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1
Souza, A. J. "On the use of the Stokes number to explain frictional tidal dynamics and water column structure in shelf seas." Ocean Science 9, no. 2 (2013): 391–98. http://dx.doi.org/10.5194/os-9-391-2013.
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Abstract. In recent years coastal oceanographers have suggested using the "Strouhal" number or its inverse, the "Stokes" number, to describe the effect of bottom boundary layer turbulence on the vertical structure of both density and currents. These are defined as the ratios of the frictional depth (δ) to the water column depth (h) or vice versa. Although many researchers have mentioned that the effects of the earth's rotation should be important, they have tended to omit it. Rotation may have an important influence on tidal currents, as the frictional depth from a fully cyclonic to a fully anticyclonic tidal ellipse can vary by up to an order of magnitude at mid latitudes. The Stokes number might appear smaller for cyclonic current ellipses (larger for anticyclonic) than it is without rotation, resulting in frictional effects being underestimated (overestimated). Here, a way to calculate a Stokes number is proposed, in which the effect of the earth's rotation is taken into account. The standard Stokes and the rotational Stokes numbers are used as predictors for the position of the tidal mixing fronts in the Irish Sea. Results show that use of the rotational number improves the predictions of fronts in shallow cyclonic areas of the eastern Irish Sea. This suggests that the effect of rotation on the water column structure will be more important in shallow shelf seas and estuaries with strong rotational currents.
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Yu, Zifeng, Yuqing Wang, and Haiming Xu. "Observed Rainfall Asymmetry in Tropical Cyclones Making Landfall over China." Journal of Applied Meteorology and Climatology 54, no. 1 (2015): 117–36. http://dx.doi.org/10.1175/jamc-d-13-0359.1.
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AbstractIn this study, the rainfall asymmetries in tropical cyclones (TCs) that made landfall in the Hainan (HN), Guangdong (GD), Fujian (FJ), and Zhejiang (ZJ) provinces of mainland China and Taiwan (TW) from 2001 to 2009 were analyzed on the basis of TRMM satellite 3B42 rainfall estimates. The results reveal that in landfalling TCs, the wavenumber 1 rainfall asymmetry shows the downshear to downshear-left maximum in environmental vertical wind shear (VWS), which is consistent with previous studies for TCs over the open oceans. A cyclonic rotation from south China to east China in the location of the rainfall maximum has been identified. Before landfall, the location of the rainfall maximum rotated from southwest to southeast of the TC center for TCs making landfall in the regions from HN to GD, TW, FJ, and ZJ. After landfall, the rotation became from southwest to northeast of the TC center from south China to east China. It is shown that this cyclonic rotation in the location of the rainfall maximum is well correlated with a cyclonic rotation from south China to east China in the environmental VWS between 200 and 850 hPa, indicating that the rainfall asymmetry in TCs that made landfall over China is predominantly controlled by the large-scale VWS. The cyclonic rotation of VWS is found to be related to different interactions between the midlatitude westerlies and the landfalling TCs in different regions. The results also indicate that the axisymmetric (wavenumber 0) component of rainfall generally decreased rapidly after landfall in most studied regions.
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Lamballais, Eric. "Direct numerical simulation of a turbulent flow in a rotating channel with a sudden expansion." Journal of Fluid Mechanics 745 (March 17, 2014): 92–131. http://dx.doi.org/10.1017/jfm.2014.30.
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AbstractThe effects of spanwise rotation on the channel flow across a symmetric sudden expansion are investigated using direct numerical simulation. Four rotation regimes are considered with the same Reynolds number$\mathit{Re}=5000$and expansion ratio$\mathit{Er}=3/2$. Upstream from the expansion, inflow turbulent conditions are generated realistically for each rotation rate through a very simple and efficient technique of recycling without the need for any precursor calculation. As the rotation is increased, the flow becomes progressively asymmetric with stabilization (destabilization) effects on the cyclonic (anticyclonic) side, respectively. These rotation effects, already present in the upstream channel, lead further downstream to an increase (reduction) of the separation size behind the cyclonic (anticyclonic) step. In the cyclonic separation, the free-shear layer created behind the step corner leads to the formation of large-scale spanwise vortices that become increasingly two-dimensional as the rotation is increased. Conversely, in the anticyclonic region, the turbulent structures in the separated layer are more elongated in the streamwise direction and also more active in promoting reattachment. For the highest rotation rate, a secondary separation is observed further downstream in the anticyclonic region, leading to the establishment of an elongated recirculation bubble that deflects the main flow towards the cyclonic wall. The highest level of turbulent kinetic energy is obtained at high rotation near the cyclonic reattachment in a region where stabilization effects are expected. The phenomenological model of absolute vortex stretching is found to be useful in understanding how the rotation influences the dynamics in the various regions of the flow.
