The layers of the Atmosphere
Table of Contents
The layers of the atmosphere entail the various envelopes of gas surrounding the earth from the ground upwards. The atmosphere has got five different layers whereby each layer is distinguished from the other based on its thermal characteristics that include the density of the gasses, chemical composition, and the movement of the gasses.
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The outermost layer of the atmosphere is known as the exosphere. The exosphere rests above the thermosphere and extends to about 6200 miles above the earth (Holstlag et al., 2013). Being the outermost part of the atmosphere, the exosphere is the first layer that protects the surface of the earth from meteors asteroids and cosmic rays and the temperature vary greatly ranging from 0 to 1700 degrees Celsius (Artinian, 2010). Also at the exosphere, molecules and atoms escape into the space orbiting the earth. Immediately below the exosphere is the thermopause which refers to the region between the exosphere and the thermosphere. The thermopause is about 375 miles above the surface of the earth.
The second layer of the atmosphere below the exosphere is known as the thermosphere. The thermosphere is also known as the upper atmosphere. It lies between 53 and 375 miles in the atmosphere (Holstlag et al., 2013). While the thermosphere is relatively thin in comparison to other layers, the gasses comprising the layer increasingly become denser as one approaches the surface of the earth (Artinian, 2010). As a result, therefore, the high-energy radiations from the sun such as ultra-violet and X-ray radiations start getting absorbed by the molecular gasses in this layer leading to regulation of temperatures on earth (Phillips & Landi, 2008). Owing to the absorption of radiation rays by the molecules at this layer, the temperatures increase with altitude, from negative 120 degrees centigrade at the bottom of the layer to about 2000 degrees centigrade pat the highest point of the atmospheric layer. Despite the high levels of temperatures within the thermosphere layer, the human skin will perceive it as being cold due to the very thin nature of the atmosphere therein. The high temperature being referred to within the layer denotes the high rates of energy absorption by the molecules in the layers (Phillips & Landi, 2008). However, with a considerably fewer molecules in the layer, the numbers of molecules are not enough to heat the skin and thus perceive the temperatures as low upon ascend.
The third layer of the atmosphere that exists below the thermosphere is known as the mesosphere. The mesosphere is located between 31 and 53 miles above the surface of the earth (Shepherd, 2000). The gaseous molecules that are comprised of this layer include oxygen molecules (Artinian, 2010). The molecules continue becoming denser as one descends towards the surface of the earth due to the increase in atmospheric pressure upon descending towards the surface of the earth. As a result, therefore, the temperatures at the layer increases gradually as one descend due to increase in radiation of heat from the sun that is reflected by clouds, gaseous molecules as well as the surface of the earth (Artinian, 2010). At the bottom of the layer, highest temperatures can be as high as negative 15 centigrade. Furthermore, in this layer, the molecular gasses are now thick enough to slow down incoming meteors, whereby they burn up, leaving sparkling trails as can always be seen at night (Palmer, 2017). Together with the stratosphere, this layer is usually regarded as the middle atmosphere. The transitional layer that separates the mesosphere from the stratosphere is known as the stratopause.
After the mesosphere comes the stratosphere. The layer is located below the mesosphere and extends between 12 and 31 miles above the surface of the earth (Labitzke & Van Loon, 2012). The layer holds up to 19 percent of the total atmospheric gasses making it vital in the establishment and maintenance of balance between the gases. However, despite having close to 19% of all gasses, the stratosphere is comprised of very little water vapor. Furthermore, within the stratosphere, temperatures increase with altitude whereby heat is produced during the process of formation of the Ozone layer that protects the surface of the earth from harmful ultra violet rays emitted from the sun (Phillips, Feldman & Landi, 2008). The heat that is produced in the Ozone layer is responsible for a temperature increase from the average of negative 51 degrees centigrade at the bottom of the tropopause, to about negative 15 degrees centigrade at the highest points of the stratosphere (Palmer, 2017). Also based on the phenomena observed, that is the increase in temperature with the altitude means that the warmer currents are located above the cooler currents in the atmosphere. As a result, within the stratosphere, there is no convection current because there is no presence of any vertical movement of the molecular gasses to cause transfer of heat energy within the layer of gasses in the atmosphere at this level (Labitzke & Van Loon, 2012). Consequently, the bottom part of this layer can be easily seen by the anvil-structured cumulonimbus clouds. The transitional layer between this layer and the next is known as the tropopause.
