Monitoring of High Wind Speeds
The accurate measurement of wind power, wind speed and direction will provide a greater help to
the weather man, particularly during cyclone time. It will also help in tracking the cyclone
accurately and to estimate its devastating potential.
India Meteorological Department has recently installed 20 High Wind Speed
Recorders (HWSR) along the East and West Coasts of India. HWSR is having a solid-state
sensor with no moving parts. It is capable of providing uninterrupted data in cyclone prone
coastal areas in severe weather conditions including high winds and heavy rains. The system
is capable of measuring wind speeds up to 0-65 mps with an accuracy of 1.5 per cent rms and
a resolution of 0.01 mps.
The system has monitored high wind speed during December 2003 Machilipatnam
cyclone. A complete description of HWSR system and the wind data as observed during the
cyclone is presented in this paper.
1. INTRODUCTION
Tropical cyclone is an atmospheric system in which very strong winds prevail
over a large part. It also consists of a huge mass of revolving moist air. Within this system
there is an annular zone close to the earth’s surface, sea or land where wind speeds of 25
to 50 mps are encountered. On rare occasions wind speed can be as high as 65 mps with
gust superposed. The winds are weaker towards the centre as well as towards the
periphery of the system. The sense of rotation of this large mass of air is anticlockwise in
the northern hemisphere. This large revolving mass of moist air has a deficiency of
atmospheric air pressure throughout the system. The deficiency of pressure at the centre is
often about 2% below the normal. The amount of pressure deficiency at the centre
determines the severity of the cyclone. The horizontal pressure gradient from the periphery
to the centre is small almost half the way and thereafter it becomes steep. This rapid
decrease of pressure with horizontal distance coupled with forces brought into play by the
rotation of earth around polar axis gives rise to the very strong winds of 25 to 50 mps or
even more. The revolving system moves as a whole and the direction of displacement in
the Indian latitudes is between West-North-West and East-North-East.