Kinematics and energetics of the mesoscale mid-ocean circulation : MODE

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 September, 1976The temporal and spatial variability of low frequency moored temperature and velocity observations, obtained as part of the Mid-Ocean Dynamics Experiment (MODE), are analyzed to study the kinematics and energetics of mesoscale eddies in the ocean. The temporal variability of the low frequency motions is characterized by three regimes: very low frequencies with periods greater than 200 days, an eddy energy containing band of 80 to 120 day periods, and high frequencies wìth periods less than 30 days. At very low frequencies, the zonal kinetic energy exceeds the meridional at all depths. In the thermocline, the very low frequency zonal flow dominates the total kinetic energy. The greatest contribution to the kinetic and potential energy in the MODE region, except for the thermocline zonal flow, is from an eddy energy containing band of 80 to 120 day periods. Eddy scale kinetic energy spatial variations are confined to this band. At high frequencies, the kinetic and potential energy scale with frequency as ω-2.5 and with depth in the WKB sense. Energy at high frequencies is partitioned evenly between zonal kinetic, meridional kinetic and potential energy and is homogeneous over 100 km. Using the technique of empirical orthogonal expansion, the vertical structure of the energetically dominant eddies is described by a few modes. The displacement is dominated by a mode with a thermocline maximum and in phase displacements with depth, while the kinetic energy is dominated by an equivalent barotropic mode. A smaller portion of the kinetic and potential energy is associated with out of phase thermocline and deep water currents and displacements. The dynamics of the mesoscale eddies are very nonlinear. Using the vertical veering of the current at MODE Center, the estimated horizontal advection of heat contributes significantly to the low frequency thermal balance. The observed very low frequency anisotropic flow is consistent with the nonlinear eddy spindown models, dominated by cascades of vorticity and energy. At high frequencies, the spectral similarity is consistent with advected geostrophic turbulence.The National Science Foundation supported the work through grants GX29034 and IDO-75-03998 and a graduate fellowship

How stationary are the internal tides in a high‐resolution global ocean circulation model?

The stationarity of the internal tides generated in a global eddy‐resolving ocean circulation model forced by realistic atmospheric fluxes and the luni‐solar gravitational potential is explored. The root mean square (RMS) variability in the M 2 internal tidal amplitude is approximately 2 mm or less over most of the ocean and exceeds 2 mm in regions with larger internal tidal amplitude. The M 2 RMS variability approaches the mean amplitude in weaker tidal areas such as the tropical Pacific and eastern Indian Ocean, but is smaller than the mean amplitude near generation regions. Approximately 60% of the variance in the complex M 2 tidal amplitude is due to amplitude‐weighted phase variations. Using the RMS tidal amplitude variations normalized by the mean tidal amplitude (normalized RMS variability (NRMS)) as a metric for stationarity, low‐mode M 2 internal tides with NRMS < 0.5 are stationary over 25% of the deep ocean, particularly near the generation regions. The M 2 RMS variability tends to increase with increasing mean amplitude. However, the M 2 NRMS variability tends to decrease with increasing mean amplitude, and regions with strong low‐mode internal tides are more stationary. The internal tide beams radiating away from generation regions become less stationary with distance. Similar results are obtained for other tidal constituents with the overall stationarity of the constituent decreasing as the energy in the constituent decreases. Seasonal variations dominate the RMS variability in the Arabian Sea and near‐equatorial oceans. Regions of high eddy kinetic energy are regions of higher internal tide nonstationarity. Key Points Internal tide stationarity measured by RMS variability normalized by amplitude Internal tide stationarity correlated with tidal amplitude Strong mesoscale eddies or currents decrease stationarity of internal tidesPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/107478/1/jgrc20664.pd

Penguin decays of B mesons

Penguin, or loop, decays of B mesons induce effective flavor-changing neutral currents, which are forbidden at tree level in the Standard Model. These decays give special insight into the CKM matrix and are sensitive to non-standard model effects. In this review, we give a historical and theoretical introduction to penguins and a description of the various types of penguin processes: electromagnetic, electroweak, and gluonic. We review the experimental searches for penguin decays, including the measurements of the electromagnetic penguins b -> s gamma and B -> K* gamma and gluonic penguins B -> K pi, B+ -> omega K+ and B -> eta' K, and their implications for the Standard Model and New Physics. We conclude by exploring the future prospects for penguin physics.Comment: 49 pages, LATEX, 30 embedded figures, submitted to Annual Reviews of Nuclear and Particle Scienc

