at the mesopause, which is the coldest part of Earth's atmosphere, with temperatures below -143 C. 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 altitudes from 47 to 51 km above sea level, and the upper boundary (the mesopause) is usually from 85 to 100 km.

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