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 668

a b c

Fig. 26.16 Spatial distribution of forecast impact (FI) for ( a ) MODIS, ( b )ATOVS,( c )SSM/I
calculated against QuikSCAT observations for 2-5 September 2006 depression

2006 depression. The verification of the model results are made with respect
to QuikSCAT wind observations. The spatial distribution of FI is presented in
Fig. 26.16 . For the MODIS experiment the spatial distribution of FI parameter
reveals a blend of positive and negative values over the Bay of Bengal region. The
assimilation of MODIS observations has produced negative impact on the 10 m wind
speed over the north Bay of Bengal and over the south-east regions of the domain,
while the central part depicts higher positive of FI for the wind speed. The ATOVS
run exhibits a more positive impact on the wind speed with the larger spatial extent
of positive values over the domain while for the SSM/I run the spatial extent of
negative values are more prominent. The magnitude of positive values for FI is less
for the SSM/I run as compared to the other two experiments.

RMSE of Wind Speed Profiles

The domain averaged values of RMSE for wind speed is depicted in Table 26.4 .
The MODIS and the ATOVS experiment have reduced the RMSE values of wind
speed for 2-5 September 2006 depression at almost all the levels except 620, 500
and 200 hPa levels when compared to the CTRL run during the forecast time valid
on 03 September 2006 12 UTC. The assimilation of SSM/I total precipitable water
did reduce the RMSE value of wind speed for all the levels as compared to CTRL
run: for the ATOVS run on 3 rd September 2006, the error increased up to 400 hPa
level and then the error started decreasing at higher levels. The MODIS experiment
has however given better results with low RMSE of wind speed on the second day
of the forecast. The SSM/I run has shown higher RMSE of wind speed on the lower
and mid-troposphere together with lower RMSE of wind speed at the upper levels
during 04 September 2006 12 UTC. The MODIS experiment shows lower RMSE
values of wind speed on the third day of forecast while the RMSE of wind speed is
higher for the ATOVS run and is lower for the SSM/I experiment at the upper levels
of the troposphere.