Transition Periods in the Diurnally-Varying Atmospheric Boundary Layer Over Land

The atmospheric boundary layer undergoes transitions between stable and convective states. Over land, in undisturbed conditions, these transitions occur daily in the morning and late afternoon or early evening. Though less well studied and presenting more challenges than the fully stable and fully convective states, such transitions have been the subject of growing interest over the last few decades. During transitions, all forcings are weak, and few simplifications are possible. Factors such as terrain, radiation, advection, and subsidence can seldom be safely neglected. Here, we review research on transitions over recent decades, with an emphasis on work published in Boundary-Layer Meteorology. The review is brief and inevitably reflects the interests and views of the authors.