solar radiation
- Solar radiation is the energy that comes from the Sun to the Earth. It is also called "insolation". The bulk of the energy that reaches the Earth is in short wavelengths.
- The shape of the earth is not completely round but in the form of a "geoid", due to which the sun rays fall on the earth obliquely instead of directly. Because of this, the earth does not receive the full energy of the sun.
- About 1.94 calories of energy reaches the upper surface of the Earth's atmosphere per square centimeter per minute. The distance between the Earth and the Sun also affects the energy received.
- On July 4, the Earth is farthest from the Sun (aphelion), at a distance of approximately 152 million km, while on January 3, the Earth is closest to the Sun (perihelion), at a distance of approximately 147 million km.
- For this reason, the energy received by the Earth from the Sun in January is more than in July.
- The effect of insolation on Earth varies from place to place due to the distribution of land and sea. In addition, atmospheric changes, such as the movement of wind and clouds, can increase or decrease the amount of insolation.
- Variations in insolation have little effect on the major weather cycles on Earth. Instead, other factors have a greater influence on daily and regional weather.
Variation in insolation at the Earth's surface
The amount of energy reaching the Earth from the sun (insolation) varies from day to day, season to season, and year to year. The main reasons for the variation in insolation are:
Factors affecting insolation:
- The Earth rotates on its axis, creating day and night, and this affects insolation. The angle of the sun's rays is also important; direct rays give more heat, while oblique rays give less energy because they travel a greater distance through the atmosphere and lose more energy.
- Day length also affects insolation, since longer days allow the Sun's rays to reach the Earth for a longer period of time, increasing insolation.
- The transparency of the atmosphere also has an effect; dust, water vapor, and other gases reduce insolation by blocking or scattering the sun's rays.
- In addition, the shape of the Earth's surface, such as the distribution of mountains, plains, and oceans, also has a slight effect on insolation.
- The Earth's axis is tilted at 66½°, which makes insolation vary at different latitudes.
- The sun rays fall obliquely on the polar regions, due to which these regions receive less energy. On the contrary, the sun rays fall directly on the equator, due to which more energy is received here.
passage of solar radiation through the atmosphere
- The sun's rays pass through the atmosphere to reach the Earth, where gases in the atmosphere, such as water vapor and ozone, absorb some of the radiation.
- The oblique rays travel a longer distance in the atmosphere and get scattered, which makes the sun appear red at sunrise and sunset. Due to this same process of scattering of light, the sky appears blue.
- The amount of insolation (energy received from the sun) varies in different parts of the Earth. Its distribution depends on location, season and environment.
Spatial distribution of solar radiation:
- The amount of insolation is highest in the tropics, about 320 watts per square meter, but it is slightly reduced near the equator due to cloud cover.
- In the polar regions the amount of insolation is only about 70 watts per square meter because the sun's rays fall obliquely.
- In subtropical deserts, such as the Sahara, insolation is highest due to clear skies and lack of clouds.
- Compared to continents and oceans at the same latitude, continental areas receive more insolation because oceans absorb the sun's rays deeper, allowing less energy to reach the surface.
- Season also affects insolation; in summer the insolation is greater in the middle and high latitudes, while in winter the amount decreases.
heating and cooling of the atmosphere
The Earth's atmosphere is heated and cooled in several ways. To understand this, it is important to know the main processes:
1. Conduction:
- The Earth's surface absorbs energy from the Sun and becomes hot, causing the air in contact with the surface to also become hot.
- This heat is transferred from the lower layers to the upper layers.
- Conduction occurs when two bodies with different temperatures come into contact, and conduction plays an important role in heating the lower layers of the atmosphere.
2. Convection:
- Warm air becomes lighter and rises, while cold air sinks, causing vertical transfer of heat in the atmosphere.
- This process helps to spread the temperature in the atmosphere and is mainly confined to the troposphere.
3. Advection:
- When wind moves horizontally (left-right), it carries heat or cold with it.
- This process is extremely important for the transfer of heat in the atmosphere.
- This is the main reason for daily weather changes in the middle latitudes and summer heat waves in the tropical regions.
4. Terrestrial Radiation:
- Short waves coming from the sun heat the earth's surface, and after getting heated the earth radiates the energy in the form of long waves.
- This radiation is absorbed by gases present in the atmosphere, such as carbon dioxide and other greenhouse gases.
