Geoscience Reference
In-Depth Information
Rainfall
Figure 26.13 i, j show the spatial distribution of 24 h accumulated precipitation valid
on 4 September 2006 12 UTC and 5 September 2006 12 UTC respectively for the
2-5 September 2006 depression.
The TRMM observation shows that the maximum precipitation is over the east
coast of India, and also over the Bay of Bengal. On the second day, the rainfall
intensity has decreased considerably indicating the weakening of the monsoon
depression. The rainfall patterns simulated by the CTRL (Fig. 26.17 a, b), ATOVS
(Fig. 26.17 c, d) and SSM/I (Fig. 26.17 e, f) runs show an unrealistically intense and
extreme precipitation over the south of the Bay of Bengal. Also, in the above
three runs, the simulated precipitation intensity is weak over the Head Bay and
over the coastal regions of Orissa at variance with the TRMM observations. The
amount of precipitation simulated by these three experiments over the Orissa coast
and the adjacent land area are less than 40 mm. However, the MODIS experiment
(Fig. 26.17 g, h) provides the best results out of all the model runs, accurately
simulating the location and intensity on the first day of the forecast. The MODIS
run, however, is at variance with TRMM observations simulating less rain over the
sea on the second day of the forecast. Moreover, the unrealistic heavy rainfall pattern
over the south Bay of Bengal seen in the other three model runs is absent in the
MODIS experiment.
Improvement Parameter ( ˜
)
The spatial distribution of the “improvement parameter” for precipitation is shown
in Fig. 26.18 for the 2-5 September 2006 depression. Positive improvement in the
precipitation features can be seen over the south of the Bay of Bengal for all the
experiments. For the MODIS experiment most of the negative values are seen
over the sea near the Head Bay region while the same is over the land for the
ATOVS experiment on 4 September 2006 12 UTC. On the second day of forecast,
the precipitation feature shows more positive improvement over the land for both
the MODIS and the ATOVS experiment. The distribution of negative
values
are prominent over the south east of the Bay of the Bengal on the first day of
forecast, while the second day witnessed a better precipitation forecast with larger
distribution of positive
˜
˜
values over the land for the SSM/I run.
RMSE of Temperature Profiles
The assimilation of temperature and humidity profiles from the ATOVS and the
MODIS sensors have reduced the RMSE values of temperature at 950, 920, 700,
500, 400 and 200 hPa levels when compared to the CTRL run for the forecast time
valid on 03 September 2006 12 UTC which is shown in Table 26.5 for the 2-5
September 2006 depression. The SSM/I run depicts lower RMSE at the upper levels
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