Impact of physical parameterization schemes on numerical simulation of super cyclone Gonu |
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| Authors: | Medha Deshpande S Pattnaik P S Salvekar |
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| Institution: | (1) Indian Institute of Tropical Meteorology, Dr. Homi Bhabha Road, Pashan, Pune, Maharashtra, 411 008, India |
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| Abstract: | The objective of this study is to investigate in detail the sensitivity of cumulus, planetary boundary layer and explicit
cloud microphysics parameterization schemes on intensity and track forecast of super cyclone Gonu (2007) using the Pennsylvania
State University-National Center for Atmospheric Research Fifth-Generation Mesoscale Model (MM5). Three sets of sensitivity
experiments (totally 11 experiments) are conducted to examine the impact of each of the aforementioned parameterization schemes
on the storm’s track and intensity forecast. Convective parameterization schemes (CPS) include Grell (Gr), Betts–Miller (BM)
and updated Kain–Fritsch (KF2); planetary boundary layer (PBL) schemes include Burk–Thompson (BT), Eta Mellor–Yamada (MY)
and the Medium-Range Forecast (MRF); and cloud microphysics parameterization schemes (MPS) comprise Warm Rain (WR), Simple
Ice (SI), Mixed Phase (MP), Goddard Graupel (GG), Reisner Graupel (RG) and Schultz (Sc). The model configuration for CPS and
PBL experiments includes two nested domains (90- and 30-km resolution), and for MPS experiments includes three nested domains
(90-, 30- and 10-km grid resolution). It is found that the forecast track and intensity of the cyclone are most sensitive
to CPS compared to other physical parameterization schemes (i.e., PBL and MPS). The simulated cyclone with Gr scheme has the
least forecast track error, and KF2 scheme has highest intensity. From the results, influence of cumulus convection on steering
flow of the cyclone is evident. It appears that combined effect of midlatitude trough interaction, strength of the anticyclone
and intensity of the storm in each of these model forecasts are responsible for the differences in respective track forecast
of the cyclone. The PBL group of experiments has less influence on the track forecast of the cyclone compared to CPS. However,
we do note a considerable variation in intensity forecast due to variations in PBL schemes. The MY scheme produced reasonably
better forecast within the group with a sustained warm core and better surface wind fields. Finally, results from MPS set
of experiments demonstrate that explicit moisture schemes have profound impact on cyclone intensity and moderate impact on
cyclone track forecast. The storm produced from WR scheme is the most intensive in the group and closer to the observed strength.
The possible reason attributed for this intensification is the combined effect of reduction in cooling tendencies within the
storm core due to the absence of melting process and reduction of water loading in the model due to absence of frozen hydrometeors
in the WR scheme. We also note a good correlation between evolution of frozen condensate and storm intensification rate among
these experiments. It appears that the Sc scheme has some systematic bias and because of that we note a substantial reduction
in the rain water formation in the simulated storm when compared to others within the group. In general, it is noted that
all the sensitivity experiments have a tendency to unrealistically intensify the storm at the later part of the integration
phase. |
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