Kerala State Syllabus 10th Standard Social Science Notes Chapter 2 In search of the Source of Wind
Atmospheric phenomena like temperature, pressure, rain and wind are essential for the existence of life on the earth. Since the axis of the earth is tilted at an angle of 231/2°, solar energy received on the surface of the earth is not always uniform. Difference in temperature causes difference in pressure. This leads to change in the direction and velocity of winds. Winds that blow in different directions with different velocity considerably influence human life. The position of continents and oceans determine the nature of winds. Thus this unit discusses different atmospheric phenomena, the winds that cause due to these phenomena and the influence of these winds in human life.
→ Atmospheric pressure : The weight of atmospheric air.
→ Mercury barometer : The instrument used for the measurement of atmospheric pressure.
→ Hecto Pascal (hPa)/ millibar : The unit used for the measurement of atmospheric pressure.
→ The factors influencing atmospheric pressure : Temperature, altitude of a place, humidity.
→ Humidity: The quantity of water vapour present in the atmosphere.
→ Isobars: Imaginary lines drawn on maps joining places having the same atmospheric pressure.
→ Global pressure belts : Generally the earth experiences the same atmospheric pressure between certain latitudes. Those latitudinal zones are called global pressure belts.
→ Horse latitudes: The subtropical high pressure belt in the Atlantic ocean devoid of winds are known as horse latitudes.
→ Doldrum : The low pressure region about 5°N and 5°S of the equator characterised by feable wind is called doldrum.
→ Wind : The horizontal movement of air from a high pressure zone to a low pressure zone is called wind.
→ The factors that influence the speed and direction of winds : Pressure gradient, Coriolis force and friction.
→ Coriolis force : Due to the force generated as a result of the rotation of the earth, any freely moving body on the earth’s surface gets deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere.
→ Ferrel’s Law : The law formulated by Admiral Ferrel on the deflection of winds under the influence of Coriolis force.
→ Planetary winds: The winds developed between global pressure belts and blow in the same direction throughout the year are called planetary winds.
→ Trade winds : The steady winds that blow continuously from subtropical high pressure belts to equatorial low pressure belt.
→ Westerlies: Winds that blow continuously from subtropical high pressure belts to subpolar low pressure belts.
→ Polar winds: Winds that blow from polar high pressure belts to subpolar low pressure belts.
→ Periodic winds : Winds that repeat at regular intervals of time and can be seasonal or diurnal.
→ Monsoon winds : Winds that change the direction with change in seasons.
→ Land breeze/ sea breeze : Winds that cause as a result of the unequal heating and cooling of land and sea and the resultant pressure change. Valley breeze : Winds that blow from valleys to the mountain tops during the day.
→ Mountain breeze: Winds that blow from the mountain tops to valleys during the night.
→ Local winds : Winds formed as a result of the local differences in atmospheric pressure.
→ Variable winds: Winds with entirely different characteristics formed during certain atmospheric situations.
→ Cyclones : A low atmospheric pressure at centre surrounded by high pressure regions with strong whirlwinds blowing.
→ Anticyclones : Phenomenon where strong whirl winds blow from high pressure centre to, the surrounding low pressure areas.