| Abbreviation | Definition |
|---|---|
| AOML | Atlantic Oceanographic Meteorological Laboratory |
| AOPC | Atmospheric Observation Panel for Climate |
| APG | Atmospheric Pressure Glow |
| API | Air Pollution Index |
| API | Atmospheric Pressure Ionization |
| APIMS | Aerospace Physiology Information Management System |
| APO | Atmospheric Potential Oxygen |
| APPI | Atmospheric Pressure Photo-Ionization |
| APT | Automatic Picture Transmission |
| AQ | Air Quality |
| AQHI | Air Quality Health Index |
| AQI | Air Quality Index |
| AR | Acid Rain |
| AR | Active Rainfall |
| AR4 | Atmospheric River category 4. Lots of rain |
| ARAD | Atmospheric Research And Applications Division |
| ARAM | Aviation Range and Aerospace Meteorology |
| ARG | Alternate Reality Game |
| ARGOS | French Satellite Data Collection System |
| ARL | Army Research Laboratory |