Class 11 Notes Chapter 8 discusses Solar Radiation, Heat Balance, and Temperature. Solar radiation is an electromagnetic energy that is released by the sun. It is the major and primary source of the land heating process and also helps in the photosynthesis process. Heat balance is a natural phenomenon that helps the atmosphere absorb a certain amount of heat from the sun and release that same amount of heat into space. To sum up, we can say the temperature of our planet is neither too hot nor too cold as it always supports the life present on it.
In this article, we are going to discuss Chapter 8 by considering Solar Radiation, Heat Balance, and Temperature in detail.
Solar Radiation
Solar radiation is an electromagnetic energy that is released by the sun. It is the major and primary source of the land heating process and also helps in the photosynthesis process. Most of the energy received by the Earth is from solar radiation. The energy received by Earth in the form of wavelength is known as insolation.
Interesting Facts
Aphelion (4th July): It is the particular date and position of a year when the distance between the sun and Earth becomes 152 million km.
Perihelion (3rd January): On this particular date and position the distance between the sun and Earth becomes 147 million km.
On the 3rd of January or the time of Perihelion, Earth receives more solar radiation.
Variability of Isolation at the Surface of the Earth
Throughout the day, across seasons, and over the course of a year, the amount and intensity of incoming solar radiation, or insolation, fluctuate. Several factors contribute to these variations:
- Earth’s Rotation: The rotation of the Earth on its axis influences the distribution of insolation.
- Angle of Sun’s Rays: The angle at which the Sun’s rays strike the Earth’s surface depends on the latitude of a location. Higher latitudes receive sunlight at a shallower angle, resulting in slanted rays. This means that the energy is distributed over a larger area, leading to decreased net energy received per unit area. Additionally, slanted rays must pass through a greater depth of the atmosphere, causing more absorption, scattering, and diffusion.
- Length of Day: The duration of daylight hours also affects the amount of insolation received.
- Transparency of the Atmosphere: The atmosphere is mostly transparent to shortwave solar radiation. However, certain gases and suspended particles in the troposphere absorb and scatter incoming radiation, affecting its distribution.
- Land Configuration: While the configuration of land, including its aspect, can influence insolation, its impact is relatively minor compared to other factors.
Passage of Solar Radiation through the Atmosphere
Solar radiation passes through the atmosphere, with certain gases and particles absorbing and scattering incoming radiation. Water vapor, ozone, and other gases in the troposphere absorb much of the near-infrared radiation, while small suspended particles scatter visible light. This scattering contributes to the coloration of the sky, such as the red hues of sunrise and sunset.
Spatial Distribution of Insolation at Earth’s Surface
Insolation received at the Earth’s surface varies widely, from approximately 320 Watt/m2 in the tropics to about 70 Watt/m2 at the poles. Subtropical deserts receive the maximum insolation due to minimal cloud cover, while the equator receives relatively less insolation compared to the tropics. Generally, continents receive more insolation than oceans at the same latitude. Additionally, the middle and higher latitudes experience less radiation during winter compared to summer.
Heating and Cooling of Atmosphere
The atmosphere experiences heating and cooling through various mechanisms:
- Conduction: When the Earth’s surface is heated by incoming solar radiation, it transfers heat to the adjacent atmospheric layers in the form of long-wave radiation. This gradual heating of the air in contact with the land is termed conduction. Conduction occurs when two bodies at different temperatures come into contact, causing energy to flow from the warmer body to the cooler one. This process is crucial for heating the lower atmospheric layers.
- Convection: As the air near the Earth’s surface is heated, it rises vertically in the form of currents, transmitting heat throughout the atmosphere. This vertical heating process is known as convection and is confined to the troposphere.
- Advection: Heat transfer through horizontal movement of air is referred to as advection. Horizontal air movement plays a significant role in influencing daily weather patterns, particularly in middle latitudes. For example, advection contributes to the occurrence of local winds like the ‘loo’ in northern India during the summer season.
Terrestrial Radiation
After receiving insolation from the Sun, the Earth’s surface emits heat energy in the form of long-wave radiation. Roughly 35 units of incoming solar radiation are reflected back to space, with the remaining 65 units absorbed by the Earth’s surface. The Earth then radiates back 51 units of heat energy, with 34 units absorbed by the atmosphere and 17 units radiated directly to space.
Heat Budget of the Earth
The Earth’s heat budget, illustrated in Figure 9.2, demonstrates a balance between incoming solar radiation and outgoing terrestrial radiation. This balance ensures that the Earth’s temperature remains relatively constant. The atmosphere indirectly receives heat from the Earth’s surface through terrestrial radiation, and this energy is eventually radiated back into space, maintaining thermal equilibrium.
