Tethered balloon measurements of Arctic boundary layer mean and turbulent structure during ASCOS

Numerical models do a poor job of representing boundary layer processes over Arctic sea ice. This results in part from a lack of in situ measurements upon which to base parameterizations tailored to the unique conditions that prevail in the Arctic. Measurements of turbulent exchange processes in the Arctic are very sparse, and almost entirely limited to the surface layer accessible from masts. During the ASCOS field campaign in August 2008, a tethered balloon was used to lift a turbulence sonde to make measurements throughout the boundary layer and within cloud. The turbulence sonde is a prototype system from Gill Instruments, incorporating a Windmaster sonic anemometer within an aerodynamic housing; we have added a motion sensing package consisting of 3-axis accelerometers and angular rate gyros, logged at 10Hz along with the sonic anemometer output; these allow the motion of the instrument package to be decoupled from the turbulent wind measurements. Mean temperature, relative humidity, and atmospheric pressure are logged at 1Hz. The tethersonde was operated in one of two modes: continuous profiling to provide detailed information on Arctic boundary layer vertical structure; and stepped profiles, with periods of 20-30 minutes at fixed levels to provide estimates of turbulent fluxes. Operated around the clock throughout the field campaign, the system provides a unique picture of Arctic boundary layer structure.