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 690

improved forecast of rainfall patterns in the third case study. The ATOVS experiment
shows significant forecast impact on the surface wind speed which is validated
against the QuikSCAT observations. There is some discernable reduction in the
RMSE of wind speed, temperature and dew-point temperature in some levels for all
the assimilation experiments. The assimilation experiments do show some difficulty
in accurately simulating the upper level features of the troposphere especially
for the dew-point temperature, which is evident from the higher RMSE of dew
point temperature at these heights. However, the assimilation of total precipitable
water from SSM/I does provide for some positive improvements in the dew-point
temperature simulation. The absence of vertical temperature and humidity profiles
from the SSM/I sensor has contributed to the lower impact of assimilation for the
SSM/I experiment. Despite the positive impact on the simulation and forecast of the
monsoon depressions with 3D-VAR assimilation technique, the results of the study
also reveals marked positioning error of the depression centre in the forecast in most
of the numerical experiments. The above marked positioning errors at large forecast
lead time clearly indicate that issues other than data assimilation are also important
and hence a solution of overcoming the marked positioning error problem requires
further detailed investigations, addressing issues, which are beyond the scope of this
study.
Acknowledgements The authors acknowledge NASA, NOAA and NCEP for providing access
to the various satellite (MODIS, ATOVS, SSM/I, QuikSCAT and TRMM) observations as well
as the NCEP GFS and FNL fields. The first author acknowledges funding support for this work
from Space Application Centre, Ahmadabad, India. The second author acknowledges the CSIR
and IIT Kharagpur, India for providing research fellowship and all research facilities to undertake
this work. The above work includes a small portion of the PhD work of the second author.
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