09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (2023)

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (1)

Chapter nine

it doesCan you feel the air around you? Did you know we live at the bottom of a big pile of air? We inhale and exhale, but we feel the air moving. This means that the moving air is wind. You already know that the earth is surrounded by air everywhere. This air envelope is an atmosphere composed of a variety of gases. These gases support life on Earth's surface.

Almost all of Earth's energy comes from the sun. In turn, Earth radiates the energy it receives from the sun back into space. As a result, the Earth neither heats up nor cools down for a period of time. Therefore, different parts of the earth absorb heat differently. This change causes pressure differences in the atmosphere. This causes heat to be transferred from one area to another via the wind. This chapter explains the processes by which the atmosphere warms and cools and the resulting temperature distribution on the Earth's surface.

solar ventilation

The Earth's surface receives most of the shortwave energy. The energy received by the earth is called incident solar radiation, abbreviated asinsolation.

Since the Earth is a spherical geoid, the sun's rays fall obliquely on the surface of the atmosphere, and the Earth intercepts very little of the sun's energy. The Earth absorbs an average of 1.94 calories per minute per square centimeter at the top of its atmosphere. The amount of solar energy received by the top of the atmosphere varies slightly throughout the year due to the varying distance between the Earth and the Sun. During its orbit around the sun, Earth will be at its furthest (152 million km) from the sun on July 4th. This position on the earth is calledAffiel. On January 3, the Earth will be at its closest approach to the Sun (147 million km). This location is calledperihelionTherefore, the solar radiation received by the earth on January 3 every year is slightly higher than that on July 4. However, the effect of this variation in solar output is overshadowed by other factors such as land-sea structure and atmospheric circulation. Therefore, this variation in solar output does not have a significant impact on the daily weather variability at the Earth's surface.

Variations in solar radiation on the Earth's surface

The amount and intensity of sunlight varies throughout the day, season and year. The factors causing these variations in solar radiation are: (i) the rotation of the Earth about its axis; (ii) the inclination of the sun's rays; (iii) the length of the day; (iv) the transparency of the atmosphere; . However, the latter two have less impact.

TonIn fact, the Earth's axis makes an angle of 66½ to the plane of its orbit around the sun, which has a greater effect on the amount of solar radiation at different latitudes.

another factor in determining the quantityInsolation is the angle of inclination at which air is received. It depends on the latitude of the place. The higher the latitude, the smaller the angle at which they coincide with the Earth's surface, resulting in oblique sunlight. The area covered by vertical rays is always smaller than the area covered by oblique rays. As more area is covered, energy is distributed and the net energy absorption per unit area decreases. Also, oblique rays have to penetrate deeper into the atmosphereHas greater absorption, scattering and diffusion.

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (2)

Figure 9.1: Summer Solstice

solar radiation through the atmosphere

The atmosphere is largely transparent to shortwave solar radiation. Incoming solar radiation penetrates the atmosphere before reaching the Earth's surface. In the troposphere, water vapor, ozone, and other gases absorb most of the near-infrared radiation.

Very small airborne particles in the troposphere scatter the visible spectrum into space and onto the Earth's surface. This process adds color to the sky. The red color of the rising and setting sun and the blue color of the sky are the result of light being scattered in the atmosphere.

protozoanStamSolar radiation on Earth's surface

The solar radiation received by the surface varies between approximately 320 W/m22Up to approx. 70 W/m in tropics2in a stick. Subtropical deserts experience the greatest insolation where the cloud cover is the least. The equator receives less solar radiation than the tropics. Generally at the same latitude as the solar radiationMore on continents than oceans. In winter, middle and high latitudes receive less radiation than in summer.

warming and cooling of the atmosphere

There are different methods of heating and cooling the atmosphere.

After the Earth is heated by solar radiation, the heat is transferred through the near-Earth atmosphere in the form of long waves. The air in contact with the ground slowly warms up, and the upper layer in contact with the lower layer also heats up. This process is calledmanage.Heat conduction occurs when two objects of different temperatures come into contact with each other, and energy flows from the hotter object to the cooler object. Heat transfer continues until the two objects reach the same temperature or contact breaks. Conduction is important for warming the lower layers of the atmosphere.

