Turbulence structures over the marginal ice zone under flow parallel to the ice edge: Measurements and parameterizations

Three aircraft-based studies of boundary-layer fronts (BLFs) were carried o ut during the experiment KABEG in April 1997 near the sea-ice edge over the Davis Strait. The boundary-layer flow was parallel to the ice edge and hen ce two independent turbulent regimes could develop in an identical synoptic framework, separated by the frontal zone along the ice edge. The zone of s trongest crosswind horizontal gradients was typically 20 km wide, while the downstream scale of the BLF was observed to be several hundreds of kilomet res. For two of the three cases the investigation of turbulence structures was possible and the results are given herein. Horizontal and vertical prof iles of turbulent fluxes and other turbulent quantities are presented. A sp ectral analysis reveals the coexistence of small-scale turbulence with roll motions. These roll motions can be hidden or can be visible as cloud stree ts. The associated transport mechanisms are highly relevant for the choice of suitable averaging intervals for turbulent flux calculations and model v alidation. Parameterizations for the vertical velocity variance, countergra dient transport, sea surface roughness and eddy diffusivity are evaluated a nd compared for this baroclinic strong-wind convective boundary-layer envir onment. Analogously, drag coefficients and bulk transfer coefficients are d erived from measurements.