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The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75 percent of the atmosphere's mass and 99 percent of its water vapor
The temperature of the troposphere generally decreases as altitude increases. The rate at which the temperature decreases, − dT / dz, is called the lapse rate.
The reason for this decrease is as follows. When a parcel of air rises, it expands, because the pressure is lower at higher altitudes. As the air parcel expands,
it pushes on the air around it, doing work; but generally it does not gain heat in exchange from its environment, because its thermal conductivity is low
(such a process is called adiabatic). Since the parcel does work and gains no heat,
it loses energy, and so its temperature decreases. (The reverse, of course, will be true for a sinking parcel of air.
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, dT / dz) is not usually equal to the adiabatic lapse rate
(or correspondingly, dS/dz \ne 0). If the upper air is warmer than predicted by the adiabatic
lapse rate (dS / dz > 0), then when a parcel of air rises and expands, it will 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 will
have a higher temperature and a lower density than its surroundings, and will continue to accelerate upward.
Maximum commercial airline information:
temperature: 32° to 95° F (0° to 35° C)
Maximum operating altitude: 10,000 feet (3000 m)
A typical commercial jet (most standard flights) cruises at around
28-35,000ft (up to 6.6 miles of altitude). The main exception is Concorde which was designed to fly at a higher altitude (and hence lower wind resistance) at around 45,000ft. Although many jets could fly at higher altitudes, they are usually certified to an altitude giving a wide safety margin. For example the new generation Boeing 737 is certified to 41,000ft (7.8 miles).
The specific fuel consumption of jet engines decreases as the outside air temperature decreases for constant engine r.p.m. and true airspeed (TAS). Thus, by flying at a high altitude, the pilot is able to operate at flight levels where fuel economy is best and with the most advantageous cruise speed.
The average depth of the troposphere is approximately 17 km (11 mi) in the middle latitudes. It is deeper in the tropical regions, up to 20 km (12 mi), and shallower near the poles, at 7 km (4.3 mi) in summer, and indistinct in winter
Jet streams, or just jets in context, are fast flowing, narrow air currents found in the atmosphere of planets at the tropopause
On Earth, the strongest jet streams are the polar jets (7-12 km or 23,000-39,000 ft above sea level) and the higher and somewhat weaker subtropical jets (10-16 km or 33,000-52,000 ft).
The wind speeds vary according to the temperature gradient, exceeding 92 kilometres per hour (50 kn), although speeds of over 398 kilometres per hour (215 kn) have been measured.