The interaction of broad oceanic flows with irregular small-scale topography

Abstract: In most parts of the ocean, the seafloor relief contains irregular topographic features with lateral scales of several kilometers, commonly referred to as bottom roughness.  A persistent stream of evidence reported in the last few years revealed the dramatic impact of roughness on the dynamics and stability of broad oceanic flows.  Surprisingly, these fine topographic features—extending vertically over just a small fraction of the ocean depth—can affect large-scale flows throughout the entire water column.  This sensitivity poses a major challenge for understanding and forecasting ocean circulation.  The difficulty is compounded by (i) the ubiquity of roughness, (ii) the lack of high-resolution bathymetric data across vast regions of the seafloor, and (iii) the prohibitive computational cost of roughness-resolving simulations.  To address this challenge, we develop the analytical “sandpaper theory” of flow-topography interaction, which evaluates the roughness-induced drag from the canonical spectrum of seafloor depth.  The sandpaper theory is formulated using the multiple-scale asymptotic method and validated by roughness-resolving simulations.  The theory-based parameterization of roughness is implemented in HYCOM (HYbrid Coordinate Ocean Model), a comprehensive general circulation model widely used for climate prediction, operational forecasting, and process-oriented studies.

Bio:  Dr. Timour Radko is a Professor of Oceanography at the Naval Postgraduate School (NPS), where he has been a faculty member since 2004.  He earned his Ph.D. in Physical Oceanography from Florida State University and worked as a Research Scientist at the Massachusetts Institute of Technology from 2000 to 2004.  Dr. Radko's research focuses on Geophysical Fluid Dynamics, with particular emphasis on the dynamics of jets and vortices, ocean turbulence and mixing, large-scale ocean circulation, double-diffusive convection, wave motion, flow-topography interactions, hydrodynamic stability, and turbulent wakes.  Timour Radko is the author of the critically acclaimed book Double-Diffusive Convection.   His research activities have been supported by numerous grants from the National Science Foundation and the Office of Naval Research.