#atmospheric physics

• Air ionization — A natural or artificial process through which gas molecules within the air composition are transformed into air ions (electrically charged); in medicine and balneology, it represents the therapeutic use of air controlledly enriched with ions (especially negative ones) to relieve respiratory, cardiovascular, or stress conditions.
• Aerological — Relating to aerology, concerning aerology; referring to the physical, dynamic, and thermodynamic study of the free atmosphere, especially the upper layers (upper troposphere, stratosphere). It applies to charts, data, or sounding stations.
• Aeropause — A transition zone or upper region of Earth's atmosphere, located beyond the dense layers, where the air density becomes so low that it can no longer provide lift for conventional aircraft or support sound wave propagation. This structural threshold marks the functional limit of classical aviation and the beginning of upper aerospace, where flight is governed exclusively by orbital mechanics.
• Anabatic — Moving upward; describes a warm, ascending air current that rises along the slope of a mountain or hill, as a result of intense ground heating under the direct action of solar radiation. This structural atmospheric phenomenon is essential in mountain meteorology, causing the formation of cumuliform clouds over ridges during midday.
• Anemoscope — A meteorological instrument or device used to indicate the direction from which the wind is blowing, without measuring its speed. Structurally, it often consists of a mobile weather vane mounted on a vertical axis that aligns aerodynamically with the air current, providing an immediate visual representation of local atmospheric circulation.
• Anticyclone — A large-scale atmospheric formation characterized by an area of high barometric pressure (barometric maximum), where values decrease from the center toward the periphery. This structural phenomenon induces a divergent movement of air masses, which circulate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere, typically being associated with stable, clear weather, devoid of precipitation, or with the formation of thermal inversions during winter.
• Anticyclonic — Pertaining to an anticyclone, specific or characteristic of high atmospheric pressure systems; rotating clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere. In synoptic meteorology, the term describes stable weather regimes, descending air movements (subsidence), and wind mass circulation around a barometric maximum.