2. WINDS,STORMS AND CYCLONES Chapter 14

3. Objectives: Recognise the causes and characteristics of wind Understand the properties of wind Analyse wind current and causes Describe the causes of thunderstorms, cyclones and tornadoes List possible safety measures during natural calamities

4. Overview True or False Air is something which we cannot see but feel its presence. It is present everywhere around us. _______ It is essential for the survival of plants and animals. _______ Moving air helps us to do many other activities such as flying kite or moving a sailboat.________ True

5. Fill in the blank Natural resources such as a_, w____, w___ and the l____ are essential for our survival However, these resources can also be the biggest destroyer of life when these are e_____ or d_____ amount For example, heavy rain causes f_____and lack of rain causes d_____. Just like water in the form of heavy rain, air is sometime quite dangerous when it blows with high speed is called s___ __. Overview continues irater ind ight xcess eficit lood rought torm

6. 1. The moving air is called ____ 2. Air when moves with high speed is called ___________ 3. A storm may be devastating in nature causing severe damage due to its ______ and strength 4. ___________ is accompanied by thunder and lightning during monsoon. wind_ storm force Thunderstorm

7. What are the causes of wind? 5. Wind is caused by the ___pic 1__ of the _Earth’s_ surface by the heat of the _Sun_. 6. This is due to the Earth’s (position)_tilt_ and ___________ shape different regions of the Earth’s surface receive _different amount of heat. 7. Thus, the temperature of the Earth’s surface near the equator ________________than that near the geographic poles of the Earth. CHECK YOURSELF uneven heating spherical gets heated up more Pic #1 Pic #2

8. What are the causes of wind? 8. As a result, air near the equator gets ________than the air in the Polar regions. 9. The hot air being lighter will __________than cold air will expands 10. The cool air moves from nearby region to occupy the vacant space near the region of ___________ 11. Hence, an air current sets up and air begins to move from one place (______region) to another place (_____ region). 12. Thus, wind is caused due to the temperature ________________ between different regions warmer Rise up cold Hot air hot difference

9. Wind is produced by uneven heating between: 10. _Equator and _geographic_ poles of the Earth due to - Earth’s _____ (23.45 degrees) - Earth’s _________ shape And it is also due to uneven heating between _____ and _________ CHECK YOURSELF tilt spherical land ocean

10. Wind is produced by uneven heating between: 11. During summer season in Northern hemisphere, the land becomes very hot as compare to the ______________. 12. The hot air above the land ________and moist air above the oceans begins to blow towards the ___________. 13. This moist and cooler rain-bearing winds move from Arabian Sea to the Bay of Bengal, give rice to air currents and bring heavy rainfall in almost all parts of India, these winds are called the ___________ monsoon winds. 14. During the winter season, dry and cold winds blow from colder north-west region of the land to the ocean. These winds cause rain in coastal Tamil Nadu whereas the rest of the country receives limited rain. These winds are called the _______________ monsoon winds oceans Rises up land summer winter

11. AIR PRESSURE We know that air is a mixture of several gases. The molecules of gases in air are in continuous Motion. When the air is confined in A container like balloon, the molecules collide with each other. 15. However, the molecules located near the wall collide with the wall, the collisions of these molecules exerts a force on the area of the wall, this is called an Air pressure on the wall of container. Pressure = Force/Areas. 16. Earth is surrounded by a blanket of air is called atmosphere 17. The name of the pressure that exerts the Earth is called atmospheric pressure

12. 3 FACTORS AFFECTING AIR PRESSURE 1. ALTITUDE the air pressure decreases as we move upwards from the surface of the Earth. This is because the number of air molecules gets reduced at higher altitude which in turn reduces atmospheric pressure. 2. Temperature, when the temperature increases, air expands and the air pressure decreases. When temperature decreases, air contracts and the air pressure increases 3. Water vapour, when the humidity is high, the air pressure is less. This is because moist air is less dense than dry air due to which it exerts less air pressure than dry air.

13. Recap 1.Wind is caused due to the temperature differences between different regions 2.From the factors affect air pressure that Temperature changes will change air pressure inversely, therefore we can say that wind is caused due to air pressure difference between different regions. 3.Wind blows from high pressure region to low pressure region. 4.When wind blows with high speed, it also blows a large amount of air from that region. Thus, the high speed wind causes reduced Pressure.

14. CHARACTERISTICS OF WIND Wind has two characteristics that play an important role in the formation of natural phenomenon like thunderstorms, cyclones, tornadoes and others. 1.Wind speed, is measured by an instrument called anemometer. The anemometer is consists of 3 to 4 cups mounted on a rod that can rotate freely on its axis. The greater the speed of the wind, the faster the cups rotate the rod. A scale is placed at the bottom of the anemometer records the wind speed in the desired unit measurement.

