![]() The physiological reactions to oxygen deprivation are insidious and affect people in different ways. In fact, the reactions of the average person begin to be impaired at an altitude of about 10,000 feet and for some people as low as 5,000 feet. At 18,000 feet, however, the partial pressure of oxygen is significantly reduced to the point that it adversely affects the normal activities and functioning of the human body. At sea level, atmospheric pressure is great enough to support normal growth, activity, and life. It starts above the mesosphere and gradually fades into outer space.Īs discussed earlier, nitrogen and other trace gases make up 79 percent of the atmosphere, while the remaining 21 percent is life sustaining, atmospheric oxygen. The last layer of the atmosphere is the thermosphere. The temperature in the mesosphere decreases rapidly with an increase in altitude and can be as cold as -90☌. Directly above this is the mesosphere, which extends to the mesopause boundary at about 280,000 feet (85 km). At the top of the stratosphere is another boundary known as the stratopause, which exists at approximately 160,000 feet. Little weather exists in this layer and the air remains stable. The atmospheric level above the tropopause is the stratosphere, which extends from the tropopause to a height of about 160,000 feet (50 km). Location of the tropopause is important because it is commonly associated with the location of the jetstream and possible clear air turbulence. ![]() The altitude of the tropopause varies with latitude and with the season of the year therefore, it takes on an elliptical shape, as opposed to round. At the top of the troposphere is a boundary known as the tropopause, which traps moisture, and the associated weather, in the troposphere. Inside the troposphere, the temperature decreases at a rate of about 2☌elsius every 1,000 feet of altitude gain, and the pressure decreases at a rate of about 1 inch per 1,000 feet of altitude gain. The vast majority of weather, clouds, storms, and temperature variances occur within this first layer of the atmosphere. The first layer, known as the troposphere, extends from sea level up to 20,000 feet (6 km) over the northern and southern poles and up to 48,000 feet (14.5 km) over the equatorial regions. Within this envelope of gases, there are several recognizable layers of the atmosphere that are defined not only by altitude, but also by the specific characteristics of that level. Argon, carbon dioxide, and traces of other gases make up the remaining 1 percent. Nitrogen accounts for 78 percent of the gases that comprise the atmosphere, while oxygen makes up 21 percent. This blanket of gases provides protection from ultraviolet rays as well as supporting human, animal, and plant life on the planet. The atmosphere is a mixture of gases that surround the Earth. ![]() It is important to note, however, that there is no substitute for experience. The following pages are designed to help pilots acquire the background knowledge of aviation weather principles necessary to develop sound decision making skills relating to weather. Whether preparing for a local flight or a long cross-country, flight-planning decisions based on aviation weather can dramatically affect the safety of the flight.Ī solid understanding of aviation weather theory provides the tools necessary to understand the reports and forecasts obtained from a Flight Service Station aviation weather specialist and other aviation weather services.
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