Earth Atmosphere Composition and Structure
Reading time: 10 min
At the beginning of this lesson, we will study the composition of the Earth's atmosphere, then we study the structure of the Earth's atmosphere, which is divided into different layers according to temperature.
Composition of Earth Atmosphere
The layer of gas that surrounds the earth is called the atmosphere. The weight of the atmosphere is 54×1013 tons. Due to gravity, almost half of the total weight of the Earth’s atmosphere is located at an altitude of 18,000 feet.
If the earth did not have an atmosphere, its temperature would reach 199 Fahrenheit (93° degrees Celsius) during the day and -301 Fahrenheit (-185° degrees Celsius) at night.
The composition of the Earth’s atmospheric gases is
- 78% nitrogen
- 21% oxygen
- 1% other gases
As you can see, 99% of the Earth’s atmosphere gases are made up of nitrogen and oxygen. The other 1% of gases play an important role in the Earth’s atmosphere. The most important of these gases are:
Water vapor (H2O), carbon dioxide (CO2), methane (CH4), hydrogen (H), helium (HE), neon (NE), argon (AR), ozone (O3), etc. Water vapor, carbon dioxide, and methane are greenhouse gases.
The role of these gases in maintaining the Earth’s thermal balance is quite obvious. Unfortunately, in this century, due to population growth and increasing destructive pollutants, the Earth’s atmosphere tends to warm.
Structure of the Atmosphere
The Earth’s atmosphere is divided into the following layers according to temperature
The height of the troposphere depends on two factors:
The height of the troposphere is 20,000 feet at the pole, 37,000 feet at the mid-latitude, and 60,000 feet at the equator. The height of the troposphere under the International Standard Atmosphere (ISA) is 36,000 feet.
Important properties of the troposphere are:
- The temperature decreases with increasing altitude, which is called the lapse rate
- All atmospheric changes such as the formation of clouds, storms, etc. occur in this layer.
- The troposphere is the closest layer to Earth.
- Air pressure decreases with increasing altitude.
- The wind speed increases with increasing altitude.
- The thickness of the troposphere is greater in summer than in winter because the warm air expands and climbs to higher altitudes, but in winter the air is denser and climbs less to higher altitudes.
It is the boundary between the troposphere and the stratosphere.
Two of the most important features of tropopause are:
- The abrupt change in temperature lapse rate
- Maximum wind speed occurs in the tropopause, known as jet streams. (As the altitude increases, the friction decreases as the air density decreases, so the wind speed increases)
Note: From the tropical tropopause to polar tropopause height decreases but temperature increases and vice versa as you can see in the below image.
Note: The height of the tropopause will vary with latitude and seasons. The height of tropopause is higher in summer and lower in winter.
The stratosphere layer starts at 11 km above sea level and extends to 50 km above sea level, which is about 160,000 feet. In this layer, first, the temperature decreases with increasing altitude, and then in the upper part of the layer with increasing altitude due to the presence of ozone gas, the temperature increases.
Clouds do not usually form in the stratosphere, but sometimes the peaks of the CB and TS clouds (lightning clouds) extend to the lower part of the stratosphere.
In this layer, due to the thin atmosphere, the air resistance decreases, so it is a suitable area for airplanes to fly.
The boundary between the stratosphere and the mesosphere is called stratopause, which is about 50 km above the ground. Atmospheric pressure in stratopause is about 1/1000 pressure at sea level and also the temperature in this part is -15 degrees Celsius (5 degrees Fahrenheit).
The height of this layer extends from 50 km to 90 km above the ground. In this layer, the temperature decreases with increasing altitude. The lowest temperature of approximately -90°C occurs between 80 and 90 km therefore, the upper parts of the mesosphere are the coldest regions of the Earth’s atmosphere.
Thin clouds of ice crystals, known as Noctilucent clouds, sometimes form at higher latitudes in the upper Mesosphere at an altitude of approximately 80 km.
The boundary between the mesosphere and the thermosphere, which is approximately 90 km above the earth’s surface.
The highest layer of the atmosphere, which is located above the mesosphere and extends from an altitude of 90 km to 10,000 km where it gradually merges into Space.
In this layer, the temperature increases with altitude so that the temperature reaches 1000 degrees Celsius.
It should be noted that sometimes the temperature in this layer reaches 2000 degrees Celsius due to solar radiation and the presence of ultraviolet rays.
In the lower part of the thermosphere, there is a layer of ionized air that starts from the mesopause and extends to an altitude of 600 km above the earth and is known as the ionosphere.
The upper part of the thermosphere is called the exosphere, which starts from about 600 km above the earth’s surface and extends up to 10,000 km, which gradually merges into space.
The standard conditions of the international atmosphere are as follows:
Temperature = 15°C or 59°F
Pressure = 1013.25 hpa or 29.92 inch/hg or 14.7 PSI or 76 cm/hg or 760 mm/hg
Height of troposphere = 36000 feet and Temperature in this height = -56.5°C (-69.7°F) | Usually round up to -57°C
Standard lapse rate = 1.98°C 2°C
Density = 1225 gr/m3
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