Dynamics of Dipoles in the Middle Atlantic Bight

Beginning with the observations made by the Warm-Core Rings program in the early 1980\u27s, several Gulf Stream warm-core rings (WCR\u27s) in the Middle Atlantic Bight (MAB) have been observed with one or more cyclones around their periphery. These ring systems are observed in the slope water between the Gulf Stream\u27s western boundary and the shelf break. Observations of ring systems have motivated a reanalysis of existing satellite surface temperature imagery, which revealed that multipole structure is common for both warm and cold core rings. This suggests that rings are better characterized as one part of multipole systems rather than as isolated vortices. Dynamical studies of ring systems have been primarily limited to numerical modeling of isolated nonlinear vortices and interactions of vortices with sloping topography. Here, a baroclinic rotating modon model is used to simulate the dynamics of a WCR paired with a peripheral cyclone, over a flat bottom. Observations of WCR 82B and a peripheral cyclone are used to constrain the model parameters. A diagnostic calculation compares model ring and cyclone velocity profiles with observations and provides estimates of ring and dipole energies, as well as an estimate of volume transport across a 150 km section representing the NAB shelf-slope front. In addition, four different methods for estimating the location of the ring and cyclone perimeters are compared. Results are also presented for two evolutionary calculations. The first calculation uses three groups of fluid parcels, allowed to evolve for 14 days, to simulate three flow features apparent in satellite imagery of the WCR 82B system. The second calculation simulates entrainment of shelf water and Gulf Stream water by allowing two long, thin patches of fluid parcels to evolve for 7.4 days. The final parcel distribution is again compared with satellite imagery for the WCR 82B system. These results show that the rotating baroclinic modon model provides a useful dynamical simulation of a dipolar ring system. The model produces a velocity field that is consistent with observations, and it allows ring and dipole energies, volume transport, and ring and cyclone perimeter position to be estimated

Integrable Unsteady Motion With an Application to Ocean Eddies

Application of the Brown-Samelson theorem, which shows that particle motion is integrable in a class of vorticity-conserving, two-dimensional incompressible hows, is extended here to a class of explicit time dependent dynamically balanced flows in multilayered systems. Particle motion for nonsteady two-dimensional flows with discontinuities in the vorticity or potential vorticity fields (modon solutions) is shown to be integrable. An example of a two-layer modon solution constrained by observations of a Gulf Stream ring system is discussed

Submesoscale dispersion in the vicinity of the Deepwater Horizon spill

Reliable forecasts for the dispersion of oceanic contamination are important for coastal ecosystems, society and the economy as evidenced by the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 and the Fukushima nuclear plant incident in the Pacific Ocean in 2011. Accurate prediction of pollutant pathways and concentrations at the ocean surface requires understanding ocean dynamics over a broad range of spatial scales. Fundamental questions concerning the structure of the velocity field at the submesoscales (100 meters to tens of kilometers, hours to days) remain unresolved due to a lack of synoptic measurements at these scales. \textcolor{black} {Using high-frequency position data provided by the near-simultaneous release of hundreds of accurately tracked surface drifters, we study the structure of submesoscale surface velocity fluctuations in the Northern Gulf Mexico. Observed two-point statistics confirm the accuracy of classic turbulence scaling laws at 200m$-$50km scales and clearly indicate that dispersion at the submesoscales is \textit{local}, driven predominantly by energetic submesoscale fluctuations.} The results demonstrate the feasibility and utility of deploying large clusters of drifting instruments to provide synoptic observations of spatial variability of the ocean surface velocity field. Our findings allow quantification of the submesoscale-driven dispersion missing in current operational circulation models and satellite altimeter-derived velocity fields.Comment: 9 pages, 6 figure