Geoscience Reference
In-Depth Information
x 10 −3
x 10 −3
5
5
0
0
−5
−5
−7
−5
−2
0
2
5
7
−5
0
5
s o −sensitivity (J Kg −1 )x 10 −3
Innovation RAOBS Temp (K)
x 10 −3
x 10 −3
1.5
1.5
1
1
0.5
0.5
0
0
−0.5
−0.5
−1
−1
−1.5
−1.5
−0.8
−0.5
−0.2
0.2
0.5
0.8
−1
0
1
s o −sensitivity (J Kg −1 )x 10 −3
Innovation AMSUA − Ch7 (K)
Fig. 9.13 Scatter diagram of innovation vs. observation impact ( left side graphics) and of forecast
sensitivity to the error variance weight coefficient vs. observation impact ( right side graphics).
Results are for the radiosonde temperatures ( top ) and AMSU-A channel 7 radiances ( bottom )
assimilated in NAVDAS-AR to produce the analysis valid at 00 UTC 2010 September 29
We conclude this section with an illustration of the statistical correlation
between the observation impact and the forecast sensitivity to the observation
error variance weight coefficient. Gelaro et al. ( 2010 ) noticed that in general, in
a given assimilation/forecast episode the percentage of observations in the DAS
that have a benefic forecast impact is in the range of 50-54 %. Their study also
investigates the relation of observation impact to innovation value, y h
.
x b /
.In
Fig. 9.13 , scatter diagrams are used to additionally illustrate the correlation between
the observation impact and the forecast sensitivity to the error variance weight
coefficient associated with the observation. For practical reasons, results are shown
for a single 24-h forecast initiated at 00 UTC 2010 September 29 for the radiosonde
temperatures and for the radiances from the AMSU-A channel 7. It is noticed
that for the majority of observations a negative (benefic) observation impact is
associated with a positive
s o -sensitivity (guidance is to reduce the assigned
o
)anda
s o -sensitivity
positive (detrimental) observation impact is associated with a negative
s o -sensitivity,
OBSI)-plane (listed in counterclockwise order, with Q-I being the positive quadrant)
the percentage distribution of the number of observations was found to be as follows.
o
(guidance is to increase the assigned
). In each quadrant of the (
 
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