Wind currents, ThunderStorms (lighting), Cyclones and Earthquakes.
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INTRODUCTION |
We will begin with some basic features concerning cyclones, wind currents, thunderstorms and earthquakes. Before we begin, remember that the moving air is called wind. Air moves from the region where the air pressure is high to the region where the pressure is low. The greater the difference in pressure, the faster the air moves. But how is the pressure differences created in nature? Is the difference in temperature involved? Let us see;Yes, because it is important to remember that on heating the air expands and occupies more space. When the same thing occupies more space, it becomes lighter. The warm air is, therefore, lighter than the cold air. That is the reason that the smoke goes up.
In the nature there are several situations, where warm air rises at a place. The air pressure at that place is lowered. The cold air from the surrounding areas rushes in to fill its place. This sets up convection in air.
WINDS CURRENTS
Wind currents are generated due to the uneven heating on the earth. And the heat that warms up the earth is produced by core of the earth and the green house effect also takes place here, but in a small manner. There are two situations:
a) Uneven heating between the equator and the poles.
You might have learnt in Geography that regions close to the Equator (the imaginary latitude line that divides the north hemisphere and the south hemisphere at 0°) gets maximum heat from the Sun. The air in these regions (temperate zone) gets warm. The warm air rises, and the cooler air from the regions in the 0-30 degrees latitude belt on either side of the equator moves in. These winds blow from the north and the south towards the equator. At the hemispheres, the air is colder than that at latitude about 60°. The warm air at these latitudes rises up and the cold wind from the Polar Regions rushes in, to take its place. In this way, wind circulation is set up from the poles to the warmer latitudes. The winds would have flown in the north-south or from south to north. A change in direction is however, caused by the rotation of the earth.
b) Uneven heating of land and water.
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 flow from the oceans towards the land. These are monsoon winds.
DO YOU KNOWN?
The word monsoon is consequent from the Arabic word “mausam”, which means ‘season’.
Clouds bring rain and give us pleasure. Farmers in our country depend mainly on rains for their harvests. There are many folk songs allied with clouds and rain. However, rains often create problems. In nature itself there are certain situations that can sometimes create disasters and pose threat to humans, animals and plants.
Let’s study two such situations, they are: cyclones and thunderstorms.
THUNDERSTORMS AND CYCLONES
Thunderstorms developed in hot, humid (moisture holding) tropical areas like India very frequently. The rising temperatures produce strong upwards rising winds. These winds carry water droplets upwards, where they freeze, and fall down again. By a process, not now understood completely, the positive charges collect near the upper edges of accumulate near the lower ones. There is accumulation of the positive charges near ground also. When the magnitude of the accumulated charges (mount up charges) becomes very large, the air which is an insulator of electricity is not able to oppose their flow. Negative and positive charges gather, producing streaks of bright light and sound. We see streaks as lighting. The process so called an electric discharge. The swift movements of the falling water droplets along with the rising air create lighting and sound. It is called thunderstorms.
DID YOU KNOWN?
Lighting conductors is a device used to protecting buildings from the effect of lighting. A metallic rod, taller than the structure, is fixed in the walls of the structure during its construction. The one end of the device is buried under deep in the ground.
HOW A THUNDERSTORMS TURNS INTO A CYCLONES?
We knew that water needs heat when it changes from liquid to vapour state. Before cloud formation, water requires 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 which heats the atmosphere around. The air tends to rise and causes drops in pressure. More air rushes to the center of the storm. This process is repeated. This cycle of events ends with the formation of very low-pressure system with high –speed winds revolving around it. It is this phenomenon is called cyclone. Let us look after the structure of cyclone. Some of the factors of cyclones for example: wind speed, wind direction, temperature and humidity supports to develop cyclones. Cyclones are worldwide phenomena.
DID YOU KNOWN?
A cyclone is has different names in different regions in the world. They are ‘hurricane’ in America and ‘typhoon’ by Japanese and Philippines. And some other name is ‘tornado’
The Structure of Cyclone.
DESTRUCTION CAUSED BY CYCLONES.
High- speed winds supplementary a cyclone can damage houses, telephones and other communication systems, trees, hospitals, etc., causing humongous loss of life and property.
Following are some disadvantages of a cyclone hit area:
1. It can destroy of miles of properties.
2. It reduces the fertility of soil.
3. Continuous heavy rainfall may further worsen the flood situation.
4. Also, the seawater enters the low-lying coastal areas, causing severe loss of life of both animals and human-beings.
DID YOU KNOWN?
Orissa was hit by a cyclone with wind speed of 200 km per hour on 18 October 1999. The cyclone smashed 45,000 houses making 7 crore people homeless. On 29 October the same year (1999), a second cyclone with wind speed of 260 km/ h hit Orissa again. It was accompanied by water waves about 9 meters high. Thousands of people lost their lives. Property worth of rupees was destroyed. The cyclone affected agriculture, transport, communication, and electricity supply.
EARTHQUAKES
An earthquake is a sudden trembling of the earth which lasts for a very short time. It is caused by the deep plates (the outer layer of the earth is not in one piece, it’s fragmented. Each fragment is called a plate). These plates are in continual motion. When they brush past one another, or a plate under another due to collision, they cause disturbance in the crust of earth. Earthquakes can cause floods, landslides and tsunamis (the word “tsunami” is another name of large waves with a great force which can destroy the earth).
DID YOU KNOWN?
A major tsunami occurred in the Indian Ocean on 26 December 2004. All the coastal areas around the ocean suffered huge wounded.
So, tremors on the earth can also be caused when a volcano erupts, or a meteor hit the crust from the outer space, or under a nuclear blast caused by human activities. Under these cases, the most earthquakes are caused by the disturbance in the plates of the earth.
However, the boundaries of the plates are the weak zones where the earthquakes are more occur. These zones are called seismic or fault zones.
DID YOU KNOWN?
The power of an earthquake is expressed in terms of a magnitude on a scale called the Richter scale. The earthquakes have higher than 7 on the Richer scale. It means earth quakes had magnitude greater than 7.5. Richer scale is not linear.
The tremors produce waves on the surface of the earth. These are called seismic waves. The waves are recorded and measured by an instrument called the seismograph.
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