12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Reanalysis and climate monitoring Lennart Bengtsson Environmental System Science Centre University of Reading, UK Thanks to ECMWF Uppala and Simmons

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Reanalysis and climate monitoring Achievements Challenges Vision

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Reanalysis Why reanalysis? Background What has been achieved Limitations

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Why reanalysis? It is required to integrate different kind of observations in a consistent way making it possible to project the observation on suitable scales of motion. Such an approach is needed for a systematic control of observational quality. Many studies require access to data in gridded form. This include diagnostic and predictive studies needed for an integrated assessment of observational data.

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Examples of re-analyses FGGE-1 ( ECMWF and GFDL) 1979 ERA-15 (ECMWF) 1990 ERA-40 (ECMWF) 2001 NCAR/NCEP- ( US Org.) 1988 JMA - 25 ( Japan Met Agency) 2005

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson How can we measure the value (operational and otherwise) of new observing systems? To use observations on its own is not feasible. Observational information must be assimilated by a model as information will have to be combined by other observations in time and space. Information content carried by the model based on previous data is as large or larger than the actual observations on its own. Observations must be controlled and filtered against an estimate, best provided by a dynamical projection of an ensemble of other data.

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Re-analyses applications Assessing the value of observing systems Numerical weather prediction Detection of climate change Understanding the climate system

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Survey on the use of ERA-40 from web

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Re-analyses applications Assessing the value of observing systems Numerical weather prediction Detection of climate change Understanding the climate system

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Conventional Surface Upperair Aircraft Satellite products TOVS radiances SSMI radiances AIRS radiances O3 data Bias modules NWP system Observations and observation equivalents from the model and analysis in database Quality and departure information Input observations How the observations were used in the analysis (feedback) Conventional feedback Surface Upperair Aircraft Satellite products TOVS feedback SSMI feedback AIRS feedback O3 feedback (Input and feedback observations in BUFR code)

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Comparison of reanalysis and land-station values Surface air temperature anomaly ( o C) with respect to Europe ERA-40 – CRUTEM2v Inadequate SYNOP coverage in ERA-40 Erroneous CLIMAT data in CRUTEM2v, corrected in HadCRUT3 (Brohan et al., 2006)

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson METEOSAT Reprocessed Winds

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Re-analyses applications Assessing the value of observing systems Numerical weather prediction Detection of climate change Understanding the climate system

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson The principle of error reduction in data assimilation

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Evolution of 1-Day Forecast Error, Lorenz Error Growth, and Forecast Skill for ECMWF Model (500 hPa NH Winter) * 0.91

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Improvements in NWP from Miyakoda (1972) to Courtesy ECMWF How long to get to D+10 in winter?

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson The impact of observations on forecast skill Experiments with different observing systems DJF 1990/91 using ERA40 observations The control system (using all observations) A terrestrial based system ( radio-sondes and aircraft obs.) A satellite based system ( satellites and surface pressure) A surface based system ( surface observations)

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Global forecasts DJF 90/91 7- day forecasts, every 6hr. Later ECMWF model T159/L60 Extra-tropics 20-90N and 20-90S 500 hPa Z, normalized SD for the period Tropics 20N-20S Wind vector field 850 and 250hPa

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Observing systems and predictive skill Northern Hemisphere extra-tropics Bengtsson and Hodges, 2004

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Observing systems and predictive skill Southern Hemisphere extra-tropics Bengtsson and Hodges, 2004

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Observing systems and predictive skill Tropics V 250 hPa Bengtsson and Hodges, 2004

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Ops 1980 ERA 2001 Ops 2001 Northern Hemisphere % Anomaly correlations of 500hPa height forecasts Ops 2001 Ops 1980 ERA 2001 Ops 2003 Northern Hemisphere %

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Anomaly correlations of 500hPa height forecasts Ops 1980 Ops 2003 Ops 2001 ERA 2001 % Australia/New Zealand %

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Re-analyses applications Assessing the value of observing systems Numerical weather prediction Detection of climate change Understanding the climate system

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Based on monthly CLIMAT station data (CRUTEM2v; Jones and Moberg, 2003) Based on ERA-40 reanalysis of SYNOP data (Simmons et al., 2004) Linear trend in two-metre temperature ( ) Mean over land: 0.30 O C/decade Mean over land: 0.32 O C/decade

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Based on monthly CLIMAT station data (CRUTEM2v; Jones and Moberg, 2003) Based on ERA-40 reanalysis of SYNOP data, sub-sampled to match CRUTEM2V Linear trend in two-metre temperature ( ) 0.27 O C/decade0.32 O C/decade Mean over land: 0.30 O C/decade

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson 500hPa temperature fits for two Antarctic stations ERA-40 Radiosonde

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Trend and variability in two-metre temperature CRUTEM2v (Jones and Moberg, 2003) ERA-40 Linear trend ( ): CRUTEM2v0.31 O C/decade ERA O C/decade NCEP0.19 O C/decade

