On the parameterization of turbulent surface fluxes over heterogeneous sea ice surfaces

Turbulent surface fluxes of momentum and sensible and latent heat as well as surface temperature, air temperature, air humidity, and wind speed were measured by the German Falcon research aircraft over the marginal ice zone (MIZ) of the northern Baltic Sea and the Fram Strait. Applying the bulk formulas and the stability functions to the measurements, the roughness lengths for momentum z 0 , sensible heat z T , and latent heat z q were calculated. As mean values over a wide range of sea ice conditions, we obtain z 0 = 5 × 10 −4 m, z T = 1 × 10 −8 m, and z q = 1 × 10 −7 m. These correspond to the following mean values (± standard deviations) of neutral transfer coefficients reduced to 10 m height, C DN 10 = (1.9 ± 0.8) × 10 −3 , C HN 10 = (0.9 ± 0.3) × 10 −3 , and C EN 10 = (1.0 ± 0.2) × 10 −3 . An average ratio of z 0 / z T ≈ 10 4 was observed over the range of 10 −6 m < z 0 < 10 −2 m and differs from previously published results over compact sea ice (10 −1 < z 0 / z T < 10 3 ). Other observational results over heterogeneous sea ice do not exist. However, our z 0 / z T ratio approximately agrees with observations over heterogeneous land surfaces. Flux parameterizations based on commonly used roughness lengths ratios ( z 0 = z T = z q ) overestimate the surface heat fluxes compared to our measurements by more than 100%.