scholarly journals Role of the Rossby Waves in the Broadening of an Eastward Jet

2012 ◽  
Vol 42 (3) ◽  
pp. 476-494 ◽  
Author(s):  
Genta Mizuta
Keyword(s):  
Potential Vorticity ◽  
Rossby Waves ◽  
Equation Model ◽  
Transient Region ◽  
Interior Flow ◽  
The Mean ◽  
The Difference ◽  
Vorticity Flux ◽  
The Waves

Abstract To investigate the effect of the Rossby waves on an eastward jet such as the Kuroshio or Gulf Stream Extensions, a series of numerical experiments is conducted using a primitive equation model. In these experiments, an inflow and an outflow imposed on the western and eastern boundaries drive an unstable narrow jet and a broad interior flow in the western and eastern regions of the model domain, respectively. The barotropic Rossby waves are radiated from the transient region between the two regions. The eddy potential vorticity flux by the waves tends to compensate for the difference in the mean potential vorticity along mean streamlines between both sides of the transient region. Instability of the jet is insufficient for this compensation and weakens the mean potential vorticity gradient too much. Moreover, as the potential vorticity of the outflow is increased, the Rossby waves are intensified in order to compensate for the increase in the difference in the mean potential vorticity. These features strongly suggest that the Rossby waves are substantial in matching a jet with an interior flow. The speed of the waves and properties of eddies in recirculations of the jet are consistent with a two-layer analytic model, which indicates that the Rossby waves are radiated from eddies in recirculations. These eddies as well as the Rossby waves increase in amplitude with the transport of the recirculation near the surface presumably because of mean advection. Therefore, the mean potential vorticity of the interior flow, the intensity of the Rossby waves, and the transport of the recirculation change consistently with one another.

Maintenance of continental boundary-layer shear through counter-gradient vorticity flux in a barotropic model

1994 ◽  
Vol 271 ◽  
pp. 55-85 ◽  
Author(s):  
Jean-Raymond Bidlot ◽  
Melvin E. Stern
Keyword(s):  
Potential Vorticity ◽  
Gulf Stream ◽  
Bottom Topography ◽  
Relative Vorticity ◽  
Boundary Currents ◽  
Vorticity Distribution ◽  
The Mean ◽  
Passive Tracers ◽  
Vorticity Flux ◽  
The Waves

The use of a classical eddy parametrization in the analysis of continental boundary currents leads to the diffusion of momentum and relative vorticity and fails to recognize that the relevant eddies are dominated by the conservation of potential vorticity, which in turn may produce an increase in the mean relative vorticity. To illustrate this effect, we examine a non-inflected barotropic shear flow destabilized by the cross-steam variation in the bottom topògraphy of a continental slope. The finiteamplitude evolution of the waves is analysed in a simple model with a step-like bottom topography and with a piecewise-uniform potential vorticity distribution. The increase in maximum mean vorticity is computed for various values of the Rossby number and the topographic elevation, and it is suggested that a similar effect, taking into account the isopycnal topography as well as the isobaths, could maintain the large inshore shear of the Gulf Stream. Cross-shelf transport of different water ‘types’ (i.e. potential vorticity and passive tracers) are also computed and suggested to be pertinent to the more realistic oceanic problem involving baroclinic effects. The numerical calculation employs the well-known method of contour dynamics, and the Green's function appropriate for the step-like topography is derived.

