Studies on the Impacts of 3D-VAR Assimilation of Satellite Observations on the Simulation of Monsoon Depressions over India - Data Assimilation for Atmospheric, Oceanic and Hydrologic Applications - page 681

a b c

Fig. 26.23 Spatial distribution of forecast impact (FI) for ( a ) MODIS, ( b )ATOVS,( c )SSM/I
calculated against QuikSCAT observations for 18-22 June 2007 depression

RMSE of Wind Speed Profiles

TheRMSEofwindspeedprofilesareshowninTable 26.7 for the 18-22 June 2007
depression. The RMSE of wind speed simulated by the ATOVS experiment shows
higher error values at most of the levels except 780, 500 and 300 hPa when compared
to the CTRL run on 20 June 2007 12 UTC. The MODIS experiment however, shows
lower RMSE of wind speed at the first two levels from the surface, after which
the errors increase while the SSM/I experiment shows higher error values of wind
speed at all the levels in the vertical as compared to the CTRL run. On 21 June 2007
12 UTC, the ATOVS run shows lower RMSE of wind speed at 950, 920 700, 620,
400, 300 and 200 hPa levels while the MODIS run gives lower RMSE of wind speed
at the four following levels, viz., 700, 400, 300 and 200 hPa only. The SSM/I run
shows better results by simulating lower error values of wind speed at this forecast
time at 920, 850, 700, 400, 300 and 200 hPa levels. On 22 June 2007 00 UTC, the
ATOVS run shows higher RMSE of wind speed for most of the levels except the
first two levels from the surface. The MODIS run, at this time, however, does not
provide a conclusive error pattern of wind speed while the SSM/I run shows higher
values of the forecast error of wind speed at all the levels in vertical.

Rainfall

TRMM observations of 24 h accumulated precipitation are shown in Fig. 26.20 i, j
valid for 21 and 22 June 2007 06 UTC. The above figure shows intense rainfall
over the Bay of Bengal. Moreover, the location of maximum precipitation is
observed over the land (landfall) on 22 June 2007 06 UTC. The rainfall features
simulated by all the numerical experiments are shown in Fig. 26.24 for the 18-22
June 2007 depression. Though all the experiments simulate the rainfall features
over the Bay of Bengal, none among them are able reproduce the landfall as
seen in the TRMM. Also, the precipitation features are overestimated in all the