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back on the surface fluxes of heat and momentum. Baroclinic eddies can also achieve exchanges between the mixed layer and the thermocline below—a process that may be important in subducting heat and atmospheric constituents like carbon into the thermocline as well as bringing nutrients up into the mixed layer, where they can be used for photosynthesis (e.g., Thomas et al. 2008 ). The balanced dynamics of baroclinic mixed-layer instabilities suggest they should undergo a seasonal cycle, following
back on the surface fluxes of heat and momentum. Baroclinic eddies can also achieve exchanges between the mixed layer and the thermocline below—a process that may be important in subducting heat and atmospheric constituents like carbon into the thermocline as well as bringing nutrients up into the mixed layer, where they can be used for photosynthesis (e.g., Thomas et al. 2008 ). The balanced dynamics of baroclinic mixed-layer instabilities suggest they should undergo a seasonal cycle, following
form of frontal instabilities ( Boccaletti et al. 2007 ; Fox-Kemper et al. 2008 ) or filaments arising from frontogenesis ( Capet et al. 2008 ; Badin et al. 2011 ; Zhong et al. 2012 ; Mensa et al. 2013 ). Dynamically, the controlling effects of geostrophy and strong stratification are no longer entirely dominant at the submesoscales and as such, these spatial and temporal scales are the resolution limit of current operational ocean models. In the Eulerian frame, active submesoscale motions
form of frontal instabilities ( Boccaletti et al. 2007 ; Fox-Kemper et al. 2008 ) or filaments arising from frontogenesis ( Capet et al. 2008 ; Badin et al. 2011 ; Zhong et al. 2012 ; Mensa et al. 2013 ). Dynamically, the controlling effects of geostrophy and strong stratification are no longer entirely dominant at the submesoscales and as such, these spatial and temporal scales are the resolution limit of current operational ocean models. In the Eulerian frame, active submesoscale motions
and is the time derivative of strain or deformation. At both sites, the mixed layer depth was ~10 m but reached ~30 m during the nights of 15 and 19 June at site 2. Stratification in the seasonal upper pycnocline immediately below the mixed layer base was N ~ 10 −2 rad s −1 . Site 1 was sampled during 2–10 June 2011. It was characterized by a very weak eddy field with 1–10-km drifter array–based confluences less than 10 −6 s −1 ~0.01 f (D. A. Birch et al. 2014, unpublished manuscript), that
and is the time derivative of strain or deformation. At both sites, the mixed layer depth was ~10 m but reached ~30 m during the nights of 15 and 19 June at site 2. Stratification in the seasonal upper pycnocline immediately below the mixed layer base was N ~ 10 −2 rad s −1 . Site 1 was sampled during 2–10 June 2011. It was characterized by a very weak eddy field with 1–10-km drifter array–based confluences less than 10 −6 s −1 ~0.01 f (D. A. Birch et al. 2014, unpublished manuscript), that
observations that suggest that frontogenesis could play an important role in facilitating cabbeling at observed fronts and motivate a theoretical study. While theories for strain-driven frontogenesis and the influence of cabbeling on frontal dynamics have been investigated in isolation (e.g., Hoskins and Bretherton 1972 ; Garrett and Horne 1978 ; Bowman and Okubo 1978 ), the combined effects of the two processes, and their role in mode water mass formation, have not been explored and will be the focus
observations that suggest that frontogenesis could play an important role in facilitating cabbeling at observed fronts and motivate a theoretical study. While theories for strain-driven frontogenesis and the influence of cabbeling on frontal dynamics have been investigated in isolation (e.g., Hoskins and Bretherton 1972 ; Garrett and Horne 1978 ; Bowman and Okubo 1978 ), the combined effects of the two processes, and their role in mode water mass formation, have not been explored and will be the focus
internal-wave field constructed to simulate that of the LatMix 2011 site with results that promise to sort out the effects of shear dispersion, adiabatic dispersion by internal waves alone, and vortical motions induced by diapycnal mixing events (M.-P. Lelong et al. 2015, manuscript in preparation). Among the original LatMix hypotheses, we considered four classes of motions that might dominate submesoscale stirring in the seasonal pycnocline: shear dispersion by internal waves; vortices induced by
internal-wave field constructed to simulate that of the LatMix 2011 site with results that promise to sort out the effects of shear dispersion, adiabatic dispersion by internal waves alone, and vortical motions induced by diapycnal mixing events (M.-P. Lelong et al. 2015, manuscript in preparation). Among the original LatMix hypotheses, we considered four classes of motions that might dominate submesoscale stirring in the seasonal pycnocline: shear dispersion by internal waves; vortices induced by
