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12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Reanalysis and climate monitoring
Lennart Bengtsson
Environmental System Science Centre
University of Reading, UK
Thanks to ECMWF
Uppala and Simmons
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Reanalysis and climate monitoring
• Achievements
• Challenges
• Vision
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Reanalysis
• Why reanalysis?
• Background
• What has been achieved
• Limitations
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Re-analyses applications
• Assessing the value of observing systems
• Numerical weather prediction
• Detection of climate change
• Understanding the climate system
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Re-analyses applications
• Assessing the value of observing systems
• Numerical weather prediction
• Detection of climate change
• Understanding the climate system
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Conventional•Surface•Upperair•Aircraft•Satellite products
TOVS radiances
SSMI radiances
AIRS radiances
O3 data
Bia
s m
odul
es
NWP systemNWP system
Observations and observation equivalents
from the model and analysis
in database
Quality anddeparture
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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Comparison of reanalysis and land-station values
Surface air temperature anomaly (oC) with respect to 1987-2001
EuropeERA-40 – CRUTEM2v
Inadequate SYNOP coverage in ERA-40
Erroneous CLIMAT data in CRUTEM2v, corrected in
HadCRUT3 (Brohan et al., 2006)
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
METEOSAT Reprocessed Winds
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Re-analyses applications
• Assessing the value of observing systems
• Numerical weather prediction
• Detection of climate change
• Understanding the climate system
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
The principle of error reduction in data assimilation
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Evolution of 1-Day Forecast Error, Lorenz Error
Growth, and Forecast Skill for ECMWF Model (500 hPa NH Winter)
1982 1987 1992 1997 2002
“Initial error” (1-dayforecast error) (m) 20 15 14 14 8
Doubling time (days) 1.9 1.6 1.5 1.5 1.2
Forecast skill (day 5 ACC) 0.65 0.72 0.75 0.78 0.84
2007
8
1.2*
0.91
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Improvements in NWP from Miyakoda (1972) to 2002. Courtesy ECMWF
How long to get to D+10 in winter?
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
The impact of observations on forecast skillExperiments 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Observing systems and predictive skillNorthern Hemisphere extra-tropics
Bengtsson and Hodges, 2004
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Observing systems and predictive skillSouthern Hemisphere extra-tropics
Bengtsson and Hodges, 2004
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Observing systems and predictive skillTropics V 250 hPa
Bengtsson and Hodges, 2004
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Ops 1980Ops 1980
ERA 2001
Ops 2001
Northern Hemisphere
%
Anomaly correlations of 500hPa height forecasts
Ops 2001Ops 1980
ERA 2001
Ops 2003
Northern Hemisphere
%
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Anomaly correlations of 500hPa height forecasts
Ops 1980
Ops 2003
Ops 2001
ERA 2001
%
Australia/New Zealand
%
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Re-analyses applications
• Assessing the value of observing systems
• Numerical weather prediction
• Detection of climate change
• Understanding the climate system
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 (1979-2001)
Mean over land: 0.30OC/decade Mean over land: 0.32OC/decade
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 (1979-2001)
0.27OC/decade 0.32OC/decade Mean over land: 0.30OC/decade
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
500hPa temperature fits for two Antarctic stations
ERA-40 Radiosonde
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Trend and variability in two-metre temperature
CRUTEM2v (Jones and Moberg, 2003)
ERA-40
Linear trend (1979-2001): CRUTEM2v 0.31OC/decade
ERA-40 0.28OC/decade
NCEP 0.19OC/decade
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Trend and variability in lower stratospheric temperature
Linear trend: MSU-4 - 0.39OC/decade
ERA-40 - 0.30OC/decade
NCEP - 0.82OC/decade
MSU-4 data analyzed by Mears et al. (2003)ERA-40 equivalent from Ben Santer
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Tropical water-vapour content
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Re-analyses applications
• Assessing the value of observing systems
• Numerical weather prediction
• Detection of climate change
• Understanding the climate system
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Global wave climatology atlasS. Caires, A. Sterl, G. Komen and V. Swail
http://www.knmi.nl/onderzk/oceano/waves/era40/atlas.html
1971 - 2000 90th percentile of significant wave height February
m
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Hurricane Katrina August 2005ECMWF operational analyses, 850 hPa vorticity
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Prediction of Atlantic hurricanes are influenced by ENSOResults from a general circulation model integrated over
30 years comparing active seasons from less active
ECHAM5/OM ERA-40
Temperature difference
Measure of divergence
Vertical wind shear
prediction verification
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
0.01
0.02
0.03
0.050.07
0.1
0.2
0.3
0.50.7
1
2
3
5
7
10
20
30
50
70
100
200
300
500
700
1000
Pressure (hPa)
60 levels 91 levels
1
2
3
4
5
6
7
8
9
10
12
14
16
18
20
25
30
35
40455055606570
91
Level number
ERA-40/ L60 ERA-Interim/ L91
65 km
81 km
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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-40 1957-2002
ERA-Interim 1989 to continue as CDAS
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
Global precipitation-evaporation 1989 (+12h forecast)
ERA-Interim (test) = 0.01ERA-40 = 0.23ERA-40 23 year Climate = 0.32
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
500mb Height Analyses for 0Z 20 Dec 2001
5500 m contour is thickened
Full NCEP Climate DataAssimilationSystem (CDAS)(120,000+ obs)
Kalman / Ensemble Filter(EnsFilt) 1895(308 surfacepressure obs)RMS = 49 m
ClimatologicalEnsemble Filter(EnsClim) 1895(308 surfacepressure obs)RMS = 96 m
CDAS-SFC obsonly 1895(308 surfacepressure obs)RMS = 96 m
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
ca.60%
2002-06
4.9 PgC
annually
Emission now 8PgC
12 September 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart 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 2007ESRIN/ESA
Reanalysis and climate monitoringLennart Bengtsson
END
Any questions?