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BARRI, MUSTAFA, and HELGE I. ANDERSSON. "Turbulent flow over a backward-facing step. Part 1. Effects of anti-cyclonic system rotation." Journal of Fluid Mechanics 665 (December 6, 2010): 382–417. http://dx.doi.org/10.1017/s0022112010004696.
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The effects of rotation on turbulent flow with separation and reattachment are investigated by means of direct numerical simulations. The backward-facing step configuration is rotated about a spanwise axis such that the sudden expansion of the channel is on the pressure side. The upstream flow is a fully developed plane Poiseuille flow subjected to orthogonal-mode rotation, which subsequently detaches from the step corner and eventually reattaches further downstream. The size of the resulting separation bubble with recirculating flow diminishes monotonically with increasing rotation rates and the reattachment distance is reduced from about 7 to 3 step heights. This is ascribed to the augmentation of the cross-stream turbulence intensity in theanti-cyclonicshear layer formed between the bulk flow and the recirculating eddy due to the destabilizing influence of the Coriolis force. The spanwise-oriented vortex cells or roller eddies found in non-rotating shear layers were disrupted by the enhanced turbulence. The flow along the planar wall is subjected to an adverse pressure gradient induced by the sudden expansion. The stabilizing influence of the system rotation in thiscyclonicshear layer tends to damp the turbulence, the flow becomes susceptible to flow separation, and a substantial cyclonic recirculation bubble is observed at the highest rotation rates. The resulting meandering of the bulk flow is associated with interactions between the anti-cyclonic shear layer at the stepped side and the cyclonic shear flow along the planar surface. These give rise to enhanced turbulence levels at the cyclonic side in spite of the otherwise stabilizing influence of the Coriolis force. Exceptionally high velocity fluctuations in the spanwise direction are observed in the vicinity of flow reattachment behind the step and ascribed to longitudinal Taylor–Görtler-like roll cells which extend into the backflow region. These roll cells arise from a centrifugal instability mechanism associated with the convex streamline curvature in the reattachment zone.
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Bartello, Peter, Olivier Métais, and Marcel Lesieur. "Coherent structures in rotating three-dimensional turbulence." Journal of Fluid Mechanics 273 (August 25, 1994): 1–29. http://dx.doi.org/10.1017/s0022112094001837.
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Numerical simulations investigating the formation and stability of quasi-two-dimensional coherent vortices in rotating homogeneous three-dimensional flow are described. In a numerical study of shear flows Lesieur, Yanase & Métais (1991) found that cyclones (respectively anticyclones) with |ω2D| ∼ O(2Ω), where ω2D is the vorticity and Ω is the rotation rate, are stabilized (respectively destabilized) by the rotation. A study of triply periodic pseudo-spectral simulations (643) was undertaken in order to investigate the vorticity asymmetry in homogeneous turbulence. Specifically, we examine (i) the possible three-dimensionalization of initially two-dimensional vortices and (ii) the emergence of quasi-two-dimensional structures in initially-isotropic three-dimensional turbulence. Direct numerical simulations of the Navier—Stokes equations are compared with large-eddy simulations employing a subgridscale model based on the second-order velocity structure function evaluated at the grid separation and with simulations employing hyperviscosity.Isolated coherent two-dimensional vortices, obtained from a two-dimensional decay simulation, were superposed with a low-amplitude three-dimensional perturbation, and used to initialize the first set of simulations. With Ω = 0, a three-dimensionalization of all vortices was observed. This occurred first in the small scales in conjunction with the formation of longitudinal hairpin vortices with vorticity perpendicular to that of the initial quasi-two-dimensional flow. In agreement with centrifugal stability arguments, when 2Ω = [ω2D]rms a rapid destabilization of anticyclones was observed to occur, whereas the initial two-dimensional cyclonic vortices persisted throughout the simulation. At larger Ω, both cyclones and anticyclones remained two-dimensional, consistent with the Taylor—Proudman theorem. A second set of simulations starting from isotropic three-dimensional fields was initialized by allowing a random velocity field to evolve (Ω = 0) until maximum energy dissipation. When the simulations were continued with 2Ω = [ω · Ω]rms/Ω, the three-dimensional flow was observed to organize into two-dimensional cyclonic vortices. At larger Ω, two-dimensional anticyclones also emerged from the initially-isotropic flow. The consequences for a variety of industrial and geophysical applications are clear. For quasi-two-dimensional eddies whose characteristic circulation times are of the order ofder of Ω−1, rotation induces a complete disruption of anticyclonic vortices, while stabilizing cyclonic ones.
