Poleward heat flux and conversion of available potential energy in Drake Passage

Energetic fluctuations of periods longer than a day are found to transport heat poleward in the Drake Passage. Heat fluxes due to these low-frequency motions are large enough to account for all of the poleward heat transport across the pol ar front necessary to balance the heat Jost to the atmosphere by waters around the Antarctic continent...

Sources of eddy energy in the Gulf Stream recirculation region

Array measurements of current and temperature made for 15 months in the main thermodine of the Gulf Stream recirculation region near 31N, 69° 30\u27W are analyzed to determine the energy sources for low-frequency fluctuations or eddies and the effect of these eddies on the mean circulation in the region...

Momentum, mass, heat, and vorticity balances from oceanic measurements of current and temperature

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution July, 1975The local dynamics of low-frequency motions in the MODE region are investigated from three arrays of moored measurements of current and temperature. Tests for lowest-order balances of horizontal momentum, mass, heat, heat and vorticity within established errors are carried out. Geostrophic comparisons of four-day averaged observed and geostrophic current differences from the MODE-l array indicate that ageostrophic balance within estimated errors is the lowest-order horizontal momentum balance. The discrepancy between observed and geostrophic current differences has a standard deviation of 1.9 cm/see which is 26% as large as the standard deviation of the current differences. In the mass balance comparisons of estimates of δυ/δχ and δν/δγ from the MODE-O Array l indicate that within estimated errors the low frequency currents are horizontally nondivergent. The standard deviation of horizontal divergence, which is the discrepancy from horizontal nondivergence, is .22 x 10 6 sec 1 which is 36% as large as the standard deviation of the estimates of horizontal derivatives of velocity. These tests significantly increase the observational basis for geostrophy and horizontal nondivergence and confirm the validity of the error estimates. In the heat balance, estimates of horizontal advection of temperature balance local time changes of temperature within estimated errors for the IWEX observations. These estimates have small errors because a representation of horizontal advection of temperature in terms of the speed and turning about the vertical of the horizontal current is used. The errors are so small that from future measurements it may be possible to estimate the sum of local change plus horizontal advection of temperature and from this sum it may be possible to estimate vertical velocity. This balance between local change and horizontal advection demonstrates that horizontal advection of spatially varying features is an important cause of local time changes. The horizontal advection could not be explained in terms of advection by the long time-averaged flow field. This suggests that the local dynamics of low-frequency motions in the MODE region are strongly nonlinear. An indication of energy transfer, which occurs in nonlinear processes, is found in a phase lag such that estimates of horizontal advection lead local changes of temperature. In the context of the baroclinic instability model this phase lag is consistent with the growth of perturbation wave energy by conversion of potential energy contained in the forty-day averaged flow field. In the vorticity balance, estimates of planetary advection account for only half the local time change of vorticity for MODE-0 Array 1 measurements. Within estimated errors these two terms do not balance, so these observations cannot be explained as manifestations of barotropic Rossby waves alone. Estimates of vortex stretching and horizontal advection of relative vorticity could not be made. A phase lag such that estimates of planetary advection lead local changes of vorticity is consistent in the context of the instability model with an increase in perturbation wave enstrophy, which must occur when the perturbation wave grows, due to the conversion of planetary enstrophy. Because of the importance of the vorticity balance for understanding the dynamics of low-frequency motions an experiment is suggested to estimate accurately all terms in the lowest-order vorticity balance. From such measurements the energy transfer and enstrophy conversion could also be estimated.Support to carry out this thesis work was provided by the Office of Naval Research under contracts N00014-66-C0241 and C0262 NR 083-004 and by the National Science Foundation Office of the International Decade of Ocean Exploration under grant IDO75-03962

Michael John Robert Fasham. 29 May 1942 — 7 June 2008

Professor Michael Fasham played a pioneering role in the development of marine ecosystem models for the study of nutrient and carbon cycling in the ocean. He is articularly celebrated for his famous Fasham–Ducklow–McKelvie model, which was the first of its kind to separate new and regenerated forms of nutrient, as well as including microbial recycling pathways. Fasham’s models provided key understanding of the links between primary production, carbon cycling and export (of organic matter from the surface to deep ocean) based on both deep and insightful parameterization inspired by his many collaborations with leading experimental and field biologists of the day, and by his expert use of data for model calibration and validation. He had the ability to see the big picture, linking observation and models to achieve a unified understanding of system dynamics. As well as the direct contributions of his own science, Fasham played a pivotal role in steering the international scientific agenda, notably his leadership of the Joint Global Ocean Flux Study which had the aim of understanding ocean carbon cycling and sinks via the coordination of extensive field programmes, synthesis and modelling. He will be remembered by those who knew him for his openness, enthusiasm and modesty, a man who was fun to know and to work with and who loved the thrill of scientific adventure and discovery

