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Multiscale interaction with topography and extreme rainfall events in the northeast Indian region

Goswami, BB and Mukhopadhyay, P and Mahanta, R and Goswami, BN (2010) Multiscale interaction with topography and extreme rainfall events in the northeast Indian region. Journal of Geophysical Research: Atmospheres, 115 (12).

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Abstract

Flash floods associated with extreme rain events are a major hydrological disaster in the northeast Indian (NEI) region because of the unique topographic features of the region as well as increased frequency of occurrence of such events. Knowledge of the spatiotemporal distribution of these events in the region and an understanding of the factors responsible for them, therefore, would be immensely useful for appropriate disaster preparedness. Using daily rainfall data from 15 stations over the region for 32 years (1975-2006), it is shown that the frequency of occurrence of these events is largest not during the premonsoon thunderstorm season but during the peak monsoon months (June-July-August). This fact together with the fact that most of these events occur during long rainy spells indicate that the extreme events in the NEI region largely occur in association with the monsoon synoptic events rather than isolated thunderstorms. We also find that the aggregate of extreme rain events over the region has a significant decreasing trend in contrast to a recent finding of an increasing trend of such events in central India (Goswami et al., 2006). This decreasing trend of extreme events is consistent with observed decreasing trend in convective available potential energy and increasing convective inhibition energy over the region for the mentioned period. Examination of the structure of convection associated with the extreme rain events in the region indicates that they occur through a multiscale interaction of circulation with the local topography. It is found that at all the stations, the events are associated with a mesoscale structure of convection that is embedded in a much larger scale convective organization. We identify that this large-scale organization is a manifestation of certain phases of the tropical convergence zone associated with the northward propagating active-break phases of the summer monsoon intraseasonal oscillation. Further, it is shown that the mesoscale circulation interacting with the local topography generates southward propagating gravity waves with diurnal period. The strong updrafts associated with the gravity waves within the mesoscale organization leads to very deep convective events and the extreme rainfall. The insights provided by our study would be useful when designing models to improve the prediction of extreme events.

Item Type: Article
Additional Information: Copyright of this article belongs to American Geophysical Union
Uncontrolled Keywords: Central India; Convective available potential energies; Convective events; Convective inhibition; Convergence zones; Daily rainfall; Disaster preparedness; Diurnal period; Extreme events; Extreme rainfall; Flash flood; Intraseasonal oscillations; Local topography; Mesoscale; Mesoscale circulation; Mesoscale structure; Multiscale interactions; Pre-monsoon; Rain events; Spatiotemporal distributions; Summer monsoon; Topographic features, Atmospheric thermodynamics; Disaster prevention; Flood control; Gravitational effects; Gravity waves; Hydrodynamics; Thunderstorms; Topography; Waves, Rain, atmospheric convection; data interpretation; disaster management; extreme event; flash flood; flood forecasting; monsoon; precipitation intensity; regional climate; spatiotemporal analysis; thunderstorm; topographic effect, India
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 22 May 2015 11:43
Last Modified: 22 May 2015 11:43
URI: http://moeseprints.incois.gov.in/id/eprint/794

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