Seasonality of the submesoscale dynamics in the Gulf Stream region

Mensa, Jean A.; Garraffo, Zulema; Griffa, Annalisa; Özgökmen, Tamay M.; Haza, Angelique C.; Veneziani, Milena

doi:10.1007/s10236-013-0633-1

Cited by 173 publications

(216 citation statements)

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“…This offers a higher degree of granularity than recent studies that have analyzed bulk seasonal differences in flow characteristics, which are then used to infer submesoscale activity. Both numerical models (Mensa et al 2013;Sasaki et al 2014) and observations (Callies et al 2015;Swart et al 2015;Buckingham et al 2016) provide strong evidence that there are seasonal modulations in submesoscale activity. In general, these reflect a steepening of the kinetic energy spectra during summer, typically with slopes around k…”

Section: Introductionmentioning

confidence: 99%

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Thompson

Lazar

Buckingham

et al. 2016

Journal of Physical Oceanography

174

227

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The importance of submesoscale instabilities, particularly mixed layer baroclinic instability and symmetric instability, on upper-ocean mixing and energetics is well documented in regions of strong, persistent fronts such as the Kuroshio and the Gulf Stream. Less attention has been devoted to studying submesoscale flows in the open ocean, far from long-term, mean geostrophic fronts, characteristic of a large proportion of the global ocean. This study presents a year-long, submesoscale-resolving time series of near-surface buoyancy gradients, potential vorticity, and instability characteristics, collected by ocean gliders, that provides insight into open-ocean submesoscale dynamics over a full annual cycle. The gliders continuously sampled a 225 km 2 region in the subtropical northeast Atlantic, measuring temperature, salinity, and pressure along 292 short (;20 km) hydrographic sections. Glider observations show a seasonal cycle in near-surface stratification. Throughout the fall (September-November), the mixed layer deepens, predominantly through gravitational instability, indicating that surface cooling dominates submesoscale restratification processes. During winter (December-March), mixed layer depths are more variable, and estimates of the balanced Richardson number, which measures the relative importance of lateral and vertical buoyancy gradients, depict conditions favorable to symmetric instability. The importance of mixed layer instabilities on the restratification of the mixed layer, as compared with surface heating and cooling, shows that submesoscale processes can reverse the sign of an equivalent heat flux up to 25% of the time during winter. These results demonstrate that the openocean mixed layer hosts various forced and unforced instabilities, which become more prevalent during winter, and emphasize that accurate parameterizations of submesoscale processes are needed throughout the ocean.

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Section: Introductionmentioning

confidence: 99%

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Thompson

Lazar

Buckingham

et al. 2016

Journal of Physical Oceanography

174

227

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“…Thus, upwelling-diffusion gives ψ ∼ κ v L/h, with h being set by the wind as in (24), thus giving a circulation strength that is linearly proportional to diffusivity, as in (22). In the strong diffusion case the diffusion itself affects the stratification, and so we get a weaker dependence of the circulation strength on κ v .…”

Section: Discussion Of Limitsmentioning

confidence: 98%

“…The optical depth of a gas is related both to the amount of gas and to its properties, and for a thin layer of gas of thickness ds we can write dτ = k A ρds (22) where k A is the mass absorption coefficient. In general the optical depth will depend on the wavelength but we shall assume it does not; that is, the atmosphere is grey.…”

