CVarBC Constrained Variational B orrection) · 2020. 11. 4. · CVarBC for AMSU-A Ch14 in ECMWF IFS...
Transcript of CVarBC Constrained Variational B orrection) · 2020. 11. 4. · CVarBC for AMSU-A Ch14 in ECMWF IFS...
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CVarBC(Constrained Variational Bias Correction)
Wei Han1,2 Niels Bormann3
1JCSDA, 2 NWPC/CMA, 3ECMWF
ECMWF/EUMETSAT NWP SAF Workshop November 2-5, 2020
On the treatment of random and systematic errors in satellite data assimilation for NWP
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Outline
l Background - The bias correction is an ill-posed problem
- PRIORI information for observation bias
l Methodology- Use of priori information as constraint- Constrained BC(CBC) and Constrained VarBC (CVarBC)
l CBC in GRAPES (2014) and CVarBC in ECMWF IFS (2016,2018)- Window channel and Upper sounding channels
- Stratospheric Temperature sounding AMSUA Ch14
l Summary and Discussions- Using Priori: Radiance Uncertainty (RU)
- Optimal estimate of parameters in CVarBC
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Motivation
l Interaction between Bias Correction and Quality Control- Window channel: cloud contamination
- Bias estimation for Non-Gaussian observations(IR: cold tail; MW: warm tail)
l How to separate observation bias and model bias from O-B?- Temperature sounding channels in stratosphere- Trace gas sounding channels, e.g. IASI Ozone channels
- Humidity sounding channels
- Developing NWP systems
l What did we know about Observation Bias?- Radiometric Uncertainty Estimation
- Systematic differences from GSICS- RT model uncertainty
l Using the PRIORI information to constrain BC
, bJJδ ∂
= − −∂
y Hx by
FSO: Forecast sensitivity to observationOver or under bias correction could lead to negative impact
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BC and QC interaction
METOP AMSUA CH4f0xx_2008011200
Mean: If bias is estimated by <O-B>, It will strongly depend on the QC,
0.7 à b=0.4; 0.1 à b=0.28
Low cloud cover
Mean Based
Mode Based
2007D08JF,ECMWF,IFS
Han and McNally 2008; Li ,McNally and Geer,2010
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“Anchor channel” method for IASI ozone channels
Han W. and McNally AP. 2010: The 4D-Var assimilation of ozone-sensitive infrared radiances measured by IASI.Q. J. R. Meteorol. Soc. 136: 2025–2037. DOI:10.1002/qj.708
Anchor channel
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Radiometric UncertaintyMeteosat-10/SEVIRI IR2013-03-01/2017-03-01
Himawari-8/AHI IR2015-07-01/2017-06-30
Tim Hewison,ITSC21
GSICS
Tobin et al ,2013
upper bounds of observation bias
STARICVS ,ATMS-GPS
GPS RO as refrence
Calibration update
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Uncertainty estimation of Satellite observations:GCOS reference Upper-air Network
ATMS
AMSU-A instruments
GRUAN O – B (TB) GAIA-CLIM project(ECMWF,UKMO)
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How to use the UNCERTAINTY INFORMATION(Priori)From GSICS、calibration and RT model in BIAS CORRECTION?
UN
CER
TAINTY
BIAS CO
RR
ECTIO
N ITSC16Connect the two GROUP
Constrained Bias Correction
Model bias and imperfect QC
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Methodology: Constrained Variational Bias Correction (CvarBC)
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Han,2014,ITSC19
Constrain the total size of bias correction to each channel(Weak Constraint)
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Slide 10
Experiments in GRAPES
Ch9
Ch4
Warm tail
Model bias
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Slide 11
AMSUA CH9(Metop_A)
0
01,, 00 0bbγ
γ
=
=
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Model Bias
1-10 June 2013
<O-B>ori BC
<O-B>C
BC<b1-b0>
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Slide 12
Two months cycle experiments in GRAPES global May-June 2013
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Slide13
There are systematic errors in model background, IF there are not enough unbiased observations to constrain the analysis.
CY42R1: Climate Run Tbias2000-2001
CY42R1: 24h Forecast T bias2014D15JF
CH14
CVarBC for AMSU-A Ch14 in ECMWF IFS: Background
Constrained VarBC in IFS
Sonde as anchor in N.H.
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CVarBC for AMSU-A Ch14 in ECMWF IFS : Background
McNally,A.P.(2007),TheassimilationofuncorrectedAMSU-Achannel14toanchortheVarBCsysteminthestratosphere.ResearchDepartmentMemorandum,ECMWF,R43.8/AM/0715.
Anchor channel
VarBC(static coefficients)
VarBC(cycle update)
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Constrained VarBC in IFS Slide15
CVarBC for AMSU-A Ch14 in ECMWF IFS : BackgroundThere are two issues need to be revisited:
1)Inter-satellite biases; 2)Scan biases.
