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Synoptic Conditions on Severe Local Storm Days During the Pre-monsoon Season in Bangladesh

Yusuke Yamane
Pioneering Research Unit for Next Generation, Kyoto University, Gokasho, Uji, Kyoto, Japan,

Abstract/ Executive Summary:

Synoptic conditions on severe local storm days during the pre-monsoon season in Bangladesh are presented in this paper. Composite meteorological fields on severe local storm days were compared with those on non-severe local storm days. Features of synoptic conditions observed on severe local storm days are in the followings: (1) Increasing of specific humidity with intensification of southerly wind along the eastern coast of Indian peninsula up to Bangladesh in the lower layer (increasing of moisture inflow from the Bay of Bengal) (2) Increasing of the lapse rate of temperature in Bangladesh caused by warming centered over inland of Indian peninsula in the lower layer and cold air advection from the north in the middle layer. Thus, potential instability of the atmosphere was increasing on severe local storm days in Bangladesh.

Keywords: Severe local storm, Synoptic condition, Bangladesh, Pre-monsoon

Location:

Start Date:

End Date:

Program Area: Risk Management in Agriculture

Non-commodity: Storm

Objectives:

The purpose of investigating synoptic conditions on severe local storm days, composite meteorological situations of severe local storm days were compared with those of non-severe local storm days (days with no report of severe local storm) in this study.

Methodology:

The data used in this study was NCEP FNL data. The period of analysis was from 2002 to 2005. The domain is from 65⁰E to 95⁰E and from 5⁰N to 27⁰N covering almost entire area of the south Asia. The data at 00 UTC (06 Bangladesh Standard Time, BST) are used in the present study. 159 severe local storm days and 381 non-severe local storm days during the pre-monsoon season were identified in the present study. Comparing composite meteorological conditions of severe local storm days with those of non-severe local storm days (days with no report of severe local storm in Bangladesh) is performed to clarify synoptic situations in the outbreaks of severe local storms.

Source of Information: 2nd International Conference on Water & Flood Management (ICWFM-2009), BUET, Dhaka, Bangladesh

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

This study presents synoptic conditions on severe local storm days during the pre-monsoon season in Bangladesh by using NCEP FNL data. Composite meteorological fields on severe local storm days (159 days) were compared with those on non-severe local storm days (381 days). The results showed that positive difference of specific humidity in the lower levels (especially, at the level of 900 hPa) in Bangladesh between severe local storm days and non-severe local storm days with the statistical significance. In addition, southerly wind was intensified in the lower levels (especially, at the level of 900 hPa) along the eastern cost of the Indian Peninsula up to Bangladesh on severe local storm days. Increasing of specific humidity on severe local storm days was due to increasing of moisture inflow from the Bay of Bengal. Positive difference of temperature between severe local storm days and non-severe local storm days caused by warming over the inland of Indian peninsula was observed at the level of 800 hPa in Bangladesh, and negative difference of temperature caused by cold air advection from the north was found at the level of 550 hPa. Therefore, the lapse rate of temperature was larger on severe local storm days. Thus, potential instability is increasing on severe local storm days in Bangladesh. Lifted Index, which is an index of potential instability, is significantly negative in Bangladesh on severe local storm days. This quantitatively indicates large potential instability is produced on severe local storm days in Bangladesh.

From this study, it can not mention synoptic dynamic mechanism of formation of potential instability in Bangladesh (for example, dynamic mechanism of intensification of southerly wind in the lower layer). Clarifying this point is the most important our work in the future.

Knowledge Management: Report/Proceedings