The spectral composition of fluxes and variances over land and sea

Aircraft are the primary platform for measuring turbulence fluxes and variances throughout the planetary boundary layer (PBL). Their mobility and maneuverability serve them well for this role, but also present the problem that both the rotational and translational motions of the aircraft need to be measured in order to obtain air motion measurements in an earth-based coordinate system. This is especially important for mesoscale turbulence where the signal levels for vertical air velocity and accuracy requirements for airplane velocity and attitude angles are more stringent. Here we discuss the measurement accuracy and limitations of current systems. We then present airborne observations from two field programs: the Boreal Ecosystem-Atmosphere Study (BOREAS) and the Tropical Ocean Global Atmospheres/Coupled Ocean Atmospohere Response Experiment (TOGA/COARE). BOREAS flights were conducted in the summertime convective PBL over the boreal forest of Canada and TOGA/COARE in the slightly convective PBL over the tropical western Pacific Ocean. The spectrally-resolved comparisons extend out to the mesoscales. This provides an interesting contrast between turbulence statistics over an extended quasi-uniform land surface and over an ocean surface.