In climate science, the term indicates a variable that a computer model predicts by integration of a physical equation, typically vorticity, divergence, temperature, surface pressure, and water vapour concentration in atmospheric models.
The term prognostic is given to some values or variables that are directly predicted by the model,1 such as temperature, water vapour, salinity, and depth in atmospheric or ocean models, i.e., variables that can be directly obtained as a model outcome. On the other hand, some other variables need to be calculated separately as derived variables, such as relative humidity, which may be a diagnostic variable obtained from the model's prognostic variables, temperature and water vapour.
Arcomano, Troy; Szunyogh, Istvan; Wikner, Alexander; Hunt, Brian R.; Ott, Edward (2023-04-28). "A Hybrid Atmospheric Model Incorporating Machine Learning Can Capture Dynamical Processes Not Captured by Its Physics‐Based Component". Geophysical Research Letters. 50 (8). doi:10.1029/2022GL102649. ISSN 0094-8276. https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL102649 ↩