Seasonal trends in the stable isotopic composition of snow and meltwater runoff in a subarctic catchment at Okstindan, Norway

2004 ◽  
Vol 35 (2) ◽  
pp. 119-137 ◽  
Author(s):  
S.D. Gurney ◽  
D.S.L. Lawrence
Keyword(s):  
Isotopic Composition ◽  
Mean Value ◽  
Mean Values ◽  
Stable Isotopic Composition ◽  
Meltwater Runoff ◽  
Stable Isotopic ◽  
The Mean ◽  
The Difference ◽  
Δ18o And Δd

Seasonal variations in the stable isotopic composition of snow and meltwater were investigated in a sub-arctic, mountainous, but non-glacial, catchment at Okstindan in northern Norway based on analyses of δ18O and δD. Samples were collected during four field periods (August 1998; April 1999; June 1999 and August 1999) at three sites lying on an altitudinal transect (740–970 m a.s.l.). Snowpack data display an increase in the mean values of δ18O (increasing from a mean value of −13.51 to −11.49‰ between April and August), as well as a decrease in variability through the melt period. Comparison with a regional meteoric water line indicates that the slope of the δ18O–δD line for the snowpacks decreases over the same period, dropping from 7.49 to approximately 6.2.This change points to the role of evaporation in snowpack ablation and is confirmed by the vertical profile of deuterium excess. Snowpack seepage data, although limited, also suggest reduced values of δD, as might be associated with local evaporation during meltwater generation. In general, meltwaters were depleted in δ18O relative to the source snowpack at the peak of the melt (June), but later in the year (August) the difference between the two was not statistically significant. The diurnal pattern of isotopic composition indicates that the most depleted meltwaters coincide with the peak in temperature and, hence, meltwater production.

The role of the Pacific Decadal Oscillation and ocean-atmosphere interactions in driving United States heatwaves

2021 ◽  
Author(s):  
Sem Vijverberg ◽  
Dim Coumou
Keyword(s):  
Rossby Wave ◽  
Rossby Waves ◽  
Low Frequency ◽  
Causal Link ◽  
Causal Mechanism ◽  
Temperature Forecast ◽  
The Pacific ◽  
Ocean Atmosphere ◽  
The Waves

<p>Heatwaves can have devastating impact on society and reliable early warnings at several weeks lead time are needed. Heatwaves are often associated with quasi-stationary Rossby waves, which interact with sea surface temperature (SST). Previous studies showed that north-Pacific SST can provide long-lead predictability for eastern U.S. temperature, moderated by an atmospheric Rossby wave. The exact mechanisms, however, are not well understood. Here we analyze Rossby waves associated with heatwaves in western and eastern US. Causal inference analyses reveal that both waves are characterized by positive ocean-atmosphere feedbacks at synoptic timescales, amplifying the waves. However, this positive feedback on short timescales is not the causal mechanism that leads to a long-lead SST signal. Only the eastern US shows a long-lead causal link from SSTs to the Rossby wave. We show that the long-lead SST signal derives from low-frequency PDO variability, providing the source of eastern US temperature predictability. We use this improved physical understanding to identify more reliable long-lead predictions. When, at the onset of summer, the Pacific is in a pronounced PDO phase, the SST signal is expected to persist throughout summer. These summers are characterized by a stronger ocean-boundary forcing, thereby more than doubling the eastern US temperature forecast skill, providing a temporary window of enhanced predictability.</p>

scholarly journals Jets and Orography: Idealized Experiments with Tip Jets and Lighthill Blocking

2007 ◽  
Vol 64 (10) ◽  
pp. 3627-3639 ◽  
Author(s):  
P. B. Rhines
Keyword(s):  
Numerical Simulations ◽  
Shallow Water ◽  
Rossby Wave ◽  
Potential Vorticity ◽  
Rossby Waves ◽  
Zonal Flow ◽  
Flow Acceleration ◽  
Westerly Flow ◽  
The Mean ◽  
Strong Control

