Answer: stratosphere

AnswerCrossword Clue
STRATOSPHEREUpper reaches
stratosphereThe very highest levels of a profession or other sphere, or of prices or other quantities
stratosphereThe layer of the earth's atmosphere above the troposphere, extending to about 50 km above the earth's surface (the lower boundary of the mesosphere)
stratospherea region of the atmosphere beginning about 41/2 to 10 miles up, in which temperature does not fall as altitude increases