Quantifying Eulerian Eddy Leakiness in an Idealized Model

An idealized eddy‐resolving ocean basin, closely resembling the North Pacific Ocean, is simulated using MITgcm. We identify rotationally coherent Lagrangian vortices (RCLVs) and sea surface height (SSH) eddies based on the Lagrangian and Eulerian framework, respectively. General statistical results show that RCLVs have a much smaller coherent core than SSH eddies with the ratio of radius is about 0.5. RCLVs are often enclosed by SSH anomaly contours, but SSH eddy identification method fails to detect more than half of RCLVs. Based on their locations, two types of eddies are classified into three categories: overlapping RCLVs and SSH eddies, nonoverlapping SSH eddies, and nonoverlapping RCLVs. Using Lagrangian particles, we examine the processes of leakage and intrusion around SSH eddies. For overlapping SSH eddies, over the lifetime, the material coherent core only accounts for about 25% and about 50% of initial water leak from eddy interior. The remaining 25% of water can still remain inside the boundary, but only in the form of filaments outside the coherent core. For nonoverlapping SSH eddies, more water leakage (about 60%) occurs at a faster rate. Guided by the number and radius of SSH eddies, fixed circles and moving circles are randomly selected to diagnose the material flux around these circles. We find that the leakage and intrusion trends of moving circles are quite similar to that of nonoverlapping SSH eddies, suggesting that the material coherence properties of nonoverlapping SSH eddies are not significantly different from random pieces of ocean with the same size

Southern Ocean isopycnal mixing and ventilation changes driven by winds

Observed and predicted changes in the strength of the westerly winds blowing over the Southern Ocean have motivated a number of studies of the response of the Antarctic Circumpolar Current and Southern Ocean Meridional Overturning Circulation (MOC) to wind perturbations and led to the discovery of the``eddy-compensation" regime, wherein the MOC becomes insensitive to wind changes. In addition to the MOC, tracer transport also depends on mixing processes. Here we show, in a high-resolution process model, that isopycnal mixing by mesoscale eddies is strongly dependent on the wind strength. This dependence can be explained by mixing-length theory and is driven by increases in eddy kinetic energy; the mixing length does not change strongly in our simulation. Simulation of a passive ventilation tracer (analogous to CFCs or anthropogenic CO$_2$) demonstrates that variations in tracer uptake across experiments are dominated by changes in isopycnal mixing, rather than changes in the MOC. We argue that, to properly understand tracer uptake under different wind-forcing scenarios, the sensitivity of isopycnal mixing to winds must be accounted for

An Investigation of Some Iodine Derivatives of Ortho and Para Halogenated Phenols

The purpose of this investigation was to prepare and investigate the composition and properties of some iodine derivatives of halogen substituted phenols. Because of the limited time available, and because of the difficulty in obtaining materials, this investigation was limited to the ortho and para halogenated p enols . In addition, the reactions and properties of ortho and para substituted compounds are usually more similar to each other than to those of the meta isomers. Compounds which were iodinated were: o-chlorophenol, p-chlorophenol, o-bromophenol, p-bromophenol, and o-iodophenol. The remaining compounds of the series, p-iodophenol, o-fluorophenol and p-fluorophenol were not available for use. Several unsuccessful attempts were made to prepare p-iodophenol from the diazonium salt obtained from p-a.minophenol. :Melting points of the products, and, as far as possible, the composition and isomeric arrangements, were determined . The determination of phenol coefficients was left for an investigator who has had experience in bacteriology

Quantifying Eulerian Eddy Leakiness in an Idealized Model

An idealized eddy‐resolving ocean basin, closely resembling the North Pacific Ocean, is simulated using MITgcm. We identify rotationally coherent Lagrangian vortices (RCLVs) and sea surface height (SSH) eddies based on the Lagrangian and Eulerian framework, respectively. General statistical results show that RCLVs have a much smaller coherent core than SSH eddies with the ratio of radius is about 0.5. RCLVs are often enclosed by SSH anomaly contours, but SSH eddy identification method fails to detect more than half of RCLVs. Based on their locations, two types of eddies are classified into three categories: overlapping RCLVs and SSH eddies, nonoverlapping SSH eddies, and nonoverlapping RCLVs. Using Lagrangian particles, we examine the processes of leakage and intrusion around SSH eddies. For overlapping SSH eddies, over the lifetime, the material coherent core only accounts for about 25% and about 50% of initial water leak from eddy interior. The remaining 25% of water can still remain inside the boundary, but only in the form of filaments outside the coherent core. For nonoverlapping SSH eddies, more water leakage (about 60%) occurs at a faster rate. Guided by the number and radius of SSH eddies, fixed circles and moving circles are randomly selected to diagnose the material flux around these circles. We find that the leakage and intrusion trends of moving circles are quite similar to that of nonoverlapping SSH eddies, suggesting that the material coherence properties of nonoverlapping SSH eddies are not significantly different from random pieces of ocean with the same size