Abstract This paper describes qualitative features of the generation of jetlike concentrated circulations, wakes, and blocks by simple mountainlike orography, both from idealized laboratory experiments and shallow-water numerical simulations on a sphere. The experiments are unstratified with barotropic lee Rossby waves, and jets induced by mountain orography. A persistent pattern of lee jet formation and lee cyclogenesis owes its origins to arrested topographic Rossby waves above the mountain and potential vorticity (PV) advection through them. The wake jet occurs on the equatorward, eastern flank of the topography. A strong upstream blocking of the westerly flow occurs in a Lighthill mode of long Rossby wave propagation, which depends on βa2/U, the ratio of Rossby wave speed based on the scale of the mountain, to zonal advection speed, U (β is the meridional potential vorticity gradient, f is the Coriolis frequency, and a is the diameter of the mountain). Mountains wider (north–south) than the east–west length scale of stationary Rossby waves will tend to block the oncoming westerly flow. These blocks are essentially β plumes, which are illustrated by their linear Green function. For large βa2/U, upwind blocking is strong; the mountain wake can be unstable, filling the fluid with transient Rossby waves as in the numerical simulations of Polvani et al. For small values, βa2/U ≪ 1 classic lee Rossby waves with large wavelength compared to the mountain diameter are the dominant process. The mountain height, δh, relative to the mean fluid depth, H, affects these transitions as well. Simple lee Rossby waves occur only for such small heights, δh/h ≪ aβ/f, that the f/h contours are not greatly distorted by the mountain. Nongeostrophic dynamics are seen in inertial waves generated by geostrophic shear, and ducted by it, and also in a texture of finescale, inadvertent convection. Weakly damped circulations induced in a shallow-water numerical model on a sphere by a lone mountain in an initially simple westerly wind are also described. Here, with βa2/U ∼1, potential vorticity stirring and transient Rossby waves dominate, and drive zonal flow acceleration. Low-latitude critical layers, when present, exert strong control on the high-latitude waves, and with no restorative damping of the mean zonal flow, they migrate poleward toward the source of waves. While these experiments with homogeneous fluid are very simplified, the baroclinic atmosphere and ocean have many tall or equivalent barotropic eddy structures owing to the barotropization process of geostrophic turbulence.

scholarly journals The Role of Volume, Conductivity, Scatter Changes of Neutrophils and Monocytes in Diagnosis of Megaloblastic Anemia

2020 ◽  
Vol 7 (12) ◽  
pp. A563-569
Author(s):  
Deepa Sowkur Anandarama Adiga ◽  
Debarshi Saha ◽  
Karthick R G ◽  
Vishnu Priya M ◽  
Purnima S Rao ◽  
...  
Keyword(s):  
Vitamin B12 ◽  
Megaloblastic Anemia ◽  
Serum Vitamin ◽  
Volume Conductivity ◽  
Degree Of Certainty ◽  
Normochromic Anemia ◽  
The Mean ◽  
The Difference ◽  
And Control

Background: Megaloblastic anemias are macrocytic normochromic anemia with mean corpuscular volume (MCV) of 100 fl-140 fl and caused by deficiency of either cobalamin (vitamin B12) or folate. However, increased MCV is not specific for megaloblastic anemia, nor is Vitamin B12 assay by chemiluminescence. We undertook this study to evaluate the possible role of Volume, Conductivity and Scatter (VCS) of WBCs derived from standard hematology analyzer to indicate megaloblastic anemia. Methods: We performed a case control study comparing data of 60 patients with low serum vitamin B12 or folate levels with 60 healthy volunteers. Comparison of the volume, conductivity and scatter parameters for neutrophils and monocytes of cases and control were done. Result: The mean neutrophil volume of cases (158.37±18.13fl) was significantly higher (p= 0.0001) compared to controls (141.26±4.22fl). Similarly, mean monocyte volume of cases (183.34±16.90fl) was significantly (p=0.0001) higher compared to controls (166.55±8.66fl). The difference in the mean conductivity of both neutrophils and monocytes between cases and controls were insignificant (p=0.43). Conclusion: Our study suggests analysis of VCS parameters for neutrophils and monocytes was a simple and objective method that substantiates the existence of subclinical deficiency of vitamin B 12 and folate with fair degree of certainty.

Spreader grafts: functional or just aesthetical?

