A study of winds exceeding 20 mph at Delhi

Abstract

A study of the winds exceeding 20 mph at Delhi has been made from the anemogram data of the five years 1946-50. The winds have been classified into three groups namely (i) winds unassociated with weather (ii) winds associated with rain or thundery conditions (iii) winds associated with duststorms and thunder storms. Characteristics of the three groups in respect of their frequencies, maximum speed, direction etc have been noted. Situations causing winds without weather and those causing weather have also been briefly indicated.

Winds exceeding 20 mph occur at Delhi in all the months of the year being most frequent in May and June and least frequent in November .Strong winds unassociated with weather are more pronounced during the period from March to June. Winds associated with rain or thundery conditions are more frequent during monsoon months. The total duration of strong winds is on the average about 600 hours per year 75 per cent of which are  associated with west to northwest directions, northwest being most frequent, west coming next, then east and then north. Winds unassociated with weather and those accompanied by rain or thundery conditions reach a maximum speed of 40-45 miles per hour. Winds associated with duststorm and thunderstorm may, however, reaches 70 mph. Winds of the first group commence generally between 1000 and 1200 IST except during May to September when they commence at about 0700 IST. Winds of the second group have a greater tendency to conclude occur at noon in March, forenoon 'in July, both in the forenoon and afternoon in September and in afternoon and evening in May and June. Winds of the third group begin in the noon and afternoon in monsoon and pre. monsoon months and in the evening or in the early hours of night in other months.