Estimates of surface roughness length in heterogeneous under-ice boundary layers.

• Main Authors: W J Shaw, T P Stanton, M G Mcphee, T Kikuchi
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2008
• Subjects: Arctic; Arctic Ocean
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.1074.8461; http://mcpheeresearch.com/publications/Shaw_etal_JGR2008.pdf

[1] Measurements obtained in the under-ice ocean boundary layer by two autonomous buoys deployed in 2004 and 2005 are used to estimate the roughness length z 0 of the underside morphology of Arctic Ocean pack ice. Two techniques are used to estimate z 0 . The first uses an extension of the law of the wall and directly measured turbulent shear stress and velocity at a single point near the ice-ocean interface. The second uses a one-dimensional numerical boundary layer model that is matched to measured velocity profiles in the outer part of the boundary layer with z 0 as an adjustable parameter. The stress-based estimates are sensitive to local morphological features, and the effect of nearby ice ridge keels on the roughness estimates is evident. Averaged over flow direction there is a significant difference in floe roughness between the 2004 and 2005 deployments. Velocity-profile-based z 0 estimates are more uniform with direction than the stress-based estimates, and the average value of the profile-based estimates lies within the range of the stress-based estimates. Averaged over flow direction, both techniques yield z 0 estimates of about 100 mm for the 2005 data set. A central question is how to best estimate a z 0 that can be applied to an individual grid cell in large-scale numerical models. The profile-based estimates are promising in this regard because they are less affected by local morphology than stress-based measurements, which must be made fairly close to the interface in order to be interpretable using a framework based on the law of the wall.