Origin of the Mediterranean outflow

Toe origin of the Mediterranean outflow is one of oceanography\u27s oldest problems. In this work, the flow of western Mediterranean deep water up and over the sill at Gibraltar is investigated from hydrographic observations and current measurements. The deep water is found to flow westward along the Moroccan continental slope in the western Mediterranean or Alboran Sea and to rise as it approaches the Strait of Gibraltar...

Eddy momentum and heat ftuxes and their effects on the circulation of the equatorial Pacific Ocean

Eddy momentum and heat fluxes are estimated from three-dimensional arrays of long time-series current meter measurements in the equatorial Pacific near 152W and 110W during 1979 to 1981. Eddies transport eastward momentum away from the equator above the core of the Equatorial Undercurrent; they transport eastward momentum toward the equator below the Undercurrent core. The vertical integral of the eddy momentum flux divergence is equivalent to a westward wind stress of 0.16 dyne cm–2. Eddies transport heat toward the equator at all depths down to 250 m. At 100 m depth and below, the eddy heat flux convergences are remarkably similar at 152W and 110W. Above 100 m, the heat flux convergence at 110W is much larger than that at 152W. The vertical integral of the average eddy heat flux convergence between 152W and 110W is equivalent to a heating of the equatorial region at a rate of 245 W m–2. Lateral eddy viscosities and diffusivities are of order 0.5 to 5 × 107 cm2 s–1, similar to those generally used in numerical models. Eddy coefficients, however, are positive only above the core of the Equatorial Undercurrent and are consistently negative below the Undercurrent core. Fluctuations with periods between 32 and 13 days and centered at 21-day period contribute the bulk of the eddy heat and momentum fluxes

Moored velocity measurements on the edge of the Gulf-Stream recirculation

Mean velocities, eddy kinetic energies and time series of velocities at several depths are presented from moored current meters for the 15 month period May 1978 to July 1979 as part of the POLYMODE Local Dynamics Experiment, centered at 31N, 69°30\u27W. The mean velocities in the upper one kilometer are toward the southwest at 2.4 to 4.4 cm/s, consistent with Worthington\u27s (1976) description of the mean circulation of the North Atlantic...

Atlantic overturning: new observations and challenges

This paper provides an introduction to the special issue of the Philosophical Transactions of the Royal Society of London of papers from the 2022 Royal Society meeting on ‘Atlantic overturning: new observations and challenges'. It provides the background and rationale for the meeting, briefly summarizes prior progress on observing the Atlantic overturning circulation and draws out the new challenges that papers presented at the meeting raise, so pointing the way forward for future research. This article is part of a discussion meeting issue 'Atlantic overturning: new observations and challenges'

Continuous estimate of Atlantic oceanic freshwater flux at 26.5°N

The first continuous estimates of freshwater flux across 26.5°N are calculated using observations from the RAPID–MOCHA–Western Boundary Time Series (WBTS) and Argo floats every 10 days between April 2004 and October 2012. The mean plus or minus the standard deviation of the freshwater flux (FW) is −1.17 ± 0.20 Sv (1 Sv ≡ 106 m3 s−1; negative flux is southward), implying a freshwater divergence of −0.37 ± 0.20 Sv between the Bering Strait and 26.5°N. This is in the sense of an input of 0.37 Sv of freshwater into the ocean, consistent with a region where precipitation dominates over evaporation. The sign and the variability of the freshwater divergence are dominated by the overturning component (−0.78 ± 0.21 Sv). The horizontal component of the freshwater divergence is smaller, associated with little variability and positive (0.35 ± 0.04 Sv). A linear relationship, describing 91% of the variance, exists between the strength of the meridional overturning circulation (MOC) and the freshwater flux (−0.37 − 0.047 Sv of FW per Sverdrups of MOC). The time series of the residual to this relationship shows a small (0.02 Sv in 8.5 yr) but detectable decrease in the freshwater flux (i.e., an increase in the southward freshwater flux) for a given MOC strength. Historical analyses of observations at 24.5°N are consistent with a more negative freshwater divergence from −0.03 to −0.37 Sv since 1974. This change is associated with an increased southward freshwater flux at this latitude due to an increase in the Florida Straits salinity (and therefore the northward salinity flux)