OBSERVATIONS OF FLUXES AND INLAND BREEZES OVER A HETEROGENEOUS SURFACE

Repeated aircraft runs at about 33 m over heterogeneous terrain are an alyzed to study the spatial variability of the mesoscale flow and turb ulent fluxes. An irrigated area, about 12 km across, generates a relat ively cool moist inland breeze. As this air flows out over the warmer, drier surrounding land surface, an internal boundary layer develops w ithin the inland breeze, which then terminates at a well-defined inlan d breeze front located about 1 1/2 km downstream from the change of su rface conditions. This front is defined by horizontal convergence, ris ing motion, and sharp spatial change of moisture, carbon dioxide, and ozone. Both a scale analysis and the observations suggest that the ove rall vertical motion associated with the inland breeze is weak. Howeve r, the observations indicate that this vertical motion and attendant v ertical transport are important in the immediate vicinity of the front , and the inland breeze does lead to significant modification of the t urbulent flux. In the inland breeze downstream from the surface wetnes s discontinuity, strong horizontal advection of moisture is associated with a rapid increase of the turbulent moisture flux with height. Thi s large moisture flux appears to be partly due to mixing between the t hin moist inland breeze and overlying drier air. As a consequence of t he strong vertical divergence of the flux in the transition regions, t he fluxes measured even as low as a few tens of meters are not represe ntative of the surface fluxes. The spatial variability of the fluxes i s also interpreted within the footprint format. Attempts are made to r econcile predictions by footprint and internal boundary-layer approach es.