Scalar Budgets in the Convective Boundary Layer

Continuous flux divergence measurements from a very tall tower provide the basis for constructing a climatology of water vapor, virtual temperature and carbon dioxide budgets in the convective boundary layer. The study site is the WLEF tower in northern Wisconsin, site of the Chequamegon Ecosystem-Atmosphere Study (ChEAS, http://cheas.umn.edu). The synoptic and seasonal evolution of these scalar budgets is analyzed, especially that of carbon dioxide. The seasonal patterns of flux divergence, mixing ratio, and net ecosystem-atmosphere exchange of CO2 are compared. A one-month phase lag between the seasonal cycle of net ecosystem-atmosphere exchange and CO2 mixing ratio implies seasonal advection and provides a stong constraint to transport models. Colocation of the tall tower with radar profiling of boundary layer development provides long-term estimates of entrainment of water vapor, virtual temperature and CO2. The methodology for the long-term eddy covariance flux measurements that are the basis for these results is reviewed. Finally, laser ceilometer observations of the seasonal course of boundary layer cloud development are compared to boundary layer thermodynamic budgets.