The Earth's Atmosphere!


The thermosphere is the biggest of all the layers in the Earth's atmosphere.The International Space Station has a stable orbit within the middle of the thermosphere, between 320 and 380 kilometers. The highly diluted gas in this layer can reach 2,500 °C (4,530 °F) during the day.The dynamics of the lower thermosphere (below approximately 120 kilometers (75 mi)) are dominated by atmosperic tide which is driven, in part, by the very significant diurnal heating.

The exosphere is the outermost layer of the Earth’s atmosphere. It starts at an altitude of about 500 km and goes out to about 10,000 km. Within this region particles of atmosphere can travel for hundreds of kilometers in a ballistic trajectory before bumping into any other particles of the atmosphere. Particles escape out of the exosphere into deep space.It starts at an altitude of about 250-500 km, but its height depends on the amount of solar activity.

The mesosphere, which means middle sphere, is the third layer of Earth's atmosphere, between the stratosphere, and the thermosphere. It is located from about 55 kilometers (35 miles) to 85 kilometers (54 miles) above the surface of Earth. Temperature here decreases with height, so within the mesosphere it is warmest at its lowest level (−5°C, or 23°F), and becomes coldest at its highest level (−80°C, or −112°F). Depending on  the latitude and season, temperatures in the upper mesosphere can be as low as −140°C (−220°F). The temperature in the mesosphere is lower than the temperature of the troposphere or stratosphere, which makes the mesosphere the coldest among the atmospheric layers. It is colder then Antarctica's lowest recorded temperature, and it is cold enough to freeze  water vapor into ice clouds, which can be seen mostly after sunset.

The stratosphere is the second major atmospheric layer above the troposphere  extending in altitude from about 8 to 30 miles high. No weather occurs in the stratosphere. The stratosphere contains over 15% of the total mass of the atmosphere, and is where the ozone layer  is located.Air temperature slowly increases with height in the stratosphere, in contrast with the troposphere where the temperature rapidly decreases with height. This unusual temperature structure is caused by absorption of sunlight by ozone.All weather stops at the top of the troposphere (called the tropopause), and the stratosphere is essentially cloud-free. If you see a tall thunderstorm with an anvil cloud , it is likely that the anvil cloud has reached the bottom of the stratosphere. At that level, atmospheric  convection stops because rising cloudy air parcels are no longer warmer than their environment, since stratospheric air is relatively warm.

The troposphere is the lowest layer of Earth's atmosphere and site of all weather on Earth. The troposphere is bonded on the top by a layer of air called the tropopause, which separates the troposphere from the stratosphere, and on bottom by the surface of the Earth. The troposphere is wider at the equator (10mi) than at the poles (5mi).-The troposphere contains 75 percent of atmosphere's mass- on an average day the weight of the molecules in the air is14.7 lb..(sq. in.)- and most of the atmosphere's water vapor. Water vapor concentration varies from trace amounts in Polar Regions to nearly 4 percent in the tropics. Most prevalent gases are nitrogen (78 percent) and oxygen (21 percent), with the remaining 1- percent consisting of argon, (.9 percent) and traces of hydrogen ozone ( a form of oxygen), and other constituents. Temperature and water vapor content in the troposphere decrease rapidly with altitude. Water vapor plays a major role in regulating air temperature because it absorbs solar energy and thermal radiation from the planet's surface.The troposphere contains 99% of the water vapor in the atmosphere. Water vapor concentrations vary with latitudinal position(north to south).

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