Timing of the morning transition to the convective boundary layer

The morning transition between the stable nocturnal situation and the daytime convective boundary layer (CBL) is of interest both for basic understanding and for initializing prognostic models. While the morning growth phase of the CBL has been studied in detail, relatively little has been published on the transition itself. In this presentation, conventional observations of surface temperature, humidity, and fluxes are combined with measurements of the onset of convection from boundary layer wind profilers to explore the timing and behavior of the transition period. The transition is defined here as the period between sunrise and the time at which the depth of convection reaches about 200 m AGL.