wetterdienst, CM-SAF, Offenbach 4 EUMETSAT, Darmstadt 5th IPWG Workshop, Hamburg, October 2010

2 Global Water Cycle The knowledge of the global water cycle is crucial for successful understanding and modeling of the climate system An important component of the water cycle is the surface fresh water flux over global oceans and its components evaporation and precipitation significant energy transport in form of latent heat Over global oceans, the total precipitation is smaller than the total evaporation and the difference should be balanced mainly by continental runoff. To which extent do modern data sets reproduce the basic features of global ocean freshwater flux components?

3 Global Water Cycle Current evaporation & precipitation satellite time series cover about 20 years Combination of evaporation & precipitation data sets is possible to assess global energy and water cycle HOAPS: evaporation and precipitation available from common source (SSM/I) Currently restricted to ocean only, since no long term global satellite based data sets for evapotranspiration over land exist Current satellite precipitation/evaporation data sets are compared with model (reanalysis) and ship based data Big Picture evaluation on the climatological & global scale

4 Satellite Derived E and P Precipitation (P): Mostly based on passive microwave (PMW) Radar, IR/VIS (blended with PMW) Evaporation (E): Bulk formula: E = (ρa/ρw) CE U (qs qa) Wind speed (U) (PMW, scatterometer) Near surface specific humidity (qa) (PMW) Sea surface saturation specific humidity (qs) (SST, Magnus formula) Latent heat transfer coefficient (CE) (Parameterization, e.g. COARE; Fairall, 2003) Freshwater Flux: E-P

5 Climate Mean Precipitation ( )

6 Climate Mean Evaporation ( )

7 Climate Mean Freshwater Flux ( )

8 Comparison of global mean time series Satellite based data sets Reanalysis data sets ECHAM climate model control run Ship observations (evaporation, NOCS)

9 model satellite Comparison of precipitation data sets

10 model satellite Comparison precip data sets - model -

11 satellite Comparison precip data sets - satellite -

12 model satellite Comparison precip data sets - zonal mean -

13 Comparison precipitation data sets A. Andersson, C. Klepp, K. Fennig, S. Bakan, H. Graßl, J. Schulz, Evaluation of HOAPS-3 ocean surface freshwater flux components, J. Appl. Met. Clim., 2010, in print

14 model satellite/ship Comparison evaporation data sets

15 ship data satellite/ship Comparison evaporation data sets model reanalysis/sat hybrid

16 model satellite Comparison evap data sets - model -

17 model satellite/ship Comparison evap data sets - satellite -

18 model satellite Comparison evap data sets - zonal mean -

19 Comparison evaporation data sets A. Andersson, C. Klepp, K. Fennig, S. Bakan, H. Graßl, J. Schulz, Evaluation of HOAPS-3 ocean surface freshwater flux components, J. Appl. Met. Clim., 2010, in print

20 Comparison freshwater flux A. Andersson, C. Klepp, K. Fennig, S. Bakan, H. Graßl, J. Schulz, Evaluation of HOAPS-3 ocean surface freshwater flux components, J. Appl. Met. Clim., 2010, in print

21 Ocean surface freshwater budget Run-off balance: River runoff long term mean: ~40.000km³/a (0.32 mm/d) HOAPS: 0.73 mm/d IFREMER/GPCC: 0.77 mm/d ERA-interim: 0.50 mm/d balance not closed, difference to runoff data within 10-15% of the global mean values of the individual evaporation and precipitation retrievals Increase in freshwater flux larger than expected increase in atmospheric storage by C-C equation (7% per C warming)

22 Application example: Response of freshwater flux parameters to NAO EVAP (E) Correlation with NAO Index RAIN (P) Freshwater Flux (E-P) A. Andersson, S. Bakan, H. Graßl, Satellite derived precipitation and freshwater flux variability and its dependence on the North Atlantic Oscillation, Tellus, 62A, 2010

23 North Atlantic Oscillation Combined HOAPS-3 (ocean) GPCC (gauge, land) data set Composite NAO+ Composite NAO- A. Andersson, S. Bakan, H. Graßl, Satellite derived precipitation and freshwater flux variability and its dependence on the North Atlantic Oscillation, Tellus, 62A, 2010

24 North Atlantic Oscillation HOAPS/GPCC Correlation with NAO Index GPCP NCEP ERAint A. Andersson, S. Bakan, H. Graßl, Satellite derived precipitation and freshwater flux variability and its dependence on the North Atlantic Oscillation, Tellus, 62A, 2010

25 Summary/Conclusions Recent data set reproduce the basic global patterns of global ocean precipitation and evaporation Long term, global satellite based data sets over land not available yet (MPI: Poster A. Löw; Landflux) Regionally large absolute differences in tropical regions Large relative differences at high latitudes Different temporal behavior among the data sets Mean ocean surface freshwater balance from satellite data nearly closed with respect to river runoff but freshwater excess beyond statistical uncertainty unrealistic temporal development Successful application of satellite data for variability studies of freshwater flux parameters HOAPS-3 data: (Posters; Fennig, Bakan, Klepp)