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Métais, Olivier, Carlos Flores, Shinichiro Yanase, James J. Riley, and Marcel Lesieur. "Rotating free-shear flows. Part 2. Numerical simulations." Journal of Fluid Mechanics 293 (June 25, 1995): 47–80. http://dx.doi.org/10.1017/s0022112095001637.
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The three-dimensional dynamics of the coherent vortices in periodic planar mixing layers and in wakes subjected to solid-body rotation of axis parallel to the basic vorticity are investigated through direct (DNS) and large-eddy simulations (LES). Initially, the flow is forced by a weak random perturbation superposed on the basic shear, the perturbation being either quasi-two-dimensional (forced transition) or three-dimensional (natural transition). For an initial Rossby number Ro(i), based on the vorticity at the inflexion point, of small modulus, the effect of rotation is to always make the flow more two-dimensional, whatever the sense of rotation (cyclonic or anticyclonic). This is in agreement with the Taylor–Proudman theorem. In this case, the longitudinal vortices found in forced transition without rotation are suppressed.It is shown that, in a cyclonic mixing layer, rotation inhibits the growth of three-dimensional perturbations, whatever the value of the Rossby number. This inhibition exists also in the anticyclonic case for |Ro(i)| ≤ 1. At moderate anticyclonic rotation rates (Ro(i) < −1), the flow is strongly destabilized. Maximum destabilization is achieved for |Ro(i) ≈ 2.5, in good agreement with the linear-stability analysis performed by Yanase et al. (1993). The layer is then composed of strong longitudinal alternate absolute vortex tubes which are stretched by the flow and slightly inclined with respect to the streamwise direction. The vorticity thus generated is larger than in the nonrotating case. The Kelvin–Helmholtz vortices have been suppressed. The background velocity profile exhibits a long range of nearly constant shear whose vorticity exactly compensates the solid-body rotation vorticity. This is in agreement with the phenomenological theory proposed by Lesieur, Yanase & Métais (1991). As expected, the stretching is more efficient in the LES than in the DNS.A rotating wake has one side cyclonic and the other anticyclonic. For |Ro(i)| ≤ 1, the effect of rotation is to make the wake more two-dimensional. At moderate rotation rates (|Ro(i)| > 1), the cyclonic side is composed of Kármán vortices without longitudinal hairpin vortices. Karman vortices have disappeared from the anticyclonic side, which behaves like the mixing layer, with intense longitudinal absolute hairpin vortices. Thus, a moderate rotation has produced a dramatic symmetry breaking in the wake topology. Maximum destabilization is still observed for |Ro(i)| ≈ 2.5, as in the linear theory.The paper also analyses the effect of rotation on the energy transfers between the mean flow and the two-dimensional and three-dimensional components of the field.
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Klotz, Bradley W., and Haiyan Jiang. "Examination of Surface Wind Asymmetries in Tropical Cyclones. Part I: General Structure and Wind Shear Impacts." Monthly Weather Review 145, no. 10 (2017): 3989–4009. http://dx.doi.org/10.1175/mwr-d-17-0019.1.
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Because surface wind speeds within tropical cyclones are important for operational and research interests, it is vital to understand surface wind structure in relation to various storm and environmental influences. In this study, global rain-corrected scatterometer winds are used to quantify and evaluate characteristics of tropical cyclone surface wind asymmetries using a modified version of a proven aircraft-based low-wavenumber analysis tool. The globally expanded surface wind dataset provides an avenue for a robust statistical analysis of the changes in structure due to tropical cyclone intensity, deep-layer vertical wind shear, and wind shear’s relationship with forward storm motion. A presentation of the quantified asymmetry indicates that wind shear has a significant influence on tropical storms at all radii but only for areas away from the radius of maximum wind in both nonmajor and major hurricanes. Evaluation of a shear’s directional relation to motion indicates that a cyclonic rotation of the surface wind field asymmetry from downshear left to upshear left occurs in conjunction with an anticyclonic rotation of the directional relationship (i.e., from shear direction to the left, same, right, or opposite of the motion direction). It was discovered that in tropical cyclones experiencing effects from wind shear, an increase in absolute angular momentum transport occurs downshear and often downshear right. The surface wind speed low-wavenumber maximum in turn forms downwind of this momentum transport.
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Souza, A. J. "On the use of the Strouhal/Stokes number to explain the dynamics and water column structure on shelf seas." Ocean Science Discussions 9, no. 6 (2012): 3723–38. http://dx.doi.org/10.5194/osd-9-3723-2012.
