A layer within the Earth's atmosphere that extends from about 50 to 85 km (31 to 53 mi) above the surface. The mesosphere is predominantly characterized by its thermal structure. On average, mesospheric temperature decreases with increasing height.

Temperatures range from as high as 12°C (53°F) at the bottom of the mesosphere to as low as −133°C (−208°F) at its top. The top of the mesosphere, called the mesopause, is the coldest area of the Earth's atmosphere. Temperature increases with increasing altitude above the mesopause in the layer known as the thermosphere, which absorbs the Sun's extreme ultraviolet radiation. In the stratosphere, the atmospheric layer immediately below the mesosphere, the temperature also increases with height. The stratosphere is where ozone, which also absorbs ultraviolet radiation from the Sun, is most abundant. The transition zone between the mesosphere and the stratosphere is called the stratopause. Mesospheric temperatures are comparatively cold because very little solar radiation is absorbed in this layer. Meteorologists who predict weather conditions or study the lowest level of the Earth's atmosphere, the troposphere, often refer to the stratosphere, mesosphere, and thermosphere collectively as the upper atmosphere. However, scientists who study these layers distinguish between them; they also refer to the stratosphere and mesosphere as the middle atmosphere. Atmosphere Meteorology Stratosphere Thermosphere Troposphere

In the lower part of the mesosphere, the difference between the temperature at the summer and winter poles is of order 35°C (63°F). This large temperature gradient produces the north-south or meridional winds that blow from summer to winter. Temperatures in the upper mesosphere are colder in summer and warmer in winter, resulting in return meridional flow from the summer to the winter hemisphere. Although the temperature gradient in the upper part of the mesosphere remains large, additional complications result in wind speeds that are much slower than they are in the lower part of the mesosphere. Winds in the east-west or zonal direction are greatest at mesospheric middle latitudes. Zonal winds blow toward the west in summer and toward the east in winter. Like their meridional counterparts, zonal winds are comparatively strong near the bottom of the mesosphere and comparatively weak near the top. Thus, on average both temperature and wind speed decrease with increasing height in the mesosphere. Atmospheric general circulation

Meteors which enter the Earth's atmosphere vaporize in the upper mesosphere. These meteors contain significant amounts of metallic atoms and molecules which may ionize. Metallic ions combined with ionized water clusters make up a large part of the D-region ionosphere that is embedded in the upper mesosphere.

The upper mesosphere is also where iridescent blue clouds can be seen with the naked eye and photographed in twilight at high summer latitudes when the Sun lights them up in the otherwise darkening sky. These clouds are called noctilucent clouds (NLC). Noctilucent clouds are believed to be tiny ice crystals that grow on bits of meteoric dust.

Large-scale atmospheric circulation patterns transport tropospheric air containing methane and carbon dioxide from the lower atmosphere into the middle atmosphere. While carbon dioxide warms the lower atmosphere, it cools the middle and upper atmosphere by releasing heat to space. Methane breaks down and contributes to water formation when it reaches the middle atmosphere. If the air is sufficiently cold, the water can freeze and form noctilucent clouds. Temperatures must be below −129°C (−200°F) for noctilucent clouds to form. These conditions are common in the cold summer mesopause region at high latitudes.