The heated air in contact with the ground rises vertically in the form of air currents, further dissipating the heat of the atmosphere. This process of vertical heating of the atmosphere is calledconvection. Convective energy transfer is restricted to the troposphere.

(Video) Solar Radiation, Heat Balance & Temperature - Chapter 9 Geography NCERT Class 11 Part 1

The horizontal movement of air is called heat transferadvection. Relatively more important is the lateral airflowbut vertical movement. in the middleLatitudes, most daily weather changes (day and night) are caused by advection only. In the tropics, especially in northern India, there is a local wind called "Loo" in summerThe result of the advection process.

Earth radiation

The solar radiation received by the earth heats the earth's surface in the form of short waves. After the earth warms, it becomes a radiator itself, radiating energy into the atmosphere in the form of long waves. This energy warms the atmosphere below. This process is called terrestrial radiation.

Longwave radiation is absorbed by atmospheric gases, especially carbon dioxide and other greenhouse gases. Thus, the atmosphere is indirectly heated by Earth's radiation.

The atmosphere is also very harmoniousTransfer heat to space. Finally, the heat absorbed from the sun returnskeep him in constant spaceThe temperature of the Earth's surface and atmosphere.

Heat Balance of Planet Earth

FFigure 9.2 shows the Earth's heat balance. The entire planet neither stores nor releases heat. It maintains its temperature. This is only possible if the heat absorbed in the form of solar radiation is equal to the heat lost by the Earth through Earth radiation.

Consider that solar irradiance is 100% at the top of the atmosphere. As it passes through the atmosphere, a certain amount of energy is reflected, scattered and absorbed. Only the rest reaches the Earth's surface. About 35 units were reflected back into space before reaching the Earth's surface. Of these, 27 units are from cloud reflections and 2 units are from snow-covered regions of the Earth. The amount of reflected radiation is calledEarth albedo.

The remaining 65 units are absorbed, with 14 units in the atmosphere and 51 units on the Earth's surface. The Earth reflects back 51 units in the form of terrestrial radiation. Of these, 17 units radiate directly into space, and the remaining 34 units are absorbed by the atmosphere (6 units are absorbed directly by the atmosphere, 9 units are absorbed by convection and turbulence, and 19 units are absorbed by latent heat of condensation). 48 units absorbed by the atmosphere(14 units from solar radiation + 34 units from ground radiation) also radiates back into space. Therefore, the total amount of radiation returned from the Earth and atmosphere is 17+48=65 units, which cancels out the total amount of 65 units received from the Sun. This is known as the Earth's thermal balance or heat balance.

This explains why the Earth neither warms nor cools despite the enormous heat transfer.

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (3)

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (4)

Figure 9.2: National heat balance

Changes in the net heat balance of the Earth's surface

As mentioned earlier, there are differences in the amount of radiation received by the Earth's surface. There is a radiation balance in one part of the country and a deficit in the other.

Figure 9.3 shows the latitudinal variation in the net radiative balance of the Earth-atmosphere system. The graph shows that the net radiation balance between 40 degrees north and south is in surplus, while regions near the poles are in deficit. Excess heat from the tropics is redistributed to the poles, resulting in too much heat accumulation in the tropics to gradually warm or excessive deficits that permanently freeze high latitudes.

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (5)

Figure 9.3: Latitudinal variation of the net radiation budget

The interaction of solar radiation with the atmosphere and Earth's surface produces heat, which is measured in temperature. While heat represents the molecular motion of particles containing asubstance, the temperature isA measure of how hot (or cold) something (or place) is in degrees.

Factors Controlling Temperature Distribution

The temperature anywhere isInfluenced by (i) the latitude of the location; (ii) the altitude of the site; (iii) the distance from the ocean, air mass circulation; (iv) the presence of warm and cold ocean currents; and (v) local aspects.

Latitude: The temperature of a place depends on the amount of solar radiation it receives. It has been explained that solar radiation varies with latitude, and therefore temperature also varies accordingly.

Altitude: The atmosphere is heated indirectly by Earth radiation from below. Therefore, places near sea level are warmer than places at higher altitudes. In other words, the temperature generally decreases with increasing altitude. The rate at which temperature decreases with altitude is called the normal rate of descent. That is, the temperature at 1000 meters is 6.5°C.