- The atmosphere is not heated directly by the Sun, but rather indirectly through this radiation coming from the Earth.
5. Radiation:
- The gases present in the atmosphere and the Earth's surface send their energy into space through radiation, which keeps the Earth's temperature balanced.
Earth's heat budget
The Earth's heat budget is the balance between how much energy the Earth receives from the Sun and how much energy it radiates back into space. This balance keeps the Earth's temperature constant.
How does the heat budget work?
- The energy received by the Earth from the Sun, called insolation, can be considered as a total of 100 units.
- Of these, 35 units are reflected and return to space, which is called the Earth's albedo. Of these 35 units, 27 units are reflected by clouds and 2 units by ice.
- The remaining 65 units are absorbed by the Earth and atmosphere, of which 14 units are absorbed by the atmosphere and 51 units by the Earth's surface.
- The Earth's surface re-radiates this energy into space in the form of terrestrial radiation. In this re-distribution, 17 units of energy are returned directly to space, while 34 units are absorbed by the atmosphere and finally sent into space.
- In total, 65 units (17 from the surface and 48 from the atmosphere) are returned to space, which balances the 65 units received from the Sun. This energy balance allows the Earth to be neither too hot nor too cold.
Variation in heat budget:
- Between 40° north and south latitudes, the energy received from the sun is more, which leads to accumulation of heat in these areas, which is called surplus.
- In contrast, in polar regions the energy received from the sun is less, leading to an energy deficit.
redistribution of heat
- Excess energy from the tropical regions reaches the polar regions through wind and ocean currents.
- This redistribution ensures that the tropics do not become too hot and the polar regions do not freeze completely, keeping the Earth's temperature balanced.
Temperature
Temperature is a measure of how hot or cold a place is. It is determined by the energy we receive from the sun (insolation) and the interaction between the Earth's surface and the atmosphere. The main factors that affect temperature are:
- Latitude: The energy received from the sun varies with latitude, causing higher temperatures at the equator, while as we move towards the poles this energy decreases, causing the temperature to decrease.
- Altitude: Temperature decreases with increasing altitude, which is called the normal lapse rate. The temperature decreases by about 6.5°C for every 1,000 metres above sea level. This is why lower places, such as plains, have higher temperatures than higher places, such as mountains.
- Distance from the Sea: The sea heats up slowly and cools down slowly, while the land heats up quickly and cools down quickly. Due to this, the temperature of the areas near the sea remains constant, while more variation in temperature is observed in the interior areas of the land.
- Air Masses: Areas with warm airmasses have higher temperatures, while areas with cold airmasses have lower temperatures.
- Ocean Currents: Warm ocean currents increase the temperature of the sea coasts, while cold currents decrease the temperature of the coasts. For example, the western coast of Europe remains relatively warm even in winter due to the influence of warm ocean currents.
- Local factors: The temperature of a place is also affected by factors such as clouds, vegetation, and urbanization. These factors play an important role in regional climate and thermal balance.
Temperature distribution
Temperatures vary in different parts of the world. This can be studied by looking at the temperature distribution between January and July. Isotherms, i.e. lines that connect places with the same temperature, help to show this distribution on maps.
Temperature distribution in January:
- The effect of latitude can be clearly seen in the temperature distribution, as isotherms are generally parallel to latitudes.
- The Northern Hemisphere experiences greater temperature variation during January, while the Southern Hemisphere has relatively less temperature variation due to the influence of the oceans.
- The Northern Hemisphere has more landmass and hence more temperature variations. For example, the Gulf Stream and North Atlantic Ocean currents carry heat into the North Atlantic Ocean, causing the isotherms to shift northward.
- At the same time, the lowest temperature recorded in the plains of Siberia during January is -18°C to -48°C. On the other hand, due to the greater influence of the oceans in the Southern Hemisphere, the isotherms remain parallel to the latitudes, and the temperature variation here is less than in the Northern Hemisphere.
Temperature distribution in July
- The effect of latitude can be clearly seen in the temperature distribution, as the isotherms lie mostly parallel to the latitudes.
- The temperature of the equatorial oceans is generally more than 27°C. In the subtropical region of Asia, especially at 30° north latitude, temperatures are found to be more than 30°C.
- Temperatures are lower in the polar and middle latitudes, with average temperatures recorded at 10°C at 40° north and south latitudes.
Temperature Variation:
