scholarly journals Mathematical Modeling of Vortex Interaction Using a Three-Layer Quasigeostrophic Model. Part 2: Finite-Core-Vortex Approach and Oceanographic Application

Mathematics ◽  
2020 ◽  
Vol 8 (8) ◽  
pp. 1267
Author(s):  
Mikhail A. Sokolovskiy ◽  
Xavier J. Carton ◽  
Boris N. Filyushkin
Keyword(s):  
Large Scale ◽  
Lower Layer ◽  
Middle Layer ◽  
Vortex Interaction ◽  
Vortex Dipoles ◽  
The North ◽  
Surface Cyclone ◽  
Vertical Density ◽  
Quasigeostrophic Model ◽  
The Stability

The three-layer version of the contour dynamics/surgery method is used to study the interaction mechanisms of a large-scale surface vortex with a smaller vortex/vortices of the middle layer (prototypes of intrathermocline vortices in the ocean) belonging to the middle layer of a three-layer rotating fluid. The lower layer is assumed to be dynamically passive. The piecewise constant vertical density distribution approximates the average long-term profile for the North Atlantic, where intrathermocline eddies are observed most often at depths of 300–1600 m. Numerical experiments were carried out with different initial configurations of vortices, to evaluate several effects. Firstly, the stability of the vortex compound was evaluated. Most often, it remains compact, but when unstable, it can break as vertically coupled vortex dipoles (called hetons). Secondly, we studied the interaction between a vertically tilted cyclone and lenses. Then, the lenses first undergo anticlockwise rotation determined by the surface cyclone. The lenses can induce alignment or coupling with cyclonic vorticity above them. Only very weak lenses are destroyed by the shear stress exerted by the surface cyclone. Thirdly, under the influence of lens dipoles, the surface cyclone can be torn apart. In particular, the shedding of rapidly moving vortex pairs at the surface reflects the presence of lens dipoles below. More slowly moving small eddies can also be torn away from the main surface cyclone. In this case, they do not appear to be coupled with middle layer vortices. They are the result of large shear-induced deformation. Common and differing features of the vortex interaction, modeled in the framework of the theory of point and finite-core vortices, are noted.

scholarly journals Large-scale snow instability patterns in western Canada: first analysis of the CAA–InfoEx database 1991–2002

2004 ◽  
Vol 38 ◽  
pp. 15-20 ◽  
Author(s):  
Urs Gruber ◽  
Pascal Hägeli ◽  
David M. McClung ◽  
Evan Manners
Keyword(s):  
Rocky Mountains ◽  
Large Scale ◽  
Weather Data ◽  
Western Canada ◽  
Coast Mountains ◽  
Ski Resorts ◽  
The North ◽  
Columbia Mountains ◽  
Observation Area ◽  
The Stability

AbstractDaily weather measurements, snow stability assessments and recorded weak layers of 23 stations covering an observation area of approximately 40 000 km2 in western Canada were analyzed. The study area includes three major mountain ranges with different snow climates. All stations included assess the stability of the snow cover. However, the focus of the avalanche safety program of the different types of operation (heli-ski operation, ski resorts and parks) varies significantly. The three stations in the Coast Mountains show the highest snow stability, followed by the South Columbia Mountains and then the North Columbia and Rocky Mountains. The weather data were analyzed to try to explain some of these differences. Intensive snowfall at relatively high temperatures proved to be important for the higher snow stability over the season in the Coast Mountains. Theweak-layer data were used to complement the snow stability assessments. Most persistent weak layers were reported in the Columbia Mountains, followed by the three stations in the Coast Mountains and trailed by the Rocky Mountains. Although some weather observations indicate climatic reasons for the smaller number of weak layers in the Rocky Mountains, it cannot be excluded that these differences are also related to the different type of operations.

scholarly journals The Production and Dissipation of Compensated Thermohaline Variance by Mesoscale Stirring

2009 ◽  
Vol 39 (10) ◽  
pp. 2477-2501 ◽  
Author(s):  
K. Shafer Smith ◽  
Raffaele Ferrari
Keyword(s):  
Large Scale ◽  
Vertical Mixing ◽  
Small Scale ◽  
Vertical Diffusion ◽  
The North ◽  
Salinity Gradients ◽  
Scale Temperature ◽  
The Mean ◽  
Geostrophic Turbulence ◽  
Quasigeostrophic Model

