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What Is Insolation In Geography

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The Angle Of Incidence

What is Insolation? | How Energy Transfer in the Atmosphere | Geography series 05

Since the earth is a geoid resembling a sphere, the suns rays strike the surface at different angles at different places. This depends on the latitude of the place.The higher the latitude, the less is the angle they make with the surface of the earth.The area covered by the vertical rays is always less than the slant rays. If more area is covered, the energy gets distributed and the net energy received per unit area decreases. Moreover, the suns rays with small angle traverse more of the atmosphere than rays striking at a large angle.

Variation In The Net Budget At The Earths Surface

  • Although the earth as a whole maintains a balance between the insolation and the terrestrial radiation, this is not true what we observe at different latitudes.
  • As we have discussed earlier, there are variations in the amount of insolation received at different latitudes.
  • In the tropical region, the amount of insolation is higher than the amount of terrestrial radiation. Hence it is a region of surplus heat. In the polar region, the heat gain is less than the heat loss. Hence it is a region of deficit heat.
  • Thus the insolation creates an imbalance of heat at different latitudes.
  • This imbalance is nullified to some extent by winds and ocean currents, which transfer heat from surplus heat regions to deficit heat regions.
  • This process of redistribution and balancing of latitudinal heat is commonly known as Latitudinal Heat Balance.

Note: Topics like Temperature, Factors controlling Temperature and Distribution of Temperature will be covered in the next article.

Article by: Jijo Sudarshan

What Is Insolation Explain The Factors Influencing It Class 11

Answer: The amount of insolation received depends on the angle of inclination of the rays. It depends on the latitude of a place. The higher the latitude the less is the angle they make with the surface of the earth resulting in slant sunrays. The area covered by vertical rays is always less than the slant rays.

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Insolation Over The Globe

Most natural phenomena on the Earth’s surfacefrom the downhill flow of a river to the movement of a sand dune to the growth of a forestare powered by the Sun, either directly or indirectly. It is the power source for wind, waves, weather, rivers, and ocean currents, as we will see here and in later chapters.

Although the flow of solar radiation to the Earth as a whole remains constant, different places on the planet receive different amounts of energy at different times. What causes this variation? Incoming solar radiation is known as insolation. It is a rate of flow of energy and is measured in units of watts per square meter . Daily insolation is the average flow rate over a 24-hour day, while annual insolation is the average flow rate over the entire year.

Insolation depends on the angle of the Sun above the horizon. It is greatest when the Sun is directly overhead, and it decreases when the Sun is low in the sky, since the same amount of solar energy is spread out over a greater area of ground surface .

Earth’s Distance From Sun

Geography: Insolation and Heat Budget

The earth is revolving around the sun in an elliptical orbit, resulting continuous change in the distance between sun and the earth on annual basis. It leads to seasonal variation in solar energy received by the earth.The mean distance between the earth and sun is about 149,600,000 kilometers.When earth position is farthest from sun is known as aphelion on July 4. It is perihelionoccurs on January 3 each year which is the closest distance. During aphelion the northern hemisphere is facing the sun and therefore receives energy about 7 percent less than the perihelion .

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Path Length And Insolation

The distance a beam of light travels affects the amount of solar energy that ultimately reaches the Earth. Light spreads outward in all directions when it is emitted from the Sun. As the light spreads, its intensity upon reaching distant locations decreases. The intensity of light decreases as the square of the distance between the Sun and receptor increases, a relationship known as the inverse square law. The Earth receives about one-half of one billionth of the Sun’s total output of energy.

The Earth-Sun distance only varies by about 3 million miles compared to an average distance of 93 million miles over the year. Thus path length doesn’t change much as the Earth revolves around the Sun. But once sunlight reaches the outer edge of the atmosphere, the thickness of the atmosphere has a significant impact on insolation. Due to the curvature of the Earth, a beam of light striking the Equator passes through less atmosphere than one at a higher latitude. As the amount of atmosphere through which the beam passes increases, the greater the chance for reflection and scattering of light to occur, thus reducing insolation at the surface.

The Angle Of Incidence Of Sun Rays:

  • As the earth is a geoid and is inclined to 66.5 degrees on the orbital plane, the sun rays reach the surface at different angles at different latitudes.
  • Due to slanting sun rays, they travel a long distance in the atmosphere and cover large areas on the surface, hence less insolation per unit area is received in higher latitudes.
  • Due to vertical sun rays, sunlight travels less distance in the atmosphere and covers fewer areas on the surface, hence more insolation per unit area.

