Aeronomie

Aeronomie is the branch of atmospheric science that studies the chemical composition and physical processes of the Earth's upper atmosphere, where solar radiation and energetic particles drive photochemical reactions and energy transfer. It focuses on the mesosphere, thermosphere, and ionosphere, regions where long mean free paths and low densities influence chemical pathways and the ionization state. The aim is to understand how composition changes in response to solar forcing, atmospheric dynamics, and particle precipitation, and how these changes affect radiation balance and communications systems.

In French and several other languages, the field is called aeronomie; in English, the term aeronomy is used. The word derives from Greek roots meaning laws of the air and the concept emerged in the mid-20th century to describe the upper-atmosphere science. Advances in spectroscopy, rockets, and satellites have made it a data-driven discipline that blends chemistry, physics, and space science.

Observations come from ground-based spectroscopy, occultation, lidar, radar, and in situ measurements on sounding rockets and orbital platforms. Models of photochemistry, transport, and energy deposition are used to interpret electron densities, ozone and HOxNOx cycles, and ion–neutral interactions. The field relies on long-term datasets to track seasonal, solar-cycle, and geomagnetic variations.

Key topics include ozone chemistry in the upper atmosphere, ionospheric composition, solar–terrestrial coupling, and the response of the upper atmosphere to climate change. Aeronomie informs space weather forecasting, radio communication and navigation reliability, satellite drag estimates, and ozone-layer assessments.