15. CHARACTERISTICS OF WIND 2. Wind direction, is the second characteristic of wind which gives the direction of the wind using an instrument called weather vane or wind vane When the wind is sufficiently strong, the arrow aligns itself such that its tip pointed towards the direction of the wind. Four directions- North, South, East and West WHAT IS THE PURPOSE OF KNOWING THE SPEED AND DIRECTION OF THE WIND ?

16. RECAP 1. Wind blows from a region of high pressure to a region of low pressure 2. Hot air expands and rises up whereas cool air contracts and sinks or descends down 3. High speed wind are accompanied with reduced pressure. 4. Wind has two characteristics – wind speed and wind direction. 5. Wind is caused due to uneven heating of the Earth’s surface. 6. Air moves from the region of low temperature to the region of high temperature. (high or low) 7. Air moves from the region of high pressure to the region of low pressure. 8. The atmospheric pressure decreases as we move upwards from the surface of the Earth. 9. Moving air decreases the air pressure

17. THUNDERSTORM a) In hot and humid tropical regions like India, thunderstorms or lightning storms are known to occur frequently. b). Thunderstorms are storms accompanied by thunder, lightning and heavy rains or sometimes accompanied by snow or hail. c). The heat of the sun in the tropical region heats up the air near the Earth’s surface. This hot air rises up. The water vapour present in air due to humidity also rises up along with hot air. As water vapour reaches the upper layer of atmosphere which is comparatively cooler than the Earth’s surface, it cools and condenses to form clouds. The clouds of water vapour further cools to form water droplets that falls towards the Earth in the form of rain. Some of the droplets freeze and fall as snow or hail, while falling down, the collision between the water droplets and ice crystals takes place due to the rising air and fast moving wind. During collision, the friction between them causes the clouds to get electrically charged. When this charged clouds get discharged, they produce huge sparks. This sparks are seen in the form of lightning. The lightning rapidly heats the air in its path that results in a loud sound that is heard as thunder. This is the reason why lightning is generally accompanied by thunder. d). Severe thunderstorm sometimes produces approximately 600 lightning strikes every minute.

18. Safety Measures During the Thunderstorm: true or false 1. Take shelter under a tall and isolated tree. ________ as it is closer to the clouds and more likely to hit by lightning than other small tress, 2. Do not use umbrella having metallic tip or base _________ 3. Avoid tall metallic structures such as electricity poles and cell phone towers, open areas and vehicles such as rooftops, parks, fields and motorbikes. ________ 4. If you are inside the house, stay close to the windows. _______ 5. Use mobile phones during thunderstorm when outside to ask for help._____ 6. Avoid standing in waterlogged places. Strictly avoid bathing in swimming pool or river.______ 7. Move into a building or dry area during thunderstorm. Closed vehicles such as cars or buses are safe place to take shelter._____ as it is closer to the clouds and more likely to hit by lightning than other small tress FALSE metal is a good conductor of electricity and allow lightning to pass through it. TRUE move away from there for safety. Away from possible lightning strikes. FALSE It is attracted to lightning TRUE If lightning strikes to water possible electrocution TRUE Safer place to stay, no possible conduct of electricity

19. CYCLONE 1.A powerful circular storms that are formed over a low pressure areas are known as cyclones. 2.They can be around 80 – 200 km in diameter. They are usually formed in warm and wet conditions, which generally found near the equator, over the warm water of oceans. 3.Cyclones are also known as hurricanes (in Atlantic and Northeast Pacific Ocean) or typhoons (in Northwest Pacific Ocean). 4.Certain factors that contribute to the development of a cyclone such as: temperature, humidity, wind speed, and wind direction. 5.A cyclone develops at the centre of a low- pressure area, the centre of a cyclone is called the eye. The diameter of the eye is around 10- 30 km. 6.At the eye, there is no rain and clouds, also the winds are fairly calm, the eye is surrounded by thick clouds and thunderstorms accompanied by heavy rain and a strong winds having speed of 150-250kph move in circles around the eye.

20. Assignment due next meeting. 1.Describe how cyclones form within 8-10 sentences only. Use your own words 2.How the current technology has enabled us to predict the possibility of occurrence of cyclone? 3.Enumerate safety measures during cyclones 4.What is tornado and safety measures? REMINDER: TOMORROW I WILL GIVE YOU EXERCISES REGARDING YOUR ASSIGNMENT THEN CHECKING AND DISCUSSION WILL FOLLOW.