Abstract Temperature–salinity profiles from the region studied in the North Atlantic Tracer Release Experiment (NATRE) show large isopycnal excursions at depths just below the thermocline. It is proposed here that these thermohaline filaments result from the mesoscale stirring of large-scale temperature and salinity gradients by geostrophic turbulence, resulting in a direct cascade of thermohaline variance to small scales. This hypothesis is investigated as follows: Measurements from NATRE are used to generate mean temperature, salinity, and shear profiles. The mean stratification and shear are used as the background state in a high-resolution horizontally homogeneous quasigeostrophic model. The mean state is baroclinically unstable, and the model produces a vigorous eddy field. Temperature and salinity are stirred laterally in each density layer by the geostrophic velocity and vertical advection is by the ageostrophic velocity. The simulated temperature–salinity diagram exhibits fluctuations at depths just below the thermocline of similar magnitude to those found in the NATRE data. It is shown that vertical diffusion is sufficient to absorb the laterally driven cascade of tracer variance through an amplification of filamentary slopes by small-scale shear. These results suggest that there is a strong coupling between vertical mixing and horizontal stirring in the ocean at scales below the deformation radius.

AMOC hysteresis in an eddy-permitting GCM and monitoring indicators

2020 ◽  
Author(s):  
Laura Jackson ◽  
Richard Wood
Keyword(s):  
North Atlantic ◽  
Large Scale ◽  
Mixed Layer Depth ◽  
Labrador Sea ◽  
Layer Depth ◽  
Weak State ◽  
The North ◽  
Vertical Density ◽  
The North Atlantic ◽  
Original Strength

<p>We conduct idealised experiments with HadGEM3-GC2, which is a pre-CMIP6 eddy-permitting GCM, to test for the presence of thresholds in the AMOC. We add fresh water to the North Atlantic for different rates and lengths of time, and then examine the AMOC recovery. In some cases the AMOC recovers to its original strength, however if the AMOC weakens sufficiently it does not recover and stays in a weak state for up to 300 years.</p><p>We test various indictors that have been proposed for monitoring the AMOC with this ensemble of experiments (and other scenarios). In particular we ask whether fingerprints can provide early warning or faster detection of weakening or recovery, or indications of crossing the threshold. We find metrics that perform best are the temperature metrics based on large scale differences, the large scale meridional density gradient, and the vertical density difference in the Labrador Sea. Mixed layer depth is also useful for indicating whether the AMOC recovers after weakening. </p>

scholarly journals Jovian Vortices and Jets

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 104 ◽  
Author(s):  
Glenn R. Flierl ◽  
Philip J. Morrison ◽  
Rohith Vilasur Swaminathan
Keyword(s):  
Lower Layer ◽  
Analytical Techniques ◽  
Computational Method ◽  
Layer Depth ◽  
Zonal Flows ◽  
Zonal Winds ◽  
Constant Potential ◽  
Quasigeostrophic Model ◽  
The Stability ◽  
Vorticity Anomaly

We explore the theory of isolated vortices in strongly sheared, deep zonal flows and the stability of these banded jets, as occur in Jupiter’s atmosphere This is done using the standard 2-layer quasigeostrophic model with the lower layer depth becoming infinite; however, this model differs from the usual layer model because the lower layer is not assumed to be motionless but has a steady configuration of alternating zonal flows. Steady state vortices are obtained by a simulated annealing computational method as generalized to fluid problems with constraints and also used in the used in the context of magnetohydrodynamics. Various cases of vortices with a constant potential vorticity anomaly atop zonal winds and the stability of the underlying winds are considered using a mix of computational and analytical techniques.

scholarly journals Origin and Route of Severe Dust Storms in West Asia (with Horizontal Visibility Less Than 1000 Meters)

2021 ◽  
Author(s):  
zainab Mohammadi ◽  
hassan lashkari
Keyword(s):  
Large Scale ◽  
Temporal Distribution ◽  
Middle Layer ◽  
Dust Storms ◽  
The West ◽  
Horizontal Visibility ◽  
Northwestern Saudi Arabia ◽  
The North ◽  
South Of Iraq ◽  
Annual Distribution

Abstract Storms are intensified atmospheric phenomena which are sometimes accompanied by heavy rainfall and sometimes by dust. Dust storms, especially storms with horizontal visibility of fewer than 1000 meters, have always been harmful and detrimental to human comfort and health. In recent decades, the worrisome phenomena of conflict, climate change, and droughts have increased the frequency of dust storms in West Asia. Identifying the source and route of dust storms is the first step in limiting the harm they inflict. To investigate this phenomenon, using the daily data of the Meteorological Organization of Iran, storms with horizontal visibility of less than 1000 meters in the southwestern region of Iran, as one of the destination areas of these storms, in a statistical period of 33 years (1987 to 2019) was extracted. First, the monthly, seasonal and annual distribution of dust storms in 13 synoptic stations in this area was investigated. Then, using the site https://www.ready.noaa.gov/HYSPLIT by backward method from the GDAS data system with a step of 0.5 degrees, the origin and path of the storms were identified. Finally, maps of each route were drawn in ArcGIS 10.6. The findings of this study revealed that the biggest number of dust storms occurred in the winter, in terms of temporal distribution (38% of storms). With 23% of storms, spring is in second position. In terms of monthly distribution, the month of January has the most storms, followed by February and December. Storms decrease in intensity as they move from the south to the north, and from the west to the east of the region. The central region of Iraq ranks first in terms of storm origin, accounting for 25% of all storms. If dust storms originating in western Iraq are added to this number, about 35% of storms in west Asia originate in western and central Iraq. Regarding the pattern of large-scale atmospheric circulation prevailing in the middle layer of the atmosphere in this region, most of these dust storms in the west-east direction, after passing through the center and south of Iraq, enter Iran. The study also shows that storms in Syria، Jordan or northwestern Saudi Arabia, are very thick. These storms cover the middle layer of the troposphere and then affect high stations such as Shahrekord and Yasuj with an altitude of more than 2000 meters.