of properties, such as passive and active tracers, from the frontal region. Dynamically, future studies will have to address the influence of forcing of the ML front, the role of seasonality in changing the baroclinicity as well as the vertical shear of the flow, the effects of the coupling of the ML front with the baroclinicity in the pycnocline, and the comparison with realistic simulations and observations, in which all these additional factors, as well as others such as the noise induced by
of properties, such as passive and active tracers, from the frontal region. Dynamically, future studies will have to address the influence of forcing of the ML front, the role of seasonality in changing the baroclinicity as well as the vertical shear of the flow, the effects of the coupling of the ML front with the baroclinicity in the pycnocline, and the comparison with realistic simulations and observations, in which all these additional factors, as well as others such as the noise induced by
instability. The overline is an appropriately defined along-front average. Since baroclinic mixed layer instabilities occur on small horizontal scales of order 0.1–10 km, they are not typically resolved by presently available global ocean models. The eddies’ effects on stratification and transport must be parameterized. Fox-Kemper et al. (2008 , hereinafter FFH ) proposed to represent the slumping of isopycnals by baroclinic mixed layer instabilities using an eddy streamfunction, similar to how the
instability. The overline is an appropriately defined along-front average. Since baroclinic mixed layer instabilities occur on small horizontal scales of order 0.1–10 km, they are not typically resolved by presently available global ocean models. The eddies’ effects on stratification and transport must be parameterized. Fox-Kemper et al. (2008 , hereinafter FFH ) proposed to represent the slumping of isopycnals by baroclinic mixed layer instabilities using an eddy streamfunction, similar to how the
( Fig. 1a ). While the Atlantis made wider ~30-km cross sections around the float, the Knorr made narrower ~10-km cross sections, closely following the float ( Fig. 1b ). The survey strategy involved intensive sampling of the water around a Lagrangian float in the mixed layer in an attempt to minimize the convoluting effects of advection on the analysis. But, it is important to note the observations were obtained in a region of strong lateral and vertical gradients in velocity, and therefore the
( Fig. 1a ). While the Atlantis made wider ~30-km cross sections around the float, the Knorr made narrower ~10-km cross sections, closely following the float ( Fig. 1b ). The survey strategy involved intensive sampling of the water around a Lagrangian float in the mixed layer in an attempt to minimize the convoluting effects of advection on the analysis. But, it is important to note the observations were obtained in a region of strong lateral and vertical gradients in velocity, and therefore the
curves diapycnal diffusivity K z , and thin solid curves the vertical gradient of horizontal displacement | χ z | = |∫ V z dt |. (a) The unstable shear and mixing decay over a buoyancy time scale δt ~ N −1 so that | χ z | remains small. (b) Unstable shear and mixing persist over an inertial time scale δt ~ f −1 , allowing | χ z | to become large in conjunction with strong mixing. The statistics of both shear and turbulence may vary in different regions of the ocean. Thus, the effects
curves diapycnal diffusivity K z , and thin solid curves the vertical gradient of horizontal displacement | χ z | = |∫ V z dt |. (a) The unstable shear and mixing decay over a buoyancy time scale δt ~ N −1 so that | χ z | remains small. (b) Unstable shear and mixing persist over an inertial time scale δt ~ f −1 , allowing | χ z | to become large in conjunction with strong mixing. The statistics of both shear and turbulence may vary in different regions of the ocean. Thus, the effects
it has been created by cabbeling. Fig . 9. The water mass transformation at a given density and time due to (a) cabbeling, (b) diffusion, and (c) both effects as defined by (17) . The volume flux divergence −(∂ F /∂ ρ )Δ ρ (Sv) for isopycnal layers of width Δ ρ = 0.005 kg m −3 at 80 days is overlaid in (a) and (b). The predicted mode water density is indicated by the dashed black line. e. Sensitivity Here, we investigate the sensitivity of the mode water properties to the initial water mass
it has been created by cabbeling. Fig . 9. The water mass transformation at a given density and time due to (a) cabbeling, (b) diffusion, and (c) both effects as defined by (17) . The volume flux divergence −(∂ F /∂ ρ )Δ ρ (Sv) for isopycnal layers of width Δ ρ = 0.005 kg m −3 at 80 days is overlaid in (a) and (b). The predicted mode water density is indicated by the dashed black line. e. Sensitivity Here, we investigate the sensitivity of the mode water properties to the initial water mass
