assimilation of cloudy amsu-a microwave radiances in 4d-var
DESCRIPTION
Assimilation of Cloudy AMSU-A Microwave Radiances in 4D-Var. Una O’Keeffe Thanks to Martin Sharpe and Stephen English IPWG Workshop, Melbourne October 2006. Overview. Motivation AMSU-A 23GHz and 31Ghz Cloud liquid water incrementing operator Assimilation set up Assimilation results. - PowerPoint PPT PresentationTRANSCRIPT
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Assimilation of Cloudy AMSU-A Microwave Radiances in 4D-Var
Una O’Keeffe
Thanks to Martin Sharpe and Stephen English
IPWG Workshop, Melbourne
October 2006
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Overview
Motivation
AMSU-A 23GHz and 31Ghz
Cloud liquid water incrementing operator
Assimilation set up
Assimilation results
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Motivation
Cloud liquid water has large impact on microwave radiances
Currently low peaking AMSU-A channels are not assimilated if significant water is present
Significant data gaps due to cloud
AMSU-A window channels contain information on liquid water which is not currently exploited
Step towards assimilation of AMSR high resolution cloud and precipitation-affected radiances
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Information on cloud liquid water
NOAA-16 ObsRTTOV8 with clw emission
RTTOV8 without clw emission23GHz
31GHz
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O-B Stats for IRclear RTTOV – 31GHz
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O-B Stats for MWcloudy RTTOV – 31GHz
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Cloud Incrementing Operator
Total moisture analysis variable used in 4D-Var
Need cloud incrementing operator that relates liquid water and specific humidity to the total water control variable
Cx+ = Cx + KCw’
Cx = model state (q,qcl,qcf,cf)
Cw’ = analysis increment (T’,p’,qT’)K = incremental transform variable between control variable
space and model parameter space (uses linearised physics).Sharpe,2005
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1D-Var Preprocessor
Currently formulated with full field total water
Up to 8% of solutions are rejected in 1D-Var with this approach
Data volume in 3D-Var is not reduced but is biased away from cloudy areas, giving negative impact
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Assimilation Experiment Set Up
Configuration: 3DVar, Dec05 four week period
10 day run to generate clear air bias corrections
Cloudy obs 23+31GHz assimilation trialassimilate NOAA-16 AMSU-A 23GHz and 31GHz
extra-tropics sea onlyfor all cloud conditions except for where rain flag is on
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Analysis Increments
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Analysis Increments
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Impact on large scale fields fit to analysis
NH | TROPICS | SH
50hPa height
500hPa and 250hPa temp
Most fields improved in SH
850hPa humidity
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Fit to observations 31GHz
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Fit to observations 31GHz
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Bias Correction of Cloudy Data…???
For this test, used N16 HIRS to define ‘clear air’ and bias corrected clear air data
Operationally, also want to use N15, N17, N18
Options:Bias correct clear air data only – ignores large cloudy biases
Bias correct all data – may degrade clear air assimilation
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Current Status
Testing different bias corrections
Investigations of 1D-Var rejections indicated issue with high retrieved LWP on the first iteration causing failures. A fix is now in place
Operational implementation planned for early 2007
PlansSSMI/SSMISAMSRAMSU-B + ice incrementing operator
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Summary
Assimilation of cloudy AMSU-A 23GHz and 31GHz data gives consistent positive impacts in SH and tropics
Some significant changes to lower level humidity cf analysis
Cloud fields improved
Unresolved issues with bias correction
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Questions?