| Term: | Mean annual ground-surface temperature (MAGST) |
| Definition: | Mean annual temperature of the surface of the ground. Permafrost exists if the Mean Annual Ground-Surface Temperature is perennially below 0C. Although the mean annual surface temperature may be below 0C, the surface temperature will fluctuate during the year, causing a layer of ground immediately beneath the surface to thaw in the summer and freeze in the winter (the Active Layer). |