Earth’s atmosphere is a system of distinct layers, each with unique characteristics that influence the planet’s environment. Among these layers, the mesosphere stands out as a fascinating region. This atmospheric layer plays a significant role in various natural phenomena, making it distinct from the layers above and below it.
Position and Temperature Extremes
The mesosphere is located above the stratosphere and below the thermosphere, extending from 50 to 85 kilometers (31 to 53 miles) above Earth’s surface. Its lower boundary is the stratopause, and its upper boundary is the mesopause. This layer is characterized by a sharp decrease in temperature with increasing altitude. The mesosphere is the coldest layer of Earth’s atmosphere, with temperatures at its top, the mesopause, reaching -90°C (-130°F).
This extreme cold is due to less solar radiation absorption. Air density in the mesosphere is significantly lower than in layers closer to Earth, meaning fewer gas molecules absorb solar energy. It also lacks significant heat sources. Heat from the stratosphere below is insufficient, and infrared radiation escapes to space due to low density.
The Meteor Incinerator
The mesosphere acts as Earth’s shield against extraterrestrial objects. Millions of meteors enter Earth’s atmosphere daily; most are sand-sized or smaller. As they plunge into the mesosphere, atmospheric friction heats them intensely. This friction causes them to glow brightly and often disintegrate, creating “shooting stars.”
Meteors become visible between 75 to 120 kilometers (47 to 75 miles) and disintegrate between 50 to 95 kilometers (31 to 59 miles). Though thin, the mesosphere’s air is dense enough to generate the necessary heat and friction. This process protects Earth’s surface, as most objects vaporize before reaching the ground.
Nature’s Highest Clouds
The mesosphere is home to a unique atmospheric phenomenon: noctilucent clouds (NLCs), also known as polar mesospheric clouds (PMCs). These are the highest clouds in Earth’s atmosphere, forming at extreme altitudes, typically between 76 to 85 kilometers (47 to 53 miles). Unlike most clouds that form in the lower atmosphere, NLCs are composed of tiny ice crystals that form on minute dust particles, possibly of cosmic origin from micrometeors.
Noctilucent clouds are observed during twilight in the summer months, especially in polar regions. This is because the mesosphere is coldest during summer at these latitudes, with temperatures dropping below -120°C (-184°F), which is necessary for the ice crystals to form. Their distinctive appearance is a glowing, electric-blue or silvery color against the dark twilight sky, as they are illuminated by the sun from below while the lower atmosphere is already in Earth’s shadow.