Structure and Properties of Atmosphere
Earth’s atmosphere refers to a layer of gases surrounding the earth, and it is retained by the gravity of the earth. Earth’s atmosphere protects life by warming the surfaces through green house effect, absorbing ultra violet radiations, and by maintaining temperature variations during daytime and night. The mass of the atmosphere is estimated to be about 5x1018 kg. The major gases of atmosphere by volume include; oxygen (21%), argon (0.93%) and nitrogen (78%) (Donald 56). This paper, therefore, explores the structure and properties of the atmosphere.
Earth’s atmosphere is divided into five major layers. The arrangement of these layers occurs from the outmost layer to the innermost layer. These layers are arranged based on air pressure and density. For instance, density and air pressure decreases with altitude while temperatures may either increase or remain constant in relative to altitude. Thus, the patterns of temperature/ altitude provide a vital metric for arranging earth’s layers. Firstly, the exosphere is the outermost layer of the atmosphere. The main components of exosphere include; helium, nitrogen, oxygen, carbon dioxide and hydrogen molecules (Atmospheric Structure par 4). These molecules are far apart from each other such that they travel hundreds of kilometers without colliding. As a result, the exosphere does not behave like a gas. Succinctly, the free moving particles adhere to ballistic trajectories hence can move in and out of the magnetosphere (Atmospheric Structure par 7).
Thermosphere forms the second region of the earth’s atmosphere. Temperatures of this region are higher than that of the exosphere. The temperature of thermosphere can rise to 1500oC. The third layer of the atmosphere is the Mesosphere. Mesosphere is the layer where most meteors burn the moment they enter the atmosphere. The fourth layer of the atmosphere is the stratosphere. Temperature of this region increases with height since there is improved absorption of ultraviolent radiations by the ozone layer. Lastly, troposphere forms the last portion of the earth’s atmosphere. Troposphere is the warmest part among the five layers. Other additional layers include; ozone layer, ionosphere, homosphere, and the planetary boundary layer (Salby 77).
At sea level, the average atmospheric pressure is equivalent to one standard atmosphere (101.3 kPa) while the total atmospheric mass is 5.1480x1018 kg. However, the atmospheric pressure varies with the state of weather and location. Ideally, scientists assert that the atmospheric mass distribution occurs as follows: 50% of the atmosphere is below 5.6 kilometers, 90% is below16 kilometers while 99.99997% is below 100 kilometers. Concisely, 99.99997% is normally referred to as Kármán line since it is the one used by astronauts for space exploration (Holton 18).
Normally, temperatures decrease with altitude from the sea level. However, in the stratosphere zone, starting from 20km, the temperatures increase with height due to the heating of ozone caused by the capture of sun rays. The same trend also occurs in thermosphere layer which is in high altitudes (Donald 64).
At sea level, the density of air is estimated to be 1.2 kg/m3 or 1.2 g/L. The air density is calculated from measurements of humidity, temperature and pressure using the normal equation of an ideal gas law. Increase in altitude decreases the atmospheric density, a variation that can be modeled using the barometric concepts. The mass of the atmosphere is estimated at 5 x1015 tonnes. The American National Center for Atmospheric Pressure estimates the total mean mass of the atmosphere to be 5.1480x 1018 kg. In addition, the annual range resulting from water vapor is estimated to be1.2 or 1.5×1015 kg (Donald 88).
Earth receives solar radiation from the sun and emits radiation back into space. Earth emits longer wavelengths of radiations that cannot be seen with naked eyes. The part of emitted and incoming radiations are either absorbed or reflected by the atmosphere. Scientists argue that photons of light interact with the atmosphere whenever light passes through the space. This radiation is referred to indirect radiation. However, direct radiation occurs when the light fails to interact with the atmosphere (Salby 81).
Different molecules in the atmosphere absorb various wavelengths of radiation. Precisely, molecules such as 03 and 02 absorb wavelengths shorter than 300 nanometers. The energy of a molecule increases whenever there is light absorption. On the other hand, objects emit light depending on their black body emission curves. Typically, hotter objects emit more radiations of short wavelengths than cooler objects. For instance, the sun’s radiation peaks at about 10,000 nm making it hard for a human being to view the radiations. The atmosphere emits infrared radiations due to its temperatures (Salby 89). The refractive index of the atmospheric gases is greater than 1. The variation in reflective index brings the bending effect of light rays over a long optical path. The reflective index of gases is pegged on the temperature gradient (Holton 76).
Earth’s atmosphere refers to layers of gases surrounding the earth. The key gases with highest volumes include; nitrogen, oxygen and argon. Earth’s atmosphere is made up of five layers namely, exosphere, thermosphere, mesosphere, stratosphere and troposphere. Furthermore, the atmosphere exhibits properties such as density, pressure, mass, optical properties, absorption, emission and reflective index.
Work Cited
Atmospheric Structure. Accessed from http://www.albany.edu/faculty/rgk/atm101/structur.htm on 23 April 2013
Donald, Ahrens. Essentials of Meteorology. San Francisco Thomson Brooks/Cole, 2005. Print.
Holton, James. Encyclopedia of Atmospheric Sciences. Amsterdam: Elsevier Science Ltd, 2002. Print.
Salby, Murry. Physics of the Atmosphere and Climate. Cambridge: Cambridge University Press, 2012. Print.