Composition and Structure of Atmosphere

Introduction to Solar Radiation, Heat Balance and Temperature

The atmosphere is the vast envelope of gases surrounding the Earth, essential for sustaining life. Although air is always present around us, we typically only feel it when it moves as wind. This chapter begins by emphasizing the role of the atmosphere and the fundamental source of Earth's energy—the Sun. The Earth receives almost all its energy from solar radiation, which it absorbs and then radiates back into space. This balance ensures that Earth neither warms up indefinitely nor cools down over time. However, the distribution of this heat is uneven across the globe, leading to pressure differences in the atmosphere. These pressure differences drive winds that transfer heat from one region to another, influencing weather and climate patterns. Understanding the processes of heating and cooling of the atmosphere and the resulting temperature distribution is crucial for grasping Earth's climatic system.

• The atmosphere is a gaseous envelope surrounding Earth, supporting life.
• Air is always present but felt mainly when in motion (wind).
• Earth receives nearly all its energy from the Sun in the form of solar radiation.
• The Earth radiates energy back to space, maintaining a heat balance.
• Unequal heat distribution causes atmospheric pressure differences and winds.
• This chapter explains solar radiation, heat balance, and temperature distribution.
• 📌 Atmosphere: The envelope of gases surrounding the Earth.
• 📌 Solar Radiation: Energy emitted by the Sun reaching Earth.
• 📌 Heat Balance: The equilibrium between incoming solar radiation and outgoing terrestrial radiation.

SOLAR RADIATION

Solar radiation is the energy emitted by the Sun, primarily in short wavelengths, which reaches the Earth's atmosphere and surface. The energy received by the Earth from the Sun is called incoming solar radiation or insolation. Due to Earth's spherical shape (geoid), the Sun's rays strike the atmosphere obliquely, and Earth intercepts only a small fraction of the Sun's total energy output. On average, the Earth receives about 1.94 calories per square centimeter per minute at the top of its atmosphere. The solar output varies slightly throughout the year because of the elliptical orbit of the Earth around the Sun. When the Earth is farthest from the Sun (aphelion, around 4th July at 152 million km), it receives slightly less solar energy, and when it is closest (perihelion, around 3rd January at 147 million km), it receives slightly more. However, this variation has minimal effect on daily weather due to other overriding factors like atmospheric circulation and land-sea distribution.

• Solar radiation is mostly short wavelength energy emitted by the Sun.
• Incoming solar radiation is termed insolation.
• Earth receives about 1.94 calories/cm²/min at the top of the atmosphere on average.
• Earth's elliptical orbit causes slight annual variation in solar energy received.
• Aphelion (farthest point) occurs on 4th July; perihelion (nearest point) on 3rd January.
• Variation in solar output is masked by atmospheric and surface factors, affecting weather minimally.
• 📌 Insolation: Incoming solar radiation received at Earth's surface or atmosphere.
• 📌 Aphelion: The point in Earth's orbit farthest from the Sun.
• 📌 Perihelion: The point in Earth's orbit closest to the Sun.