Cloudburst events observed over Uttarakhand during monsoon season 2017 and their analysis

Cloudburst is an extreme weather event characterised by the occurrence of a large amount of rainfall over a small area within a short span of time with a rainfall of 100 mm or more in one hour. It is responsible for flash flood, inundation of low lying areas and landslides in hills causing extensive damages to life and property. During monsoon season 2017 five number of cloudburst events are observed over Uttarakhand and analysed. Self Recording Rain Gauge (SRRG) and 15 minutes interval data from the newly installed General Packet Radio Service (GPRS) based Automatic Weather Station (AWS) are able to capture the cloudburst events over some areas in Uttarakhand. In this paper, an attempt has been made to find out the significant synoptic and thermodynamic conditions associated with the occurrence of the cloudburst events in Uttarakhand. These 5 cases of cloudburst events that are captured during the month of June, July and August 2017 in Uttarakhand are studied in detail. Synoptically, it is observed that the existence of trough at mean sea level from Punjab to head Bay of Bengal running close to Uttarakhand, the movement of Western Disturbance over north Pakistan and adjoining Jammu & Kashmir and existence of cyclonic circulation over north Rajasthan and neighbourhood are favourable conditions. Also, the presence of strong south-westerly wind flow from the Arabian Sea across West Rajasthan and Haryana on upper air charts are found during these events. Thermodynamically, the Convective Available Potential Energy (CAPE) is found to be high (more than 1100 J/Kg) during most of the cases and vertically integrated precipitable water content (PWC) is more than 55mm. The GPRS based AWS system can help in prediction of the cloud burst event over the specified location with a lead time upto half to one hour in association with radar products.

Diurnal variation of cloudiness during southwest monsoon season using I NSAT-IB radiance data

An attempt has been made to study the diurnal variation of convective clouds. For this study 3 hourly full resolution infrared data of INSAT-IB have been used for the monsoon season (Jun-Sep) of 1987-89. The area of study extends from 35°N to 25°S and 40oE to l00oE, which is subdivided into small areas of 2.5x 2.5 Lat./Long. Mean temperature and the fractional area covered by clouds colder than a given threshold temperature over each sub area are the parameters used for this study. Two threshold temperatures. namely 265°K & 235oK are chosen to represent convective clouds and deep convective clouds respectively. Using the three hourly observations, times of maximum and minimum convective activity are also obtained. Maximum convective activity is observed over head Bay of Bengal at about noon and this maximum migrates westward onto land till midnight and swings back to oceanic area by morning. This eastwest oscillation is less over equatorial regions (open ocean).

Cyclonic storm of 13-14 September 1958 in the Bay of Bengal - A radar study

Photographs of radar observations taken at Calcutta of a cyclonic storm of 13.14 September 1958 in the head Bay of Bengal are presented in the paper. It is interesting that with a cyclone of moderate inters. city, the eye of the storm was clearly seen on the radarscope in the form of a 'hook', which enabled accurate location of the storm. Such detection of the eye on the radarscope is the first of its kind in the Indian latitudes. The observed dimension and movement of the 'eye' and the associated observed precipitation echoes around the storm centre are discussed.

A Transformed Coordinate Model to Predict Tide and Surge Along the Head Bay of Bengal- Application to Cyclone of 1991 and 1970

The head Bay of Bengal region is one of the most vulnerable regions for extreme water levels associated with severe tropical cyclones. The shallow nature of the head Bay, presence of a large number of deltas formed by major rivers and high tidal range are responsible for storm surge flooding in the region. Specifically, the rise and fall of tidal phases influence the height, duration, and arrival time of peak surge along the coast. The objective of the present study is to evaluate the tide-surge interaction during the super cyclone of 1991 and 1970. A transformed coordinate model is developed to estimate the possible water levels along the coast of Bangladesh.GANIT J. Bangladesh Math. Soc.Vol. 35 (2015) 7-25