Articles of the Month

06-June-2015

Western Disturbance

WD is the term used in India, Pakistan, Bangladesh and Nepal to describe an extratropical storm originating in the Mediterranean, that brings sudden winter rain and snow to the northwestern parts of the Indian subcontinent.This is a non-monsoonal precipitation pattern driven by the Westerlies. The moisture in these storms usually originates over the Mediterranean Sea and theAtlantic Ocean. Extratropical storms are a global, rather than a localized, phenomena with moisture usually carried in the upper atmosphere (unlike tropical storms where it is carried in the lower atmosphere). In the case of the subcontinent, moisture is sometimes shed as rain when the storm system encounters the Himalayas.

Western Disturbances are important to the development of the Rabi crop in the northern subcontinent, 

which includes the locally important staple wheat.

Role of Western Distrubance

Western Disturbance causes winter and pre monsoon season rainfall across north Pakistan northwest India. Winter months Rainfall has great importance in agriculture, particularly for the rabi crops. Wheat among them is one of the most important crops, which helps to meet India’s food security. During the season, normally 4-5 western disturbances in a month can be seen over north Pakistan. Some of the western disturbances bring well-distributed and good rainfall, while some pass with negligible rain or sometimes no rain. The Western disturbance affects day-to-day weather of north Pakistan especially during winter season. It is usually associated with cloudy sky, higher night temperatures, unusual rain etc. Over the plains of Punjab, it brings cold wave conditions and occasionally dense fog and cold day conditions. These conditions remain stable until it is disturbed by another Western Disturbances.

emperatures, unusual rain etc. Over the plains of Punjab, it brings cold wave conditions and occasionally dense fog and cold day conditions. These conditions remain stable until it is disturbed by another Western Disturbances.

Role of Western Disturbance befor South West Moonsoon

When the Western Disturbance moves across upper Pakistan before the onset of monsoon, a temporary advancement of monsoon current appears over the North Punjab,KP ,Jammu and Kashmir etc. When it passes across north Pakitan, it helps to increase monsoon activity over Punjab and Kashmir.The numbers of western disturbances start declining after winter to pre-monsoon season. During hot weather months of April and May, they move across north Pakistan. Monsoon current generally progresses from east to west in northern Himalayan region of Pakistan. But western disturbances follows reverse trend i.e. they move from west to east across north Pakistan with consequent rise in pressure carrying cold pool of air. So it helps to activate monsoon in certain parts of north Pakistan.During winter,there is an inflow of low pressure depressions called western disturbances in north-Pakistan.These westerly depressions originate in Pakistan and enter Pakistan after ,Iran and Iraq and Afghanistan.They intensify over the Pakistan and north west India and move eastwards causing wheat.

Tropical Cyclone Basins

04-June-2015

Traditionally, areas of tropical cyclone formation are divided into seven basins. These include the northAtlantic Ocean, the eastern and western parts of the northern Pacific Ocean, the southwestern Pacific, the southwestern and southeastern Indian Oceans, and the northern Indian Ocean (Arabian Sea and Bay of Bengal). The western Pacific is the most active and the north Indian the least active. An average of 86 tropical cyclones of tropical storm intensity form annually worldwide, with 47 reaching hurricane/typhoon strength, and 20 becoming intense tropical cyclones (at least of Category 3 intensity)

This map shows the tracks of all tropical cyclones monitored by the Joint Typhoon Warning Center in the North Indian Ocean from 1980 to 2005. The points show the locations of each storm at six-hour intervals. The colour represents the storm's maximum sustained wind speeds as classified in the Saffir-Simpson Hurricane Scale (see below), and the shape of the data points represent the nature of the storm.

In this article we will discuss about Indian Oceans. This basin is divided into two areas: the Bay of Bengal and the Arabian Sea, with the Bay of Bengal dominating (5 to 6 times more activity). Still, this basin is the most inactive worldwide, with only 4 to 6 storms per year. This basin's season has a double peak: one in April and May, before the onset of the monsoon, and another in October and November, Although it is an inactive basin, the deadliest tropical cyclones in the world have formed here, including the 1970 Bhola cyclone, which killed 500,000 people. Nations affected include India, Bangladesh, Sri Lanka, Thailand,Myanmar, and Pakistan. Rarely do tropical cyclones that form in this basin affect theArabian Peninsula or Somalia; however, Cyclone Gonu caused heavy damage in Oman on the peninsula in 2007.

Tracks of all tropical cyclones in the northern Indian Ocean between 1980 and 2005