The impact of ozone depleting substances on the circulation, temperature, and salinity of the Southern Ocean: An attribution study with CESM1(WACCM)

Observations show robust changes in the circulation, temperature, and salinity of the Southern Ocean in recent decades. To what extent these changes are related to the formation of the ozone hole in the late twentieth century is an open question. Using a comprehensive chemistry-climate Earth system model, we contrast model runs with varying and with fixed surface concentrations of ozone depleting substances (ODS) from 1955 to 2005. In our model, ODS cause the majority of the summertime changes in surface wind stress which, in turn, induce a clear poleward shift of the ocean's meridional overturning circulation. In addition, more than 30% of the model changes in the temperature and salinity of the Southern Ocean are caused by ODS. These findings offer unambiguous evidence that increased concentrations of ODS in the late twentieth century are likely to have been been an important driver of changes in the Southern Ocean

Mixing by ocean eddies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2012.Cataloged from PDF version of thesis.Includes bibliographical references (p. 163-175).Mesoscale eddies mix and transport tracers such as heat and potential vorticity laterally in the ocean. While this transport plays an important role in the climate system, especially in the Southern Ocean, we lack a, comprehensive understanding of what sets mixing rates. This thesis seeks to advance this understanding through three related studies. First, mixing rates are diagnosed from an eddy-resolving state estimate of the Southern Ocean, revealing a meridional cross-section of effective diffusivity shaped by the interplay between eddy propagation and mean flow. Effective diffusivity diagnostics are then applied to quantify surface mixing rates globally, using a, kinematic model with velocities derived from satellite observations; the diagnosed mixing rates show a rich spatial structure, with especially strong mixing in the tropics and western-boundary-current regions. Finally, an idealized numerical model of the Southern Ocean is analyzed, focusing on the response to changes in win( stress. The sensitivity of the meridional overturning circulation to the wind changes demonstrates the importance of properly capturing eddy mixing rates for large-scale climate problems.by Ryan Abernathey.Ph.D

Seasonality of the mesoscale inverse cascade as inferred from global scale-dependent eddy energy observations

Author Posting. © American Meteorological Society, 2022. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 52(8), (2022): 1677-1691, https://doi.org/10.1175/jpo-d-21-0269.1.Oceanic mesoscale motions including eddies, meanders, fronts, and filaments comprise a dominant fraction of oceanic kinetic energy and contribute to the redistribution of tracers in the ocean such as heat, salt, and nutrients. This reservoir of mesoscale energy is regulated by the conversion of potential energy and transfers of kinetic energy across spatial scales. Whether and under what circumstances mesoscale turbulence precipitates forward or inverse cascades, and the rates of these cascades, remain difficult to directly observe and quantify despite their impacts on physical and biological processes. Here we use global observations to investigate the seasonality of surface kinetic energy and upper-ocean potential energy. We apply spatial filters to along-track satellite measurements of sea surface height to diagnose surface eddy kinetic energy across 60–300-km scales. A geographic and scale-dependent seasonal cycle appears throughout much of the midlatitudes, with eddy kinetic energy at scales less than 60 km peaking 1–4 months before that at 60–300-km scales. Spatial patterns in this lag align with geographic regions where an Argo-derived estimate of the conversion of potential to kinetic energy is seasonally varying. In midlatitudes, the conversion rate peaks 0–2 months prior to kinetic energy at scales less than 60 km. The consistent geographic patterns between the seasonality of potential energy conversion and kinetic energy across spatial scale provide observational evidence for the inverse cascade and demonstrate that some component of it is seasonally modulated. Implications for mesoscale parameterizations and numerical modeling are discussed.This work was generously funded by NSF Grants OCE-1912302, OCE-1912125 (Drushka), and OCE-1912325 (Abernathey) as part of the Ocean Energy and Eddy Transport Climate Process Team