com www.GOALias.blogspot.com www.GOALias ... - fun learning

www.GOALias.blogspot.com8.5 T8.5 THUNDERSTORMSAND CYCLONESThunderstorms develop in hot, humidtropical areas like India very frequently.The rising temperatures produce strongupward rising winds. These winds carrywater droplets upwards, where theyfreeze, and fall down again. The swiftmovement of the falling water dropletsalong with the rising air create lightningand sound. It is this event that we call athunderstorm. You will read aboutlightning in higher classes.If a storm is accompanied bylightning, we must take the followingprecautions:• Do not take shelter under anisolated tree. If you are in a foresttake shelter under a small tree. Donot lie on the ground.• Do not take shelter under anumbrella with a metallic end.• Do not sit near a window. Opengarages, storage sheds, metalsheds are not safe places to takeshelter.• A car or a bus is a safe place totake shelter.• If you are in water, get out and goinside a building.How a thunderstorm becomesa cycloneYou know that water requires heat whenit changes from liquid to vapour state.Does the water give back heat whenvapour condenses into liquid? Can yourecall any experience to support this?Structure of a cycloneThe centre of a cyclone is a calm area.It is called the eye of the storm. A largecyclone is a violently rotating mass ofair in the atmosphere, 10 to 15 kmhigh. The diameter of the eye variesfrom 10 to 30 km (Fig. 8.11). It is aregion free of clouds and has lightwinds. Around this calm and clear eye(Fig. 8.12), there is a cloud region ofabout 150 km in size. In this regionthere are high-speed winds (150–250km/h) and thick clouds with heavyrain. Away from this region the windspeed gradually decreases. Theformation of a cyclone is a verycomplex process. A model is shown inFig. 8.11.Before cloud formation, water takesup heat from the atmosphere to changeinto vapour. When water vapour changesback to liquid form as raindrops, thisheat is released to the atmosphere. Theheat released to the atmosphere warmsthe air around. The air tends to rise andcauses a drop in pressure. More airrushes to the centre of the storm. Thiscycle is repeated. The chain of eventsends with the formation of a verylow-pressure system with veryhigh-speed winds revolving around it.It is this weather condition that we calla cyclone. Factors like wind speed,wind direction, temperature andhumidity contribute to the developmentof cyclones., SWINDSINDS, , STORMSAND CYCLONES8787