21. Formation of Cyclones

22. Forecasting and Warning 1. How current technology has enabled us to predict the possibility of occurrence of cyclones? It is with the help of the satellites and cyclone detection radars, the Meteorological Department can locate and track an approaching cyclone and issue a cyclone alert or cyclone watch, 48 hours in advance, with the help of various modes of communication devices such as TV and radio

23. Safety Measures or precautions in case of a cyclone warning is issued by the concern authorities or before/ during cyclones (6) 1.Stay indoors, preferably on the ground or in the basement during the storm 2.Keep and emergency medical kit at home 3.Water supplies may get contaminated due to flood caused by the cyclones. Store enough food material and drinking water in waterproof bags and neatly covered containers. 4.Keep emergency phone numbers of hospitals, police, relatives and friends always with you 5.Keep torch lights with extra batteries always ready as electricity supply may get disconnected 6.Keep yourself ready to shift to a safe area with essential supplies such as water, food and clothes in case of cyclone warning

24. 1.What is Tornado? Tornado is a twisting funnel of violently spinning wind with its narrow end towards the land. 2. How Tornado is formed? Tornado is formed when a column of cold air, funnel –like in shape, sinks from a storm cloud. The air from the Earth’s surface, which is comparatively warm, rises up and starts revolving around the cold air column with a very high speed. 3. Differentiate cyclones from tornadoes Tornadoes are quiet small as compared to cyclones, but their wind speed is very high and can reach up to 500 kph. The funnel-like structure of a tornado engulfs everything that comes in its way including cars, buses, trees, debris, huts or even small houses. Generally, tornadoes are short lived and do not move beyond 20 kilometre. 4. What common countries that this tornado occur? Tornadoes can occur anywhere when conditions are right, they are most common in countries like USA but they hardly occur in countries like India

25. 3 Safety Measures of Tornado 1.Take shelter in a room situated deep inside the house having no windows or in the basement. 2.If you are in a room having doors and windows, then take shelter under a table where debris cannot reach 3.Bend down on your knees and protect your head and neck using your arms.

26. Run through NATURAL PHENOMENON Powerful circular storms formed over low-pressure area, generally near the equator, over the warm waters of the oceans CYCLONES Storm that is accompanied by heavy rains, lightning, thunder and sometimes even snow and hail. THUNDERSTORMS TORNADOES Violently spinning funnel –shaped wind with the narrow end towards the ground, generally formed over land

27. TRACK YOUR PROGRESS 1.Fill in the blanks. a.Thunderstorm occur in _hot_ and _humid_ tropical areas. b.The eye_ of a cyclone is surrounded by strong circular winds c.Cyclones become weak as it reaches the _eye d.Tornadoes are smaller in size than cyclones

28. TRACK YOUR PROGRESS 5. _Anemometer is used to measure wind speed 6. _Uneven heating of Earth’s surface causes wind to blow 7. On heating, air _expands and rises up 8. Air present near the equator gets heated up more than air near the Polar regions 9. Moist air is less dense than dry air. 10. Instrument that measures wind direction weather vane or wind vane 11. Centre of cyclone is called an eye 12. A funnel-shaped wind that spins with very high speed tornado 13. Pressure exerted by air around us is called air pressure 14. Moist winds that are responsible for bringing heavy rains monsoon

29. TRACK YOUR PROGRESS 2. MATCHING TYPE Column A Column B 1.Air Pressure a. Moving air in the atmosphere 2.Air current b. Rain-bearing winds from the sea to the land 3. Cyclone c. Accompanied by strong winds, rain, thunder and lightning 4. Monsoon winds d. The pressure exerted by the air 5. Thunderstorm e. Air moving from high to low pressure area 6. Tornado f. A powerful circular storms formed over low-pressure area 7. Wind g. A violently spinning funnel-shaped wind with the narrow end towards the ground

30. TRACK YOUR PROGRESS 3. Choose the correct answer. 1.Which of the following are not associated with cyclones a. Heavy rains b. Sea waves c. Strong wind d. Volcanic eruption 2. In which direction atmosphere exerts pressure on us? a.Upward b. Downward c. sideways d. All sides 3. We should not take shelter under tall trees during a thunderstorm because ____ a.Tall trees give out CO2 during lightning b.Tall trees can be uprooted by strong winds c.Tall trees are more likely to be hit by a lightning d.Both b and c d d d d d d

31. TRACK YOUR PROGRESS 4. A region having low temperature gives rise to ______ a.low-pressure regionc. High-pressure region b.Strong windd. Gentle breeze 5. Air pressure decreases with __________ a.Decreasing altitudec. Increasing altitude b.Does not change at alld. Both a and b c c c c

32. STATE TRUE OR FALSE 1.Water heats up more quickly than the surface of the Earth _____ 2.During thunderstorm, wind moves in a circle around a low pressure area ______ 3.In winters, winds blow from sea to land _______ 4.The coastline are more vulnerable to cyclones than tornadoes ______ 5.Tornado becomes weaker when it reaches the land ________ false true