2015 ◽  
Vol 53 (4) ◽  
pp. 332-339
Author(s):  
R. Xavier ◽  
S. Azeredo-Lopes ◽  
A. Papoila
Keyword(s):  
Functional Improvement ◽  
Nasal Airway ◽  
Nasal Airflow ◽  
Functional Effect ◽  
Nasal Breathing ◽  
The Mean ◽  
The Difference ◽  
The Aesthetic ◽  
Peak Nasal Inspiratory Flow

Objective: Spreader grafts are commonly used in rhinoplasty to achieve an aesthetic improvement of the nose or a functional improvement of the nasal airway. Currently, the aesthetic role of spreader grafts is well established. The functional effect of these grafts, however, has been controversial due to the lack of studies clearly demonstrating an increase on nasal airflow assigned to spreader grafts. The purpose of this study is to evaluate the effect of spreader grafts on nasal breathing. Methods: Nasal breathing of 72 consecutive patients undergoing rhinoplasty was evaluated by measuring peak nasal inspiratory flow (PNIF) before surgery and six months after surgery. Results: The mean preoperative PNIF of the 72 patients included in this study was 79.44 l/min and the mean postoperative PNIF was 110.42 l/min (p < 0.001). In 37 patients of this study no spreader grafts were used. In this group of patients the mean PNIF values changed from 73.24 l/min before surgery to 99.46 l/min after surgery. In the group of 35 patients in whom spreader grafts were used the mean PNIF values changed from 86.00 l/min before surgery to 122.00 l/min after surgery. The increase in the mean PNIF value after rhinoplasty was slightly higher in the group of patients with spreader grafts than in the group of patients without spreader grafts. The difference in the postoperative increase of PNIF between these two groups of patients, however, is not statistically significant. Conclusions: This study suggests that patients undergoing rhinoplasty have a statistically significant improvement in nasal breathing after surgery. However, patients receiving spreader grafts in a non-randomized way do not have statistically significant greater benefit than those who do not.

scholarly journals A Dynamically Consistent Closure for Zonally Averaged Ocean Models

2011 ◽  
Vol 41 (11) ◽  
pp. 2242-2258 ◽  
Author(s):  
Nils Brüggemann ◽  
Carsten Eden ◽  
Dirk Olbers
Keyword(s):  
Boundary Layer ◽  
Pressure Difference ◽  
Meridional Flow ◽  
Equation Model ◽  
Western Boundary ◽  
Primitive Equation ◽  
Zonal Velocity ◽  
The Mean ◽  
The Difference ◽  
Averaged Models

Abstract Simple idealized layered models and primitive equation models show that the meridional gradient of the zonally averaged pressure has no direct relation with the meridional flow. This demonstrates a contradiction in an often-used parameterization in zonally averaged models. The failure of this parameterization reflects the inconsistency between the model of Stommel and Arons and the box model of Stommel, as previously pointed out by Straub. A new closure is proposed. The ocean is divided in two dynamically different regimes: a narrow western boundary layer and an interior ocean; zonally averaged quantities over these regions are considered. In the averaged equations three unknowns appear: the interior zonal pressure difference Δpi, the zonal pressure difference Δpb of the boundary layer, and the zonal velocity uδ at the interface between the two regions. Here Δpi is parameterized using a frictionless vorticity balance, Δpb by the difference of the mean pressure in the interior and western boundary, and uδ by the mean zonal velocity of the western boundary layer. Zonally resolved models, a layer model, and a primitive equation model validate the new parameterization by comparing with the respective zonally averaged counterparts. It turns out that the zonally averaged models reproduce well the buoyancy distribution and the meridional flow in the zonally resolved model versions with respect to the mean and time changes.

scholarly journals A Note on the Role of Mean Flows in Doppler-Shifted Frequencies

