CLIMATES: Earth's atmosphere

 The atmosphere:

    Seen from space, the Earth is surrounded by a blue haze. It is the atmosphere : a gas blanket retained by gravity, which envelops our planet and makes life possible there.
The atmosphere is surprisingly thin. If you could drive it through it, it would only take you 10 minutes to cross the lower layer, the troposphere, home to meteorological phenomena, and approximately 3 hours to reach space. Due to gravity, the troposphere is the densest layer of the atmosphere ; it contains 80 % of the air and almost all of the moisture. The troposphere, which is warmed by the Sun and agitated by the Earth's rotation, is a swirling mass of clouds. The air becomes thinner as one rises in the atmosphere, and the atmosphere is gradually lost in the vacuum of space.

The layers of the atmosphere:

    The atmosphere is divided by scientists into different layers depending on their temperature. The latter decreases as one rises in the troposphere, but rises in the stratosphere. The boundary between these two layers is called the tropopause ; where the air is cold and dry : there is almost no humidity, and therefore a particularly calm weather.

Over the clouds !

    Clouds form in the troposphere. Only the largest storm clouds can pass into the stratosphere. Airplanes fly in the upper troposphere or in the lower stratosphere : they therefore sometimes cross thick cloud banks to reach their cruising altitude. So when they emerge in these layers of clouds, passengers can admire magnificent shows.

Winds of globe :

    Winds are generated by the heat of the Sun and the rotation of the Earth. Warmed by tropical sunlight, the air from the equator rises to the top of the troposphere then expands north and south, losing most of its moisture in tropical rains. To the north and to the south, the dry air flows, creating the conditions of the desert. Some of this air returns to the equator in trade winds, diverted westward by the rotation of the Earth. The rest move towards the poles, forming the sales of the west or westerlies and encounter cold polar air. When the two masses meet, the hottest air returns to the troposphere.

Crossing the Atlantic :

    The trade winds are so sure that explorers once used them to reach the Americas. The Genoese Christophe Colomb crossed the Atlantic for the first time in 1492, carried by the trade winds, and returned thanks to the westerlies (westerly wind).

Jet streams:

    During the Second World War, crews flying over the North Pacific found that they went faster when heading east than when heading west. Scientists found that strong winds developed at high altitudes due to large differences in temperature and pressure. These are the jet streams. There are two in the troposphere. So, airplane pilots borrow them in order to reduce flight time between the United States and Europe.