Wind, Types of Wind, Daily and Seasonal Variations PDF

B.SC. HONS AG. Wind, Types of Wind, Daily and Seasonal Variation of Wind Speed @AGRICULTURAL_STUDIES  WHAT IS WIND ? Wind Air in horizontal motion is known as “Wind”. Winds are named by the direction they come from. Windward refers to the direction a wind...

B.SC. HONS AG. Wind, Types of Wind, Daily and Seasonal Variation of Wind Speed @AGRICULTURAL_STUDIES  WHAT IS WIND ? Wind Air in horizontal motion is known as “Wind”. Winds are named by the direction they come from. Windward refers to the direction a wind comes from and leeward is the direction towards which it flows. The wind which flows more frequently from one direction than any other is called as “Prevailing wind”  Importance of wind for crops: Transports heat in either sensible or latent form, from lower to higher latitudes Provides the moisture (to the land masses) which is necessary for precipitation Moderate turbulence promotes the consumption of carbon – dioxide by photosynthesis. Wind prevents frost by disrupting a temperature inversion Wind dispersal of pollen and seeds is natural and necessary for certain agricultural crops, natural vegetation, etc.  DO YOU KNOW ? Wind turning to the right from its courses (clock wise direction) is called Veering wind. And that turning to the left (anti-clock wise direction) is called Backing wind.  FACTORS AFFECTING WIND 1. PRESSURE GRADIENT FORCE 2. Frictional force 3. Coriolis force 4. Gravitational force  Pressure Gradient Force The differences in atmospheric pressure produces pressure gradient force. The rate of change of pressure with respect to distance is the pressure gradient. Pressure Gradient Force operates from the high pressure area to a low pressure area and causes wind movement. The pressure gradient is strong where the isobars are close to each other and is weak where the isobars are apart. Since a closely spaced gradient implies a steep pressure change, it also indicates a strong wind speed. The wind direction follows the direction of change of pressure, i.e. perpendicular to the isobars.  Coriolis Force The rotation of the earth about its axis affects the direction of the wind. This force is called the Coriolis force. It has great impact on the direction of wind movement. Due to the earth’s rotation, winds do not cross the isobars at right angles as the pressure gradient force directs, but get deflected from their original path. This deviation is the result of the earth’s rotation and is called the Coriolis effect or Coriolis force. Due to this effect, winds in the northern hemisphere get deflected to the right of their path and those in the southern hemisphere to their left, following Farrell’s Law (the law that wind is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, derived from the application of the Coriolis effect to air masses). This deflection force does not seem to exist until the air is set in motion and increases with wind velocity, air mass and an increase in latitude. The Coriolis force acts perpendicular to the pressure gradient force (pressure gradient force is perpendicular to an isobar)  Frictional Force The irregularities of the earth’s surface offer resistance to the wind movement in the form of friction. It affects the speed of the wind. It is greatest at the surface and its influence generally extends up to an elevation of 1 – 3 km. Over the sea surface the friction is minimal. Over uneven terrain, however, due to high friction, the wind direction makes high angles with, isobars and the speed gets retarded. PLANETARY / PRIMARY/ PREVAILING /PERMANENT Winds 1. Trade wind: Wind blows from subtropical high pressure located at about 30° N and S towards the low pressure at equator. These winds are called trade winds. In northern hemisphere, trade winds blow from north-east and in the southern hemisphere from south-east due to coriolis force. The equatorial trough of low pressure belt (doldrums) lies in the vicinity of equator 5° N and S, though it extends more to south than to north. The air remains warm and moist throughout the equatorial low belt (doldrums).  PLANETARY / PRIMARY/ PREVAILING /PERMANENT Winds 2. Westerlies In the middle latitude (30 to 60° N and S), the winds blow from subtropical high pressure belt (30°) in each hemisphere to sub-polar low pressure region (60°). Due to N-S pressure gradient, winds blow from south to north and due to Coriolis force it is deflected towards east and thus forms the westerly winds. These are also called middle latitude westerlies. In the northern hemisphere, these wind blows from south-west (SW) and in southern hemisphere from north-west (NW) directions. 3. Polar easterlies: In the polar region, pressure gradient is from polar to sub-polar region in both the hemispheres. Due to Coriolis force, winds blowing from north to south become north-easterly in northern hemisphere. These are called polar easterlies  PLANETARY / PRIMARY/ PREVAILING /PERMANENT Winds 3. Polar easterlies: In the polar region, pressure gradient is from polar to sub-polar region in both the hemispheres. Due to Coriolis force, winds blowing from north to south become north-easterly in northern hemisphere. These are called polar easterlies LOCAL WINDS Land and Sea Breezes Ocean water is slower to warm up and cool down than land. So the sea surface is cooler than the land in the daytime. It is also cooler than the land in the summer. The opposite is also true. The water stays warmer than the land during the night and the winter. These differences in heating cause local winds known as land and sea breezes A sea breeze blows from sea to land during the day or in summer. That’s when air over the land is warmer than air over the water. The warm air rises. Cool air from over the water flows in to take its place. A land breeze blows from land to sea during the night or in winter. That’s when air over the water is warmer than air over the land. The warm air rises. Cool air from the land flows out to take its place. LOCAL WINDS Mountain and Valley Breezes The air on a mountain slope warms more than the air over the nearby valley. The warm air rises and brings cool air up from below. This is a valley breeze. At night the mountain slope cools more than the air over the valley. The air flows downhill creating a mountain breeze. YOU SHOULD ALSO KNOW >> Katabatic winds move the same way as mountain and valley breezes. However, they are much stronger. Katabatic winds form over a high plateau that is surrounded by mountains. In winter, the plateau grows cold. Air sinks through the gaps in the mountains. Over Antarctica and Greenland, these winds are frigid. SEASONAL Monsoons WINDS Monsoons are like land and sea breezes, but on a larger scale. They occur because of seasonal changes in the temperature of land and water. In the winter, they blow from land to water. In the summer, they blow from water to land. In regions that experience monsoons, the seawater offshore is extremely warm. The hot air absorbs a lot of the moisture and carries it over the land. Summer monsoons bring heavy rains on land. Monsoons occur in several places around the globe. The most important monsoon in the world is in southern Asia. These monsoons are important because they carry water to the many people who live there.  THANK YOU 😁 IF YOU LIKE CONTENT OF AGRICULTURAL STUDIES, THEN DO SUSCRIBE TO IT & SHARE AS MUCH AS YOU CAN. ❤