Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.a21e0293k&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #A21E-0293
Physics
[3309] Atmospheric Processes / Climatology, [3322] Atmospheric Processes / Land/Atmosphere Interactions, [3374] Atmospheric Processes / Tropical Meteorology, [5739] Planetary Sciences: Fluid Planets / Meteorology
Scientific paper
Monsoon depressions (MDs)are probably the most important rain bearing systems that occur during the Indian summer monsoon season. The unique topography of Indian peninsula and Indo-china region favor the formation and development of MDs in the warm and moist air over the Bay of Bengal. After formation the MDs move in a north-northwest track along the monsoon trough to the warmer and drier heat low regions of Northwest India and Pakistan. The dynamic structure of MDs is largely maintained by convergence of atmospheric water vapor flux coupled with the lower tropospheric divergent circulation (Chen et al., 2005), and they weaken rapidly after landfall due to the lack of surface moisture fluxes (Dastoor and Krishnamurti, 1991). In the present study we explored the association between pre-storm wetness conditions and the post-landfall situation of MDs using 54-year long observations (1951-2004) of 183 MDs and daily surface rainfall. Our analysis suggests that the MD’s post-landfall behavior is most sensitive to mean inland rainfall between To-1 to To-8 days (the pre-storm rainfall), where To is the day of formation of MD in the Bay of Bengal. Further, pre-storm rainfall over a broad region along the monsoon trough is found to exhibit the maximum association with the MDs inland lifespan. We further carried out the unsupervised classification of pre-storm rainfall patterns using Self Organizing Map(SOM), a topology preserving map that maps data from higher dimensions onto a two dimensional grid(Kohenen, 1990). The SOM patterns of rainfall indicate that pre-storm wetness is strongly associated with the inland penetration length of MDs with wetter conditions supporting MDs to survive longer after the landfall. Although the pre-storm inland wetness has not been found to be associated with the formation of MDs and a number of MDs form during relatively dry inland conditions during the early (June) and late (September) phases of monsoon, the inland-penetration and post-landfall lifespan of these MDs was found significantly smaller compared to those formed under wetter inland conditions. Interestingly, the formation of a considerably larger number of MDs was associated with axially concentrated (around monsoon trough) patterns of pre-storm rainfall than the wide-spread patterns. The inland rainfall patterns are possibly the manifestation of the strength and orientation of Tropical Convergence Zone (TCZ) that also supports the genesis of MDs through the enhancement of barotropic instability. References Chen T.C., J.H. Yoon, and S.Y. Wang, 2005 : Westward propagation of the Indian monsoon depression. Tellus, 57A, 758-769. Dastoor A., and T.N. Krishnamurti, 1991: The landfall and structure of a tropical cyclone : The sensitivity of model predictions to soil moisture parameterizations. Boundary Layer Meteorol., 55, 345-380. Kohenen, T., 1990 : The self organizing map. Proc IEEE .78(9):1464-1480.
Kishtawal C. M.
Niyogi Dev
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The Association of Pre-storm Ground Wetness with Inland Penetration of Monsoon Depressions : A Study Using Self Organizing Maps (SOM) C.M. Kishtawal Meteorology and Oceanography Group, Space Applications Center, Ahmedabad, INDIA Dev Niyogi2 Department of A does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
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