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Abstract. In recent years coastal oceanographers have suggested the use of the "Strouhal" number or it's inverse the "Stokes" number, which have been defined as the ratios of the frictional depth (δ) to the water column depth (h) or vice versa, to describe the effect of bottom boundary layer turbulence on the vertical structure of both density and currents. Although they have mention that the effects of rotation should be important, they have tended to omit it. This omission may be important when talking about tidal currents as the frictional depth from a fully cyclonic to a fully anticyclonic tidal ellipse can vary up to an order of magnitude in the mid latitudes; so that the stokes number might appear smaller (larger) than it is resulting in frictional effects being underestimated (overestimated). Here a way to calculate a Stokes number, in which the effect of the Earth's rotation is taken into account, is suggested. Then the standard Stokes and the rotational Stokes numbers are used as predictors for the position of the tidal mixing fronts in the Irish Sea. Results show that the rotational number improves prediction of the front in shallow cyclonic areas of the eastern Irish Sea. This suggest that the effect of rotation on the water column structure will be more important in shallow shelf seas and estuaries with strong rotational currents.
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Kaluza, Thorsten, Daniel Kunkel, and Peter Hoor. "Composite analysis of the tropopause inversion layer in extratropical baroclinic waves." Atmospheric Chemistry and Physics 19, no. 10 (2019): 6621–36. http://dx.doi.org/10.5194/acp-19-6621-2019.
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Abstract. The evolution of the tropopause inversion layer (TIL) during cyclogenesis in the North Atlantic storm track is investigated using operational meteorological analysis data (Integrated Forecast System from the European Centre for Medium-Range Weather Forecasts). For this a total of 130 cyclones have been analysed during the months August through October between 2010 and 2014 over the North Atlantic. Their paths of migration along with associated flow features in the upper troposphere and lower stratosphere (UTLS) have been tracked based on the mean sea level pressure field. Subsets of the 130 cyclones have been used for composite analysis using minimum sea level pressure to filter the cyclones based on their strength. The composite structure of the TIL strength distribution in connection with the overall UTLS flow strongly resembles the structure of the individual cyclones. Key results are that a strong dipole in TIL strength forms in regions of cyclonic wrap-up of UTLS air masses of different origin and isentropic potential vorticity. These air masses are associated with the cyclonic rotation of the underlying cyclones. The maximum values of enhanced static stability above the tropopause occur north and northeast of the cyclone centre, vertically aligned with outflow regions of strong updraft and cloud formation up to the tropopause, which are situated in anticyclonic flow patterns in the upper troposphere. These regions are co-located with a maximum of vertical shear of the horizontal wind. The strong wind shear within the TIL results in a local minimum of Richardson numbers, representing the possibility for turbulent instability and potential mixing (or air mass exchange) within regions of enhanced static stability in the lowermost stratosphere.
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Cresswell, George. "A CYCLONIC EDDY NORTH OF LOMBOK." Marine Research in Indonesia 29 (May 11, 2018): 13–17. http://dx.doi.org/10.14203/mri.v29i0.417.
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A satellite drifter that passed from south to north through Lombok Strait in early 1988 became trapped in a cyclonic eddy 100 km north of Lombok. The eddy, which was 130 km by 80 km, had a rotation period of 10 days.
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Zong, Huijun, and Liguang Wu. "Synoptic-Scale Influences on Tropical Cyclone Formation within the Western North Pacific Monsoon Trough." Monthly Weather Review 143, no. 9 (2015): 3421–33. http://dx.doi.org/10.1175/mwr-d-14-00321.1.
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Abstract Tropical cyclones (TCs) always develop from synoptic-scale disturbances. While early studies suggested that the presence of synoptic-scale disturbances may enhance large-scale conditions for TC formation, recent studies argued that TC-precursor disturbances can establish a rotation-dominant area, which can play a crucial role in organizing convective activity and converting convective heating to rotational energy for storm-scale intensification. To demonstrate the synoptic-scale influence of TC-precursor disturbances, 91 TC formation events within the monsoon trough over the western North Pacific during 2000–10 were examined by separating TC-precursor disturbances from the low-frequency background. The composite analysis shows that the synoptic disturbances indeed enhance the mid- and low-level relative vorticity and convergence, but contribute little to reducing vertical wind shear. The dynamic composite that is conducted with respect to disturbance centers indicates that TC-precursor disturbances within the monsoon trough establish a rotation-dominant region with a radius of less than 550 km. The cyclonic rotation increases with time 72 h prior to TC formation and nearly all air particles keep recirculating in the core area with a radius of about 220 km. Analysis of a specific case suggests that vorticity increase occurs through the merger of mesoscale convective systems in the rotation-dominant area. The enhancing rotation in the core area may efficiently convert diabatic heating to kinetic energy for TC formation. Thus, it is suggested that the important role of TC-precursor disturbances in TC formation is the establishment of a limited, rotation-dominant area.