Distance from the sea: Another factor that affects temperature is the location of the site relative to the sea. Compared with the land, the ocean warms up slowly and emits heat slowly. The Earth is rapidly warming and cooling. Therefore, temperature fluctuations are smaller at sea than on land. Seaside locations are moderately affected by temperature-regulating sea and land breezes.

Air masses and ocean currents: Like land and sea breezes, passing air masses can also affect temperature. Places affected by warm air masses have higher temperatures, and places affected by cold air masses have lower temperatures. Likewise, coastal areas with warm currents are warmer than coastal areas with cold currents.

(Video) NCERT Class 11 Physical Geography Chapter 9: Solar Radiation, Heat Balance and Temperature | English

Temperature Distribution

You can get a good idea of ​​the global temperature distribution by looking at the temperature distribution in January and July. Temperature distributions are often displayed on maps using isotherms. thisThermostat It is a line connecting places with the same temperature. Figure 9.4(a), (b) shows the distribution of surface air temperature in January and July.

In general, the effect of latitude on temperature is well represented on maps because isotherms are usually parallel to latitude. The deviation from this general trend was more pronounced in January than in July, especially in the northern hemisphere. existNorth SeaThe Earth's hemisphere is much larger than the southern hemisphere. Thus, the influence of land and ocean currents is well represented. In January, the isotherms diverge northward over oceans and southward over continents. This can be observed in the North Atlantic. The presence of warm currents, the Gulf Stream, and the North Atlantic Drift lead to warming in the North Atlantic, with isotherms bending northward. Temperatures dropped sharply over land, and the isotherms turned southward in Europe.

In the Siberian lowlands this is very evident. The average January temperature at 60°E, 80°N and 50°N is minus 20°C°N width. The average temperature in January is above 27°C, above 24°C in the tropics of the equatorial sea, and 2°C to 0°C in the middle latitudesI18°C to -48°C in the interior of Eurasia.

ocean impactn well expressedin the southern hemisphere. hInstead, the isotherms are more or less parallel to latitude, and the temperature changes more gradually than in the northern hemisphere. The 20°C, 10°C, and 0°C isotherms are parallel to the latitudes 35°S, 45°S, and 60°S.

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (6)

Figure 9.4(a): Distribution of soil air temperature in January

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (7)

Figure 9.4(b): Distribution of soil air temperature in July

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (8)

Figure 9.5: Temperature range from January to July

In July, the isotherms are usually parallel to the latitude. Equatorial oceans recorded temperatures in excess of 27°C. On land, above 30°C is observed in the Asian subtropical continental region at 30°N latitude. 10°C isotherm flows along 40°N and 40°N°The temperature is 10°C.

FFigure 9.5 shows the subject rangeis the temperatureBetween January and July. Maximum rangetemperature above 60°coverNortheastern Eurasia. This is due to the continental nature. The minimum temperature range is 3°C between 20° DI 15°N.

temperature inversion

In general, the temperature decreases with increasing altitude. It is called the normal deviation rate. Sometimes the situation reverses, and so does the normal rate of termination. This is called a temperature inversion. Reversals are usually brief, but still common. Long winter nights with clear skies and calm air are ideal conditions for an inversion. During the day, heat is dissipated at night, and by early morning the ground is cooler than the air above. In polar regions, temperature inversions exist year-round.

The surface temperature inversion contributes to the stability of the lower atmosphere. Soot particles collect below the temperature inversion and spread horizontally, filling the lower layers of the atmosphere. Morning fog is common, especially in winter. This reversal usually lasts for a few hours until the sun rises and beings warm the earth.

Temperature inversions can occur in hills and mountains due to air loss. Cold air from hills and mountains that appear at night flows under the influence of gravity. Because cold air is so heavy and dense, it behaves almost like water, moving downhill and collecting in pockets of warm air above and deep in the valley floor. This is calledair outlet.Protect plants from freezing damage.

Planck's law states that the hotter a body is, the more energy it radiates, at shorter wavelengths.

Specific heat is the amount of energy required to raise the temperature of one gram of a substance by one degree Celsius.


1. Multiple choice questions.

(i) At noon on June 21, the sun is directly overhead:

(a) Equator (c) 23,5°N

(Video) Class 11 Geography Chapter 9|Solar Radiation, Heat Balance, and Temperature - Introduction

(b) 23,5° S(d) 66,5° S

(ii) Which of the following cities has the longest daylight hours?

