MesosphereEdit
The mesosphere is the middle layer of Earth's atmosphere, lying above the stratosphere and below the thermosphere. It stretches from roughly 50 kilometers up to about 85–90 kilometers above the planet’s surface, with the upper boundary known as the mesopause. In this region the air is extremely thin and the temperature generally falls with increasing altitude, making the mesosphere colder than the layers below and above it.
Because of its altitude and thin air, the mesosphere is a natural frontier for atmospheric science. It is the stage where most meteors burn up as they plunge through the atmosphere, creating streaks of light that have fascinated observers for centuries. It is also where some of the faint ice clouds known as noctilucent clouds form during the polar summer, offering a visible clue about the dynamics of the upper atmosphere. The mesosphere hosts a complex set of waves, tides, and chemical processes that connect the surface weather we experience with the space environment that surrounds Earth.
Structure and dynamics
The mesosphere sits between the stratosphere below and the thermosphere above. The boundary with the stratosphere is the stratopause, while the boundary with the thermosphere is the mesopause. The temperature profile in the mesosphere is the opposite of what you find in the deeper layers: it cools with height, reaching its coldest values near the mesopause, typically around minus 90 degrees Celsius. The low density of air in this region makes heat transfer inefficient, so radiative and chemical processes dominate the energy balance.
The chemical composition of the mesosphere is similar to the lower atmosphere in its major constituents—nitrogen, oxygen, and argon—but at vastly lower pressures. Ozone and other trace gases are present in far smaller amounts than in the stratosphere, yet the mesosphere hosts important photochemical cycles driven by ultraviolet radiation from the Sun. Wind and temperature in the mesosphere are modulated by gravity waves and atmospheric tides that originate in the troposphere and stratosphere, propagating upward and shaping mesoscale structures. These waves and flows can produce rapid and localized variations in temperature and wind, and they play a key role in the global circulation of the upper atmosphere.
Meteoric ablation is a defining process of the mesosphere. As meteoroids enter the atmosphere, their surfaces heat up and vaporize in this region, creating bright trails and depositing energy and material into the surrounding air. This ablation partly seeds the upper-atmosphere chemistry and helps explain some of the spectral emissions observed during meteor showers. The same region is also the cradle of noctilucent clouds in polar regions, high-altitude ice clouds that form near the mesopause under very cold conditions and are visible after sunset or before dawn in summer.
Observations, instruments, and missions
Studying the mesosphere requires a mix of direct and remote sensing approaches because the region is too high for most aircraft and too low for routine orbital measurements to fully sample continuously. Key methods include:
- Sounding rockets that briefly reach mesospheric altitudes to carry sensors and acquire in situ measurements of temperature, wind, and composition.
- Ground-based radars and lidars that infer winds, temperatures, and density profiles by analyzing reflected signals and laser backscatter.
- Satellites in higher orbits equipped with instruments to infer mesospheric properties, often by observing emissions or by combining measurements from multiple altitude layers. Notable missions and instruments include those associated with the TIMED program, which focuses on the thermosphere, ionosphere, and mesosphere, and the SABER instrument that retrieves temperatures and related parameters from infrared observations. TIMED SABER
- Optical observations of noctilucent clouds and nightglow, which provide clues about upper-atmosphere dynamics and humidity at extreme altitudes. Noctilucent clouds
- Ground-based observations of meteoric phenomena and spatiotemporal patterns of atmospheric waves, which help constrain models of energy transport in the upper atmosphere. Meteors Gravity waves
The mesosphere is studied as part of broader efforts to understand space weather and the Earth’s climate system. Changes in the upper atmosphere can influence satellite orbits, radio communications, and the behavior of charged particles near Earth, making mesospheric research relevant to both science and national technology interests. Research in this domain also informs discussions about how the atmosphere responds to natural variability and human-induced changes in the climate system, including the role of CO2-induced cooling in the upper atmosphere and its potential effects on mesospheric dynamics and cloud formation. Ozone Atmosphere
Relevance to science and risks
The mesosphere sits at an important intersection of atmospheric chemistry, dynamics, and space physics. Its processes influence the chemical makeup of the upper atmosphere, the propagation of waves from lower layers, and the interaction between solar radiation and Earth’s atmosphere. By studying the mesosphere, scientists gain insight into:
- How energy is transported through the atmospheric column and how this affects global circulation. Gravity waves
- The formation and evolution of noctilucent clouds and what they reveal about upper-atmosphere humidity and temperature. Noctilucent clouds
- The ablation of meteoroids and the delivery of material and energy that moderate upper-atmosphere chemistry. Meteors
- The connections between the mesosphere and space weather, including how charged particles interact with the upper atmosphere and impact satellite systems. Space weather
Linking mesospheric science to practical concerns—such as satellite operations, radio communication, and navigation systems—helps explain why observers and policymakers alike track upper-atmosphere conditions, even as the region remains largely inaccessible to routine direct observation. The study of the mesosphere thus serves a dual purpose: advancing fundamental understanding of atmospheric physics and supporting the reliable functioning of technologies that depend on the near-Earth space environment. SABER TIMED