The diurnal cycle and the meridional extent of the tropics

Abstract An explanation is proposed for the meridional extent of the Hadley cells: that diurnal waves forced by solar heating are trapped between −30 and 30 degrees. These baroclinic waves give rise to the daily nature of tropical meteorology, and, we propose, ultimately to the intensified mixing and circulation associated with the Hadley cells and the shape of the tropopause. This conceptual explanation is validated with basic scaling arguments and with two diurnally forced one-layer models: one linear and the other nonlinear, the latter with a simple closure for mixing and entrainment by breaking waves