| 6-DOF | Six Degree Of Freedom | |
| AA | Academic Alliance | |
| AASE | Airborne Arctic Stratospheric Expedition | |
| AAWO | Association of American Weather Observers | |
| AAWS | Average Annual Wind Speed | |
| AB | Aurora Borealis | |
| ABL | Atmospheric Boundary Layer | |
| ABLE | Atmospheric Boundary Layer Experiment | |
| ACARS | ARINC Communication Addressing and Reporting System | |
| ACCA | Automatic Cloud Cover Assessment | |
| ACES | Altus Cumulus Electrification Study | |
| ACFP | Advanced Computer Flight Plan | |
| ACIA | Arctic Climate Impact Assessment | |
| ACMAD | African Centre of Meteorological Application for Development | |
| ACMAD | African Centre of Meteorological Applications for Development | |
| ACMAD | African Centre for Meteorological Applications for Development | |
| ACON | Atlantic Coast Observer Network | |
| ACP | Atmospheric Chemistry Program | |
| ACP | Aluminium Composite Panel | |
| ACRF | ARM Climate Research Facility | |
| ACRID | Advanced Climate Research Infrastructure for Data | |
| ACRIM | Active Cavity Radiometer Irradiance Monitor | |
| ACRP | Atmospheric Composition Research Program | |
| ACRS | Astrographic Catalog Reference Stars | |
| ACSG | Atmospheric Chemistry SubGroup | |