(a) Trivandrum (c) Hyderabad

(b) Chandigarh (d) Nagpur

(iii) The atmosphere is heated primarily by:

(a) Shortwave solar radiation (c) Longwave terrestrial radiation

(b) reflect solar radiation (d) diffuse solar radiation

(iv) Match the following elements together.

(i) Sun exposure – (a) The difference between the mean temperature of the warmest month and the mean temperature of the coldest month

(ii) Albedo –(b) Lines connecting the isothermal points

(iii) Isotherms –(c) Incident solar radiation

(iv) Annual scope— (d) Percentage of visible light reflected by an object

(v) Glavni razlog za toEarth experiences its highest temperatures in the subtropics of the Northern Hemisphere, not at the equator:

(a) Subtropical regions tend to have lower cloud cover than equatorial regions.

(b) Summer days are longer in subtropical regions than in equatorial regions.

(c) The "greenhouse effect" is enhanced in subtropical regions compared with equatorial regions.

(d) Subtropical regions are closer to oceanic regions than equatorial regions.

2. Answer the following questions in about 30 words.

(i) How does the uneven distribution of heat on Earth in space and time contribute to weather and climate variability?

(ii) What factors control the temperature distribution on the Earth's surface?

(iii) Why is the daily maximum temperature in India in May and not after the summer solstice?

(iv) Why is there a large annual temperature difference in the Siberian Plain?

3. Answer the following questions in about 150 words.

(Video) Fundamental of Physical Geography | Solar Radiation, Heat & Temperature | CL11 - CH 9 | LIVE SESSION

(i) How do the latitude and inclination of the Earth's axis of rotation affect the amount of radiation received at the Earth's surface?

(ii) Discuss the process by which the earth-atmosphere system maintains heat balance.

(iii) Comparing the global temperature distribution in January between the northern and southern hemispheres.

project work

Select a weather station in your city or near your city. LabelRetrieve the temperature data from the observatory's climate table:

(i) Record the altitude, latitude and time period of the average for the observatory.

(ii) Definitions of terms related to temperature given in the table.

(iii) Compute the mean daily and monthly temperatures.

(iv) Draw a graph of the daily mean maximum temperature, daily mean minimum temperature, and mean temperature.

(v) Calculate the annual temperature difference.

(vi) Find out which months the daily range is intemperatureare the highest and lowest.

(vii) List influencing factorsDetermine the temperature at the location and explain possible temperaturesReason for temperature fluctuations in January, May, July and October.


Observatory: New Delhi (Safdarjung)

Latitude: 28°35°'N

Based on observations: 1951 - 1980

Altitude: 216 meters

09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (9)

Daily average monthly temperature

January09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (10)

possible09: Solar Radiation; Heat Balance and Temperature/Physical Geographical Basis (11)

annual temperature difference

Average maximum temperature in May-Average temperature in January

(Video) Class 11 Geography Chapter9 | Solar Radiation-Solar Radiation, Heat Balance, and Temperature

Annual temperature difference = 32.75°C – 14.2°C = 18.55°C


What is the solar radiation heat balance? ›

terrestrial radiation) are also radiated back into space. Thus, the total radiation returning from the earth and the atmosphere respectively is 17+48=65 units which balance the total of 65 units received from the sun. This is termed the heat budget or heat balance of the earth.

What is heat balance in physical geography? ›

It maintains its temperature. This can happen only if the amount of heat received in the form of insolation equals the amount lost by the earth through terrestrial radiation. This balance between the insolation and the terrestrial radiation is termed as the heat budget or heat balance of the earth.

What is radiation in physical geography? ›

Image courtesy of the Department of Energy Office of Science. Atmospheric radiation is the flow of electromagnetic energy between the sun and the Earth's surface as it is influenced by clouds, aerosols, and gases in the Earth's atmosphere. It includes both solar radiation (sunlight) and long-wave (thermal) radiation.

Does solar radiation heats the air near the equator and this low density heated air is buoyed up? ›

Solar radiation heats the air near the equator, and this low density heated air is buoyed up. At the surface it is displaced by cooler more dense higher pressure air flowing from the poles. In the upper atmosphere near the equator the air thus tends to low back toward the poles and away from the equator.


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