scholarly journals Northern Hemisphere Rossby Wave Initiation Events on the Extratropical Jet—A Climatological Analysis

2018 ◽  
Vol 31 (2) ◽  
pp. 743-760 ◽  
Author(s):  
Matthias Röthlisberger ◽  
Olivia Martius ◽  
Heini Wernli
Keyword(s):  
Northern Hemisphere ◽  
Rossby Wave ◽  
North Pacific ◽  
Large Scale ◽  
Tropical Convection ◽  
The Arctic ◽  
Subtropical Anticyclone ◽  
The North ◽  
Surface Cyclone ◽  
Wave Forms

A climatology of Rossby wave initiation (RWI) events on the Northern Hemisphere midlatitude jet is compiled by applying an objective RWI identification algorithm to the ERA-Interim dataset. In winter, RWI events occur most frequently over the northwestern Pacific and less often over the North Atlantic. In summer, the total number of RWI events is lower than in winter and the North Pacific RWI region shifts toward the Tibetan Plateau. Composite analysis of the large-scale flow prior to, during, and after winter North Pacific RWI events shows an upstream wave train propagating across Asia on the Arctic waveguide prior to RWI. The composite wave forms on a relatively weak zonal jet streak, exhibits a baroclinic structure, and is strongly amplified by latent heat release in the warm conveyor belt of a deepening surface cyclone. Moreover, the wave forms in a region of large-scale upper-level deformation, upstream of a preexisting ridge. Further, active tropical convection affects the longitude where RWI occurs and thus acts as a geographical anchor for RWI. Individual RWI events are characterized by preferred combinations of these composite features: a strong surface cyclone tends to occur in concert with strong latent heating and a pronounced positive PV anomaly aloft. A second group of co-occurring features contains active tropical convection, a strengthened subtropical anticyclone, and the downstream ridge. These feature groups might be regarded as idealized archetypal RWI scenarios, although numerous intermediate events exist where features from both groups occur together.

scholarly journals PHYSICAL MODELING OF SCOUR AROUND TRIPOD FOUNDATION STRUCTURES FOR OFFSHORE WIND ENERGY CONVERTERS

2011 ◽  
Vol 1 (32) ◽  
pp. 67 ◽  
Author(s):  
Arne Stahlmann ◽  
Torsten Schlurmann
Keyword(s):  
Physical Modeling ◽  
Large Scale ◽  
Near Field ◽  
Wind Farms ◽  
Test Site ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
The North ◽  
Complex Foundation ◽  
The Stability

As a step to further develop the share of renewable energies, the first German offshore test site alpha ventus has been installed in the North Sea in 2009 in water depths of 30 m, where experience shall be gained and made available for future offshore wind farms. Regarding converter foundations in deep water, it is well known that in most cases scour phenomena occur around the structures. Due to the complexity of the tripod foundations, significant knowledge gaps in scour progression in general and especially in detail as well as its probable effects on the stability and durability are given. Therefore, investigations on scouring phenomena around complex foundation structures like the tripod are carried out within the research project. The investigation method consists of a unique combination of local scour monitoring as well as physical and numerical modeling, whereas the physical modeling part was carried by means of 1:40 laboratory tests and 1:12 large-scale physical model tests in wave flumes. The results show that scours around the tripod foundation do not only occur directly around the foundation piles, but also in the near-field of the structure. Compared to first in-situ measured scours in the test site, at least a good qualitative agreement of the modeled scour depths and evolutions could be shown.

scholarly journals A MATHEMATICAL MODEL FOR THE LARGE-SCALE TRANSPORT OF HEAT AND WATER IN THE TAUPO VOLCANIC ZONE OF NEW ZEALAND

