| 4DDA | Four-Dimensional Data Assimilation | |
| A&P | Analysis and Prediction | |
| A/OGCM | Coupled Atmosphere/Ocean General Circulation Model | |
| AA | Assistant Administrator | |
| AAAG | Atlantic Arc Aquaculture Group | |
| AAAS | American Association for the Advancement of Science | |
| AABW | AntArctic Bottom Water | |
| AAIW | AntArctic Intermediate Water | |
| AAM | Atmospheric Angular Momentum | |
| AAOE | Airborne Antarctic Ozone Experiment | |
| AAOT | Acqua Alta Oceanographic Tower | |
| AAPB | Aerobic Anoxyenic Phototrophic Bacteria | |
| AARC | Arctic Antarctic Research Center | |
| AARI | Arctic and Antarctic Research Institute | |
| AARS | Automated Aircraft Reporting System | |
| AAS | American Astrophysical Society | |
| AAS | Advanced Automation System | |
| AASE | Airborne Arctic Stratospheric Expedition | |
| AASR | Annual Aquaculture Statistical Report | |
| AB | Asymmetric Balance | |
| ABISS | Automated Benthic Image Scaling System | |
| ABL | Atmospheric Boundary Layer | |
| ABLE | Atmospheric Boundary Layer Experiment | |
| ABLE | Arctic Boundary Layer Expedition | |
| ABMN | Aquatic Biodiversity Monitoring Network | |