Extracting the internal tide from data: Methods and observations from the Mixed Layer Dynamics Experiment

Several methods are developed for analyzing data containing a highly variable internal tide. In particular, the methods are aimed at the analysis of moored observations with relatively few measurements in the vertical. The analysis depends upon an "elliptical decomposition" that is a generalization of the familiar "rotary decomposition." The technique is applied to velocity and temperature observations in the upper ocean made during the Mixed Layer Dynamics Experiment (MILDEX) in the northeast Pacific Ocean, about 700 km west of Santa Barbara, California, during October-November 1983. The observed propagation direction and amplitude of the internal tide was highly variable in time. It was anticipated that the wave could be propagating from the continental shelf where it is presumed to be generated. However, most of the time the internal tide appears to be propagating parallel to the coast. This result suggests the importance of density and velocity structure at mesoscale and frontal scale in affecting the propagation of the internal tide

On eddy viscosity, energy cascades, and the horizontal resolution of gridded satellite altimeter products

Author Posting. © American Meteorological Society, 2013. 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 43 (2013): 283–300, doi:10.1175/JPO-D-11-0240.1.Motivated by the recent interest in ocean energetics, the widespread use of horizontal eddy viscosity in models, and the promise of high horizontal resolution data from the planned wide-swath satellite altimeter, this paper explores the impacts of horizontal eddy viscosity and horizontal grid resolution on geostrophic turbulence, with a particular focus on spectral kinetic energy fluxes Π(K) computed in the isotropic wavenumber (K) domain. The paper utilizes idealized two-layer quasigeostrophic (QG) models, realistic high-resolution ocean general circulation models, and present-generation gridded satellite altimeter data. Adding horizontal eddy viscosity to the QG model results in a forward cascade at smaller scales, in apparent agreement with results from present-generation altimetry. Eddy viscosity is taken to roughly represent coupling of mesoscale eddies to internal waves or to submesoscale eddies. Filtering the output of either the QG or realistic models before computing Π(K) also greatly increases the forward cascade. Such filtering mimics the smoothing inherent in the construction of present-generation gridded altimeter data. It is therefore difficult to say whether the forward cascades seen in present-generation altimeter data are due to real physics (represented here by eddy viscosity) or to insufficient horizontal resolution. The inverse cascade at larger scales remains in the models even after filtering, suggesting that its existence in the models and in altimeter data is robust. However, the magnitude of the inverse cascade is affected by filtering, suggesting that the wide-swath altimeter will allow a more accurate determination of the inverse cascade at larger scales as well as providing important constraints on smaller-scale dynamics.BKA received support from Office of Naval Research Grant N00014-11-1-0487, National Science Foundation (NSF) Grants OCE-0924481 and OCE- 09607820, and University of Michigan startup funds. KLP acknowledges support from Woods Hole Oceanographic Institution bridge support funds. RBS acknowledges support from NSF grants OCE-0960834 and OCE-0851457, a contract with the National Oceanography Centre, Southampton, and a NASA subcontract to Boston University. JFS and JGR were supported by the projects ‘‘Global and remote littoral forcing in global ocean models’’ and ‘‘Agesotrophic vorticity dynamics of the ocean,’’ respectively, both sponsored by the Office of Naval Research under program element 601153N.2013-08-0

Global modeling of internal tides within an eddying ocean general circulation model

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91777/1/25-2_arbic_hi.pd

Indirect Evidence For Substantial Damping of Low-Mode Internal Tides In the Open Ocean

