Convective heat transfer over wintertime leads and polynyas

Leads and polynyas are areas of open water or thin ice surrounded by thicker ice. In winter they are ideal natural laboratories for studying convective heat transfer from the ocean. First, the relevant length scales are much larger than those possible in the laboratory. Second, the large water-air temperature difference provides a wide range of unstably stratified conditions. Third, the surrounding sea ice is a very stable platform on which to place turbulence instruments. Here we analyze three data sets obtained over Arctic leads and polynyas in winter. First, we compute the bulk aerodynamic transfer coefficient for sensible heat at neutral stability appropriate at a reference height of 10 m, CHN10. For fetches over the warm lead or polynya larger than ∼100 m, CHN10 has the value typically reported over the open ocean at lower latitudes, 1.00 × 10−3. At fetches much 0.15. Because we have data over a wide enough stability range to evaluate how C* depends on δ/L, in effect, we develop a new algorithm for computing sensible and latent heat transfer in fetch-limited, convective conditions. This algorithm could be especially useful for sensing the turbulent heat fluxes over leads and polynyas remotely because it depends only weakly on surface level wind speed, which is difficult to determine remotely over an ice-covered ocean.