ICSE IX GEOGRAPHY- Insolation and Heat Balance- [Standard IX]

DIFFERENTIAL HEATING AND COOLING OF LAND AND WATER

Name the factors affecting upon temperature of a place.

The factors affecting the temperature of a place are

1. Differential heating and cooling of land and water,
2. Latitude, distance from the sea
3. Wind direction
4. Natural vegetation
5. Clouds
6. Humidity

The landmass gets heated and cooled fast while oceans take longer time to get heated and cooled. Explain.

Land gets heated through the process of conduction. The insolation heats up the thin surface layer of the earth quickly. It cools down faster as well.

Oceans heat by the process of convection the insolation goes below the surface of water to a greater depth than on land and is distributed over large volume. It takes a longer time to cool down. 

Warm currents along the coast make the coastal areas warmer and cold currents make them cooler than usual. Explain.

The water mass, i.e. seas and oceans retain heat for a longer period. Equatorial waters remain hot and give rise to hot currents, while the polar waters are cold. The winds from the oceans and ocean currents transport heat or cold.

Warm currents flow from equatorial to polar latitudes transporting warm water to cooler regions.

Cold currents flow from higher polar latitudes to lower latitudes in equatorial regions carrying cool water to warm regions.

In this way, warm currents along the coast make the coastal areas warmer and cold currents make them cooler than usual.

The parts of Western Europe remain ice free in winter.
The ports of Norway remain frost free in winter.
On the same latitude the ports of British Isles stay open while ports of north East Canada remain frozen. Why?

Warm currents along the coast make the coastal areas warmer and cold currents make them cooler than usual.

The ports of British Isles are washed by the warm North Atlantic Drift which raises the winter temperature of the British Isles.
Due to the influence of the Warm Drift, the port of British Isles remains open during the winter season, while the ports on the north-east coast of Canada, located in the same latitudes, remain frozen for several months because of the influence of the cold Labrador Current.

LATITUDE

Temperature of a place largely depends on the latitude of a place.

Temperature decreases with increase in latitude on either side of the equator due to the spherical shape of the earth.

Sun's rays strike the earth at varying angles of incidence owing to spherical shape of the earth and its inclination on its axis.

State the difference slanting and direct rays.

The sun’s slanting /oblique rays which fall over the temperate zone travel a longer distante, but also heat a larger area leading to lower temperatre.

The sun's direct rays which fall over the Torrid Zone travel shorter distance and heat up a smaller surface area leading to higher temperature.

Temperate regions receive less heat than tropics. Why?

Owing to the inclined axis and revolution of the earth on its axis, the Mid-day sun is almost overhead within the tropics but at oblique angles outside the tropics. Beyond the Torrid Zone sun's rays travel longer distance.

·        Much of the heat is absorbed by clouds and water vapours or reflected back by dust particles.

·        The sun's rays fall in a slanting position and heat up a larger area. Thus beyond the Torrid Zone temperature goes on falling.

Name the five temperature zones on the Earth and the basis of their division.

The higher the latitude the colder the place; on this basis the earth is divided into 5 temperature zones.

These are: the Torrid Zone between the Tropics of Cancer and Capricorn; the North Temperate Zone and the South Temperate Zone and, the two Frigld Zones.

 

DISTANCE FROM THE SEA

How does the interchange of breeze maintain the heat balance in coastal areas?

Sun's rays pass through water to a great depth.

Water takes time to heat to cool and because it is mobile and the warm water mixes easily with the cold water.

Ø  Land gets heated more rapidly by the sun's rays because the heat obtained by the area does not mix with other areas of land. Hence the land gets heated or cooled more quickly than the water.

Ø  Thus during the day, the land is hotter than the sea. The hot air over the land becomes lighter and goes upwards. This creates a low pressure area over the land.

Ø  The air above the sea is cooler during this time. When this air blows towards the low pressure area over the land, it lowers the temperature of the air on land. Such cool breeze that blows over the earth is known as Sea Breeze.This sea breeze cools the coastal regions.

Ø  In the night, the situation is the reverse. The sea remains warmer than the land, so the breeze blows from land to sea. This land breeze makes the sea cooler.

Ø  Thus, the interchange of breeze maintains the heat balance. The areas, close to the sea have lower daily and annual ranges o temperatures.

The areas close to the sea have lower daily and annual ranges of temperatures. Why?

Areas close to the sea are affected by the moderating influence of the sea which results in warm days and cool nights influenced by the sea and land breezes. Thus they have lower daily and annual ranges of temperatures.

The temperature of Delhi is less than that of Chennai in December

North India has a greater range of temperature than south India.
Mumbai is warmer than Nagpur in winter. Why?

Mumbai is a lies on the coast of Arabian Sea whereas Nagpur lies in the interior away from the influence of the sea. Mumbai is warmer than Nagpur due to the moderating influence of the sea.

Ø  Land gets heated through the process of conduction. The insolation heats up the thin surface layer of the earth quickly. It cools down faster as well.

Ø  Oceans heat by the process of convection the insolation goes below the surface of water to a greater depth than on land and is distributed over large volume. It takes a longer time to cool down. 

Ø  Since land heats up and cools down faster than the water, the land is warmer than the ocean in summer and cooler than the ocean in winter. This causes the oceans to have a moderating effect on the coastal areas.

Thus Mumbai is warmer than Nagpur.

