Atmosphere : Properties and Standard Atmosphere
ATMOSPHERE An atmosphere is a layer or a set of layers of gases surrounding a planet or other material body, that is held in place by the gravity of that body. It is more likely to be retained if the gravity is subject to high and the temperature of the atmosphere is low. The atmosphere of Earth is composed of nitrogen, oxygen, argon with carbon dioxide and other gases in trace amounts. It helps to protect living organisms from genetic damage by solar ultraviolet radiation, solar wind and cosmic rays. The current composition of the Earth's atmosphere is the product of billions of years of biochemical modification of the Paleoatmosphere by living organisms. Source: Wikipedia
ATMOSPHERIC PROPERTIES Temperature: Temperature is the measure of thermal or internal energy of the molecules within an object or gas. Density: Density measures the heaviness of an object. Pressure: Pressure is the force exerted over a given area or object, either because of gravity pulling on it or other motion the object has. Humidity: Humidity is a measure of the amount of moisture in the air. Source: Climate.ncsu.edu
Standard Atmosphere It is important to understand the definition of various altitudes that are usually used to analyse and compare the performance of flying vehicles in standard atmosphere. The gravitational force experienced by any aircraft varies with altitude. Also, an aircraft experiences variation in aerodynamic forces with altitude. Standard atmosphere is defined in order to relate flight tests, wind tunnel tests general airplane design and performance to a common reference. Let us define certain terms that are essential to understand and characterize standard atmosphere. 1. Absolute altitude (h a ) The altitude as measured from the centre of the earth. 2. Geometric altitude (h g ) The altitude as measured from the mean sea level. 3. Geo-potential altitude (h) The geometric altitude corrected for the gravity variation. Source: nptel.ac.in
Where, 1.Absolute Altitude (h a ) 2.Geometric Altitude (h g ) 3.Geo-potential Altitude (h) 4.Mean Radius of Earth (r) Figure : Schematic diagram representing geometric altitude and absolute altitude Source: nptel.ac.in
Plot representing variation of temperature with altitude Standard atmosphere: 1. From early on, researchers conducted experiments with sounding rockets and hot air balloons to study about the variation of temperature with altitude. 2. Typical pattern of variation of temperature to altitude is shown in Figure. One can easily notice that there are some vertical lines (known as constant temperature or isothermal regions) and inclined lines (known as gradient regions). Source: nptel.ac.in
LAYERS OF THE ATMOSPHERE The atmosphere is comprised of layers based on temperature. These layers are, Troposphere, Stratosphere, Mesosphere And Thermosphere. A further region at about 500 km above the Earth's surface is called the Exosphere. The atmosphere can be divided into layers based on its temperature, as shown in the figure. Source: niwa.co.nz
Troposphere : It is the lowest part of the atmosphere - the part we live in. The lowest part of the troposphere is called the boundary layer. The top of the troposphere is called the tropopause. Stratosphere: This extends upwards from the tropopause to about 50 km. Temperatures in the stratosphere are highest over the summer pole, and lowest over the winter pole.
Mesosphere: The region above the stratosphere is called the mesosphere. Here the temperature again decreases with height, reaching a minimum of about -90 C at the "mesopause". Thermosphere and Ionosphere: The thermosphere lies above the mesopause. The ionosphere reflects and absorbs radio waves, allowing us to receive shortwave radio broadcasts in New Zealand from other parts of the world.
Exosphere: The region above about 500 km is called the exosphere. It contains mainly oxygen and hydrogen atoms. They follow "ballistic" trajectories under the influence of gravity.
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