2013 ◽  
Vol 43 (2) ◽  
pp. 432-441 ◽  
Author(s):  
Theo Gerkema ◽  
Leo R. M. Maas ◽  
Hans van Haren
Keyword(s):  
Doppler Shift ◽  
Wave Dispersion ◽  
The Other ◽  
Mean Flow ◽  
Fixed Position ◽  
Doppler Shifts ◽  
The Mean ◽  
The Difference ◽  
The One

Abstract The purpose of this paper is to resolve a confusion that may arise from two quite distinct definitions of “Doppler shifts”: both are used in the oceanographic literature but they are sometimes conflated. One refers to the difference in frequencies measured by two observers, one at a fixed position and one moving with the mean flow—here referred to as “quasi-Doppler shifts.” The other definition is the one used in physics, where the frequency measured by an observer is compared to that of the source. In the latter sense, Doppler shifts occur only if the source and observer move with respect to each other; a steady mean flow alone cannot create a Doppler shift. This paper rehashes the classical theory to straighten out some misconceptions. It is also discussed how wave dispersion affects the classical relations and their application.

scholarly journals Alignment of Hurricane-like Vortices on f and β Planes

2009 ◽  
Vol 66 (6) ◽  
pp. 1779-1792 ◽  
Author(s):  
Robert W. Jones ◽  
Hugh E. Willoughby ◽  
Michael T. Montgomery
Keyword(s):  
Rossby Waves ◽  
Critical Radius ◽  
Swirling Flow ◽  
Baroclinic Instability ◽  
Necessary Condition ◽  
Initial Condition ◽  
The Mean ◽  
Nonlinear Solutions ◽  
The Waves ◽  
Pv Gradient

Abstract A nonlinear, two-layer, vortex-tracking semispectral model (i.e., Fourier transformed in azimuth only) is used to study the evolution of dry, but otherwise hurricane-like, initially tilted vortices in quiescent surroundings on f and β planes. The tilt projects onto vorticity asymmetries that are dynamically vortex Rossby waves. Since the swirling wind in the principal mean vortex used here decays exponentially outside the eyewall, it has an initial potential vorticity (PV) minimum. The resulting reversal of PV gradient meets the necessary condition for inflectional (i.e., barotropic or baroclinic) instability. Thus, the vortex may be inflectionally stable or unstable. On an f plane, the tilt precesses relatively slowly because the critical radius, where the phase speeds of the waves match the mean swirling flow, is far from the center. An alternative Gaussian-like PV monopole that has a monotonic outward decrease of PV is stable to inflectional instability. It has a smaller critical radius and rapid tilt precession. Generally, vortices with fast tilt precession are more stable, as are stronger vortices in higher latitudes. On a β plane, the interaction between the symmetric vortex and the planetary PV gradient induces β gyres that push the vortex poleward and westward. The interaction between the β gyres and the planetary PV gradient may either create a PV minimum or intensify a minimum inherited from the initial condition. Thus, the nonlinear β effect reduces the ability of the vortex to recover from initial tilt, relative to the same vortex on an f plane. This result contrasts with previous studies of barotropic vortices on f planes, where the linear and nonlinear solutions were nearly identical.

A two-equation model for contaminant dispersion in natural streams

1987 ◽  
Vol 178 ◽  
pp. 257-277 ◽  
Author(s):  
Ronald Smith
Keyword(s):  
Equation Model ◽  
Time Of Arrival ◽  
Contaminant Exposure ◽  
Dispersion Process ◽  
Contaminant Dispersion ◽  
Natural Streams ◽  
The Mean ◽  
Mean Time ◽  
Temporal Spread

A simple two-equation model is derived which has the properties that the total contaminant exposure, the mean time of arrival, the temporal spread, and the skewness, are asymptotically correct at large distances downstream of a discharge. The role of changes in the breadth of a river upon the dispersion process is investigated by a means of an illustrative example. This reveals cubic dependence upon the breadth, and hence the great importance of wide reaches of rivers as regards contaminant dispersion.

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