scholarly journals On wind-driven energetics of subtropical gyres

2020 ◽  
Author(s):  
William K. Dewar ◽  
Quentin Jamet ◽  
Bruno Deremble ◽  
Nicolas Wienders
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Multiple Scales ◽  
Numerical Study ◽  
Mean Field ◽  
Western Boundary ◽  
The North ◽  
The Mean ◽  
The One ◽  
Mean Circulation

<p>The flow of energy in the wind-driven circulation is examined in a <br>combined theoretical and numerical study. Based on a multiple scales <br>analysis of the ocean interior, we find the mesoscale field is strongly <br>affected by the ventilated thermocline, but no feed back from the eddies <br>to the large scale is found.  We then analyze the western boundary <br>region arguing that the associated currents divide between coastal jets, <br>which conserve mean energy, and open ocean, separated jet extensions<br>where the mesoscale is energized by the mean field.   It is the <br>separated jet zone where the primary loss of general circulation energy <br>to the mesoscale occurs.  Connections to the `Thickness Weighted <br>Average' form of the primitive equations are made which support the <br>differing roles of the eddies in these regions.  These ideas are then <br>tested by an analysis of a regional primitive equation 1/12-degree <br>numerical model of the North Atlantic. The predictions of the theory are <br>generally supported by the numerical results.  The one exception is that <br>topographic irregularities in the coastal jet spawn eddies, although <br>they contribute modestly to the energy budget.  We therefore conclude <br>the primary sink of wind input into the mean circulation is in the <br>separated jet, and not the interior.  The analysis also shows<br>wind forcing is much smaller than the interior energy fluxes. Thus, the <br>general circulation is characterized as recirculating energy in the <br>manner of a Fofonoff gyre.</p>

scholarly journals Simulated Relationships between Regional Temperatures and Large-Scale Circulation: 125 kyr BP (Eemian) and the Preindustrial Period

2005 ◽  
Vol 18 (19) ◽  
pp. 4032-4045 ◽  
Author(s):  
Nikolaus Groll ◽  
Martin Widmann ◽  
Julie M. Jones ◽  
Frank Kaspar ◽  
Stephan J. Lorenz
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Temperature Sensitive ◽  
Proxy Data ◽  
Large Scale Circulation ◽  
The North ◽  
Temperature Signal ◽  
Northern Winter ◽  
The Mean ◽  
Mean Circulation

Abstract To investigate relationships between large-scale circulation and regional-scale temperatures during the last (Eemian) interglacial, a simulation with a general circulation model (GCM) under orbital forcing conditions of 125 kyr BP is compared with a simulation forced with the Late Holocene preindustrial conditions. Consistent with previous GCM simulations for the Eemian, higher northern summer 2-m temperatures are found, which are directly related to the different insolation. Differences in the mean circulation are evident such as, for instance, stronger northern winter westerlies toward Europe, which are associated with warmer temperatures in central and northeastern Europe in the Eemian simulation, while the circulation variability, analyzed by means of a principal component analysis of the sea level pressure (SLP) field, is very similar in both periods. As a consequence of the differences in the mean circulation the simulated Arctic Oscillation (AO) temperature signal in the northern winter, on interannual-to-multidecadal time scales, is weaker during the Eemian than today over large parts of the Northern Hemisphere. Correlations between the AO index and the central European temperature (CET) decrease by about 0.2. The winter and spring SLP anomalies over the North Atlantic/European domain that are most strongly linearly linked to the CET cover a smaller area and are shifted westward over the North Atlantic during the Eemian. However, the strength of the connection between CET and these SLP anomalies is similar in both simulations. The simulated differences in the AO temperature signal and in the SLP anomaly, which is linearly linked to the CET, suggest that during the Eemian the link between the large-scale circulation and temperature-sensitive proxy data from Europe may differ from present-day conditions and that this difference should be taken into account when inferring large-scale climate from temperature-sensitive proxy data.

scholarly journals Intermediate-Depth Circulation of the Indian and South Pacific Oceans Measured by Autonomous Floats

