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a
15 JST
#001
#002
#003
#004
#005
#000
#010
#007
#008
#009
#011
#006
(mm)
(m /s)
b
17 JST
#001
#002
#003
#004
#005
#000
#007
#010
#011
#008
#009
#006
(mm)
(m /s)
Fig. 20.6
Horizontal distributions of 1 h rainfall (
shaded regions
) and horizontal wind at the height
of 20 m (
vectors
) reproduced by the Inner LETKF at (
a
)15JSTand(
b
)17JST.
Circles
in (
b
)
indicate the intense rainfall regions which extended northwestward.
Arrows
in (
a
) indicate the
small rainfall regions that developed into the intense rainfall regions at 17 JST
expected that analyzed values of the Outer LETKF inside and around the domain
of the Inner LETKF were modified by this procedure. To investigate the impacts
of this procedure, the spread distributions of rainfall and sea level pressure were
compared with ones obtained by performing the assimilation without the Inner
LETKF (Fig.
20.7
). In this case, the rainfall distribution of the Outer LETKF was
similar to that obtained by performing the assimilation without the Inner LETKF
(Figs.
20.5
aand
20.7
a). However, the spread distributions of the Outer LETKF
region were affected by the Inner LETKF. Namely, the spread of rainfall in the Inner
LETKF became larger and that of sea level pressure became smaller, when the Inner
LETKF was used (indicated by arrows in Figs.
20.7
c, d). These small spreads of sea
level pressure expanded outside of the domain of the Inner LETKF (Figs.
20.5
band
20.7
b). This comparison indicates that the Inner LETKF influences the analysis of
the Outer LETKF, though the impact was not large in this study.
Next, the convection cells near the boundaries of the Inner LETKF are described.
Because the analyzed values of the Outer LETKF within the domain of the Inner
LETKF were replaced with the analyzed values of the Inner LETKF, this procedure
might lead to the generation of unrealistic convection cells near the boundary of the
Inner LETKF, especially when the analyzed horizontal winds between the Inner and
Outer LETKFs are greatly different. Figure
20.8
shows the rainfall and horizontal
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