Everything about Troposphere totally explained
The
troposphere is the lowest portion of
Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its
water vapor and
aerosols.
The average depth of the troposphere is about 11 km (7 miles) in the middle latitudes. It is deeper in the tropical regions (up to 20 km (12 miles)) and shallower near the poles (about 7 km (4 miles) in summer, indistinct in winter). The lowest part of the troposphere, where
friction with the Earth's surface influences air flow, is the
planetary boundary layer. This layer is typically a few hundred meters to 2 km (1.2 miles) deep depending on the
landform and time of day. The border between the troposphere and stratosphere, called the
tropopause, is a
temperature inversion.
The word troposphere derives from the
Greek "tropos" for "turning" or "mixing," reflecting the fact that
turbulent mixing plays an important role in the troposphere's structure and behavior. Most of the phenomena we associate with day-to-day
weather occur in the troposphere.
»
If the air contains
water vapor, then cooling of the air can cause the water to condense, and the behavior is no longer that of an ideal gas. If the air is at the
saturated vapor pressure, then the rate at which temperature drops with height is called the
saturated adiabatic lapse rate. More generally, the actual rate at which the temperature drops with altitude is called the
environmental lapse rate.
In the troposphere, the average environmental lapse rate is a drop of about 6.5 °C for every 1 km (1000 meters) increase in height.
The environmental lapse rate (the actual rate at which temperature drops with height,
) isn't usually equal to the adiabatic lapse rate (or correspondingly,
). If the upper air is warmer than predicted by the adiabatic lapse rate (
), then when a parcel of air rises and expands, it'll arrive at the new height at a lower temperature than its surroundings. In this case, the air parcel is denser than its surroundings, so it sinks back to its original height, and the air is stable against being lifted. If, on the contrary, the upper air is cooler than predicted by the adiabatic lapse rate, then when the air parcel rises to its new height it'll have a higher temperature and a lower density than its surroundings, and will continue to accelerate upward.
Temperatures decrease at middle latitudes from an average of 15°C at sea level to about -55°C at the beginning of the
tropopause. At the
poles, the troposphere is thinner and the temperature only decreases to -45°C, while at the
equator the temperature at the top of the troposphere can reach -75°C.
Tropopause
The tropopause is the boundary region between the troposphere and the stratosphere.
Measuring the temperature change with height through the troposphere and the stratosphere identifies the location of the tropopause. In the troposphere, temperature decreases with altitude. In the stratosphere, however, the temperature remains constant for a while and then increases with altitude. The region of the atmosphere where the lapse rate changes from positive (in the troposphere) to negative (in the stratosphere), is defined as the tropopause.
Thus, the tropopause is an
inversion layer, and there's little mixing between the two layers of the atmosphere.
Further Information
Get more info on 'Troposphere'.
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