Characteristics of Diurnal Variation of Summer Monsoon Rainfall over ...

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slope of the Meghalaya Plateau or climbs over a deep. (several hundred meters to 1 km) pool of cold air and triggers precipitation over northeastern Bangladesh ...
Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 5(3): 217-221 © Scholarlink Research Institute Journals, 2014 (ISSN: 2141-7016) jeteas.scholarlinkresearch.org, Journal of Emerging Trends in jeteas.scholarlinkresearch.com Engineering and Applied Sciences (JETEAS) 5(3):217-221 (ISSN: 2141-7016)

Characteristics of Diurnal Variation of Summer Monsoon Rainfall over Bangladesh and its Adjacent Areas 1

M. T. H. Bhuiyan, 2M. D. I. Bhuyan, 3M. N. Chowdhury, 4 Choudhury Wahid and 5S. B. Faruque 1

Scientific Officer, DRiCM, Bangladesh Council of Scientific and Industrial Research (BCSIR); 2 Department of Physics, Mawlana Bhashani Science and Technology University, Tangail, Bangladesh; 3 University of Asia Pacific (UAP), Dhaka, Bangladesh; 4 Metropolitan University, Sylhet, Bangladesh; 5 Department of Physics, Shahjalal University of Science & Technology, Sylhet, Bangladesh. Corresponding Author: M. N. Chowdhury _________________________________________________________________________________________ Abstract This paper attempts to look into the diurnal variation of Summer Monsoon (JJAS) rainfall and its features over Bangladesh and its adjacent areas using Tropical Rainfall Measuring Mission (TRMM) 3B42 satellite gridded data for the period of 2001–2010. This analysis reveals dual maxima of three hourly rainfall which occur during noon to afternoon (1200 LST-1500 LST) and late night to early morning (0300 LST-0600 LST) periods over the study area. It also reveals that the interested area receives greater amount of daytime rainfall than the nighttime rainfall for last decade (2001-2010) and are not influenced by the heavy or less (drought) rainfall occurring years. Study on spatial variation of precipitation discloses that the maximum precipitation is observed near the coastal areas and northern regions of our studying domain. It is evident from the study that the monsoon season over these regions shows a gradual shift. But the most interesting outcome is we have found distinguished periodicity in the rainfall data pattern for three hourly rainfalls as well as daily and monthly even yearly total of daytime or nighttime rainfall whatsoever we consider. __________________________________________________________________________________________ Keywords: climatology, monsoon, diurnal variation, precipitation, convective activity. and in what order they changes day-to-day and hourto-hour or if there is any regular pattern in rainfall.

INTRODUCTION In climatology, the diurnal cycle is one of the most basic forms of climate patterns. The most familiar of such patterns is the diurnal temperature variation. Such a cycle may be approximately sinusoidal or include components of a truncated sinusoid (due to the sun's rising and setting). Diurnal rainfall variation means the daily or hourly variation of rainfall. Knowledge of the diurnal variation of precipitation is important for a complete understanding of the variability of the global energy and water balance as well as in applications to water resource management and hydrology. Bangladesh is one of the regions of heaviest rainfall in the world. The maximum climatic rainfall over Bangladesh is approximately 6000 mm during the summer monsoon [Matsumoto et al., 1996] and 60% of its annual rainfall happens during summer monsoon season. Since both social and economic life of this region mostly depends on agriculture which is mainly depends on the monsoon rainfall, so the beginning and ending of the monsoon season is very important for this area. The objective of this study is to address the question of how interannual diurnal and nocturnal summer rainfalls vary

A little research work has been done on the diurnal variations of precipitation in Bangladesh using remote sensing data. A study about the mechanism of the high late-night-early morning precipitation [A. Kataoka et. al., 1995] reveals that, at night, strong southwesterly monsoon winds transport a large amount of moisture over Bangladesh. The highly equivalent potential temperature air mass climbs the slope of the Meghalaya Plateau or climbs over a deep (several hundred meters to 1 km) pool of cold air and triggers precipitation over northeastern Bangladesh. Former study over the Bay of Bengal finds that the northwest side of the bay near most of the land-based rainfall, convective activity is organized into much larger and longer-lived systems. The diurnal cycle of all the systems over the bay, regardless of size, shows a 0600 local time (LT) maximum in very cold cloud tops (infrared brightness temperature, 210 K), with genesis occurring between 2100 LT and 0300 LT and the strength of the diurnal cycle varies greatly with location-with the northwest side of the bay 217

Journal of Emerging Trends in Engineering and Applied Sciences (JETEAS) 5(3):217-221 (ISSN: 2141-7016) we put these data into Excel sheet in order to analysis them.

experiencing both the highest amount of very cold cloudiness and the strongest diurnal cycle [P. Zuidema et al., 2002]. A study on diurnal variation of convective activity reveals that the diurnal variation of convective activity for tropical Asia finds maximum at 1700 LST and 1400 LST and minimum at 1100 LST and 2100 LST over land and sea respectively [N. Islam and T. Hayashi et al., 2004]. Toru Terao et. al., 2005, shows that the midnight to early morning rainfall peak is commonly seen in northeastern Bangladesh, Meghalaya and Assam area. N. Islam et. al., 2006, using Japanese Geostationary Meteorological Satellite (GMS-5) finds that the cloud embedded area (CEA) shows afternoon (1700 LST) and morning (0003 LST) peaks over land typically composed of relatively small deep (