Section: Equations Of Radiative Transfermentioning

confidence: 99%

See 1 more Smart Citation

2014 program to study : climate physics and dynamics

Provenzale¹,

Ferrari²,

Flierl³

2015

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PrefaceThe 2014 Geophysical Fluid Dynamics Summer Study Program started on June 16th, with the topic of Climate Physics and Dynamics. The topic proved very timely and attracted an unprecedented number of applications from brilliant students. Professors Kerry Emanuel (MIT) and Geoff Vallis (Exeter) gave the principal lectures. They began with the simplest energy balance models and then included adjustment of the vertical profiles by convection (dry and moist). Kerry delved more deeply into convection and the processes found in "cloud-permitting" models, including island effects and the spontaneous formation of clusters surrounded by dry regions. Geoff discussed the larger-scale dynamics of the atmosphere and oceans, including the transports by eddies and the thermohaline circulation. This year, we webcast the principal lectures, with order 50 connections per day from viewers at many universities worldwide.Antonello Provenzale, Raffaele Ferrari, and Glenn Flierl co-directed the summer and invited a large number of top researchers in the dynamics of climate, so that we had a broad critical view on the status of modelling and theory. As usual, the visitors presented new ideas and approaches to geophysical dynamics, and the visitors, staff, and fellows engaged in intense discussions on the porch and in the lecture room. The long-term staff members ensured that the fellows never lacked for guidance; many of them explored unfamiliar topics but were still able to develop new insights. In 2014, the Sears Public Lecture was delivered by Professor Cecilia Bitz, University of Washington, who discussed "The Future of Arctic and Antarctic Sea Ice." She noted that both the Arctic and Antarctic have experienced record sea ice coverage in the last decade. The Arctic has experienced record losses, especially in summer, while the Antarctic has had expanding sea ice. She considers how this is possible in an era of global climate change, and what we can expect in the future. Cecilia overcame problems with the microphone and engaged the audience both in answering question and in discussions at the reception and refreshments following the talk.Anne Doucette, Julie Hildebrandt, and Janet Fields made sure that the administrative side of the program ran with admirable efficiency. Matt Barton ensured the webcast was high quality. We continue to be indebted to WHOI for their support and to the Academic Programs Office, who once more (with the cooperation of the weather!) provided a perfect atmosphere.i ii Principal LecturesKerry Fellows' Reports PreambleAs opposed to expectations, there is not going to be much GFD in this lecture. There will be no equations of motion. The reason is that to understand climate, it is necessary to merge understanding of the large-scale motion with the thermodynamics and specifically with radiative transfer. Most problems that have not been solved in climate science are connected to the interaction of radiative transfer with water substances. This lecture will therefore review how radiation passing through ...

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“…Meanwhile, regional GCMs that directly resolve submesoscale motions show a potential increase in total eddy kinetic energy (EKE) by a factor of two [2,8] as compared to simulations where these motions are not resolved. The contribution of submesoscales to regional EKE may also exhibit seasonal cycles [9,10].…”

Section: Introductionmentioning

confidence: 99%

Submesoscale Turbulence over a Topographic Slope

Lazar

Zhang

Thompson

2018

Fluids

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Abstract:Regions of the ocean near continental slopes are linked to significant vertical velocities caused by advection over a sloping bottom, frictional processes and diffusion. Oceanic motions at submesoscales are also characterized by enhanced vertical velocities, as compared to mesoscale motions, due to greater contributions from ageostrophic flows. These enhanced vertical velocities can make an important contribution to turbulent fluxes. Sloping topography may also induce large-scale potential vorticity gradients by modifying the slope of interior isopycnal surfaces. Potential vorticity gradients, in turn, may feed back on mesoscale stirring and the generation of submesoscale features. In this study, we explore the impact of sloping topography on the characteristics of submesoscale motions. We conduct high-resolution (1 km × 1 km) simulations of a wind-driven frontal current over an idealized continental shelf and slope. We explore changes in the magnitude, skewness and spectra of surface vorticity and vertical velocity across different configurations of the topographic slope and wind-forcing orientations. All of these properties are strongly modulated by the background topography. Furthermore, submesoscale characteristics exhibit spatial variability across the continental shelf and slope. We find that changes in the statistical properties of submesoscale motions are linked to mesoscale stirring responding to differences in the interior potential vorticity distributions, which are set by frictional processes at the ocean surface and over the sloping bottom. Improved parameterizations of submesoscale motions over topography may be needed to simulate the spatial variability of these features in coarser-resolution models, and are likely to be important to represent vertical nutrient fluxes in coastal waters.

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Seasonality of the submesoscale dynamics in the Gulf Stream region

Cited by 173 publications

References 74 publications

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

Open-Ocean Submesoscale Motions: A Full Seasonal Cycle of Mixed Layer Instabilities from Gliders

2014 program to study : climate physics and dynamics

Submesoscale Turbulence over a Topographic Slope

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