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Zhang, Yu, Jintao Gu, Shengli Chen, Jianyu Hu, Jinyu Sheng, and Jiuxing Xing. "Sensitivity study of energy transfer between mesoscale eddies and wind-induced near-inertial oscillations." Ocean Science 21, no. 3 (2025): 1047–63. https://doi.org/10.5194/os-21-1047-2025.
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Abstract. Analyses of current observations and numerical simulations at two moorings in the northern South China Sea reveal the transfer of near-inertial energy between the background currents associated with mesoscale eddies and near-inertial currents (NICs). A series of numerical experiments are conducted to determine important parameters affecting the energy transfer between idealized mesoscale eddies and NICs generated by rotating winds. Speeds of NICs transferred by both cyclonic and anticyclonic mesoscale eddies increase linearly with the wind stress and eddy strength. The transferred NICs in anticyclonic eddies have current amplitudes about 6 times larger than in cyclonic eddies. The translation speed of the mesoscale eddy and the wind rotation frequency also affect the conversion of NICs. The energy transfer rate is elevated with the increase in the positive Okubo–Weiss parameter. A simple theoretical analysis is conducted to verify our findings based on numerical results. Analytical solutions confirm the evident asymmetry of the energy transfer between anticyclonic and cyclonic eddies and quantitatively demonstrate the relationship between the wind stress and the near-inertial energy transferred by mesoscale eddies.
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Coletti, F., and T. Arts. "Aerodynamic investigation of a rotating rib-roughened channel by time-resolved particle image velocimetry." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 225, no. 7 (2011): 975–84. http://dx.doi.org/10.1177/0957650911410624.
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Particle image velocimetry (PIV) is used to study the turbulent flow over the rib-roughened wall of a cooling channel model in rotation. The aspect ratio is 0.9, the blockage ratio is 0.1 and the rib pitch-to-height ratio is 10. The flow direction is outward, with a Reynolds number of 1.5 × 104 and a rotation number of 0.3 in both rotational directions. The PIV system rotates with the channel, allowing to directly measure the relative flow velocity with high spatial and temporal resolution. Coriolis forces affect the stability of the shear layers: cyclonic (anticyclonic) rotation inhibits (enhances) the turbulent motion, influencing velocity, vorticity, and turbulence intensity of the flow. The time-resolved measurements show the effect of rotation on the shear layer instability and on the consequent formation of spanwise vortices, as well as on the time trace of the reattachment point. Turbulent energy spectra suggest that all temporal scales are affected by rotation.
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Zhurbas, Victor, Germo Väli, and Natalia Kuzmina. "Rotation of floating particles in submesoscale cyclonic and anticyclonic eddies: a model study for the southeastern Baltic Sea." Ocean Science 15, no. 6 (2019): 1691–705. http://dx.doi.org/10.5194/os-15-1691-2019.
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Abstract. We hypothesized that the overwhelming dominance of cyclonic spirals on satellite images of the sea surface could be caused by some differences between the rotary characteristics of submesoscale cyclonic and anticyclonic eddies. This hypothesis was tested by means of numerical experiments with synthetic floating Lagrangian particles embedded offline in a regional circulation model of the southeastern Baltic Sea with very high horizontal resolution (0.125 nautical mile grid). The numerical experiments showed that the cyclonic spirals can be formed from both a horizontally uniform initial distribution of floating particles and from the initially lined-up particles during an advection time of the order of 1 d. Statistical processing of the trajectories of the synthetic floating particles allowed us to conclude that the submesoscale cyclonic eddies differ from the anticyclonic eddies in three ways favoring the formation of spirals in the tracer field: they can be characterized by (a) a considerably higher angular velocity, (b) a more pronounced differential rotation and (c) a negative helicity.
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Thompson, Richard L., Bryan T. Smith, Jeremy S. Grams, et al. "Tornado Damage Rating Probabilities Derived from WSR-88D Data." Weather and Forecasting 32, no. 4 (2017): 1509–28. http://dx.doi.org/10.1175/waf-d-17-0004.1.
