Earth's Atmosphere
Introduction
The Earth's atmosphere is a layer of gases, commonly known as air, that surrounds the Earth and is retained by Earth's gravity. The atmosphere of Earth protects life on Earth by creating pressure allowing for liquid water to exist on the Earth's surface, absorbing ultraviolet solar radiation, warming the surface through heat retention (greenhouse effect), and reducing temperature extremes between day and night.
Composition and Structure
The Earth's atmosphere is composed of 78% nitrogen, 21% oxygen, and trace amounts of other gases including argon and carbon dioxide. The atmosphere also contains a variable amount of water vapor, on average around 1%. The atmosphere has a mass of about 5.15×10^18 kg, three quarters of which is within about 11 km (6.8 mi; 36,000 ft) of the surface.
The atmosphere becomes thinner and thinner with increasing altitude, with no definite boundary between the atmosphere and outer space. The Kármán line, at 100 km (62 mi), or 1.57% of Earth's radius, is often used as the border between the atmosphere and outer space.
Atmospheric Layers
The Earth's atmosphere can be divided into five main layers. These layers are mainly determined by whether temperature increases or decreases with altitude. From highest to lowest, these layers are:
Exosphere
The exosphere is the outermost layer of Earth's atmosphere. It extends from the exobase, which is located at the top of the thermosphere at an altitude of about 700 km above sea level, to about 10,000 km (6,200 mi; 33,000,000 ft) where it merges into the solar wind.
Thermosphere
The thermosphere is the second-highest layer of Earth's atmosphere. It extends from the mesopause (which separates it from the mesosphere) at an altitude of about 80 km (50 mi; 260,000 ft) up to the thermopause at an altitude range of 500–1000 km (310–620 mi; 1,600,000–3,300,000 ft).
Mesosphere
The mesosphere is the third highest layer of Earth's atmosphere, occupying the region above the stratosphere and below the thermosphere. It extends from the stratopause at an altitude of about 50 km (31 mi; 160,000 ft) to the mesopause at 85–100 km (53–62 mi; 280,000–330,000 ft) above sea level.
Stratosphere
The stratosphere is the second-lowest layer of Earth's atmosphere. It lies above the troposphere and is separated from it by the tropopause. This layer extends from the top of the troposphere at roughly 12 km (7.5 mi; 39,000 ft) above Earth's surface to the stratopause at an altitude of about 50–55 km (31–34 mi; 164,000–180,000 ft).
Troposphere
The troposphere is the lowest layer of Earth's atmosphere. It extends from Earth's surface to an average height of about 12 km (7.5 mi; 39,000 ft), although this altitude varies from about 9 km (5.6 mi; 30,000 ft) at the geographic poles to 17 km (11 mi; 56,000 ft) at the equator.
Physical Properties
The physical properties of the Earth's atmosphere include temperature, density, mass, and the proportion of individual gases. The atmosphere is more accurately modeled with a customized equation for each layer that takes gradients of temperature, molecular composition, solar radiation and gravity into account.
Weather and Climate
The Earth's atmosphere is a key factor in the weather and climate on the planet. The movement of air in the atmosphere (caused by differences in temperature and pressure) creates weather patterns and climatic zones. The atmosphere also plays a key role in the water cycle, acting as a reservoir for evaporation and condensation.
Impact on Radio Transmission
The Earth's atmosphere affects the propagation of radio waves, which are a type of electromagnetic radiation. This is due to the ionosphere, a region of the atmosphere that is ionized by solar radiation. The ionosphere can refract, reflect, and attenuate radio waves, affecting their propagation.