Transcript Reanalysis and climate monitoring

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
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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
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
Input observations
TOVS radiances
SSMI radiances
AIRS radiances
NWP system
Bias modules
Conventional
•Surface
•Upperair
•Aircraft
•Satellite products
How the observations
were used in the analysis
(feedback)
Observations and
observation equivalents
from
the model and analysis
in database

Quality and
departure
information
Conventional feedback
•Surface
•Upperair
•Aircraft
•Satellite products
TOVS feedback
SSMI feedback
AIRS feedback
O3 feedback
O3 data
(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 (oC) with respect to 1987-2001
ERA-40 – CRUTEM2v
Inadequate SYNOP
coverage in ERA-40
12 September 2007
ESRIN/ESA
Erroneous CLIMAT data in
CRUTEM2v, corrected in
HadCRUT3
(Brohan
Reanalysis
and climate
monitoringet al., 2006)
Lennart Bengtsson
Europe
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)
1982 1987 1992 1997 2002
ÒInitial errorÓ(1-day
forecast error) (m)
20
15
14
14
8
Doubling time (days)
1.9
1.6
1.5
1.5
1.2
Forecast skill (day 5 AC C)
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0.65 0.72 0.75 0.78 0.84
Reanalysis and climate monitoring
Lennart Bengtsson
2007
8
1.2*
0.91
Improvements in NWP
from Miyakoda (1972) to 2002. 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
Anomaly correlations of 500hPa height forecasts
Northern Hemisphere
Ops 2003
Ops 1980
%
Ops 2001
ERA 2001
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson
Anomaly correlations of 500hPa height forecasts
Australia/New Zealand
Ops 2003
Ops 2001
Ops 1980
%
ERA 2001
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
Linear trend in two-metre temperature (1979-2001)
Mean over land: 0.30OC/decade
Based on monthly CLIMAT
station data (CRUTEM2v;
12 September
2007
Jones
and
Moberg,
2003)
ESRIN/ESA
Mean over land: 0.32OC/decade
Based on ERA-40 reanalysis
of SYNOP data
Reanalysis and climate monitoring
(Simmons et al., 2004)
Lennart Bengtsson
Linear trend in two-metre temperature (1979-2001)
Mean over land: 0.30OC/decade
Based on monthly CLIMAT
station data (CRUTEM2v;
12 September
2007
Jones
and
Moberg,
2003)
ESRIN/ESA
0.32OC/decade
0.27OC/decade
Based on ERA-40 reanalysis
of SYNOP data, sub-sampled
Reanalysis and climate monitoring
to match CRUTEM2V
Lennart Bengtsson
500hPa temperature fits for two Antarctic
stations
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
ERA-40Lennart Bengtsson
Radiosonde
Trend and variability in two-metre temperature
CRUTEM2v (Jones and Moberg, 2003)
ERA-40
CRUTEM2v
0.31OC/decade
ERA-40
0.28OC/decade
0.19OC/decade
ReanalysisNCEP
and climate monitoring
Linear trend (1979-2001):
12 September 2007
ESRIN/ESA
Lennart Bengtsson
Trend and variability in lower stratospheric temperature
MSU-4 data analyzed by Mears et al. (2003)
ERA-40 equivalent from Ben Santer
Linear trend:
12 September 2007
ESRIN/ESA
MSU-4
- 0.39OC/decade
ERA-40 - 0.30OC/decade
O
NCEPReanalysis
- 0.82
C/decade
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
http://www.knmi.nl/onderzk/oceano/waves/era40/atlas.html
1971 - 2000
90th 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
Temperature
difference
Measure of
divergence
ECHAM5/OM
ERA-40
prediction
verification
Vertical
wind shear
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/ L60
ERA-Interim/ L91
81 km
0.01
1
0.02
2
0.03
3
65 km
4
5
0.2
6
Pressure (hPa)
0.3
7
0.5
0.7
1
8
9
10
2
12
3
14
5
7
10
16
18
20
20
30
25
50
70
100
30
35
40
45
50
55
60
65
70
200
300
12 September 2007
ESRIN/ESA
500
700
1000
Reanalysis and climate
monitoring
60 levels
91 levels
Lennart Bengtsson
91
Level number
0.05
0.07
0.1
ERA-Interim 1989  to continue as CDAS
ERA-40 1957-2002
•
•
•
•
•
•
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
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson
Much improved
500hPa height
forecasts
Anomaly
correlation of
500hPa height,
averaged for
12UTC forecasts
from 1 January to
31 December 1989
Northern hemisphere
ERA-new
ERA-40
Operations
Southern hemisphere
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson Day
Much improved
tropical 850hPa
wind forecasts
RMS error of
vector wind,
averaged for
12UTC forecasts
from 1 January to
31 December 1989
vs analyses
ERA-new
ERA-40
Operations
vs radiosondes
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson Day
Global precipitation-evaporation 1989
(+12h forecast)
ERA-Interim (test)
= 0.01
ERA-40
= 0.23
ERA-40 23 year Climate= 0.32
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson
In summary
• 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?
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 2001
Full NCEP
Climate Data
Assimilation
System (CDAS)
Climatological
Ensemble Filter
(EnsClim) 1895
(308 surface
pressure obs)
RMS = 96 m
(120,000+ obs)
CDAS-SFC obs
only 1895
Kalman /
Ensemble Filter
(EnsFilt) 1895
(308 surface
pressure obs)
RMS = 96 m
(308 surface
pressure obs)
RMS = 49 m
12 September 2007
ESRIN/ESA
5500 m contour
is thickened
Reanalysis and climate monitoring
Lennart Bengtsson
Emission now
8PgC
2002-06
4.9 PgC
annually
ca.60%
12 September 2007
ESRIN/ESA
Reanalysis and climate monitoring
Lennart Bengtsson
ERA-70?
ERA-Interim
•
•
•
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
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