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Trend and variability in lower stratospheric temperature Linear trend: MSU O C/decade ERA O C/decade NCEP O C/decade MSU-4 data analyzed by Mears et al. (2003) ERA-40 equivalent from Ben Santer

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Tropical water-vapour content

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Re-analyses applications Assessing the value of observing systems Numerical weather prediction Detection of climate change Understanding the climate system

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Global wave climatology atlas S. Caires, A. Sterl, G. Komen and V. Swail th percentile of significant wave height February m

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Hurricane Katrina August 2005 ECMWF operational analyses, 850 hPa vorticity

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Prediction of Atlantic hurricanes are influenced by ENSO Results from a general circulation model integrated over 30 years comparing active seasons from less active ECHAM5/OMERA-40 Temperature difference Measure of divergence Vertical wind shear prediction verification

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Challenges Trends in the free atmosphere The water cycle Surface fluxes between the surface and the atmosphere Extending the re-analyses back in time before upper air observations

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson ERA-40/ L60ERA-Interim/ L91 65 km 81 km

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Data-assimilation system T159L60 T255L91 New humidity analysis and improved model physics 3D-Var FGAT 12 hour 4D-Var Satellite level-1c radiances Better RTTOV and improved use of radiances especially IR Assimilation of rain affected radiances from SSM/I Adaptive bias correction Improved use of radiosondes Bias correction and homogenization based on ERA-40 Correction of SHIP/ SYNOP surface pressure biases Use of reprocessed Meteosat winds New set of Altimeter wave height data 1991 ERA ERA-Interim 1989 to continue as CDAS

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Much improved 500hPa height forecasts Day Southern hemisphere Anomaly correlation of 500hPa height, averaged for 12UTC forecasts from 1 January to 31 December 1989 ERA-new ERA-40 Operations Northern hemisphere

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Much improved tropical 850hPa wind forecasts Day vs radiosondes RMS error of vector wind, averaged for 12UTC forecasts from 1 January to 31 December 1989 vs analyses ERA-new ERA-40 Operations

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Global precipitation-evaporation 1989 (+12h forecast) ERA-Interim (test)= 0.01 ERA-40= 0.23 ERA year Climate= 0.32

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Reanalysis does have a role to play in the study of recent climate trends It can help in the detection and correction of problems in the instrumental record ERA-40 represents a clear step forward for the depiction of trends Insights into deficiencies are provided by analysis and background fits to observations, analysis increments and comparisons with simulations and other reanalyses There is considerable potential for improvement of reanalysis – more so than for improvement of the database of past observations? In summary

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson The passage of time –will limit impact of (or enable us to avoid) the problematic early-satellite period –will see gradually increasing impact from new and improved observations, such as from radio occultation Reduction of bias in background forecasts –from better basic climatology of the assimilating model –from better time-variation of radiatively active constituents –from improvements to the data assimilation process Better handling of remaining model biases in data assimilation –apply model bias term estimated from most recent period What will lead to better trends in future reanalyses?

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Better correction of biases in observations –homogenization and correction of radiosonde data –variational correction of radiance biases Better observation operators –forward radiative transfer model for SSU –incorporation of volcanic aerosol effects for HIRS radiances Better quality control of observations –deciding when and when not to use data from specific instruments/channels Better collection of observations –such as filling gaps in pre-1967 SYNOPS, pre-1977 snow cover Time-variation in observation/background error variances –giving more weight to pre-1979 southern hemisphere radiosondes What will lead to better trends in future reanalyses?

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Visions Extending the re-analyses to incorporate the full 20th century. How feasible is this? Extending re-analyses to the fully coupled climate system. To incorporate bio-geochemical processes Applying re-analyses ideas on other planetary atmospheres ( e.g Venus, Mars)

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson 500mb Height Analyses for 0Z 20 Dec m contour is thickened Full NCEP Climate Data Assimilation System (CDAS) (120,000+ obs) Kalman / Ensemble Filter (EnsFilt) 1895 (308 surface pressure obs) RMS = 49 m Climatological Ensemble Filter (EnsClim) 1895 (308 surface pressure obs) RMS = 96 m CDAS-SFC obs only 1895 (308 surface pressure obs) RMS = 96 m

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson ca.60% PgC annually Emission now 8PgC

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Could start in 2010 depending on resources ~ 1940 Important components Recovery of observations Variational technique aimed for reanalysis Comprehensive adaptive bias handling Handling of model bias Improved SST & ICE dataset ERA-Interim ERA-70?

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Some comments to climate monitoring Climate monitoring should be undertaken in an integrated mode applying the conceptual ideas from the re-analyses Major efforts are needed to determine biases so overlapping of satellite sensors is needed as well as the use of complementary instruments ( e.g. GPS occultation versus temperature retrievals) Operational time of particular instruments should ideally cover representative climate periods ( several decades)

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson END Any questions?

12 September 2007 ESRIN/ESA Reanalysis and climate monitoring Lennart Bengtsson Trend and variability in lower stratospheric temperature ERA-40 MSU: RSS MSU: UAH Radiosonde: RATPAC Radiosonde: HadAT2 CCSP (2006) Santer et al. (2004)