On development of convective boundary layer

The time series of the mixed layer depth, Z_i, and stable layer height from March through October of 1998 are derived from a 915 MHz boundary-layer profiling radar and the CO₂ mixing ratio measured from a very tall tower in northern Wisconsin. The mixed layer depths from the profiler are in good agreement with the radiosonde measurements. Maximum Z_i occurs in May, coincident with the maximum daytime surface sensible heat flux. Incoming radiation is higher in June and July, but a greater proportion is converted to latent heat by the photosynthesizing vegetation. An empirical relationship between Z_i and the square root of the cumulative surface sensible heat flux is obtained allowing estimates of Z_i from measurements of heat flux under certain conditions. In fair weather conditions the residual layer was observed by the profiler on several nights in each month. The synoptic mean vertical velocity (subsidence rate) is estimated from the temporal development of the residual mixed layer height during the night. The influence of subsidence on the development of the mixed, stable, and residual layers is discussed. The CO₂ jump across the inversion at night is also estimated from the tower measurements.