Presentation on the Atmosphere

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Human factors and limitations group presentation Introduction The atmosphere. The earth’s atmosphere can be described as a layered system of gases blanketing the earth made up of five layers which differ in pressure, temperature, altitude and composition of gases. Two gases make up the bulk of the earth’s atmosphere: nitrogen, which comprises 78% of the atmosphere and oxygen which accounts for 21%. Various trace gases make up the remainder. “Weather is the state of the atmosphere at a specific time and place, with respect to temperature, precipitation and other factors such as cloudiness”. The weather as well as the climate is affected by many factors. You may actually be surprised by some of the forces that actually influence the weather. Ie. Mountains and cities. The five layers of the atmosphere include the troposphere, stratosphere, mesosphere, thermosphere and exosphere. Troposhere The troposphere is the first layer of the atmosphere; it is where all the weather actually occurs because it contains almost all of the atmospheres water vapour. It starts at the earth’s surface and extends upwards between 30,000ft at the poles to 56,000ft in altitude at the equator, dependant on the season. It is generally higher in summer than winter (NB – why?). 90% of the total mass of the atmosphere is contained at this level. Within this layer there is a temperature reduction with increased altitude and this is referred to as the lapse rate. The air pressure at the top of the troposphere, also known as the tropopause is only 10% of that at sea level. Thunderstorms, clear air turbulence and jet streams occur in the tropopause. It consists of high winds and thermal currents containing air of varying density and temperature. The troposphere is a very important layer to pilots and jet aircraft as optimum performance occurs here, between 30,000 and 39,000ft.

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