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Transcript of Slide 1 The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting FY-3 satellite data tuning and...
Slide 1
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
FY-3 satellite data tuning and assimilation
Qifeng Lu
National Satellite Meteorological Center, CMA, BeijingEmail: [email protected]
ECMWF
Thanks to all who contributed to this work
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Outline
Microwave sounding data in NWP and climate research: operational satellites from the US, Europe & China : 1978-2020
China’s FY-3A satellite: The Microwave Temperature Sounder (MWTS)
Identifying and characterising MWTS biases using NWP fields:
Passband shifts
Radiometer non-linearities
Improved Assimilation of MWTS
Initial Assessment of FY-3B
Summary and conclusion
Next Steps: Early results from the evaluation of MSU and AMSUA from 1978-2011
Slide 3
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
US
Europe
China
• Microwave sounding data provides information on temperature and humiditywhich has been widely used in :
• Operational NWP data assimilation systems and;• Climate research – to determine long term trends in atmospheric state
• The US has launched a series of polar satellites, dating back to 1978;• Europe began to contribute in 2006 (MetOp-A)• China began to contribute in 2008 (FY-3A)
Operational Sounding Satellites
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
The importance of MW sounding data in NWP
Largest positive impact (per system)is obtained from microwavetemperature sounding data
Forecast sensitivity toobservations (FSO)Is an adjoint based technique for assessing the influence of observing systems on forecast accuracy
(from C. Cardinali, ECMWF)
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting 5
ok
Microwave TemperatureSounder (MWTS)4 channel (~MSU)
Microwave HumiditySounder (MWHS)5 channel (~MHS)
InfraredAtmospheric Sounder(IRAS) 20 channels (~HIRS/3)
Microwave Radiation Imager10 channels (~AMSR-E)
The FY-3A/B Instrument Suite
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Approach involves a comparison of observations (OBS) with simulated observations based on short range (up to T+9 hour) forecast fields (‘First Guess’, FG) and radiative transfer modelling → ‘FG departures’
FG is ‘proxy’ for truth → ‘FG departures’ (OBS – FG) indicate error in the measurements or RT modelling
High accuracy of the NWP fields results from the large & diverse range of observations assimilated (MW sounders, Advanced IR sounders, GPSRO, radiosondes … etc)
Able to detect biases at ~0.1K level for temperature sounders (MWTS and IRAS), sensitivity slightly lower for MW humidity sounders & imagers (~0.5K)
Similar work ongoing at NOAA/NCEP, UK Met Office and DWD
Initial Data Quality Assessment at ECMWF:General Approach
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Initial FY-3A Evaluation
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Microwave TemperatureSounder
Microwave HumiditySounder
Infrared Sounder
Microwave Imager
STDEV (first guess departures):measures the misfit between model & measurement (in TB
space)
FY-3A data quality is comparable with MetOp/Aqua equivalents
Initial Data Quality Assessment at ECMWF:Comparison of FY-3A with MetOp & Aqua
Slide 9
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Full System OSEs: Full System + FY-3A VASS suite (MWTS, MWHS, IRAS)T511, 3 month experiment
positiveimpact from FY-3A
The impact of the FY-3A data is :
• neutral in SH
• slightly positive in the NH
Initial Data Quality Assessment at ECMWF:Assimilation Experiments
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Characterising MWTS biases using NWP fields
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Comparison of MWTS and AMSU-A Brightness Temperatures
State dependent inter-satellite (MWTS vs AMSU-A) biases:
Region 1 (tropics): MWTS TBs warm relative to AMSU-ARegion 2 (high northern latitudes) : No significant bias
Brightness temperature map from cycle 2008091700
Characterize the MWTS
1
2
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Schematic of error terms
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
MWTS-2 MWTS-3 MWTS-4
First Guess Departures (K) ,i.e.,Observation minus Simulation
Pre-launch measured passband
Optimised passband
• from line-by-line modelling• uncertainties of ~32-55 MHz detected and corrected
Non-linearity corrected
AMSU-A equivalent
Characterising the FY-3A MWTS:Detecting and Correcting passband errors and Non-linearities
Slide 14
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Characterising the FY-3A MWTS:Assessing corrections in the CMA-GRAPES model
Pre-launch measured passbandOptimised passbandOptimised + non-linearity corrected
→ the corrections, developed at ECMWF, improve the (OBS-GRAPES_MODEL) fits.
Slide 15
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
MWTS OSEs Forecast Verification: Z at 200, 500 and 700 hPa
Improvementdue to MWTS data
Normalised differences in RMSErrors in Z, verified against own analysis90% confidence intervals shown
Small improvementsin SH in going from:
original data
→ recalibrated (low weight)
→ recalibrated (high weight)
NH close to neutralwith some benefit in recalibrated data
PRELAUNCH_MWTS(full system + original MWTS data)
HIOBSERR_MWTS(Full system + optimised MWTSwith low weight)
LOWOBSERR_MWTS(Full system + optimised MWTSwith high weight)
Slide 16
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
MWTS: current status
Ground system changes implemented at CMA, March 2011
STD of 0.2 K is normally monitored
MetOp AMSU-A Ch. 9FY-3A MWTS-4
Slide 17
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Initial FY-3B Evaluation
Slide 18
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
FY-3B MWTS FG DepartureChannel 3: 54.072 GHz
• Correction of passband measurement bias and radiometer non-linearity has been implemented in pre-processing at NSMC/CMA
• No significant problems with the MWTS-2 and -3 observations
• Cross scan bias is dominant & accounts for non-gaussian FG departures (corrected by variational bias correction scheme):
After VarBCSTDEV(O-FG) = 0.17 K
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
FY-3B MWTS FG DepartureChannel 4: 57.3353 GHz
• Strong cross scan biases & regional biases detected
•
• Variational bias correction unable to significantly reduce these biases
• Work is ongoing to improve the correction of these anomalies
Slide 20
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
MWTS FG Departure
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Slide 24
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Summary FY-3A data has been evaluated at ECMWF through a comparison with simulated
radiances & full assimilation experiments in which FY-3A data is introduced in the
ECMWF system.
The study revealed, and corrected, biases in FY-3A MWTS related to :
Uncertainties in the passband centre frequencies
Radiometer non-linearities
These corrections bring the MWTS data close to the quality of equivalent AMSU-A
data & in assimilation experiments this MWTS data delivers improvements in forecast
accuracy.
The high value of NWP in Cal/Val of new satellite sensors has been clearly
demonstrated – further improvements in FY-3A and FY-3B data are expected, and it is
hoped NWP will again play a crucial role for FY-3C, …. FY-3G !
A powerful new general approach to diagnosing an important group of biases
affecting microwave sounders has been developed.
This work demonstrates the significant benefits of close collaboration between
satellite agencies and NWP centres.
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The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Next Steps: Initial results from an evaluation of MSU and AMSUA from
1978
Slide 26
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
MSU CH3 (54.96 GHz): NOAA-6 to NOAA-14Fr
eque
ncy
Shift
/ M
Hz
STD
(FG
_DEP
)Im
prov
emen
t in
STD
(FG
_DEP
)
• LbL modelling based on ERA-Interim fields• 1 cycle per month: 1979 -2011
•Blue dots represent FG_DEP after shift correction•Colour dots before
Slide 27
The 4th THORPEX-Asia Science Workshop and 9th ARC Meeting
Finally … Thanks !
We would also like to acknowledge the contribution of colleagues from across the world (from CMA, ECMWF, UK Met Office and others besides) who made this work possible
And finally - thanks to the local organizing committee for their hospitality here in the wonderful city of Kunming !