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Insolation And Heat Budget

  • 1. Atmosphere is open energy system.It receives energy from both directions .Compared with sun , earths energy canbe negligible.All life processes and all exchanges of matter andenergy between the earths atmosphere and thesurfaces of the oceans and lands are driven by solarenergy.The planetary circulation systems of atmosphere andoceans are also driven by solar energy.Water changes in various forms over the globe also driven by solar energy.Sun is the energy source of the earth.
  • 2. Emitted from sun It is a spectrum Most of it is visible light rays Energy emitted by earth isterrestrial radiation Higher temperature of an object emits shorter-wave ofradiation.The radiant energy received from the sun,transmitted in a form analogous to shortwave,and travelling at the rate of 1,86,000 miles per second.That it reaches earth in 8 minutes 20 seconds.
  • 3. The prime source of the energy injected intoour atmosphere is the sun. The sun is constantly releasing energy in alldirection. This energy is known as solar radiation. It is a electro-magnetic wave energy radiating fromsun, which is also called Insolation. All weather phenomena are affected by variousmeteorology parameters which all affected byInsolation
  • 4. incoming Solar Radiation Insolation is a measure of Solar Radiationincident of a surface. It is the amount of solar energy received over agiven area in a given time. It is commonly expressed in:kilowatt-hours per square meter per daywatts per square meter.
  • Albedo Solar Radiation And Humans


    Today, albedo is a major concern for humans worldwide. As industrial activities increase air pollution, the atmosphere itself is becoming more reflective because there are more aerosols to reflect insolation. In addition, the low albedo of the worlds largest cities sometimes creates urban heat islands which impacts both city planning and energy consumption.

    Solar radiation is also finding its place in new plans for renewable energy- most notably solar panels for electricity and black tubes for heating water. These items dark colors have low albedos and therefore absorb nearly all of the solar radiation striking them, making them efficient tools for harnessing the suns power worldwide.

    Regardless of the suns efficiency in electricity generation though, the study of solar radiation and albedo is essential to the understanding of Earths weather cycles, ocean currents, and locations of different ecosystems.

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    The Angle Of Incidence Of The Suns Rays

    • Since the earth is a geoid resembling a sphere, the suns rays strike the surface at different angles at different places. This depends on the latitude of the place.
    • The higher the latitude, the less is the angle they make with the surface of the earth.
    • The area covered by the vertical rays is always less than the slant rays. If more area is covered, the energy gets distributed and the net energy received per unit area decreases.
    • Moreover, the suns rays with small angle traverse more of the atmosphere than rays striking at a large angle.
    • Longer the path of the suns rays, greater is the amount of reflection and absorption of heat by the atmosphere. As a result, the intensity of insolation is less.

    Ground Slope And Insolation

    The slope of the surface that a beam of light strikes affects the intensity of energy it receives. Slope affects insolation intensity in two ways, 1) the degree of slope inclination, and 2) the orientation of the slope to incoming light.

    The effect of ground slope is to change the angle that a beam of light strikes the earth . Figure \ shows a beam of light striking horizontal slope at a 45o angle on the left. On the right, the slope is tilted to a 45o angle while keeping the beam coming to the earth as it was before. By tilting the surface into the Sun, you effectively increase the sun angle. Increasing the sun angle increases the intensity of energy received at the surface.

    Orientation, or direction the slope is facing also affects the amount of insolation received. Slopes facing into the Sun receive more while those that face away receive less. Some surfaces can be shaded during a portion of the day by obstructions reducing the amount of insolation received by them.

    Video: Daylight simulation in Wenatchee National Forest, Washington

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    What Is Inversion Of Temperature Class 9 Icse

    This reversal of temperature is known as the inversion of temperature. Inversion of temperature takes place in the mountainous regions when cold air sinks down to the valleys and basins due to its greater weight. The upper layer retains its warmth. In such circumstances, the temperature increases with height.

    Geographical Role Of Insolation: Discussion


    In context to the study, it can be inferred that the mechanism of insolation to that of geographical connotation, both are intertwined in the process. In regards to the geographical concept, it incorporates the physical aspects of earth starting from the atmosphere, sun, light, land, soil, water, and every possible thing. On the other hand, insolation is a part of the geographical aspect of the study. The prior importance of the two is categorised by their evident importance on the formation of the air around us. The sun radiation emitted and accumulated by the earth is crucial as excess amounts of radiation, heat, and energy received can be harmful leading to excess rise in temperature and contributing towards global warming.

    Similarly, the deprivation of sun radiation or energy can result in extreme falls within the temperature. Neither of the aspects of insolation is joyful, thus it can be inferred that insolation is a vital process for the effective functioning of earth and the atmosphere. On further analysis, it can be determined how geography plays an inseparable role in the formation and functionality of the isolation process.

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    Transparency Of The Atmosphere

    Atmosphere is not transparent for all the radiation coming from the sun because of different composition and layers. It is also one of the controlling factors of insolation to reach earth surface. The atmosphere is composed of gases, water vapour and particulate matters.The atmosphere is a mixture of gases,such as nitrogen, oxygen , Argon, carbon dioxide, Neon , Helium , Methane , Krypton , Ozone , Nitrous oxide , Hydrogen and Xenon . The atmosphere also contains water vapour, water in the gaseous state.

    The longer the duration of daylight, the more the insolation received per day.


