Search Results
pairs in each bin for the shallow and deep set are shown in Fig. 1f . The number of pairs increases from less than 100 at the smallest separation to close to 10 000 at separations of 300 km, with the deeper set having more pairs. For the particles more than 1000 pairs were available for each separation bin (not shown). All error bars in this study are derived using the bootstrapping algorithm. We estimate the metric 1000 times, performing random draws with repetition, and use the 5th and 95th
pairs in each bin for the shallow and deep set are shown in Fig. 1f . The number of pairs increases from less than 100 at the smallest separation to close to 10 000 at separations of 300 km, with the deeper set having more pairs. For the particles more than 1000 pairs were available for each separation bin (not shown). All error bars in this study are derived using the bootstrapping algorithm. We estimate the metric 1000 times, performing random draws with repetition, and use the 5th and 95th
.1 . Adcroft , A. , 1995 : Numerical algorithms for use in a dynamical model of the ocean. Ph.D. thesis, Imperial College London, 116 pp . Balluch , M. , and P. Haynes , 1997 : Quantification of lower stratospheric mixing processes using aircraft data . J. Geophys. Res. , 102 , 23 487 – 23 504 , doi: 10.1029/97JD00607 . Ferrari , R. , and K. L. Polzin , 2005 : Finescale structure of the T – S relation in the eastern North Atlantic . J. Phys. Oceanogr. , 35 , 1437 – 1454 , doi: 10
.1 . Adcroft , A. , 1995 : Numerical algorithms for use in a dynamical model of the ocean. Ph.D. thesis, Imperial College London, 116 pp . Balluch , M. , and P. Haynes , 1997 : Quantification of lower stratospheric mixing processes using aircraft data . J. Geophys. Res. , 102 , 23 487 – 23 504 , doi: 10.1029/97JD00607 . Ferrari , R. , and K. L. Polzin , 2005 : Finescale structure of the T – S relation in the eastern North Atlantic . J. Phys. Oceanogr. , 35 , 1437 – 1454 , doi: 10
Abstract
This study demonstrates that oceanic vertical velocities can be estimated from individual mooring measurements, even for nonstationary flow. This result is obtained under three assumptions: (i) weak diffusion (Péclet number ≫ 1), (ii) weak friction (Reynolds number ≫ 1), and (iii) small inertial terms (Rossby number ≪ 1). The theoretical framework is applied to a set of four moorings located in the Southern Ocean. For this site, the diagnosed vertical velocities are highly variable in time, their standard deviation being one to two orders of magnitude greater than their mean. The time-averaged vertical velocities are demonstrated to be largely induced by geostrophic flow and can be estimated from the time-averaged density and horizontal velocities. This suggests that local time-mean vertical velocities are primarily forced by the time-mean ocean dynamics, rather than by, for example, transient eddies or internal waves. It is also shown that, in the context of these four moorings, the time-mean vertical flow is consistent with stratified Taylor column dynamics in the presence of a topographic obstacle.
Abstract
This study demonstrates that oceanic vertical velocities can be estimated from individual mooring measurements, even for nonstationary flow. This result is obtained under three assumptions: (i) weak diffusion (Péclet number ≫ 1), (ii) weak friction (Reynolds number ≫ 1), and (iii) small inertial terms (Rossby number ≪ 1). The theoretical framework is applied to a set of four moorings located in the Southern Ocean. For this site, the diagnosed vertical velocities are highly variable in time, their standard deviation being one to two orders of magnitude greater than their mean. The time-averaged vertical velocities are demonstrated to be largely induced by geostrophic flow and can be estimated from the time-averaged density and horizontal velocities. This suggests that local time-mean vertical velocities are primarily forced by the time-mean ocean dynamics, rather than by, for example, transient eddies or internal waves. It is also shown that, in the context of these four moorings, the time-mean vertical flow is consistent with stratified Taylor column dynamics in the presence of a topographic obstacle.
