Satellite Bias Correctionfor CFSRR

Haixia Liu, Russ Treadon, Robert Kistler, John Derber, Suru Saha and Hua-lu Pan

Nov. 7, 2007

with input from Jack Woollen, Quanhua Liu, Moorthi Shrinivas, Cathy Thiaw and others

radiance usedradiance NOT used

……

(Reference)

What’s needed to assimilate radiance?

• CRTM model, CRTM coeff files

• satinfo which contains the usage flag, obs error and Instrument/observation characteristics (microwave/IR, etc.)

• Radiance obs bias correction is needed.

Why bias correction (BC)?

• RTM are subject to systematic errors.

• Radiance obs contain systematic errors.

• Magnitudes of these errors are comparable with radiance changes corresponding to typical errors in the T from short-range forecast model.

• Try to use radiance to improve the accuracy of the T field during DA process.

Satellite Bias Correction in GSIObservation bias b

airscan bbb

Scan bias (slowly evolve)

Air mass bias (dependent on atmospheric state)

is the coefficients of predictors p

Pbair ConstantZenith angle Cloud liquid waterSquare of T lapse rateT lapse rate etc.

Adaptive BC in GSIAllow temporal variation of the coefficients using data assimilation

Variational bias correction

)()(

)()()()(),(1

21

1

211

21

TTT

bT

bbT

b

pxHyRpxHy

BxxBxxxJ

Find the optimal to minimize the cost function J through the variational procedure.

xHyRxHyxxBxxxJ Tb

Tb 1

211

21 )()(),(

VS

• 2 BC files are required to run gsi

1) Coefficients for predictor part of BC (biascr.gdas.*)

• Updated within inner loop of analysis

2) Slowly evolving angle dependent part of BC (satang.gdas.*)

• Updated in separate job step following analysis using Tb innovation file

• Method:Start from guess values and run a training period.

Experiments were conducted to see if this procedure can lead to convergence to the operational values (‘truth’) after the training period.

AMSU Blue: EXPRed: CNTL

Preliminary Results

Blue: EXP

Red: CNTL

HIRS

Scan bias and air mass mean bias compensate to each other.

Combine the scan bias and mean term together to avoid the compensation between them. Remove predictor zenith angle.

• The coefficients for predictor cloud liquid water should not start from 0 since this term evolves very slowly. Only applied to amsua data available after 199810. Will start from average value used in operation.

GSI codes and scripts ready for CFSRR

• Modify GSI code and analysis script to handle pre-NOAA-14 satellites/sensors.

• Modification made in GSI and link to new CRTM which considers co2 leaking in cell pressure modulator which ssu data suffers.

• GSI is basically frozen for CFSRR now.

Generating satinfo historical files

• The satinfo historical files are generated every 6 hours from 1979 to present. The satellite/sensor/channel use flag is turned on/off in satinfo files based on the GMAO blacklist and data availability at NCEP.

• Amsua_aqua channel 4 is going to be used as QC purpose rather than assimilated. Amsua_n16 chn4 is in monitor mode.

• Questions: hirs2_n11 in 2nd period is extended to 20000426 and ssu_n11 is extended to 20040616 (GMAO ends using them at Feb 1999 and ERA40 ends using them in Sep 1998); ssu-n12 data is going to be used extending from 19970530 to the end of 1998.

satellite sensor Start date End date

tirosn Hirs2 19790101 19800121

Msu 19790101 19790626

ssu 1979010119800129

1980012119810205

N06 Hirs2 19790713 19830418

Msu 1979070119851015

1983041819861118

ssu Same as msu

N07 Hirs2 19810824 19850205

Msu 19810801 19850219

ssu Same as msu

N08 Hirs2 19830501 19840621

Msu Same as hirs2

ssu

N09 Hirs2 19850225 19881102

Msu 19850225 19870308

ssu 19850225 19881102

N10 Hirs2 19861126 19910902

msu Same as hirs2

N11 Hirs2 19881108 19941231

Msu Same as hirs2

ssu

N11 2nd period

Hirs2 19970715 19990226

Msu Same as hirs2

ssu

N12 Hirs2 19910916 19911225

19920308 19930610

19930619 19970530

Msu 19910916 19970524

N14 Hirs2 19950501 20060925

Msu Same as hirs2

ssu 19950119 20060505

N15 Hirs3 19981026[hl1]  20000607

amsua 19981026 21001231

amsub Same as amsua

N16 Hirs3 200101[hl2] 26 20040521

amsua 20010124 20021121

20021128 21001231

amsub 20010124 21001231

N17 Hirs3 20020715 21001231

amsua 20020715[hl3]  20031028

amsub Same as hirs3

 [hl1] Hirs3_n15 are not used any more by GDAS in operation. [hl2] Hirs3_n16 are not used any more by GDAS in operation. [hl3] Amsua_n17 are not used any more by GDAS in operation.

N18 Hirs4 Not use

amsua 20051101 21001231

mhs Same as amsua

Metop-a Hirs4 20070521 21001231

amsua Same as hirs4

mhs

aqua airs 20021012 21001231

amsua Same as hirs4

G08 sndr 19940413 20030401

G10 sndr 19970425 20060621

G11 sndr 20060621[hl1]  20070529

sndrD1 20070529 21001231

sndrD2

sndrD3

sndrD4

G12 sndr 20030401 20070529

sndrD1 20070529 21001231

sndrD2

sndrD3

sndrD4

 [hl1] Sndr_g11 are not used any more by GDAS in operation.

4 Simultaneous Streams

• Jan 1979 – Sep 1986 8 years• Apr 1986 – Oct 1993 7 1/2 years• Apr 1993 – Oct 2000 7 1/2 years• Apr 2000 – Feb 2010 10 years

6 month overlap for ocean and land spin ups

Total of 33 years of Reanalysis

Future work

• 21 satellite bias correction spin up experiments should be done by the end of 2007.

• Sensitivity of bias to the atmospheric IC. Start from r2 or gdas of the previous cycle?

Tests on amsua_n15 indicate that the bias correction is not very sensitive to the IC (the current predictors chosen can identify obs bias from NWP model error.)

• Possible issues related to SSU bias correction and assimilation.