2005 ◽  
Vol 35 (5) ◽  
pp. 683-707 ◽  
Author(s):  
Russ E. Davis
Keyword(s):  
Indian Ocean ◽  
Seasonal Variability ◽  
World Ocean ◽  
South Pacific ◽  
Western Boundary ◽  
Mean Flow ◽  
The North ◽  
The Indian Ocean ◽  
The Mean ◽  
Mean Circulation

Abstract As part of the World Ocean Circulation Experiment, 306 autonomous floats were deployed in the tropical and South Pacific Ocean and 228 were deployed in the Indian Ocean to observe the basinwide circulation near 900-m depth. Mean velocities, seasonal variability, and lateral eddy diffusivity from the resultant 2583 float-years of data are presented. Area averages, local function fits, and a novel application of objective mapping are used to estimate the mean circulation. Patterns of mean circulation resemble those at the surface in both basins. Well-developed subtropical gyres, twice as strong in the Indian Ocean as in the Pacific, feed western boundary currents. Tropical gyres are separated by eastward flow along the equator in both hemispheres of both basins, although the Indian subcontinent splits the north Indian tropical gyre. The Antarctic Circumpolar Current (ACC) and west wind drifts are prominent in both basins, generally tending slightly southward but deviating to the north behind the Del Cano, Kerguelen, and Campbell Plateaus and, of course, South America. Remarkably, the eastern boundaries of the southern subtropical gyres in all three basins apparently occur in the ocean interior, away from land. The Indian Ocean’s subtropical gyre, and perhaps part of the South Atlantic’s, reaches east to a retroflection just upstream of the Campbell Plateau south of New Zealand. Seasonal variability at 900 m is focused around the equator with weaker variability found near certain bathymetric features. There is a remarkable agreement between the observed seasonable variability and that predicted by the Jet Propulsion Laboratory (JPL)–Estimating the Circulation and Climate of the Ocean (ECCO) data-assimilating numerical model. Aside from seasonal effects, eddy variability is greatest along the equator, in tropical and subtropical western basins, and along the ACC. Integrals of velocity across regional passages (Tasman Sea, Mozambique Channel) provide useful reference for hydrographic analyses of transport. Across whole ocean basins, however, the uncertainty associated with the appropriate continuity relation for horizontal flow (e.g., geostrophy vs nondivergence) is comparable to the mean flow.

scholarly journals Two-term expansion of the ground state one-body density matrix of a mean-field Bose gas

2021 ◽  
Vol 60 (3) ◽  
Author(s):  
Phan Thành Nam ◽  
Marcin Napiórkowski
Keyword(s):  
Density Matrix ◽  
Ground State ◽  
Mean Field ◽  
Interaction Strength ◽  
Bose Gas ◽  
Body Density ◽  
The Mean ◽  
The One ◽  
Mean Field Regime ◽  
Number Of Particles

AbstractWe consider the homogeneous Bose gas on a unit torus in the mean-field regime when the interaction strength is proportional to the inverse of the particle number. In the limit when the number of particles becomes large, we derive a two-term expansion of the one-body density matrix of the ground state. The proof is based on a cubic correction to Bogoliubov’s approximation of the ground state energy and the ground state.

Analysis of Turbulence in the Tip Region of a Waterjet Pump Rotor

2010 ◽  
Author(s):  
Huixuan Wu ◽  
Rinaldo L. Miorini ◽  
Joseph Katz
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Multiple Scales ◽  
Tip Clearance ◽  
Mean Flow ◽  
Production Characteristic ◽  
Pump Rotor ◽  
The Mean ◽  
Turbulence Production ◽  
Waterjet Pump

A series of high resolution planar particle image velocimetry measurements performed in a waterjet pump rotor reveal the inner structure of the tip leakage vortex (TLV) which dominates the entire flow field in the tip region. Turbulence generated by interactions among the TLV, the shear layer that develops as the backward leakage flow emerges from the tip clearance as a “wall jet”, the passage flow, and the endwall is highly inhomogeneous and anisotropic. We examine this turbulence in both RANS and LES modelling contexts. Spatially non-uniform distributions of Reynolds stress components are explained in terms of the local mean strain field and associated turbulence production. Characteristic length scales are also inferred from spectral analysis. Spatial filtering of instantaneous data enables the calculation of subgrid scale (SGS) stresses, along with the SGS energy flux (dissipation). The data show that the SGS energy flux differs from the turbulence production rate both in trends and magnitude. The latter is dominated by energy flux from the mean flow to the large scale turbulence, which is resolved in LES, whereas the former is dominated by energy flux from the mean flow to the SGS turbulence. The SGS dissipation rate is also used for calculating the static and dynamic Smagorinsky coefficients, the latter involving filtering at multiple scales; both vary substantially in the tip region, and neither is equal to values obtained in isotropic turbulence.

