Translations of Encyclopedia about Geology

Atmosphere and Weather

Atmosphere is the outer cover of the earth. It envelops the solid earth and is linked to it by the earth's gravity. As a result of the heat of the sun, it is in constant motion. These constant changes of air masses relate to our weather.

The atmosphere consists of approximately 78 percent of nitrogen, 21 percent oxygen, 0.9 percent argon, and approximately 0.04 of carbon dioxide. In addition, there are traces of neon, hydrogen, helium, ozone, methane, and oxides of nitrogen. In the course of history of the earth, this cover had undergone many changes. In the beginning, that is to say, more than 4.5 billion years ago, the atmosphere contained mostly hydrogen, carbon dioxide, and carbon monoxide.

When the solar wind scattered this original atmosphere, a new blanket formed from the gases escaping from the interior of the earth. The main components were carbon dioxide, oxides of nitrogen, hydrogen, sulphur dioxide, and water vapour. Condensed water vapour ultimately gave rise to our oceans and rivers. There formed the first life forms. Some of these organisms were capable of photosynthesis, resulting in the release of oxygen approximately 2 billion years ago. It took another 1.5 billion years for life organisms to be able to begin breathing in our atmosphere.

The atmosphere protects us against cosmic and solar rays by weakening or absorbing them. The atmosphere is made up of layers what are distinguished by the prevailing temperature, gas composition, and ionisation. When air rises through the atmosphere, the air density decreases. In an altitude of ten kilometres, breathing already becomes difficult, because as a result of falling air pressure the oxygen content is very low.

Weather is determined by certain atmospheric phenomena, such as air temperature, air humidity, pressure, movement (wind, windstorm), and eventually their strength and direction, as well as by precipitation (rain, snow). These atmospheric phenomena become visible by means of characteristic cloud formations.

In accordance with their altitude, the clouds are classified into upper, mid-, and lower levels. Within these levels we distinguish ten basic types of clouds. The corresponding table was compiled in 1803 by L. Howard, an amateur meteorologist. He classified individual clouds by their formation and altitudes, and named them using Latin language.

Any type of water falling from the atmosphere to the earth is called precipitation. It may be rain, snow, hail, or frost. In general, the amount of precipitation is measured in millimetres, calculating how much liquid water would cover the surface in the place where measurements are taken.

Wind is produced by the horizontal differences of the atmospheric pressure of neighbouring air masses. Dense air from the region of high air pressure flows into the less dense, and therefore lighter, air of the low pressure. The wind speed increases with the increasing pressure difference. Cold front forms when cold air collides with warm air. Cold air slides underneath the warm air and pushes it upwards. The strength of the wind is measured in metres per second and is given as a value on the so-called Beaufort scale. Forests, mountain ranges, oceans, and deserts also have bearing on the speed of wind.

There are global wind systems, local winds (mountains and valleys), marine wind, continental wind, and seasonal winds (monsoon). We study weather with the help of numerous meteorological stations, meteorological satellites, radio probes, and other tools. We obtain more or less accurate weather forecasts. In view of the magnitude of the atmosphere, it is not always easy to predict the weather with accuracy, even when we use computers.

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