The average or mean value, computed from observations at various locations on a horizontal plane, an isobaric surface, or the earth's surface; sometimes used in the study of atmospheric turbulence as a surrogate for the ensemble average. In the real atmosphere, area averages can be acquired using remote sensors such as radar, sodar, and lidar, or they can be approximated using an appropriate flight track of a research aircraft. In numerical models, area averages can be computed using data from grid points at a constant model level. See ergodic condition.