On the use of current meter data to assess the realism of ocean model simulations

The evaluation of ocean simulations against observed datasets is essential to assess their realism and to guide model development, but often remains qualitative, and ignores certain datasets. This paper presents a three-dimensional, quantitative comparison of a 1/6° Atlantic numerical simulation (CLIPPER) with the WOCE current meter dataset in terms of mean velocity and eddy kinetic energy. Our metrics reveal the good behaviour of CLIPPER open boundary conditions and forcing with respect to full-depth current records. Due to its still moderate resolution, however, the model globally underestimates the observed mean speeds and eddy activity. This discrepancy is barely noticeable at low latitudes but increases toward the poles, probably since the poleward decrease of the Rossby radius exceeds that of the horizontal grid step. At least in this eddy-admitting regime, it is suggested that the numerics of geopotential-coordinate models like ours dissipate mean and eddy momentum at depth and adversely affect current–topography interactions.

[1]  Mathew E. Maltrud,et al.  Eulerian and Lagrangian Statistics from Surface Drifters and a High-Resolution POP Simulation in the North Atlantic , 2002 .

[2]  Bernard Barnier,et al.  Variability of the meridional overturning circulation of the North Atlantic: sensitivity to overflows of dense water masses , 2003 .

[3]  M. Maltrud,et al.  An eddy resolving global 1/10° ocean simulation , 2005 .

[4]  J. Verron,et al.  Comparison of near‐surface mean and eddy flows from two numerical models of the South Atlantic Ocean , 2001 .

[5]  B. Barnier,et al.  A new analysis of hydrographic data in the Atlantic and its application to an inverse modeling study , 1998 .

[6]  A. Adcroft,et al.  Representation of Topography by Shaved Cells in a Height Coordinate Ocean Model , 1997 .

[7]  Jean-Marc Molines,et al.  Circulation characteristics in three eddy-permitting models of the North Atlantic , 2001 .

[8]  C. Wunsch,et al.  How well does a 1/4° global circulation model simulate large-scale oceanic observations? , 1996 .

[9]  D. Sandwell,et al.  Global seafloor topography from dense satellite altimetry and sparse ship soundings , 1997 .

[10]  J. O'Brien,et al.  Dynamical Response of the Oceanic Eddy Field to the North Atlantic Oscillation: A Model-Data Comparison , 2004 .

[11]  P. Delecluse,et al.  OPA 8.1 Ocean General Circulation Model reference manual , 1998 .

[12]  M. Arhan,et al.  Direct Observations of the Mean Circulation at 48°N in the Atlantic Ocean , 1989 .

[13]  Michael Ghil,et al.  DAMÉE-NAB: the base experiments , 2000 .

[14]  Gurvan Madec,et al.  Agulhas eddy fluxes in a 1/6° Atlantic model , 2002 .

[15]  S. G. L. Smith,et al.  Velocity Probability Density Functions from Altimetry , 2000 .

[16]  Walter H. F. Smith,et al.  Global Sea Floor Topography from Satellite Altimetry and Ship Depth Soundings , 1997 .

[17]  How realistic is the high frequency signal of a 0.1 resolution ocean model , 2003 .

[18]  J. McClean,et al.  Comparisons of mesoscale variability in the Semtner‐Chervin 1/4° model, the Los Alamos Parallel Ocean Program 1/6° model, and TOPEX/POSEIDON data , 1997 .

[19]  Bruno Blanke,et al.  Variability of the Tropical Atlantic Ocean Simulated by a General Circulation Model with Two Different Mixed-Layer Physics , 1993 .

[20]  E. Fahrbach,et al.  Structure and transports of the East Greenland Current at 75°N from moored current meters , 1999 .

[21]  J. Verron,et al.  How Topographic Smoothing Contributes to Differences between the Eddy Flows Simulated by Sigma- and Geopotential-Coordinate Models , 2002 .

[22]  Aliasing inertial oscillations in a 1/6° Atlantic circulation model: impact on the mean meridional heat transport , 2001 .

[23]  M. Arhan,et al.  Mesoscale Variability Transition from the Western to the Eastern Atlantic along 48°N , 1989 .

[24]  W. Merryfield,et al.  Eddy fluxes and topography in stratified quasi-geostrophic models , 1999, Journal of Fluid Mechanics.

[25]  Anand Gnanadesikan,et al.  Transient Response in a Z-Level Ocean Model That Resolves Topography with Partial Cells , 1998 .

[26]  Thierry Penduff,et al.  The North Atlantic Subpolar Gyre in Four High-Resolution Models , 2005 .

[27]  M. Crépon,et al.  Yucatan Channel flow: Observations versus CLIPPER ATL6 and MERCATOR PAM models , 2003 .

[28]  Interannual variation of Gulf Stream heat transport in a high-resolution model forced by reanalysis data , 2004 .

[29]  G. Madec,et al.  An eddy-permitting model of the Atlantic circulation: evaluating open boundary conditions , 2001 .

[30]  J. Molines,et al.  On the seasonal variability and eddies in the North Brazil Current: insights from model intercomparison experiments , 2001 .

[31]  W. Dewar,et al.  On the dynamics of the Zapiola Anticyclone , 1999 .

[32]  N. Fisher,et al.  A correlation coefficient for circular data , 1983 .