scholarly journals The mean tilt of sunspot bipolar regions: theory, simulations and comparison with observations

2020 ◽  
Vol 495 (1) ◽  
pp. 238-248
Author(s):  
N Kleeorin ◽  
N Safiullin ◽  
K Kuzanyan ◽  
I Rogachevskii ◽  
A Tlatov ◽  
...  
Keyword(s):  
Coriolis Force ◽  
Large Scale ◽  
Mean Field ◽  
Wolf Number ◽  
Additional Contribution ◽  
Solar Cycles ◽  
Dynamo Theory ◽  
Large Scale Magnetic Field ◽  
Budget Equation ◽  
The Mean

ABSTRACT A theory of the mean tilt of sunspot bipolar regions (the angle between a line connecting the leading and following sunspots and the solar equator) is developed. A mechanism of formation of the mean tilt is related to the effect of the Coriolis force on meso-scale motions of super-granular convection and large-scale meridional circulation. The balance between the Coriolis force and the Lorentz force (the magnetic tension) determines an additional contribution caused by the large-scale magnetic field to the mean tilt of the sunspot bipolar regions at low latitudes. The latitudinal dependence of the solar differential rotation affects the mean tilt, which can explain deviations from Joy’s law for the sunspot bipolar regions at high latitudes. The theoretical results obtained and the results from numerical simulations based on the non-linear mean-field dynamo theory, which takes into account conservation of the total magnetic helicity and the budget equation for the evolution of the Wolf number density, are in agreement with observational data of the mean tilt of sunspot bipolar regions over individual solar cycles 15–24.

482Direct oral anticoagulant rivaroxaban in very old and frail patients: A one-year prospective follow-up of a large-scale cohort (SAFIR-AC)

2019 ◽  
Vol 40 (Supplement_1) ◽  
Author(s):  
O Hanon ◽  
J Vidal ◽  
E Chaussade ◽  
J P David ◽  
N Boulloche ◽  
...  
Keyword(s):  
Ischemic Stroke ◽  
Major Bleeding ◽  
Large Scale ◽  
Bleeding Risk ◽  
Geriatric Population ◽  
Very Old ◽  
The Mean ◽  
One Year ◽  
The One

