forecast model bias correction in ocean data assimilation g. chepurin, jim carton, and d. dee* univ....
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![Page 1: Forecast model bias correction in ocean data assimilation G. Chepurin, Jim Carton, and D. Dee* Univ. MD and *GSFC Bias in ocean data assimilation Two-stage](https://reader035.vdocuments.mx/reader035/viewer/2022062422/56649e705503460f94b6e58b/html5/thumbnails/1.jpg)
Forecast model bias correction in ocean data assimilation
G. Chepurin, Jim Carton, and D. Dee*Univ. MD and *GSFC
• Bias in ocean data assimilation• Two-stage bias correction algorithm
– Bias model– Results from a series of 30-yr assimilation
experiments
Manuscript available: {http://www.atmos.umd.edu/~carton/bias}
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Bias is the difference between the state forecast and the true state
ftft
0ε 0
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Time-mean bias along equator
20C“Cold tongue is too cold, while the thermocline in the central basin is too diffuse”
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Annual cycle of mixed layer bias in subtropics (10N-30N)
Dec
June
“Too hot in summer, too cold in winter”
of TT
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Time-evolution of forecast
error along equator
“Forecast error is episodic, linked to ENSO”
100m
Tim
e
Mixed layer
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Two stage algorithm to correct systematic aspects of forecast error
)( ffofa ωββ HL
fofa ωωωω ~~ HK
Stage I
Stage II
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Three-term bias forecast model
fk
tifk
kAe G )(ˆ
Time-
mea
n bi
as
Ann
ual c
ycle
bia
s
ENSO
-link
ed
bias
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Correcting time-mean bias
along Pacific Eq
This is business as usual
This is what results when time-mean bias is modeled
20C
20C
of ww
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Correcting time-mean biasCorr time-mean bias
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Correcting annual cycle bias
Business as usual Annual cycle bias correction
Dec
June
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Annual cycle of forecast error before correction
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Annual cycle of forecast error after correction
BeforeAfter
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Correcting ENSO biasbe
for e
afte
rCorEOF1,SOI = 0.7
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Summary of the impact of bias
correction
time mean
+annual cycle
+ENSO variability
RMS (fcst-obs)
ML temp Thermocline depth
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Conclusions
• Half of the {forecast – observation} differences in high variability regions are due to bias. The largest contribution is time-mean followed by annual cycle and interannual variability.
• Two-stage correction works well in addressing these.
Manuscript available: {http://www.atmos.umd.edu/~carton/bias}
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The End