2009 ◽  
Vol 50 (3) ◽  
pp. 343-354
Author(s):  
GRAHAM WEIR
Keyword(s):  
New Zealand ◽  
Large Scale ◽  
Lower Layer ◽  
Middle Layer ◽  
Taupo Volcanic Zone ◽  
Heat Output ◽  
Volcanic Zone ◽  
Spreading Model ◽  
Geothermal Fluids ◽  
Constant Rate

AbstractA three-layer compartmental model of the geological structure in the Taupo Volcanic Zone of New Zealand is developed, based on the assumptions of isostasy (constant geostatic pressure at 25 km depth) and a constant rate of volcanism. The upper layer consists of volcanic infill to a depth of about 2500 m, then a middle layer of greywacke-like material to a depth of about 15 km, and a lower layer of andesitic-like material to a depth of 25 km. Our model assumptions predict that the area of each layer increases at a constant rate; that there is a constant ratio between the rate of energy production from volcanic activity and geothermal convection; and that there is the possibility of an abrupt change from rhyolitic to basaltic volcanism, if the middle layer becomes sufficiently thin. Two models are considered: a rifting and a spreading model. Both models predict the lower layer has an andesitic-like density. The spreading model has difficulty matching heat output with observed extension rates. The rifting model predicts the observed extension rates, but requires very deep circulation of groundwater to be consistent with observed chemical and isotopic properties of geothermal fluids.

scholarly journals Lateral Coupling in Baroclinically Unstable Flows

2008 ◽  
Vol 38 (6) ◽  
pp. 1267-1277 ◽  
Author(s):  
Michael A. Spall ◽  
Joseph Pedlosky
Keyword(s):  
Growth Rate ◽  
Large Scale ◽  
Lower Layer ◽  
Maximum Amplitude ◽  
Lateral Coupling ◽  
Internal Deformation ◽  
Lateral Displacements ◽  
Quasigeostrophic Model ◽  
Mean State ◽  
The Way

Abstract A two-layer quasigeostrophic model in a channel is used to study the influence of lateral displacements of regions of different sign mean potential vorticity gradient (Πy) on the growth rate and structure of linearly unstable waves. The mean state is very idealized, with a region of positive Πy in the upper layer and a region of negative Πy in the lower layer; elsewhere Πy is zero. The growth rate and structure of the model’s unstable waves are quite sensitive to the amount of overlap between the two regions. For large amounts of overlap (more than several internal deformation radii), the channel modes described by Phillips’ model are recovered. The growth rate decreases abruptly as the amount of overlap decreases below the internal deformation radius. However, unstable modes are also found for cases in which the two nonzero Πy regions are separated far apart. In these cases, the wavenumber of the unstable waves decreases such that the aspect ratio of the wave remains O(1). The waves are characterized by a large-scale barotropic component that has maximum amplitude near one boundary but extends all the way across the channel to the opposite boundary. Near the boundaries, the wave is of mixed barotropic–baroclinic structure with cross-front scales on the order of the internal deformation radius. The perturbation heat flux is concentrated near the nonzero Πy regions, but the perturbation momentum flux extends all the way across the channel. The perturbation fluxes act to reduce the isopycnal slopes near the channel boundaries and to transmit zonal momentum from the region of Πy > 0 to the region on the opposite side of the channel where Πy < 0. These nonzero perturbation momentum fluxes are found even for a mean state that has no lateral shear in the velocity field.

scholarly journals The Interaction of Recirculation Gyres and a Deep Boundary Current

2018 ◽  
Vol 48 (3) ◽  
pp. 573-590 ◽  
Author(s):  
Isabela Astiz Le Bras ◽  
Steven R. Jayne ◽  
John M. Toole
Keyword(s):  
North Atlantic ◽  
Lower Layer ◽  
Western Boundary ◽  
Boundary Current ◽  
The North ◽  
Topographic Slope ◽  
Recirculation Gyres ◽  
Deep Current ◽  
Quasigeostrophic Model ◽  
Recirculation Gyre

AbstractMotivated by the proximity of the Northern Recirculation Gyre and the deep western boundary current in the North Atlantic, an idealized model is used to investigate how recirculation gyres and a deep flow along a topographic slope interact. In this two-layer quasigeostrophic model, an unstable jet imposed in the upper layer generates barotropic recirculation gyres. These are maintained by an eddy-mean balance of potential vorticity (PV) in steady state. The authors show that the topographic slope can constrain the northern recirculation gyre meridionally and that the gyre’s adjustment to the slope leads to increased eddy PV fluxes at the base of the slope. When a deep current is present along the topographic slope in the lower layer, these eddy PV fluxes stir the deep current and recirculation gyre waters. Increased proximity to the slope dampens the eddy growth rate within the unstable jet, altering the geometry of recirculation gyre forcing and leading to a decrease in overall eddy PV fluxes. These mechanisms may shape the circulation in the western North Atlantic, with potential feedbacks on the climate system.

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