Anchor
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Constrained VarBC in IFS Slide16
Drift to model bias without anchorBias correction of AMSU-A Ch14 in IFS CY41R2:1) Free VarBC will drift gradually;2) It will also affect the bias correction of Ch13 and Ch12;
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Constrained VarBC in IFS Slide17
Implementation of Constrained VarBC in IFS and CY41R2 experiments
AMSU-A alpha Bias0 B(bias0)*
Channel14 0.3 0 1.4
Channel13 0.0 0 0.85
Channel12 0.0 0 0.5
*Same as observation error
CVarBC
2 10 0[ ( , ) ] [ ( , ) ]T
bh hα −− −b R x β bx β
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Constrained VarBC in IFS Slide18
Temporal Evolution of bias correctionMETOP-ANOAA-18
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Constrained VarBC in IFS
Scan bias correctionCNTL: anchor channel CVarBC
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CVarBC: AMSU-A 14 bias corrections
NOAA-18
• Total size of bias correction• Inter-satellite biases• Scan biases
METOP-A
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AMSU-A Ch14 <O-B>(2014-12-15~ 2014-12-31)
NOAA-18
NOAA-19
METOP-A
METOP-B
CNTL CVarBC
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Constrained VarBC in IFS
Mean Bias Correction in 2014D15JF
CNTL VarBC CVarBC
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Constrained VarBC in IFS
Verification using MLS Temperature retrieval
MEAN(MLS-CNTL),2014D15JF MEAN(CNTL-CVarBC), 2014D15JF
Thanks Rossana!
STD(MLS-CNTL),2014D15JF <STD_CVarBC-STD_CNTL>, 2014D15JF
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Temperature bias at 1hPa MEAN(MLS-CNTL),2014D15JF
MEAN(MLS-CVarBC), 2014D15JF
MEAN(MLS-CNTL),2014D15JF
Using MLS Temperature as reference
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Constrained VarBC in IFS
Impact on the fit of other observations
Other channels
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Constrained VarBC in IFS
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Constrained VarBC in IFS
Impact of Constrained VarBC on AMSUA CH14on Forecast (2014D15JF and 2015JJA)
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One year experiments (2015-2016)
• Test the implementation for a long time series and with weak constraint 4D-Var
NO
AA-18M
ETOP-B
Bias Correction
Bias Correction
O-B, unbcor
O-B, unbcor12 1
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Weak constraint 4D-Var,VarBC
improvement
CrIS:
STDEV O – B:
IASI:
improvement
High peaking channels
Heather Lawrence, 2017
CNTLCVarBC VarBC+WC
VarBC
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CVarBC of AMSUA Ch14:Impact on forecasts
Z T
Heather Lawrence, 2017
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CVarBC (since 5 June 2018, IFS CY45R1)
https://confluence.ecmwf.int/display/FCST/Implementation+of+IFS+cycle+45r1
Andy Brown,2018
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Summary and Discussionsl Potential use of CVarBC
- Reanalysis- Window channels
- Stratosphere amd mesosphere sounding
- Humidity sounding
- Chemistry DA
l Priori information of observation Bias- Systematic bias
- Uncertainty- GSICS, GAIA-CLIM?
l How to determine the regularization parameter?- Posteriori estimation ?
- Balance with anchor observations?
- Deal with model bias?
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Regularizaiton Parameter Estimation: DA+Inverse Problem
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ReferencelAuligné, T., McNally, A. P. and Dee, D. P., 2007: Adaptive bias correction for satellite data in a numerical weather prediction system. Q.J.R. Meteorol. Soc., 133: 631–642. doi: 10.1002/qj.56lEyre, J., 2016: Observation bias correction schemes in data assimilation systems: a theoretical study of some of their properties. Q.J.R. Meteorol. Soc.. doi: 10.1002/qj.2819lHan W. and McNally AP, 2008: Bias correction of window channels on microwave and infrared sounders, NWP-SAF Visiting Scientist Report NWPSAF-EC-VS-016.lHan W. and McNally AP. 2010: The 4D-Var assimilation of ozone-sensitive infrared radiances measured by IASI. Q. J. R. Meteorol. Soc. 136: 2025–2037. DOI:10.1002/qj.708 lHan W., 2014: Constrained Bias Correction (CBC) for satellite radiance assimilation, 19th International TOVS Study Conference, 6 March - 1 April 2014,Jeju Island, South Korea. lHan W. and Bormann N., 2016,Constrained adaptive bias correction for satellite radiance assimilation in the ECMWF 4D-Var system, ECMWF Technical Memoranda, 783. lHan W. 2017: Constrained variational bias correction for satellite radiances assimilation, The 21st International TOVS Study Conference (ITSC-21), Darmstadt, Germany. 29 November - 5 December 2017.lMcNally, A.P. ,2007: The assimilation of uncorrected AMSU-A channel 14 to anchor the VarBC system in the stratosphere. Research Department Memorandum, ECMWF, R43.8/AM/0715.lTobin, D., et al. 2013: Suomi-NPP CrIS radiometric calibration uncertainty, J. Geophys. Res. Atmos., 118, 10,589–10,600, doi:10.1002/jgrd.50809.