Boundary impulse response functions in a century-long eddying global ocean simulation

Results are presented from a century-long 1/10° global ocean simulation that included a suite of age-related passive tracers. In particular, an ensemble of five global Boundary Impulse Response functions (BIRs, which are statistically related to the more fundamental Transit Time Distributions, TTDs) was included to quantify the character of the TTD when mesoscale eddies are explicitly simulated rather than parameterized. We also seek to characterize the level of variability in water mass ventilation timescales arising from eddy motions. The statistics of the BIR timeseries are described, and it is shown that the greatest variability occurs at early times, followed by a remarkable conformity between ensemble members at longer timescales. The statistics of the first moment of the BIRs are presented, and the upper-ocean spatial distribution of the standard deviation of the first moment of the BIRs discussed. It is shown that variations in the BIR first moment with respect to the ensemble average are typically only a few percent, and that the variability slightly decreases with increasing ensemble size, implying that only a few ensemble members may be necessary for a reasonable estimate of the TTD. The completeness of the estimated TTD, i.e., the degree to which the century long BIRs capture the range of global ocean ventilation timescales is discussed, and the potential for extrapolation of the BIR to longer times is briefly explored. Several regional BIRs were also simulated in order to quantify the relative abundance of fluid parcels that originate in specific geographical locations.

[1]  Rainer Feistel,et al.  Accurate and Computationally Efficient Algorithms for Potential Temperature and Density of Seawater , 2003 .

[2]  T. Haine,et al.  On transit-time distributions in unsteady circulation models , 2008 .

[3]  François Primeau,et al.  Characterizing Transport between the Surface Mixed Layer and the Ocean Interior with a Forward and Adjoint Global Ocean Transport Model , 2005 .

[4]  M. Maltrud,et al.  Measures of the Fidelity of Eddying Ocean Models , 2006 .

[5]  W. Large,et al.  Sensible and Latent Heat Flux Measurements over the Ocean , 1982 .

[6]  Thomas W. N. Haine,et al.  Relationships among tracer ages , 2003 .

[7]  Samar Khatiwala,et al.  Age Tracers in an Ocean GCM , 2001 .

[8]  James J. Hack,et al.  A New Sea Surface Temperature and Sea Ice Boundary Dataset for the Community Atmosphere Model , 2008 .

[9]  Matthew H. England,et al.  The Age of Water and Ventilation Timescales in a Global Ocean Model , 1995 .

[10]  Timothy M. Hall,et al.  Transit-Time and Tracer-Age Distributions in Geophysical Flows , 2000 .

[11]  John M. Haynes,et al.  Ice cloud microphysics retrievals from millimeter radar and visible optical depth using an estimation theory approach , 2003 .

[12]  François Primeau,et al.  The diffusive ocean conveyor , 2006 .

[13]  M. Holzer,et al.  Title The path-density distribution of oceanic surface-to-surface transport Permalink , 2008 .

[14]  J. Dukowicz,et al.  Implicit free‐surface method for the Bryan‐Cox‐Semtner ocean model , 1994 .

[15]  Ross J. Murray,et al.  Explicit Generation of Orthogonal Grids for Ocean Models , 1996 .

[16]  K. Koltermann,et al.  WOCE Global Hydrographic Climatology , 2004 .

[17]  Thomas W. N. Haine,et al.  A Generalized Transport Theory: Water-Mass Composition and Age , 2002 .

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

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

[20]  Stephen G. Yeager,et al.  Diurnal to decadal global forcing for ocean and sea-ice models: The data sets and flux climatologies , 2004 .

[21]  R. C. Malone,et al.  Global eddy-resolving ocean simulations driven by 1985-1995 atmospheric winds , 1998 .

[22]  W. Large,et al.  Oceanic vertical mixing: a review and a model with a nonlocal boundary layer parameterization , 1994 .

[23]  M. Maltrud,et al.  Transit-Time Distributions in a Global Ocean Model , 2006 .

[24]  T. Haine,et al.  On Ocean Transport Diagnostics: The Idealized Age Tracer and the Age Spectrum , 2002 .