Insolation

Solar radiation

Both A and R are true and R is the correct explanation of A.

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

Insolation

Terrestrial radiation

Heat balance

51%

direct contact; circulatory motion

A : 14; B : 34

Altitude

conduction , convection

night time

Valley Breeze

The Sun continuously radiates heat and light energy in all the directions. It is known as solar radiation.

Solar radiation is the only primary source of light and heat on the Earth.

The amount of solar energy received by the Earth is called insolation.

Two main characteristics of insolation are-

1. The Sun's energy reaches the Earth as short wave rays.
2. Out of the total 100% solar energy, only 51% reaches the Earth, 35% is reflected back into space and only 14% is absorbed by the atmospheric layers including the ozone during insolation.

Two advantages of convectional heating of the atmosphere are-

1. Convection currents in the atmosphere cause sea breeze. During the day, the air over land becomes warmer and rises. Cool air from oceans moves in to take its place causing sea breeze.
2. At night, land breeze happens due to the opposite of this. Land surface gets cooled more quickly than the ocean surface. Air over land flows towards the ocean causing land breeze.

Four factors that affect the temperature of a place are-

1. Latitude of a place
2. Altitude of a place
3. Distance from the sea
4. Slope of the land

Due to spherical shape of the Earth, mid latitudes get less insolation resulting in moderate climate with normal temperature ranging from 15°C to 30°C. The duration of sunshine is greater in summer than winter. So the summer is warm and winter is cold.

Temperature keeps on decreasing with increase in altitude. There is a fall of 1°C in temperature on climbing every 166 metres. Hence, the temperature on a mountain is lower than the temperature on a sea shore.

The Tropic of Cancer passes mid-way across India. On June 21, the rays of the Sun falls directly over the Tropic of Cancer as the North Pole get tilted towards the Sun. The southern hemisphere is tilted away from the Sun during this time. Hence, July is hot.

On December 22nd, the Southern Hemisphere is tilted towards the Sun and the Sun rays fall vertically over the Tropic of Capricorn, while the Northern Hemisphere is tilted away from the Sun. So, India, which lies in the Northern Hemisphere experience winters in December.

The atmosphere absorbs 34 units of the Earth's radiation, but it absorbs only 14 units of the Sun's incoming radiation. Thus, the atmosphere is heated more by terrestrial radiation given out by the Earth than by the incoming insolation from the Sun.

At night, the atmosphere acts as a greenhouse and keeps the Earth's surface warm by preventing the terrestrial radiation from escaping into space. During the day, the atmosphere absorbs 14% of insolation and thus regulates temperature on Earth.

The temperature of a place depends on the latitude of a place as temperature decreases with increase in latitude on either side of the equator due to the spherical shape of the Earth and its annual revolution around the Sun.

Also, the mid day Sun is almost overhead within the tropics but at oblique angles outside the tropics.

(i) North India lies away from the water bodies and experiences continental type of climate whereas South India being near the water bodies experiences maritime climate. Also, North India comes in temperate zone as it lies towards the north of Tropic of Cancer whereas South India falls in Torrid Zone towards the south of Tropic of Cancer. Due to these reasons, North India has a greater range of temperature than South India.

(ii) The temperature of Delhi is less than that of Chennai in December because Delhi lies beyond the Tropic of Cancer, in the Temperate zone. So in December, it receives slanting rays of the sun. But Chennai is located in Torrid zone and hence, it receives vertical rays of the sun throughout the year. Therefore, the temperature of Delhi is lesser during the December.

(iii) Desert areas experience a high day temperature and a much lower night temperature because desert areas are covered with sand. The physical property of the sand is to get heated up quickly and cool down abruptly. So, the day temperature is very high and the night temperature is very low.

Below labelled diagram shows the Heat Budget of the Earth:

The five temperature zones of the Earth are-

1. Torrid Zone
2. North Temperate Zone
3. South Temperate Zone
4. North Frigid Zone
5. South Frigid Zone

The rate of decrease of temperature with height is about 6°C per km above the sea level, so on climbing every 166 metres, there is a fall of 1°C in temperature. It is known as Normal Lapse Rate.

(i) Distance from the sea affects the temperature of a place as the sea breeze blowing from the sea towards the land cools the coastal regions during the day. At night, the land breeze makes the sea cooler. This interchange of breeze maintains the heat balance. Hence, the areas close to the sea have a lower daily and annual ranges of temperatures and enjoy a moderate climate than the areas lying in the interior.