                                                                       ALTITUDE

Define altitude.

Altitude is the height of a place above the mean sea level.

Air is cooler at higher altitudes than on the earth's surface. Explain. / The temperature decreases with altitude. / Mountains are cooler than plains. / It is cooler on the mountain slopes than on the plains in summer./ Ooty is cooler than Kochi. /Nainital is cooler than Agra

The temperature decreases with height because the atmosphere is heated from below, more by terrestrial radiation than by incoming solar radiation

Heat absorption capacity is more in the lower layers than in upper layers where its density is less. Explain.

Air on the surface of the earth is denser and contains more carbon dioxide, water vapours and other gases. Hence its heat absorption capacity is more in the lower layers than in upper layers where its density is less.

Temperature of the atmosphere and altitude are inter-related. Explain.

The higher the altitude, the lesser the temperature

This is because of the following factors:

(i) Air is cooler at higher altitudes than on the earth's surface. The main reason for decrease of temperature with height is that the atmosphere is heated from below, more by terrestrial radiation than by incoming solar radiation.

(ii) Air on the surface of the earth is denser and contains more carbon dioxide, water vapors and other gases. Hence its heat absorption capacity is more in the lower layers than in upper layers where its density is less.

What is normal lapse rate?

The rate of decrease of temperature with height is about 6°C per km. above the sea level.

This means that on climbing every 166 meters, there is a fall of 1°C in temperature.  It is known as Normal Lapse Rate.  It is usually more in summer than in winter.

This explains why it is cooler at the top of a mountain than at the bottom or why hill resorts in summer in tropical countries have a pleasant climate than the plains.

 

Under what conditions would temperature increase with increase in altitude?

Temperature inversion is a reversal in the normal tendency of air to get colder with height. Temperature inversion is a natural phenomenon which occurs in the middle latitude, in the valleys and hollows, on clear, calm winter nights when radiation has caused cooling and the air has sunk down, at the same time on the mountain slopes the air is warmer.

As the altitude increases, the density of air decreases thus the amount of heat absorbed decreases with height, why?

The earth’s atmosphere is heated by the energy absorbed by the molecules of gases and impurities present in the air. Due to lessening effect of gravity on the increasing altitude, the density of air decreases as a result of reduction of gases and impurities present in the air.

Thus the amount of heat absorbed decreases with height. The average rate of change in temperature is 1 degree for every 166 meters of height in the troposphere.

WIND DIRECTION NATURAL VEGETATION CLOUD COVER AND HUMIDITY

What is the effect of warm wind over the surface they blow?

Warm winds that blow from the sea into land are moisture-laden and cause rainfall on land especially when they strike against a barrier. Such winds lower temperature of the place that they blow into.

How are higher latitudes warmed by winds from lower latitudes?

Lower latitudes are warmer than the higher latitudes; winds blowing from lower latitudes to higher latitudes warm the higher latitude.

Vegetative areas are not hot.

A forest surface absorbs about 90 per cent of the solar energy. Most of this energy absorbed is used by plants in the process of transpiration making these not very hot.

Vegetative cover absorbs more sunshine than snow fields.

A snow surface absorbs only about 20 per cent and reflects the 8o% back in the atmosphere.

A forest surface absorbs about 90 per cent of the solar energy. Most of this energy absorbed is used by plants in the process of transpiration. 

Deserts are hot during day and cold by night. /Deserts experience extremes of temperature.

Desert areas experience a high day temperature and a much lower night temperature.

In hot desert areas there are no cloud covers.

So there is high insolation during day time and rapid loss of heat due to terrestrial radiation at night.

So deserts are hot during day and cold by night.

Equatorial regions experience high humidity.

In hot-wet regions the dense cloud cover prevents incoming insolation as well as checks outgoing radiation. Thus the humidity levels are high and average temperatures here are not more than 30°C.

A desert region has a high range of temperature than a forest region.

Hot deserts have no cloud cover, which allows high insolation during the day and rapid loss of heat due to terrestrial radiation at night resulting in high range of temperature.

On the other hand forests absorb 9O% insolation and the solar energy absorbed by plants is used in the process of transpiration resulting in low range of temperature.

How is temperature measured?

Thermometers are used to measure temperature

There are two scales measure temperature. - The Centigrade Scale and the Fahrenheit scale.

The centigrade scale has 100 divisions while the Fahrenheit scale has 18O divisions. One scale can be converted to the other with the help of the conversion formula:

F = (°C x 9 /5) + 32. Thus 86°F = 30°C.

Though the angle of incidence is maximum around noon, the maximum temperature is recorded at about 3 p.m. Why?

Starting from sunrise, the temperature shows a gradual increase until midday and then remains fairly constant for a couple of hours before beginning to fall again.
Though the angle of incidence is maximum arourd noon, the maximum temperature is recorded at about 3 p.m.
 This is because the heating of the atmosphere takes place from below and consequently there is a time lag.

Isotherms are lines on the map joining places having the same mean temperatures.

Diurnal Range of Temperature is difference between the maximum and, minimum temperature on any one day.

The Mean Monthly Temperature is the average of mean temperatures of all the days in the

The mean monthly temperature is calculated on the basis of average values of mean temperature of the days for each month.

Mean Annual Range of Temperature is the seasonal difference in temperature or the difference between the mean temperature of the hottest month and the mean temperature of the coldest month.