Introduction
The atmosphere comprises moisture and gases that surround the planet or any other material. The atmosphere is held in place by the gravity of the planet. The atmosphere is made up of several layers that have varying temperatures and pressure. It extends from the surface of the earth and stretches several miles into space. The atmosphere has several physical characteristics, which play a major role in protecting the earth and its inhabitants from the harmful solar radiations and other dangers from space. The presence of the atmosphere is what makes the earth habitable otherwise; it would be as unproductive as the moon.
Layers of the Atmosphere
(Retrieved from Saha, 2008)
The earth’s atmosphere is made up of numerous concentric layers where each one has different features. The layers are also known as spheres. Temperature variations in the atmosphere play a significant role in defining these layers. Understanding the conditions within these layers offer the aviation personnel the much-needed knowledge about the atmospheric environments of these spheres. The boundaries between the layers are known as pauses. The atmospheric layers around the earth include the following.
Troposphere
In this layer, there is pollution, varying weather systems, and heavy volcanic gases. One of the main characteristics of the troposphere is that the temperature of the air decreases as one goes up with increasing the distance from the earth’s surface (FAA, 2006). Since temperature features define the layer, one would expect that it would be thicker around the warmer regions and thin over the cold areas. The thickness of this layer varies with latitudes, as it is thick around the equator and thinner at the poles (Saha, 2008). The troposphere ends at the tropopause where the temperature stops reducing with elevation.
Stratosphere
The layer lies above the tropopause. It is estimated that it extends to a height of 50 kilometers from the surface of the earth. The most important feature found in this section is the ozone layer, which plays a significant role in ensuring that the harmful sun radiations do not reach the earth thus protecting life. Therefore, the ozone layer plays the role of a protective umbrella (FAA, 2006). The layer is usually calm and consists of clean air and does not contain water vapor thus the clouds may not form. In this sphere, the temperature increases as the altitude increases, this is the opposite of the troposphere. The increase of temperature with height prevents the vertical winds; hence, only horizontal winds are witnessed. The horizontal winds are almost parallel with the surface of the earth, and the absence of the vertical winds result in a relatively calm atmosphere without turbulences thus ensuring smooth flights. The absence of clouds provides clear visibility for pilots (Villare, 2005). Therefore, due to these conditions, the layer is good for airplane operations. Just above the stratosphere, the temperature does not increase with height up to a given level, which is known as the stratopause.
Mesosphere
This layer begins just above the stratopause, is said to be about 52 kilometers from the surface of the earth, and stretches for 80 kilometers from the ground. In this layer, the temperature decreases as the height increases just like in troposphere. Stratosphere does not play any significant role in supporting life (FAA, 2006). However, the light of the sun passes through this layer, and the molecules are charged in a process known as ionization. The charged particles are usually concentrated in a zone called the D-layer. The layer reflects the radio waves, which emanate from the earth. Due to this effect, the D-layer prevents communication between the astronauts and the earth. In this sphere during summer, especially at night, there are spectacular display shining clouds that are visible in high latitudes. The spectacular view is assumed to be meteoric dust, which is coated with ice that reflects the sunlight, thus producing the view (Saha, 2008).
Thermosphere
The sphere is found at around 80km from the surface of the earth. It is estimated to extend to 60000km from the earth’s surface. The temperatures in this layer keep increasing as the altitude increases (FAA, 2006). However, the temperature in this layer may not be felt as in other layers since the molecules of the air are far apart. Thus, the temperatures only apply to individual molecules. This layer also blocks radio wave communications due to ionization (Saha, 2008). On the upper layer of the thermosphere, there is a higher concentration of the ions and this section is called magnetosphere which is also known as the earth’s magnetic field that influences particle movement around the earth. The thermosphere has no definable upper layer as it blends with the space.
Atmosphere Composition
The Earth’s atmosphere is composed of a combination of different gases. However, few of them are important for human survival. The gases that are in high concentration are oxygen, nitrogen, and carbon dioxide. Additionally, these gases play a crucial role in supporting life on earth. Nitrogen makes up the largest composition of gases, but it is not readily used in the human body. However, nitrogen is very vital in the respiratory process as it saturates the body tissues and fluids. Therefore, it is important for aviators be aware of gas disorders in high altitudes (Saha, 2008). Oxygen is the second most abundant gas in the air.
The respiration process combines sugars and oxygen, thus meeting the requirements of the body. In high altitudes, the level of oxygen reduces drastically, and lack of oxygen in the body might cause psychological changes, which may result in death. Thus, oxygen is very important to aviators. Thirdly, carbon dioxide is produced by cellular respiration. Although the carbon dioxide is not in large capacities, it plays a major role in ensuring the supply of oxygen on earth (FAA, 2006). Lastly, there are traces of other gases such as helium, xenon, and argon but they are not as useful as nitrogen, carbon dioxide, and oxygen.
Atmospheric Pressure
Atmospheric pressure, which is also known as the barometric pressure is the force that is exerted by the atmosphere at any given point. Different forms of atmospheric pressure can be defined in different ways depending on the method used to measure them (Saha, 2008). Notably, the atmospheric pressure reduces as the altitude rises, thus making it one of the major concerns of the aircrew since the diffusion of oxygen is directly related to the atmospheric pressure. Although the atmospheric pressure reduces with the increase in height, the gas concentration remains stable. The changes in atmospheric pressure of oxygen may drastically affect the breathing functionality of the human body (C.I.B.A.F, 2009). A significant reduction in pressure of oxygen gas may lead to physiological impairment of an individual. However, the impairment may not be noticed immediately, especially at low altitudes, but the effects are likely to be felt progressively as the altitude increases. The reduction of nitrogen pressure in high areas may lead to a reduction in the solubility of the nitrogen in the body, a situation that may result in decompression sickness (FAA, 2006). Therefore, it is important for aviators to understand these changes in the earth’s atmosphere since they change as the altitude increases.