Abstract Background/Introduction Age is one of the strongest predictors/risk factors for ischemic stroke in subjects with atrial fibrillation (AF). Direct oral anticoagulants (DOACs) have been shown to be effective in the prevention of this condition; however, clinical evidence on bleeding risk with this therapeutic strategy in very old and frail geriatric patients is poor. Purpose To assess bleeding risk in French geriatric patients aged ≥80 years and diagnosed with AF newly treated with rivaroxaban. Methods Subjects, presenting to one of 33 geriatric centers, with non-valvular AF and recent initiation of a treatment with rivaroxaban were enrolled in the study and followed-up every 3 months for 12 months. Clinical and routine laboratory data and evaluation scores, such as HAS-BLED, HEMORR2HAGES, ATRIA, and CHA2DS2-VASc, as well as comprehensive geriatric evaluation were reported. Major bleeding, as defined in ROCKET AF study, was reported at each visit, and this primary outcome was adjudicated by an independent committee. Results of this cohort were compared with findings from a similar cohort treated with vitamin K antagonists (VKAs) from the same centers (n=924). Results A total of 1045 subjects were enrolled in the study of whom 995 (95%) had a one-year follow-up (analyzed population). The mean (standard deviation (SD)) age was 86.0 (4.3) years, with the majority of patients being female (61%), 23% aged 90 years or older, and 48% having an estimated glomerular filtration rate (eGFR) <50 mL/min. The main comorbidities were hypertension in 77% of subjects, malnutrition 49%, anemia 43%, dementia 39%, heart failure 36%, and falls 27%. The mean (SD) score for CHA2DS2-VASc was 4.8 (1.4), HAS-BLED 2.4 (0.9), Mini-Mental State Examination (MMSE) 21.5 (6.9), Activities of Daily Living (ADL) 4.4 (1.9), and Charlson Comorbidity Index 6.7 (2.0). The one-year rate of major bleeding events was 6.4% of which 0.8% were fatal and 1.1% intracranial hemorrhages (ICH), whereas the one-year rate of ischemic stroke was 1.4% and all-cause mortality 17.9%. Computed with VKA cohort findings and adjusted for age, gender, eGFR and Charlson score, this would result in a hazard ratio of 0.54 (95% confidence interval [CI], 0.38 to 0.78) for major bleeding, 0.36 (0.17 to 0.76) for ICH, 0.62 (0.29 to 1.33) for ischemic stroke, and 0.82 (0.65 to 1.02) for all-cause mortality, in favor of rivaroxaban. Conclusions This is the first large-scale prospective study in geriatric population in AF subjects treated with DOAC (rivaroxaban) Major bleeding risk appeared higher in very old than younger population, however major bleeding and ICH rates were significantly lower with rivaroxaban than with VKAs when used in the same geriatric population. This study indicates that Rivaroxaban can be used in very old and frail patients for the treatment of non-valvular AF. Acknowledgement/Funding Unrestricted grant from Bayer

scholarly journals Effect of fluctuations on mean-field dynamos

2018 ◽  
Vol 84 (4) ◽  
Author(s):  
A. Alexakis ◽  
S. Fauve ◽  
C. Gissinger ◽  
F. Pétrélis
Keyword(s):  
Turbulent Flows ◽  
Mean Field ◽  
Liquid Sodium ◽  
Mean Flow ◽  
Dynamo Action ◽  
Scale Separation ◽  
Turbulent Fluctuations ◽  
The Mean ◽  
The One ◽  
The Magnetic Field

We discuss the effect of different types of fluctuations on dynamos generated in the limit of scale separation. We first recall that the magnetic field observed in the VKS (von Karman flow of liquid sodium) experiment is not the one that would be generated by the mean flow alone and that smaller scale turbulent fluctuations therefore play an important role. We then consider how velocity fluctuations affect the dynamo threshold in the framework of mean-field magnetohydrodynamics. We show that the detrimental effect of turbulent fluctuations observed with many flows disappears in the case of helical flows with scale separation. We also find that fluctuations of the electrical conductivity of the fluid, for instance related to temperature fluctuations in convective flows, provide an efficient mechanism for dynamo action. Finally, we conclude by describing an experimental configuration that could be used to test the validity of mean-field magnetohydrodynamics in strongly turbulent flows.

scholarly journals Characterizing the dynamo in a radiatively inefficient accretion flow

2020 ◽  
Vol 494 (4) ◽  
pp. 4854-4866 ◽  
Author(s):  
Prasun Dhang ◽  
Abhijit Bendre ◽  
Prateek Sharma ◽  
Kandaswamy Subramanian
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Mean Field ◽  
Compact Object ◽  
Rotational Instability ◽  
Test Field ◽  
Poloidal Magnetic Field ◽  
Accretion Flow ◽  
The Mean ◽  
Value Decomposition

ABSTRACT We explore the magneto-rotational instability (MRI)-driven dynamo in a radiatively inefficient accretion flow (RIAF) using the mean field dynamo paradigm. Using singular value decomposition (SVD) we obtain the least-squares fitting dynamo coefficients α and γ by comparing the time series of the turbulent electromotive force and the mean magnetic field. Our study is the first one to show the poloidal distribution of these dynamo coefficients in global accretion flow simulations. Surprisingly, we obtain a high value of the turbulent pumping coefficient γ, which transports the mean magnetic flux radially outwards. This would have implications for the launching of magnetized jets that are produced efficiently in presence a large-scale poloidal magnetic field close to the compact object. We present a scenario of a truncated disc beyond the RIAF where a large-scale dynamo-generated poloidal magnetic field can aid jet launching close to the black hole. Magnitude of all the calculated coefficients decreases with radius. Meridional variations of αϕϕ, responsible for toroidal to poloidal field conversion, is very similar to that found in shearing box simulations using the ‘test field’ (TF) method. By estimating the relative importance of α-effect and shear, we conclude that the MRI-driven large-scale dynamo, which operates at high latitudes beyond a disc scale height, is essentially of the α − Ω type.