(ii) Land is heated and cooled faster than the sea because water is mobile and the warm water mixes easily with the cold water and is neither heated nor cooled quickly. On the other hand, the Sun's rays heat a piece of land more rapidly because unlike water, the heat obtained by the area remains confined to that area and does not mix with other areas of land.

(iii) The ports of the western coast of Europe remain ice-free during winter due to the warm effect of the Gulf Stream and North Atlantic Drift.

Below labelled diagram shows that the vertical rays are hotter than slanting rays:

Distance from the sea affects the temperature of a place as the sea breeze blowing from the sea towards the land cools the coastal regions during the day. At night, the land breeze makes the sea cooler. This interchange of breeze maintains the heat balance. Hence, the areas close to the sea have a lower daily and annual ranges of temperatures and enjoy a moderate climate than the areas lying in the interior.

During the day the sea breeze blowing towards the land from the sea keeps the coastal region cool and during the night the land breeze blowing from the land towards the sea makes the sea cooler.

This interchange of breeze maintains the heat balance. Hence, the areas close to the sea have a lower daily and annual ranges of temperatures and enjoy a moderate climate than the areas lying in the interior.

(i) At higher latitudes, the rays of the Sun fall in an oblique way. Oblique rays not only travel a longer distance, but also heat a larger area. Thus, they have less heating power. Hence, with higher latitudes, the temperature goes on decreasing.

(ii) The vertical rays of the Sun give more insolation than the slanting rays because vertical rays travel a shorter distance and heat up a smaller surface area leading to higher temperatures whereas slanting rays not only travel a longer distance, but also heat a larger area. Thus, they have less heating power.

(iii) 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 90% insolation and the solar energy absorbed by plants is used in the process of transpiration resulting in low range of temperature.

Below labelled diagram shows the land and sea breeze:

If the entire solar energy were to reach the Earth instead of just 51%, there would be several significant consequences. Here are some reasons to support this answer:

1. Increased Temperature — The Earth's surface would experience a significant increase in temperature. The additional solar energy would lead to a substantial rise in average global temperatures, resulting in hotter climates worldwide. This increase in temperature could have far-reaching effects on ecosystems, weather patterns, and human habitats.
2. Ecosystem Disruption — The increased solar energy would disrupt ecosystems and ecological balances. Many species have evolved to adapt to the existing amount of solar radiation. A sudden influx of additional energy could lead to shifts in vegetation patterns, changes in animal behavior and migration patterns, and the disruption of delicate ecological relationships.
3. Water Cycle Changes — The increased solar energy would accelerate the water cycle. Higher temperatures would lead to increased evaporation rates, which would result in more moisture in the atmosphere. This, in turn, could intensify precipitation, leading to more frequent and intense rainfall, storms, and even extreme weather events like hurricanes.
4. Impact on Human Health — The amplified solar radiation could have adverse effects on human health. Increased exposure to ultraviolet (UV) radiation could lead to a higher incidence of skin cancer, cataracts, and other UV-related health issues. It would necessitate enhanced sun protection measures and a heightened risk awareness.
5. Energy Overload — The Earth's energy systems would face challenges in handling the excess solar energy. Our current energy infrastructure is designed to accommodate the amount of solar energy that reaches the Earth. If the energy input were to increase drastically, it could strain power grids, transmission lines, and other energy-related infrastructure, requiring significant upgrades and modifications.
6. Climate Instability — The sudden influx of solar energy would disrupt the delicate balance of Earth's climate system. It could potentially trigger feedback loops that amplify the warming effect, leading to a runaway greenhouse effect. This could result in further temperature increases, exacerbating climate change and its associated consequences.

Yes, Greenhouse Gases affect the Earth's heat budget as can be understood by the following examples:

1. Greenhouse Effect — Greenhouse gases, such as carbon dioxide (CO₂) and methane (CH₄), trap heat from the sun, preventing it from escaping back into space.
2. Increased Temperatures — The presence of greenhouse gases in the atmosphere leads to an increase in average global temperatures, contributing to global warming.
3. Climate Change — The buildup of greenhouse gases alters the balance of the Earth's heat budget, resulting in changes in climate patterns, including temperature shifts and extreme weather events.
4. Human Activities — Human activities, like burning fossil fuels and deforestation, release large amounts of greenhouse gases into the atmosphere, intensifying the greenhouse effect and impacting the Earth's heat budget.