The case for quasi-steady models in describing the physics of dayside merging



The magnetosphere varies on all measured temporal and spatial scales. Because this variability is apparent in so many data sets, and because dynamical behavior is intrinsically exciting, a large majority of space physicists have always emphasized transients. We quite agree that merging transients exist, although we believe that they are directly driven by the variable input from the magnetosheath (we have proposed examples ourselves). In emphasizing “quasi-steady” in this discussion, we only mean that specifying the interplanetary magnetic field (IMF) and solar wind conditions (or more precisely, magnetosheath conditions) also pretty well specifies the state of the dayside magnetosphere.