Geoscience Reference
In-Depth Information
26.4.1
Monsoon Depression That Formed During 19 to 22
September 2006
A low pressure area formed over the north-east Bay off Arakan coast and the
adjoining east-central Bay in the evening of 18 September 2006. The system was
over the north-east Bay on 19 September 2006 and became well marked in the same
evening. The low pressure area moved over Gangetic West Bengal and adjoining
Bay on 20 September 2006 and subsequently intensified into a depression on 21
September 2006 03 UTC, close to Jamshedpur, India. The depression remained
stationary over Jamshedpur till 21 September 2006 12 UTC and then moved slightly
north-westwards and was centered in Jharkhand, about 50 km east of Ranchi, at
03 UTC and 12 UTC of 22 September 2006. The depression moved in the north-
eastward direction and lay centered close to Dhanbad on 23 September 2006 03 and
12 UTC. The land depression caused heavy rainfall over the north-eastern and the
central parts of India during 21-24 September 2006.
26.4.1.1
Numerical Experiment
The WRF model is configured with 24 vertical levels and with two domains of 36
and 12 km grid spacing, using a two way nesting option. The number of grid cells in
the east-west (EW)-north-south (NS) direction being,
for
the coarser and finer resolutions, respectively. The physics options employed in the
WRF model utilized in this study include the WRF Single Moment (WSM) class-
3 simple ice scheme for micro physics, Rapid Radiative Transfer Model (RRTM)
scheme for long wave radiation, NOAH land surface model for land surface, Kain-
Fritsch scheme for cumulus parameterization and the Yonsei University (YSU)
scheme for the Planetary boundary layer parameterization scheme. The NCEP-GFS
forecast data available at a horizontal resolution of
118
130
and
271
271
1
ı
1
ı
and a time resolution
of 6 h have been used to develop the initial and lateral boundary conditions. Four
numerical experiments are performed to study the impact of temperature, humidity
and total precipitable water separately in the simulated structure of monsoon
depression. All the simulations are started with the same initial conditions on 18
September 2006 18 UTC, but the observations are assimilated at different times
depending on the availability of the satellite data over the domain. For a given
analysis/forecast time the satellite observations that fall in
min window is
assimilated. The first experiment, called the control (CTRL) run, has utilized the
NCEP-GFS data for creating initial and lateral boundary conditions. The model
integrations are performed from 18 September 2006 18 UTC to 22 September 2006
12 UTC without any assimilation of satellite observations. The second experiment,
called the “ATOVS run” which started at 18 UTC on 18 September 2006 and has
assimilated the ATOVS temperature and humidity profiles into the model using
˙
90
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