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Abstract Previous work with observations from the NEXRAD (WSR-88D) network in the United States has shown that the probability of damage from a tornado, as represented by EF-scale ratings, increases as low-level rotational velocity increases. This work expands on previous studies by including reported tornadoes from 2014 to 2015, as well as a robust sample of nontornadic severe thunderstorms [≥1-in.- (2.54 cm) diameter hail, thunderstorm wind gusts ≥ 50 kt (25 m s−1), or reported wind damage] with low-level cyclonic rotation. The addition of the nontornadic sample allows the computation of tornado damage rating probabilities across a spectrum of organized severe thunderstorms represented by right-moving supercells and quasi-linear convective systems. Dual-polarization variables are used to ensure proper use of velocity data in the identification of tornadic and nontornadic cases. Tornado damage rating probabilities increase as low-level rotational velocity Vrot increases and circulation diameter decreases. The influence of height above radar level (or range from radar) is less obvious, with a muted tendency for tornado damage rating probabilities to increase as rotation (of the same Vrot magnitude) is observed closer to the ground. Consistent with previous work on gate-to-gate shear signatures such as the tornadic vortex signature, easily identifiable rotation poses a greater tornado risk compared to more nebulous areas of cyclonic azimuthal shear. Additionally, tornado probability distributions vary substantially (for similar sample sizes) when comparing the southeast United States, which has a high density of damage indicators, to the Great Plains, where damage indicators are more sparse.
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VOROBIEFF, PETER, and ROBERT E. ECKE. "Turbulent rotating convection: an experimental study." Journal of Fluid Mechanics 458 (May 10, 2002): 191–218. http://dx.doi.org/10.1017/s0022112002007814.
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We present experimental measurements of velocity and temperature fields in horizontal planes crossing a cylindrical Rayleigh–Bénard convection cell in steady rotation about its vertical axis. The range of dimensionless rotation rates Ω is from zero to 5×104 for a Rayleigh number R = 3.2×108. The corresponding range of convective Rossby numbers is ∞ > Ro > 0.06. The patterns of velocity and temperature and the flow statistics characterize three basic flow regimes. For Ro [Gt ] 1, the flow is dominated by vortex sheets (plumes) typical of turbulent convection without rotation. The flow patterns for Ro ∼ 1 are cyclone-dominated, with anticyclonic vortices rare. As the Rossby number continues to decrease, the number of anticyclonic vortex structures begins to grow but the vorticity PDF in the vicinity of the top boundary layer still shows skewness favouring cyclonic vorticity. Velocity-averaging near the top of the cell suggests the existence of a global circulation pattern for Ro [Gt ] 1.
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Shilo, Elad, Yosef Ashkenazy, Alon Rimmer, Shmuel Assouline, and Yitzhaq Mahrer. "Wind Spatial Variability and Topographic Wave Frequency." Journal of Physical Oceanography 38, no. 9 (2008): 2085–96. http://dx.doi.org/10.1175/2008jpo3886.1.
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Abstract The association of topographic waves with wind action has been documented in several natural lakes throughout the world. However, the influence of the wind’s spatial variability (wind stress curl) on the frequency of topographic waves has only been partially investigated. Here the role of wind stress curl on the frequency of topographic waves in an idealized elliptic paraboloid basin has been studied both analytically and numerically. It is shown that the analytical solution is the sum of an elliptic rotation determined by the wind stress curl and two counterrotating circulation cells, which propagate cyclonically after the wind ceases. Furthermore, it is shown that cyclonic elliptical rotation (associated with positive wind stress curl) increases the rotation frequency of the double-gyre pattern while anticyclonic elliptical rotation (associated with negative wind stress curl) decreases the oscillatory mode frequency. It is also shown that bottom friction has some effect on the structure of the double-gyre pattern but hardly affects the oscillatory frequency. Numerical solutions of the depth-integrated nonlinear shallow-water equations confirmed that the frequency of the topographic wave increases (decreases) when forcing the model with cyclonic (anticyclonic) wind curl.
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McKiver, William Joseph. "Influence of a Background Shear Flow on Cyclone–Anticyclone Asymmetry in Ageostrophic Balanced Flows." Fluids 9, no. 9 (2024): 208. http://dx.doi.org/10.3390/fluids9090208.
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In this paper, we study how cyclonic and anticyclonic vortices adapt their shape and orientation to a background shear flow in an effort to understand geophysical vortices. Here we use a balanced model that incorporates the effects of rotation and density stratification to model the case of an isolated vortex of uniform potential vorticity subjected to a background shear flow that mimics the effect of surrounding vortices. We find equilibrium states and analyze their linear stability to determine the vortex characteristics at the margin of stability. Differences are found between the cyclonic and anticyclonic equilibria depending on the background flow parameters. When there is only horizontal strain, the vertical aspect ratio of the vortex does not change, whereas increasing the imposed background strain rate causes a change in the horizontal cross section, with cyclones being more deformed than anticyclones for a given value of strain. Vertical shear not only causes changes in the vertical axis but also causes the vortex to tilt away from it upright position. Overall, anticyclonic equilibria tend to have a more circular horizontal cross section, a longer vertical axis, and a larger tilt angle with respect to cyclonic equilibria. The strongest asymmetry between the horizontal cross section of cyclonic and anticyclonic vortices occurs for low values of vertical shear, while the strongest asymmetry in the vertical axes and tilt angle occurs for large vertical shear. Finally, by expanding the vortex shape and orientation in terms of the strain rate, we derive simple formulas that provide insights into how the vortex equilibria depend on the background flow.
