The upper boundary of the stratosphere is called stratosphere.
Temperature is lowest at the top of the mesosphere,which is also called the mesosphere.
The mesosphere (/ˈmɛsoʊsfɪər/; from Greek mesos "middle" ) is the layer of the Earth's atmosphere that is directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as the altitude increases. This characteristic is used to define its limits: it begins at the top of the stratosphere (sometimes called the stratopause), and ends at the mesopause, which is the coldest part of Earth's atmosphere with temperatures below −143 °C (−225 °F; 130 K). The exact upper and lower boundaries of the mesosphere vary with latitude and with season (higher in winter and at the tropics, lower in summer and at the poles), but the lower boundary is usually located at heights from 50 to 65 kilometres (164,000 to 213,000 ft; 31 to 40 mi) above the Earth's surface and the upper boundary (mesopause) is usually around 85 to 100 kilometres (53 to 62 mi).[2][3][4][5]
The stratosphere and the mesosphere are collectively referred to as the "middle atmosphere",[6] which spans heights from approximately 10 kilometres (33,000 ft; 6.2 mi) to 100 kilometres (62 mi; 330,000 ft). The mesopause, at an altitude of 80–90 km (50–56 mi),[citation needed] separates the mesosphere from the thermosphere—the second-outermost layer of the Earth's atmosphere. This is also around the same altitude as the turbopause, below which different chemical species are well mixed due to turbulent eddies. Above this level the atmosphere becomes non-uniform; the scale heights of different chemical species differ by their molecular masses.
The term near space is also sometimes used. This term does not have a technical definition, but typically refers the region of the atmosphere up to 100 km (65,000 and 328,000 feet), roughly between the Armstrong limit (above which humans need a pressure suit to survive) up to the Kármán line where astrodynamics must take over from aerodynamics in order to achieve flight. The definition of near space can vary depending on the source, but in general near space comprises the altitudes above where commercial airliners fly but below orbiting satellites. Some sources distinguish between the terms "near space" and "upper atmosphere," so that only the layers closest to the Karman line are called near space.