Numerical simulations as process studies of ocean turbulence: two case studies

Sutanu Sarkar, Ph.D.
Chair and Professor, Mechanical and Aerospace Engineering Department
University of California, San Diego

Vertical  mixing,  essential  to  maintain  the  fluxes  of  nutrients  and  the  temperature/salinity structure of the ocean, is thought to originate at boundaries.  With the advent of increasingly powerful computational resources, the scope and accuracy of turbulence resolving simulations as environmental process studies has seen rapid progress.  We will discuss two case studies. The first is an upper ocean problem that concerns the vertical structure of the Equatorial Under Current (EUC) system, an important oceanic component of the El Nino/ La Nina oscillation. Ocean  observations  show  intermittent  and  vertically  coherent  patches  of  turbulence  in  the undercurrent, despite the stability of the local background, along with internal wave signals. Our simulations show similar coherent patches of turbulence and help explain their origin. The second  case  study  involves  the  conversion  of  barotropic  surface  tides  to  larger  amplitude internal waves (the so-called internal tides) at rough, bottom topography. Observations suggest hot  spots  of  mixing  where  the  slope  angle  is  critical,  that  is  equal  to  the  internal  wave propagation  angle. Through  simulations,  we  examine  the  critical  slope  case  and  show  the existence of thick regions of stratified turbulence at sloping topography that are qualitatively different from thin turbulent boundary layers on a non-sloping bottom.

Sutanu Sarkar received his B. Tech from IIT Bombay, M. S. from Ohio State University and Ph. D. from Cornell University. After a position at ICASE, NASA Langley Research Center, he joined UCSD where he is the Blasker  Professor  of  Engineering  and  the  Chair  of  the  department  of Mechanical and Aerospace Engineering. His primary research interests are in the areas of simulation and modeling of turbulent flows, transport and mixing in the environment, and energy. He has received a NASA group achievement  award  (1994),  the  Bessel  Award  from  the  Humboldt Foundation (2001), and was elected Fellow, American Physical Society (2006), Associate Fellow, AIAA (2009) and Fellow, ASME (2010).