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Hart, John E. "Sidewall Instability and Eddy Generation in a Rotating Fluid Subject to Periodic Forcing." Applied Mechanics Reviews 47, no. 6S (1994): S118—S122. http://dx.doi.org/10.1115/1.3124385.
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Laboratory experiments concerned with the generation of waves and vortices by sidewall instability in a rotating cylinder containing a homogeneous liquid are described. Motions are driven by modulating the basic rotation rate Ω of the cylinder sinusoidally in time at amplitude δ and frequency γ. In addition, a rotating lid, revolving differentially at rate ω provides a steady bias to the motion. The basic state consists of an axisymmetric flow composed of solid body rotation, sloshing periodically in time, with a Stokes-Stewartson boundary layer at the cylinder’s vertical wall. This oscillatory boundary layer is subject to a number of quasi-geostrophic (depth independent) and ageostrophic (depth varying) instabilities. At low values of the rotation modulation δ, the dominant instabilities are ageostrophic small scale propagating-horizontal and stationary-spiral roll vortices that are imbedded in the vertical boundary layer adjacent to the wall, along with propagating vertically-oriented waves that are also trapped in the boundary layer. These instabilities are found only when ω > 0. As the modulation amplitude is increased from zero, columnar vortices form by barotropic instability of the Stokes-Stewartson layer, and for sufficiently supercritical conditions these eddies may penetrate deep into the interior. At low modulation frequency (long period forcing), the interaction of the instabilities with the fluctuating horizontal shear results in a predominance of anticyclonic vortices. On the other hand, at moderate to high frequency modulation dipoles are favored. The formation of both ageostrophic and columnar instabilities is enhanced when the gyre is biased by a cyclonic steady surface stress (ω > 0). Gyres with anticyclonic bias (tending to generate a cyclonic boundary layer) are more stable.
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Chaouat, Bruno. "Simulations of Channel Flows With Effects of Spanwise Rotation or Wall Injection Using a Reynolds Stress Model." Journal of Fluids Engineering 123, no. 1 (2000): 2–10. http://dx.doi.org/10.1115/1.1343109.
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Simulations of channel flows with effects of spanwise rotation and wall injection are performed using a Reynolds stress model. In this work, the turbulent model is extended for compressible flows and modified for rotation and permeable walls with fluid injection. Comparisons with direct numerical simulations or experimental data are discussed in detail for each simulation. For rotating channel flows, the second-order turbulence model yields an asymmetric mean velocity profile as well as turbulent stresses quite close to DNS data. Effects of spanwise rotation near the cyclonic and anticyclonic walls are well observed. For the channel flow with fluid injection through a porous wall, different flow developments from laminar to turbulent regime are reproduced. The Reynolds stress model predicts the mean velocity profiles, the transition process and the turbulent stresses in good agreement with the experimental data. Effects of turbulence in the injected fluid are also investigated.
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Evans, Clark, Morris L. Weisman, and Lance F. Bosart. "Development of an Intense, Warm-Core Mesoscale Vortex Associated with the 8 May 2009 “Super Derecho” Convective Event*." Journal of the Atmospheric Sciences 71, no. 3 (2014): 1218–40. http://dx.doi.org/10.1175/jas-d-13-0167.1.
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Abstract In this study, the dynamical processes contributing to warm-core meso-β-scale vortex formation associated with the 8 May 2009 “super derecho” are examined utilizing two complementary quasi-Lagrangian approaches—a circulation budget and backward trajectory analyses—applied to a fortuitous numerical simulation of the event. Warm-core meso-β-scale vortex formation occurs in a deeply moist, potentially stable environment that is conducive to the development of near-surface rotation and is somewhat atypical compared to known derecho-supporting environments. Air parcels in the vicinity of the developing vortex primarily originate near the surface in the streamwise vorticity-rich environment, associated with the vertical wind shear of the low-level jet, immediately to the east of the eastward-moving system. Cyclonic vertical vorticity is generated along inflowing air parcels primarily by the ascent-induced tilting of streamwise vorticity and amplified primarily by ascent-induced vortex tube stretching. Descent-induced tilting of crosswise vorticity contributes to cyclonic vertical vorticity generation for the small population of air parcels in the vicinity of the developing vortex that originate to its north and west. No consistent source of preexisting vertical vorticity is present within the environment. Cyclonic circulation on the scale of the warm-core meso-β-scale vortex increases in the lower troposphere in response to the mean vortex-scale convergence of cyclonic absolute vorticity and the local expulsion of eddy anticyclonic vertical vorticity generated within the system’s cold pool. Increased cyclonic circulation is partially offset by the system-scale tilting of horizontal vorticity associated with the low-level jet, rear-inflow jet, environmental vertical wind shear, and rotational flow of the warm-core vortex itself.
