The layer of the Atmosphere between the Stratosphere and the Thermosphere occurring between approximately 50km and 90km above the surface.
The Mesosphere is characterised by falling temperature with height - temperatures fall to -100°C. Thin clouds comprised of ice crystals, Noctilucent Clouds, sometimes occur at higher latitudes in the higher part of the Mesosphere at approximately 80km in altitude.
The boundary between the Stratosphere and the Mesosphere is known as the Stratopause.
The boundary between the Mesosphere and the Thermosphere is known as the Mesopause