Greenstone

All Geology books Selective books for competitive exams

Tropical cyclones are regarded as one of the most devastating natural calamities in the world. They originate and intensify over warm tropical oceans. These are ferocious storms that originate over oceans in tropical areas and move over to the coastal areas causing violent winds, very heavy rainfall, and storm outpourings. NAMES OF CYCLONE IN DIFFERENT REGIONS Cyclones in the Indian Ocean Hurricanes in the Atlantic Typhoons in the Western Pacific and the South China Sea Willy-willies in Western Australia CONDITIONS FOR THE FORMATION OF TROPICAL CYCLONE The conditions which favour the formation and intensification of tropical cyclone storms are:  Large sea surface with a temperature higher than 27° C Presence of the Coriolis force Small differences in the vertical wind speed A pre-existing weak- low-pressure area or low-level-cyclonic circulation Upper divergence above the sea level system  FORMATION OF CYCLONE The energy that strengthens the storm comes from the condensati

CLASSIFICATION OF PLANETARY WINDS The winds blowing almost in the same direction throughout the year are called prevailing or permanent winds. These are also called as invariable or planetary winds because they involve larger areas of the globe. On the other hand, winds with seasonal changes in their directions are called seasonal winds (e.g., monsoon winds). On an average, the location of high and low pressure belts is considered to be stationary on the globe (though they are seldom stationary). Consequently, winds blow from high pressure belts to low pressure belts. The direction of such winds remains more or less the same throughout the year though their areas change seasonally. Visualize Earth's Wind System Thus, such winds are called permanent winds. Since these winds are distributed all over the globe and these are related to thermally and dynamically induced pressure belts and rotation of the earth and hence they are called planetary winds. These winds include

MEANING OF JET STREAMS The strong and rapidly moving circumpolar westerly air circulation in a narrow belt of a few hundred kilometres width in the upper limit of troposphere is called jet stream. The circulation of westerly jet stream is confined between poles and 20° latitudes in both the hemispheres at the height of 7.5-14 km. According to  WHO, ‘a strong narrow current concentrated along a quasi- horizontal axis in the upper troposphere or in the stratosphere characterized by strong vertical and lateral wind shear and featuring one or more velocity maxima is called jet stream’. Click here for 3D Visualization of Jet streams PROPERTIES OF JET STREAMS: (1) The circulation of jet streams is from west to east in a narrow belt of a few hundred kilometres width at the height of 7.5 -14 km in the upper troposphere. (2) On an average, jet steams measure thousands of kilometers in length, a few hundred kilometers in width and a few kilometers (2-4 km) depth. (3) Generally, the

The horizontal movement of air is controlled by - Pressure Gradient force- This is the main driving force of global winds. This creates a wind from high-pressure, surplus areas to low-pressure, deficit areas. The closer isobars are together, the stronger the wind is. Coriolis force - This is the deflection of wind due to the Earth’s rotation. Deflecting right in the northern hemisphere and left in the southern, with an increasing effect towards the poles. It is not present in the equator. Geostropic wind - In mid-latitudes, the Pressure Gradient and Coriolis force are balanced. Therefore, air moves parallel to the isobars rather than from regions of high pressure to low pressure. Centripetal force- Air moving towards a low-pressure area in a defected path accelerates towards the centre of low pressure Frictional forces - Frictional drag from the Earth's surface decreases wind speed and modifies it's direction, crossing isobars as it moves from high-pressure regions