Winds, Storms and Cyclones Science(chap-8)

                                            Winds, Storms and Cyclones    Science(chap-8)

§  The moving air is called the wind.

§  Air around us exerts pressure.

§  Increased wind speed is, indeed, accompanied by a reduced air pressure.

§  Air always moves from the region where the air pressure is high to the low pressured region.

§  The greater the difference in pressure, the faster the air moves.

§  On heating, the air expands and occupies more space and becomes lighter. Therefore, the warm air is lighter than the cold air.

§  When warm air rises at a place, the air pressure of that place is lowered. The cold air from the surrounding area rushes in to fill its place. This sets up convection in air.

§  Wind currents are generated because of uneven heating between the equator and the poles.

§  The regions close to the equator get maximum heat from the sun. The air from these warm regions when rises up, the cooler air from the regions in between 0’-30’ degree latitude belt on either side of the equator moves in. these winds blow from the north and the south towards the equator.

§  At the Poles, the air is cooler than that at latitudes about 60 degrees. The warm air at these latitudes rises up and the cold wind from the Polar regions rushes in, to take its place. In this manner, wind circulation is set up from the Poles to the warmer latitudes.

§  A change in direction of wind is caused by the rotation of the earth.

§  In summer, near the equator the land warms up faster and most of the time the temperature of the land is higher than that of water in the oceans. The air over the land gets heated and rises. This causes the winds to blow from the ocean towards the land. This wind is known as monsoon wind.

§  The winds from the oceans carry water and brings rain. It is a part of water cycle. The monsoon winds carry water and it rains.

§  The word ‘monsoon’ is derived from the Arabic word ‘mausam’ which means season.

§  Uneven heating of wind especially the Rajasthan desert of India generates monsoon winds from south-west direction in summer. These winds carry lots of water from the Indian ocean.

§  In winter season, the direction of the wind blow gets reversed from the land to the ocean.

§   Uneven heating of land and water in winter generates winds from the north-west colder land. These cooler winds carry little water, hence bring small amount of rain in winter.

§  Uneven heating on the earth is the main cause of wind movements.

§  Thunderstorms & Cyclones:

§  Thunderstorms develop in hot, humid tropical areas like India very frequently.

§  The rising temperatures produce strong upward rising winds. These winds carry water droplets upwards, where they freeze and fall down again.

§  The swift movement of the falling water droplets along with the rising air creating lightning and sound is called thunderstorm.

§  Before cloud formation, water takes up heat from the atmosphere to change into vapour. When water vapour changes back to liquid form as raindrops, this heat is released to the atmosphere and warms the air around. The air tends to rise and causes a drop of pressure. When more air rushes  to the centre of the storm, the chain of events ends with the formation of low pressure system with high speed winds revolving around it. This weather condition is called Cyclone.

§  The centre of a cyclone which is called as the eye of the storm is a calm area. The diameter of the eye varies from 10- 30 kms region.

§  Around the calm and clear eye of the cyclone, there is a cloud region of about 150 kms in size. In this area there blows high speed wind (150-250km/hr) and thick clouds with heavy rain. Away from this region the wind speed gradually decreases.

§  Factors like wind speed, wind direction, temperature and humidity lead to the formation of cyclones.

§  Cyclones are very destructive in nature. Strong winds push water towards the shore even if the storm is hundreds of kilometers away.

§  The low pressure in the eye lifts water surface in the centre. The rising of water may be as high as 3-12 meters.

§  The whole coastline of India is vulnerable to cyclones, particularly the east coast lines.

§  A cyclone is known to different names in different parts of the world. It is called a ‘hurricane’ in America. In Philippines and Japan it is called ‘typhoon’.

§  A Tornado is a dark funnel shaped cloud that reaches from the sky to the ground. A violent tornado can be as small as a meter and as large as a kilometer or even wide.

§  The funnel of a tornado sucks dust, debris and everything near it at the base(due to low pressure) and throws them out near the top.

§  The instrument used to measure wind speed is called Anemometer.