Physiological Zones of the Atmosphere
Physiological Zones of the Atmosphere
Human beings do not have the capability of adapting to the physical changes that may occur in the different sections of the atmosphere. Human evolution took place on the earth’s surface and they are usually vulnerable to changes in temperature and pressure that happen during aerial flight and ascent. Therefore, due to these factors, the atmosphere is then divided based on altitude into three physiological zones as seen in the diagram above. The zones are based on pressure changes that occur as individual ascends and the different effects on human physiology. The physiological zones are indicated below.
The Efficient Zone
It extends from the sea level upwards up to about 10000 feet. The aircrews in this zone have a feel of the physiological environment. Although the pressure of the atmosphere usually drops, the humans can operate in this area without putting on any protective gears (Saha, 2008). However, to fly above this range, it may need adjustments. The minor complications that may be experienced in the efficient zone area are an expansion of gases in the digestive tract and ear and sinus blocking (FAA, 2006). Additionally, without oxygen supplement, reduced visibility at night is likely to reduce above 4000 feet.
The Deficient Zone
This zone ranges from 10000 feet at its lowest and 50000 feet at the highest point. The atmospheric pressure in this zone is low, thus making it risky to operate unless there is supplemental oxygen or the use of pressurized cabin systems (Villaire, 2005). If the aircraft goes to the uppermost limit of the deficient zone, the reduced pressure leads to regular trapped-gas disorders.
The Space Equivalent Zone
The zone stretches to over 50000 feet and continues to the atmosphere. In fact, it cannot support human life, as it is very hostile. Thus, flying in the equivalent zone one needs to have a completely artificial atmospheric environment. Contact with these thrilling pressures and temperatures at these high altitudes will result in quick death (C.I.B.A.F, 2009). Due to low pressure and high temperatures, the moisture in the human body begins to boil and becomes water vapor.
Human beings have a surprising ability to adapt to their environment. The body of a human usually adjusts in accordance with changes in temperature and acclimates to different atmospheric pressure that varies from one place to another. The human body is designed in a way that it can adapt to places that have reduced oxygen supply by increasing the respiratory rate. However, it is important to note that lack of oxygen in the air is likely to cause death in a span of five to eight minutes. In the atmospheric layers, the pressure usually varies from one level to the next thus affecting the human body mechanisms (FAA, 2006). At the lowest level (troposphere), the human has the capability of surviving at any altitude since the layer has the necessary conditions that support life. On the other hand, this region usually affects the aircraft due to the presence of water vapor, which leads to the formation of clouds thus causing poor visibility.
The layer above the troposphere is the stratosphere and can support life if certain conditions are met. The zone usually contains the ozone layer that protects the harmful ultra-violet rays from reaching the earth’s surface. When operating in this layer, individuals are required to carry life-supporting equipment and ensure that the atmospheric pressure is balanced with the pressure of the body. In this region, the human may experience hypoxia due to reduced oxygen supply that may cause disorientation and in extreme cases may cause death. However, in this section, it is where most of the flight takes place since there is less or no turbulence as the air is calm (Villaire, 2009). Worth noting is that the aircraft flying in this region must be pressurized to balance the air pressure in the aircraft and the outside pressure.
Just above the stratosphere, there is the mesosphere layer that cannot support life due to reduced oxygen levels. Nonetheless, the human can survive if they use specialized equipment. In this layer, flying can also take place, but with modified and pressurized aircraft. In Mesosphere the human beings are required to have 100% oxygen support, since the levels of the gas are low (Saha, 2008). Lastly, there is the thermosphere, which is said to be extremely hostile to human survival. The pressure in this area is extremely low, and the temperatures are high reaching 900 degrees. However, the temperatures are not usually felt since the air molecules are far apart from each other and individual molecule holds the heat. If humans are exposed to these conditions without any protection, the water in their bodies may boil and become gases and eventually die instantly. The levels of oxygen in this region are very low; hence it is almost impossible for human survival (Saha, 2008). The aircraft flying in this layer mostly the rockets must be specially designed and have protective modifications to ensure they overcome the adverse conditions experienced in this section.
From the discussion, it is important to note that the atmosphere is a critical component that plays a significant role in supporting life. The atmosphere is divided into sub-sections that are known as spheres, which have several components that include gases and moisture in varying quantities. Each of the sphere has its given conditions. The troposphere is the most important layer since it supports life. The other spheres have harsh conditions that may require preventive measures and in the extreme cases, they need life support systems and specially modified aircraft to overcome the adverse conditions. In the atmosphere, nitrogen occupies the largest portion, oxygen is the second most common gas and important for human survival, while Carbon dioxide is the third. However, there are traces of other gases though in low quantities. The atmosphere further is divided into other sub-sections depending on atmospheric pressure. The sections include the efficient zone where the temperature and pressure decreases as the altitude rises. In fact, those sections can support life. Secondly, there is the deficient zone, which is above 10000 feet, and a risky area to operate unless under special preventive measures. Lastly, there is the space equivalent zone, which is a hostile area for human survival and requires special pressurized equipment for human survival.
References
Saha, K. (2008). The Earth’s atmosphere: Its physics and dynamics. Berlin: Springer.
Symposium, C. I. B. A. F. (2009). High altitude physiology: Cardiac and respiratory aspects. Hoboken: John Wiley & Sons.
Villaire, N. E. (2005). Applied aviation physiology. Melbourne, Fla.: Villaire & Hansrote.
Federal Aviation Administaration (FAA) (2006 April 04). Introduction to Aviation Physiology. Retrieved from https://www.faa.gov/pilots/training/airman_education/media/introaviationphys.pdf
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