The final layer that exists just above the surface of the earth is the troposphere and extends from the surface to a height of between 4 and 12 miles depending in the features or the position on the surface of the earth (Ahrens, 2012). The thickness of the troposphere varies with the distance from the equator. At the equator, the altitude of the layer is about 11 to 12 miles. At 50°N and 50°S, it is about 5.5 miles, and at the poles, the altitude is under 4 miles high (Ahrens, 2012). Also, the density of the gasses within this layer decreases with altitude. The air becomes thinner as one descends. Therefore, the temperature in the layer declines with the rise in altitude. As one goes into higher altitudes, the temperature drops from the average of 17-degree centigrade to about negative 51-degree centigrade at the top of the tropopause (Ahrens, 2012).
Apart from using gaseous composition, the other way of classifying atmospheric layers is by using the physiological effects they have on the human body. By using this mode of categorizing layers of the atmosphere, we end up with three zones that is the physiological efficient, physiological deficient and space equivalent zones.
PHYSIOLOGICAL EFFICIENT ZONE AND ITS EFFECT ON THE HUMAN BODY
The first zone is the physiological efficient zone. It depicts the zone of the atmosphere between the see level to about 10000 feet above, with the atmospheric pressure of varying between 760 to 523 mm/Hg (Palmer, 2017). The human body is adapted to function normally in the lower regions of this zone due to the ample pressure and temperature that are conducive for human survival. The lower region supports circulation and gaseous exchange in human through the establishment and maintenance of balance between the atmospheric pressure and the blood pressure as well as surface tension of the lungs surfaces to support circulation and gaseous exchange respectively. Also at the lower regions of the zone, the human body can suffer from minor trapped gas complications in the ears, sinus and gastrointestinal tract (Artinian, 2010). On the other hand, the upper regions of the physiological efficient zone will result in complications for the body such as headaches, shortness of breath, and dizziness if one is exposed to the region for way too long due to the low atmospheric pressure.
PHYSIOLOGICAL DEFICIENT ZONE AND ITS EFFECT ON THE HUMAN BODY
The second zone is known as the physiological deficient zone. It is located at altitudes of between 10000 to 50000 feet above sea level (Artinian, 2010). The atmospheric pressure associated with this zone is between 523 to 87 mm/Hg. The majority of aviation operations take place within this zone. The effects of the physiological deficient zone to the human body include the development of physiological complications such as hypoxia and decompression sickness due to the relatively low atmospheric pressures associated with the region (Artinian, 2010). Due to the low atmospheric pressure of the region as well as low density of atmospheric gases such as oxygen that supports the physiological functions in the human body, the zone is deficient for human survival. On the other hand, to effectively cope in the zone airplanes establish a hybrid environment for the passengers with regulated temperature, pressure and concentration of oxygen to create a physiological efficient zone.
SPACE EQUIVALENT ZONE AND ITS EFFECTS ON THE HUMAN BODY
The final zone is known as the space equivalent zone. The zone is located between 50000 to 100000 miles above sea level and the atmospheric pressure associated with the region is between 87 to 0 mm/Hg (Palmer, 2017). The region is very hostile to the physiological well-being of the human body due to extremely high temperature as well as lower pressure as compared to the circulatory and surface tension of the lungs. Therefore, unprotected exposure of the human body above 50000 miles causes severe distortion in the physiological functions of the body such as circulation and gaseous exchange resulting in death (Artinian, 2010). This is mainly due to low pressure resulting in increased amount of trapped gases in the lungs that hinder gaseous exchange in humans. For human to cope, a simulated physiological efficient zone has to be created through the use of special protective suit.
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