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Atmosphere is a mixture of gases and it also contains liquid and solid elements. Gases can be put into groups. 1 constant gases: nitrogen, oxygen, argon, xenon, krypton, neon, helium 2 amount of gases which change over longer period of time ( methane, hydrogen, ozone, carbon dioxide ) 3amount of gases which change in a few days or weeks: water vapour, carbon monoxide, ammonia. The composition of the atmosphere:78% à nitrogen, 21% à oxigene, 0,9% à argon, 0,03% à carbon, 0,07% à other elements. The structure of the atmosphere: The atmosphere is divided into various concentric layers according to rate of temperature change, composition and electrical nature. These spheres are separated from each other by pauses. 1Troposphere: the lowest and the most important part of the atmosphere. This is about 10-12 km thick, most of the weather activity that affects human life takes place in this layer. Temperature decreases with height in the troposphere, it is -56 ^oC at the tropopause. 2Stratosphere: it extends upwards from an altitude of some 11 km to 50 km. This is a tranquil zone. The upper part contains the ozone layer. this layer plays a vital role in the defence of our life: it filters the harmful UV rays of the Sun. 3Mesosphere: temperature decreases there. The mesopause is the coldest part of the atmosphere ( -92 - -120 ^oC ). Meteors burn there.4Thermosphere: the layer of increasing temperature. It also called ionosphere because it consist of ionised material. It reflects radio waves.5Exosphere and magnetosphere: the outermost layers of the atmosphere.

Solar radiation and its effects:Solar rays travel a long way through the atmosphere until they heat up the air. The atmospheric elements modifying radiation, the surface, air currents near the surface and sea currents. Only a part of the radiation reaches the surface: 30% of it is reflected and 15% is absorbed in the atmosphere. Two kind of radiation reach the surface: direct radiation and diffuse radiation. 50% of the radiation reaches the surface, this is called insolation. Greenhouse effect: the surface emits long waves. A part of this radiation escapes to the space through the atmosphere. This process generated heat and this heat is radiated back towards the surface. Without the greenhouse effect the average temperature of the surface would be -20 instead of the present 15oC.Influencing factors:sun angle: the most intensive the heating in the area. Heating becomes less intensive if we move from the Equator towards the polar region. .Landform: slopes modify the angle at which radiation reaches the surface -Exposure: the position of a place in relation to compass direction-Duration of radiation: this can be measured in hours per year.-Material of the surface: continents heat faster than oceans and seas. Oceans cool down slower.-Albedo: it means the ratio of the total solar radiation falling on a surface to the amount reflected from it.-Wind and ocean current pattern.