scholarly journals Regional to Global Evolution of Impacts of Parameterized Mountain-Wave Drag in the Lower Stratosphere

2020 ◽  
Vol 33 (8) ◽  
pp. 3093-3106 ◽  
Author(s):  
Christopher G. Kruse
Keyword(s):  
General Circulation ◽  
Large Scale ◽  
Climate Model ◽  
Wave Drag ◽  
Mountain Wave ◽  
Global Features ◽  
Mountain Ranges ◽  
The North ◽  
Global Evolution ◽  
And Diffusion

AbstractMountain ranges are regional features on Earth, as are the regions of mountain-wave drag (MWD) exerted by dissipating atmospheric gravity waves generated by flow over them. However, these regional drags have significant global- or zonal-mean impacts on Earth’s atmospheric general circulation (e.g., slowing of the polar night jet). The objective of this work is to understand the regional to global evolution of these impacts. The approach is to track the evolution of MWD-generated potential vorticity (PV) over the winter using the Whole Atmosphere Community Climate Model (WACCM). Within an ensemble of winter-long runs with and without MWD, lower-stratospheric PV is generated over mountains and advected downstream, generating large-scale PV banners. These PV banners are diffused but survive this diffusion and are reinforced over downstream mountain ranges, accumulating into zonal-mean or global features within WACCM. A simple 2D model representing sources, advection, and diffusion of “passive PV” recreates the salient features in the WACCM results, suggesting the winter-long evolution of MWD-generated PV can be crudely understood in terms of horizontal advection and diffusion within a global vortex. In the Northern Hemisphere, cyclonic, equatorward PV banners accumulate zonally into a single zonally symmetric positive PV anomaly. The anticyclonic, poleward PV banners also accumulate into a zonally symmetric feature, but then diffuse over the North Pole into a negative PV polar cap. In the Southern Hemisphere, the same processes are at work, though the different geographic configuration of mountain ranges leads to different patterns of impacts.

scholarly journals An Explanation for the Sensitivity of the Mean State of the Community Atmosphere Model to Horizontal Resolution on Aquaplanets

2017 ◽  
Vol 30 (13) ◽  
pp. 4781-4797 ◽  
Author(s):  
Adam R. Herrington ◽  
Kevin A. Reed
Keyword(s):  
Moisture Transport ◽  
General Circulation ◽  
Large Scale ◽  
General Circulation Models ◽  
Horizontal Resolution ◽  
Hadley Cell ◽  
Community Atmosphere Model ◽  
The Mean ◽  
Atmosphere Model ◽  
Mean State

The sensitivity of the mean state of the Community Atmosphere Model to horizontal resolutions typical of present-day general circulation models is investigated in an aquaplanet configuration. Nonconvergence of the mean state is characterized by a progressive drying of the atmosphere and large reductions in cloud coverage with increasing resolution. Analyses of energy and moisture budgets indicate that these trends are balanced by variations in moisture transport by the resolved circulation, and a reduction in activity of the convection scheme. In contrast, the large-scale precipitation rate increases with resolution, which is approximately balanced by greater advection of dry static energy associated with more active resolved vertical motion in the ascent region of the Hadley cell. An explanation for the sensitivity of the mean state to horizontal resolution is proposed, based on linear Boussinesq theory. The authors hypothesize that an increase in horizontal resolution in the model leads to a reduction in horizontal scale of the diabatic forcing arising from the column physics, facilitating finescale flow and faster resolved convective updrafts within the dynamical core, and steering the coupled system toward a new mean state. This hypothesis attempts to explain the underlying mechanism driving the variations in moisture transport observed in the simulations.

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