Geoscience Reference
In-Depth Information
that the assimilation of SSM/I total precipitable water has resulted in significant
positive impact on the simulation of the humidity profiles in a numerical mesoscale
model. The results obtained in this study indicate that the mesoscale model predicts
the moisture fields in the lower levels better than that of the upper levels. The above
result is due to the availability of more moisture information at the lower levels (
Cox
et al. 1998
).
Apparent Heat Source and Moisture Sink
The main driving energy associated with the tropical disturbances is the latent heat
release due to cumulus convection. Many studies have investigated the formation
and evolution of the tropical cloud clusters, which manifest due to intense con-
vection (
Manabe et al. 1970
;
Wallace 1971
;
Nitta 1970
). The study of monsoon
depression, one of the prominent tropical monsoonal disturbances, associated with
deep cumulus convection and large cloud clusters, provides an excellent case for a
detailed diagnostic study with a special emphasis on convective processes. The main
purpose of this section is to diagnose the role of the vertical distribution of heating
and cooling associated with convection in the monsoonal environment. Following
Ya n a i e t a l .
(
1973
), heat and moisture budget analysis has been performed for the
model experiments in this section. To be consistent with the model simulated heat
and moisture fields, the computations for the heat and moisture budget analysis are
performed in
coordinates. The budget analysis for heat and moisture has also
been performed for NCEP-FNL analysis in
¢
coordinates for comparing the model
diagnostics with the analysis. Apart from the heat and moisture budget analysis,
the time averaged and area averaged temperature anomaly and relative vorticity of
the simulated depression in the vertical have also been validated with the respective
fields of NCEP-FNL analysis. All the three cases of monsoon depressions, which
are part of our investigation, are utilized for this analysis.
Figure
26.11
a, b depict the 60 h time averaged profiles of the area averaged
apparent heat source (Q
1
) and apparent moisture sink
¢
respectively for the
19-22 September 2006 monsoon depression that formed over the Bay of Bengal.
The area averages were computed for
.
Q
2
/
3
ı
3
ı
region around the centre of the
depression. As can be seen from Fig.
26.11
a, the CTRL experiment is showing
the maximum heating rate at the model height of
. The MODIS run also
simulates a similar heating profile as that of the CTRL run, but with a lower
magnitude. Considering the NCEP-FNL analysis as the true estimate of heating,
it is clear that both the CTRL and the MODIS experiments overestimate the
rate of heating in the vertical. The magnitude of heating rate in the ATOVS and
the SSMI experiments are lower when compared to the other two experiments and
the NCEP-FNL analysis. The maximum heating rates due to moisture effects is seen
in the CTRL run among all the four model experiments, reaching a maximum of
about
¢
D
0:55
Kday
1
over the mid-troposphere. The vertical heating rate simulated by
the MODIS experiment closely follows the NCEP-FNL analysis which implies that
the MODIS experiment better simulates the apparent moisture sink in the vertical.
16
Search WWH ::
Custom Search