Heat and momentum transfer between the upper ocean and drifting sea ice are fundamental to understanding the energy balance at the surface of an ice covered ocean. One facet of the multi-disciplinary approach for the SHEBA (Surface Heat Budget of the Arctic) experiment is measuring turbulent stress and sensible heat flux in the oceanic boundary layer, then parameterizing the turbulent transfer processes in terms of more easily measured variables, such as ice drift speed and deviation of mixed layer temperature from freezing. To this end, instrument clusters capable of measuring inertial-subrange fluctuations in three components of velocity, temperature, and salinity were deployed at multiple levels on a rigid mast suspended beneath 2-m thick ice at the main SHEBA drift station. As of late Jun, 1998, the mast has been operating more or less continuously since Oct 8, 1997. Data processing starts by screening to ensure that all three current-meter rotors are turning (this typically requires a mean current of 6-7 cm/s at the instrument level, relative to the drifting ice); then dividing the time series into 15-m "flow realizations." Ensemble Reynolds stress and heat flux are estimated from zero-lag covariances of vertical velocity with horizontal velocity and temperature respectively. A local turbulence closure model is used to extrapolate measured fluxes to surface (interface) values.
Based on previous experience, candidate bulk models include a Rossby similarity expression relating interface stress to ice velocity relative to undisturbed geostrophic oceanic current, and a heat exchange equation wherein heat flux is proportional to the product of interface friction velocity and elevation of mixed layer temperture above freezing. Bulk exchange coefficients will be derived by regression. A wide range of conditions have been encountered already at SHEBA, ranging from very small vertical heat flux during severe storms in November and December, to values in excess of 100 W m-2 in the "lee" of a newly formed pressure ridge during March. Preliminary estimates of the exchange coefficients are reasonably consistent with results from earlier Arctic and Antarctic projects