Лекция: Variations with latitude and season
Variations of atmospheric composition with latitude and season are particularly important in the case of water vapour and ozone.
Ozone content is low over the equator and high in subpolar latitudes in spring. If the distribution were solely the result of photochemical processes, the maximum would occur in June near the equator, and the anomalous pattern must be due to a poleward transport of ozone. The movement is apparently from higher levels (30-40 km) in low latitudes towards lower levels (20-25 km) in high latitudes during winter months. Here the ozone is stored during the polar night, giving rise to an ozone-rich layer in early spring under natural conditions. It is this springtime feature that has been disrupted by the Antarctic ozone 'hole'. The type of circulation responsible for this transfer is not yet known with certainty, although it does not seem to be a simple direct one.
The water vapour content of the atmosphere is closely related to air temperature and is therefore greatest in summer and in low latitudes. There are, however, obvious exceptions to this generalization, such as the tropical desert areas of the world.
The carbon dioxide content of the air (averaging almost 360 parts per million (ppm)) has a large seasonal range in higher latitudes in the northern hemisphere associated with photosynthesis and decay of the biosphere. At 50 °N, the concentration ranges from 351 ppm in late summer to 363 ppm in spring. The low summer values are related to the assimilation of CO2 by the cold polar seas. Over the year, a small net transfer of CO2 from low to high altitudes takes place to maintain an equilibrium content in the air.
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