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    The incoming solar energy that is intercepted by the earth is known as insolation. The earth absorbs some insolation and radiates it back into space via terrestrial radiation. On the earth’s surface, the amount of insolation received is not uniform. It changes depending on the location and time. In comparison to the tropics, the equator receives less insolation. In general, at the same latitude, the continent receives more insolation than the oceans. This phenomenon is called the distribution of insolation.

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    Insolation Or Incoming Solar Radiation

    • As we all know, the sun is the primary source of energy for the earth. The sun radiates its energy in all directions into space in short wavelengths, which is known as solar radiation.
    • The earths surface receives only a part of this radiated energy .
    • The energy received by the earths surface in the form of short waves is termed as Incoming Solar Radiation or Insolation.
    • The amount of insolation received on the earths surface is far less than that is radiated from the sun because of the small size of the earth and its distance from the sun.
    • Moreover, water vapour, dust particles, ozone and other gases present in the atmosphere absorb a small amount of solar radiation.
    • The solar radiation received at the top of the atmosphere varies slightly in a year due to the variations in the distance between the earth and the sun.
    • During the earths revolution around the sun, the earth is farthest from the sun on 4th July. This position of the earth is called aphelion. On 3rd January, the earth is nearest to the sun. This position is called perihelion.
    • Due to this variation in the distance between the earth and the sun, the annual insolation received by the earth on 3rd January is slightly more than the amount received on 4th July.
    • However, the effect of this variation is masked by some other factors like the distribution of land and sea and the atmospheric circulation. Hence the variation does not have a greater effect on daily weather changes on the surface of the earth.

    What Is The Zenith Angle And How Does It Affect Insolation

    Incoming Solar Radiation | Factors Affecting Insolation | Climatology | Geography by Ma’am Richa

    1. The angle made by two lines, one drawn from the observer to the Sun at its position and the other drawn directly over the observer’s head, is called the zenith angle. Note that the zenith angle is measured from vertical, regardless of the slope of the land. When the shadow of an object is directly underneath the object, the zenith angle is 0°.

    2. This figure shows the Sun at four different positions, corresponding to four different zenith angles . The 10 thin orange rays of sunlight represent equal amounts of energy . The brackets on the ground indicate the width over which that same amount of sunlight strikes the surface.

    3. In this example, if the zenith angle is 0°, as happens near the equator and in the tropics, the 10 rays of sunlight intersect the Earth’s surface over a width of 10 meters. The light is perpendicular to the surface, so the area receives the maximum amount of energy possible.

    4. In a subtropical latitude, with a zenith angle of 30°, the 10 rays of sunlight are spread out over a wider area, so the surface receives less insolation per square meter compared to a site at the equator, but not much less .

    5. If the zenith angle is larger, like 60° in a high-latitude location, the 10 rays of sunlight are spread out over 20 m , so any area receives only 50% of the sunlight per square meter that the equator does.

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    Solar Radiation And The Earth’s Albedo

    • M.A., Geography, California State University – East Bay
    • B.A., English and Geography, California State University – Sacramento

    Nearly all of the energy arriving on planet Earth and driving the various weather events, oceanic currents, and distribution of ecosystems originates with the sun. This intense solar radiation as it is known in physical geography originates in the suns core and is eventually sent to Earth after convection forces it away from the suns core. It takes approximately eight minutes for solar radiation to reach the Earth after leaving the suns surface.

    Once this solar radiation arrives on Earth, its energy is distributed unevenly across the globe by latitude. As this radiation enters the Earths atmosphere it hits near the equator and develops an energy surplus. Because less direct solar radiation arrives at the poles, they, in turn, develop an energy deficit. To keep energy balanced on the Earths surface, the excess energy from the equatorial regions flows toward the poles in a cycle so energy will be balanced across the globe. This cycle is called the Earth-Atmosphere energy balance.

    How Does Insolation Vary By Time And Location On Earth’s Surface

    The amount of sunlight that reaches the surface varies greatly with latitude, due to the reinforcing effects of zenith angle and atmospheric attenuation. These variations in insolation result in huge ranges in temperature between the warm, tropical regions of the world and the cold, polar regions.

    The least variation in insolation through the year occurs in equatorial regions, which do not experience summer versus winter. The length of daylight in equatorial regions is always around 12 hours, and zenith angles are always small. The Sun is directly overhead in March and September and nearly so the rest of the year, so temperatures remain warm throughout most of the year.

    Polar regions experience the maximum variation in insolation. During the summer this region has 24 hours of sunlight, allowing fully lit outdoor excursions, but during the winter there is no sunlight. Even during the summer, large zenith angles prevent insolation from increasing too much. The combination of months of darkness and low insolation causes polar areas to have very cold average temperatures.

    Areas between the tropical and polar regions, such as those in the mid-latitudes, experience an intermediate amount of variability in insolation and so typically have distinct seasons. The mid-latitudes have some sunlight and darkness every day, with longer days and lower zenith angles during the relatively warm summer. The winter has shorter days and larger zenith angles, so it is colder than the summer.

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