Variation in Net Heat Budget at Earth’s Surface
There are variations in the amount of radiation received at different latitudes, resulting in regional differences in the net radiation balance. Figure 8.3 illustrates that regions between 40 degrees north and south experience a surplus of net radiation balance, while polar regions have a deficit. The surplus heat from the tropics is redistributed towards the poles, preventing excessive heating in the tropics or permanent freezing in high latitudes due to accumulated heat deficit.
Temperature
Temperature, a measure of heat resulting from the interaction between insolation and the atmosphere and Earth’s surface, is crucial for understanding climatic patterns. While heat signifies the molecular movement of a substance’s particles, temperature quantifies how hot or cold something is.
Factors Influencing Temperature Distribution:
- Latitude: Temperature is influenced by the amount of insolation received, which varies with latitude. Regions closer to the equator receive more direct sunlight and hence have higher temperatures, while polar regions receive less sunlight and have lower temperatures.
- Altitude: Generally, temperature decreases with increasing altitude. Places at higher elevations experience lower temperatures because the atmosphere is indirectly heated by terrestrial radiation from below. The rate of temperature decrease with height is termed the normal lapse rate.
- Distance from the Sea: Proximity to large water bodies moderates temperature fluctuations. Land areas heat up and cool down more quickly than oceans. Coastal areas experience milder temperature variations due to the moderating influence of sea breezes.
- Air Masses and Ocean Currents: Temperature is influenced by the movement of air masses and ocean currents. Warm air masses lead to higher temperatures, while cold air masses result in lower temperatures. Similarly, regions affected by warm ocean currents experience higher temperatures.
Global Distribution of Temperature:
Temperature distribution varies across the globe, as illustrated by isotherms—lines connecting places with the same temperature. In January, isotherms generally parallel latitudes, but deviations occur due to landmasses and ocean currents. The Northern Hemisphere experiences more pronounced temperature variations due to its larger land surface area. In July, isotherms generally align with latitudes.
The effect of oceans on temperature distribution is more pronounced in the Southern Hemisphere, where temperature variations are more gradual. The range of temperature between January and July varies significantly across regions, with the highest range observed in continental areas due to continentality.
Inversion of Temperature
Typically, as elevation increases, temperature decreases, following the normal lapse rate. However, there are instances where this pattern is reversed, known as temperature inversion. Although usually short-lived, temperature inversion is not uncommon. Clear, calm winter nights are conducive to inversion, as the Earth cools faster than the air above it by early morning.
In polar regions, temperature inversion occurs consistently throughout the year. Surface inversion, which occurs when cooler air is trapped beneath warmer air, stabilizes the lower layers of the atmosphere. Particles like smoke and dust accumulate beneath the inversion layer, leading to horizontal spread and the formation of dense fogs, particularly in winter mornings. This inversion typically dissipates within a few hours as the sun begins to warm the Earth.
In hilly or mountainous areas, temperature inversion can also occur due to air drainage. Cold air, generated at higher elevations during the night, flows downhill under gravity’s influence. This dense, cold air accumulates in valleys and depressions, with warmer air above, a phenomenon known as air drainage. This process helps protect plants from frost damage.
Additionally:
- Plank’s law describes how hotter bodies emit more energy with shorter wavelengths of radiation.
- Specific heat refers to the amount of energy required to raise the temperature of one gram of a substance by one Celsius degree.
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Solar Radiation, Heat Balance and Temperature- FAQs
Why is the heat balance important?
Earth’s heat balance is and extremely important factor in what makes the Earth livable. The fact that the Earth can respond to slight changes in the amount of incoming radiation to maintain a fairly stable temperature is a result of Earth’s energy budget.
What is the relationship between solar radiation and temperature?
When the sun’s rays strike Earth’s surface near the equator, the incoming solar radiation is more direct (nearly perpendicular or closer to a 90˚ angle). Therefore, the solar radiation is concentrated over a smaller surface area, causing warmer temperatures.
What is the heating effect of solar radiation?
The heating effect is caused by infrared radiation transferring heat between the surface, water, and air.
Is solar radiation hot or cold?
During the day, the sun sends heat to the earth. The technical term for this is solar radiation. The earth also radiates heat back out, but at a lower rate. The net result is a rise in temperatures when the sun is up.
What is the main cause of solar radiation?
Solar radiation also called as the solar resource or just sunlight, is a general term for the electromagnetic radiation emitted by the sun. Solar radiation can be captured and turned into useful forms of energy, such as heat and electricity, using a variety of technologies.
What are the different types of solar radiation?
The term solar radiation usually refers to electromagnetic waves, including light. The three major types of solar radiation are the visible, infrared, and ultraviolet wavelengths of light. Light travels from solar emissions from the sun to planet Earth.
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