A global high-resolution ocean circulation model forced by atmospheric fields and the M2 tidal constituent is used to explore plausible scenarios for the damping of low-mode internal tides. The plausibility of different damping scenarios is tested by comparing the modeled barotropic tides with TPXO8, a highly accurate satellite-altimetry-constrained tide model, and by comparing the modeled coherent baroclinic tide amplitudes against along-track altimetry. Five scenarios are tested: (1) a topographic internal wave drag, argued here to represent the breaking of unresolved high vertical modes, applied to the bottom flow (default configuration), (2) a wave drag applied to the barotropic flow, (3) absence of wave drag, (4) a substantial increase in quadratic bottom friction along the continental shelves (with wave drag turned off), and (5) application of wave drag to the barotropic flow at the same time that quadratic bottom friction is substantially increased along the shelves. Of the scenarios tested here, the default configuration (1) yields the most accurate tides. In all other scenarios (2–5), the lack of damping on open ocean baroclinic motions yields baroclinic tides that are too energetic and travel too far from their sources, despite the presence of a vigorous mesoscale eddy field which can scatter and decohere internal tides in the model. The barotropic tides are also less accurate in the absence of an open ocean damping on barotropic motions, that is, in scenarios (3) and (4). The results presented here suggest that low-mode internal tides experience substantial damping in the open ocean

Location and dynamics of the Antarctic Polar Front from satellite sea surface temperature data

The location of the Antarctic Polar Front (PF) was mapped over a 7-year period (1987-1993) within images of satellite-deprived sea surface temperature. The mean path of the PF is strongly steered by the topographic features of the Southern Ocean. The topography places vorticity constraints on the dynamics of the PF that strongly affect spatial and temporal variability. Over the deep ocean basins the surface expression of the PF is weakened, and the PF meanders over a wide latitudinal range. Near large topographic features, width and temperature change across the front increase, and large-scale meandering is inhibited. Elevated mesoscale variability is seen within and downstream of these areas and may be the result of baroclinic instabilities initiated where the PF encounters large topographic features. The strong correlations between topography and PF dynamics can be understood in the context of the planetary potential vorticity (PPV of flH) field. Mean PPV at the PF varies by more than a factor of 2 along its circumpolar path. However, at the mesoscale the PF remains within a relativity narrow range of PPV values around the local mean. Away from large topographic features, the PF returns to a preferred PPV value of ~25 x 10¯⁹m¯¹s¯¹ despite large latitudinal shifts. The mean paths of the surface and subsurface expressions of the PF are closely coupled over much of the Southern Ocean

Toward Realistic Nonstationarity of Semidiurnal Baroclinic Tides in a Hydrodynamic Model

Semidiurnal baroclinic tide sea surface height (SSH) variance and semidiurnal nonstationary variance fraction (SNVF) are compared between a hydrodynamic model and altimetry for the low‐ to middle‐latitude global ocean. Tidal frequencies are aliased by ∼10‐day altimeter sampling, which makes it impossible to unambiguously identify nonstationary tidal signals from the observations. In order to better understand altimeter sampling artifacts, the model was analyzed using its native hourly outputs and by subsampling it in the same manner as altimeters. Different estimates of the semidiurnal nonstationary and total SSH variance are obtained with the model depending on whether they are identified in the frequency domain or wave number domain and depending on the temporal sampling of the model output. Five sources of ambiguity in the interpretation of the altimetry are identified and briefly discussed. When the model and altimetry are analyzed in the same manner, they display qualitatively similar spatial patterns of semidiurnal baroclinic tides. The SNVF typically correlates above 80% at all latitudes between the different analysis methods and above 60% between the model and altimetry. The choice of analysis methodology was found to have a profound effect on estimates of the semidiurnal baroclinic SSH variance with the wave number domain methodology underestimating the semidiurnal nonstationary and total SSH variances by 68% and 66%, respectively. These results produce a SNVF estimate from altimetry that is biased low by a factor of 0.92. This bias is primarily a consequence of the ambiguity in the separation of tidal and mesoscale signals in the wave number domain.Key PointsHydrodynamic models incorporating mesoscale dynamics and tides are beginning to resolve stationary and nonstationary baroclinic tidesThe ratio of nonstationary to total semidiurnal variance computed from altimetry and HyCOM simulations agrees at low and middle latitudesComparisons of analysis methodologies show that total and nonstationary semidiurnal variances are underestimated in altimetry on averagePeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152034/1/jgrc23624_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/152034/2/jgrc23624.pd