Abstract
Direct measurements of oceanic turbulent parameters were taken upstream of and across Drake Passage, in the region of the Subantarctic and Polar Fronts. Values of turbulent kinetic energy dissipation rate ε estimated by microstructure are up to two orders of magnitude lower than previously published estimates in the upper 1000 m. Turbulence levels in Drake Passage are systematically higher than values upstream, regardless of season. The dissipation of thermal variance χ is enhanced at middepth throughout the surveys, with the highest values found in northern Drake Passage, where water mass variability is the most pronounced. Using the density ratio, evidence for double-diffusive instability is presented. Subject to double-diffusive physics, the estimates of diffusivity using the Osborn–Cox method are larger than ensemble statistics based on ε and the buoyancy frequency.
Abstract
Direct measurements of oceanic turbulent parameters were taken upstream of and across Drake Passage, in the region of the Subantarctic and Polar Fronts. Values of turbulent kinetic energy dissipation rate ε estimated by microstructure are up to two orders of magnitude lower than previously published estimates in the upper 1000 m. Turbulence levels in Drake Passage are systematically higher than values upstream, regardless of season. The dissipation of thermal variance χ is enhanced at middepth throughout the surveys, with the highest values found in northern Drake Passage, where water mass variability is the most pronounced. Using the density ratio, evidence for double-diffusive instability is presented. Subject to double-diffusive physics, the estimates of diffusivity using the Osborn–Cox method are larger than ensemble statistics based on ε and the buoyancy frequency.
the mixed layer depth. Our mixed layer time series is motivated by near-surface variability in the float CTD data, but it is difficult to construct an objective algorithm that finds a similar trend. The reliance of these results on mixed layer depth highlights both the current lack of understanding of the vertical distribution of near-surface momentum transport and the sensitivity of the slab model to its parameterization. c. Wave observations The highest-amplitude near-inertial waves we observe
the mixed layer depth. Our mixed layer time series is motivated by near-surface variability in the float CTD data, but it is difficult to construct an objective algorithm that finds a similar trend. The reliance of these results on mixed layer depth highlights both the current lack of understanding of the vertical distribution of near-surface momentum transport and the sensitivity of the slab model to its parameterization. c. Wave observations The highest-amplitude near-inertial waves we observe
horizontal velocity , a linear background shear is removed from absolute horizontal velocity measurements. To estimate the aspect ratio and intrinsic frequency, 14 sets of coherent velocity and buoyancy maxima/minima were identified from profiles using a peak detection algorithm and confirmed by eye. The amplitudes at the maxima/minima were then applied in Eqs. (A10) and (A11) . By isolating maxima in this way we assume that the variability is dominated by a single monochromatic wave. Energy density
horizontal velocity , a linear background shear is removed from absolute horizontal velocity measurements. To estimate the aspect ratio and intrinsic frequency, 14 sets of coherent velocity and buoyancy maxima/minima were identified from profiles using a peak detection algorithm and confirmed by eye. The amplitudes at the maxima/minima were then applied in Eqs. (A10) and (A11) . By isolating maxima in this way we assume that the variability is dominated by a single monochromatic wave. Energy density
Oceanographic Institution. One of the instruments was deployed at most CTD stations along each SR1b section occupation and recorded vertical gradients in velocity and temperature on centimeter scales (from which ϵ and χ were respectively computed) at 512 Hz to within 100 m of the ocean floor. Data processing was conducted using algorithms developed originally for the High Resolution Profiler ( Polzin and Montgomery 1996 ; Naveira Garabato 2009 ). Variances of the vertical gradients in velocity and
Oceanographic Institution. One of the instruments was deployed at most CTD stations along each SR1b section occupation and recorded vertical gradients in velocity and temperature on centimeter scales (from which ϵ and χ were respectively computed) at 512 Hz to within 100 m of the ocean floor. Data processing was conducted using algorithms developed originally for the High Resolution Profiler ( Polzin and Montgomery 1996 ; Naveira Garabato 2009 ). Variances of the vertical gradients in velocity and
