Our planet and 'surrounded by a gaseous mass with a complex composition formed millions of years ago as a result of photochemical and thermodynamic processes associated with major geological upheavals that led to the current structure of the planet.
This gaseous mass follows the shape of the earth, shows a flattening at the poles and a bulge in the equatorial and tropical zones, and also 'attracted to the earth's surface and is driven by its own weight as a whole by the motion of the earth's rotation around its axis . Because of the efficiency of the force of gravity 'to escape Earth's atmosphere prevents the planet and make it a desert cold.
The air we breathe and 'in reality a mixture of gases of different composition: the main ones are nitrogen (chemical symbol N) for about 78% Oxygen (chemical symbol O 2) for about 20%, Carbon Dioxide (CO2 ) to 0.1%, these are added in very small percentages of the halogens and rare gases.
The layers of the atmosphere
The atmosphere on the basis of its composition and the concentration of the main elements that characterize it, can be divided into OMOSFERA (up to 80 km altitude) and ETEROSFERA (80-600 km altitude). The first layer and dell'OMOSFERA ' The troposphere, the troposphere is home to major weather events, it focuses on the 3 / 4 of all water vapor and has a thickness varying with latitude (as 'low at the poles and more' high at the equator) in the troposphere the temperature decreases more 'or less regularly from the ground up to about +20 ° C to - 55 ° C. The next layer called the tropopause, and 'a thin film thickness of 100-300 meters and is characterized by an isothermal and the presence of strong horizontal currents of great intensity, known as the jetstream.
The top layer instead said Stratosphere extends up to 40 km altitude, and in it the temperature increases with altitude while remaining a total of almost constant cloud features (nacreous clouds) are present in this layer also presents strong horizontal currents however, that a reversal of direction on a seasonal basis.
The overlying layer called the mesosphere, the stratosphere separated from stratopause, reaches up to 80 km altitude, and 'characterized by a fluctuating trend in the first temperature (first increases then decreases with altitude), then increasing to 300 ° C, and by the presence of clouds nottelucenti. Mesopause and the 'transition layer between the mesosphere and the thermosphere and reaches temperatures of about -70 ° C / - 100 ° C. Instead the thermosphere extending up to 400 km altitude, the temperature it increases with altitude. The thermosphere has layers of ionized gas (the ionosphere), which allows the propagation of radio waves, but, above all, and 'seat of important phenomena such as electric and geomagnetic polar auroras.
The last layer, the exosphere and 'separated from the TERMOPAUSA thermosphere, exosphere temperature and the' constant with altitude.
Water is the liquid most popular and the most important substance on Earth: use it to drink, to wash, swim in it, and we complain when it rains ...
The water affects our lives in many ways: first of all determines where we live, the local weather, so if we can grow crops and produce enough food. Large amounts of water are also used in industry, for example in cooling processes of large power plants or as a solvent. There are huge amounts of water collected in the oceans and seas, only a small percentage is located on the continents, but also ultimately comes from the ocean, which is expected to return from the rivers.
Solar radiation causes the water to evaporate into the air from rivers, lakes and oceans. This water vapor, rising, cools and condenses to form water droplets in clouds gathered.
When the droplets are large enough, they fall to earth as rain. Part of this water evaporates and returns to the air, some is used by plants, but how much more conspicuous seeps through the ground or into rivers eventually flow into the sea. The cycle then starts over again.
This continuous movement of water from the surface of the earth to the clouds and then back to earth as rain is called the water cycle (hydrologic cycle). The annual global water cycle is closely linked to large flows of energy in the atmosphere. The total volume of water in the atmosphere has been estimated at about 1.3 x 10 13 m 3 (13,000 km 3), largely in the vapor phase, in contrast oceans contain about 1.35 x 10 18 m 3 of water (1350 million km 3).
The ratio between the volumes of water in the oceans and the atmosphere is 1 / 100000, roughly the same as the ratio between the water contained in a thimble and one in a bathtub. Nevertheless, the water vapor in the atmosphere is one of the most important factors in determining the weather and climate, especially for the large amount of energy put into play when water changes its state of aggregation between the gas phase (steam), liquid and solid, and for his contribution as a greenhouse gas.
The differential heating of Earth's surface by the Sun creates the conditions that underlie transfers of large air masses between the equator and poles: while the equatorial regions receive more heat than they lose, the areas closest to the pin lose more heat than they receive.
Two basic convection currents at high altitude (symmetrical, from the equator to the poles) distributed in a more balanced heat. (The transfer of air pressure differences are determined by the winds).
An important role in this transport of heat and energy is related to water, which evaporates in the equatorial areas, is transported as a result of air masses to the poles in the form of vapor, condenses into clouds, falls as rain or snow that the report again on the earth's surface and then into the seas.
The concept of humidity controls the rate of evaporation, cloud formation, the time and place of precipitation. Humidity is the amount of water vapor in the atmosphere: the main contributions are evaporation from the surface of the earth and plant transpiration. Precipitation is the phenomenon that in turn decreases the presence of water in the atmosphere.
Meteorologists have defined several ways to indicate the humidity, which can be divided into two categories: those that express the actual amount or concentration of water vapor in the air and those that relate to the actual amount present with the potential quantity that the air could hold if saturated with water. The air becomes saturated when it says contains the maximum amount possible.