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Liu, Yuhan, Yongqiang Jiang, Chaohui Chen, et al. "Numerical Simulation of Tornado-like Vortices Induced by Small-Scale Cyclostrophic Wind Perturbations." Atmosphere 16, no. 1 (2025): 108. https://doi.org/10.3390/atmos16010108.
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This study introduces a tornado perturbation model utilizing the cyclostrophic wind model, implemented through a shallow-water equation framework. Four numerical experiments were conducted: a single cyclonic wind perturbation (EXP1), a single low-geopotential height perturbation (EXP2), a cyclonic wind perturbation with a 0 Coriolis parameter (EXP3), and a single anticyclonic wind perturbation (EXP4). The outputs showed that in a static atmosphere setting, a small-scale cyclonic wind perturbation generated a tornado-like pressure structure. The centrifugal force in the central area exceeded the pressure gradient force, causing air particles to flow outward, leading to a pressure drop and strong pressure gradient. The effect of the Coriolis force is negligible for meso-γ-scale and smaller systems, while for meso-β-scale and larger systems, it begins to have a significant impact. The results indicate that a robust cyclonic and an anticyclonic wind field can potentially generate a pair of cyclonic and anticyclonic tornadoes when the horizontal vortex tubes in an atmosphere with strong vertical wind shear tilt, forming a pair of positive and negative vorticities. These tornadoes are similar but have different rotation directions.
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Cai, Tao. "Large-scale Vortices in Rapidly Rotating Rayleigh–Bénard Convection at Small Prandtl number." Astrophysical Journal 923, no. 2 (2021): 138. http://dx.doi.org/10.3847/1538-4357/ac2c68.
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Abstract One prominent feature in the atmospheres of Jupiter and Saturn is the appearance of large-scale vortices (LSVs). However, the mechanism that sustains these LSVs remains unclear. One possible mechanism is that these LSVs are driven by rotating convection. Here, we present numerical simulation results on a rapidly rotating Rayleigh–Bénard convection at a small Prandtl number Pr = 0.1 (close to the turbulent Prandtl numbers of Jupiter and Saturn). We identified four flow regimes in our simulation: multiple small vortices, a coexisting large-scale cyclone and anticyclone, large-scale cyclone, and turbulence. The formation of LSVs requires that two conditions be satisfied: the vertical Reynolds number is large ( Re z ≥ 400 ), and the Rossby number is small (Ro ≤ 0.4). A large-scale cyclone first appears when Ro decreases to be smaller than 0.4. When Ro further decreases to be smaller than 0.1, a coexisting large-scale cyclone and anticyclone emerges. We have studied the heat transfer in rapidly rotating convection. The result reveals that the heat transfer is more efficient in the anticyclonic region than in the cyclonic region. Besides, we find that the 2D effect increases and the 3D effect decreases in transporting convective flux as the rotation rate increases. We find that aspect ratio has an effect on the critical Rossby number in the emergence of LSVs. Our results provide helpful insights into understanding the dynamics of LSVs in gas giants.
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Jaimes, Benjamin, Lynn K. Shay, and George R. Halliwell. "The Response of Quasigeostrophic Oceanic Vortices to Tropical Cyclone Forcing." Journal of Physical Oceanography 41, no. 10 (2011): 1965–85. http://dx.doi.org/10.1175/jpo-d-11-06.1.
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Abstract The response of quasigeostrophic (QG) oceanic vortices to tropical cyclone (TC) forcing is investigated using an isopycnic ocean model. Idealized oceanic currents and wind fields derived from observational data acquired during Hurricane Katrina are used to initialize this model. It is found that the upwelling response is a function of the curl of wind-driven acceleration of oceanic mixed layer (OML) currents rather than a function of the wind stress curl. Upwelling (downwelling) regimes prevail under the TC’s eye as it translates over cyclonic (anticyclonic) QG vortices. OML cooling of ~1°C occurs over anticyclones because of the combined effects of downwelling, instantaneous turbulent entrainment over the deep warm water column (weak stratification), and vertical dispersion of near-inertial energy. By contrast, OML cooling of ~4°C occurs over cyclones due to the combined effects of upwelling, instantaneous turbulent entrainment over regions of tight vertical thermal gradients (strong stratification), and trapping of near-inertial energy that enhances vertical shear and mixing at the OML base. The rotational rate of the QG vortex affects the dispersion of near-inertial waves. As rotation is increased in both cyclones and anticyclones, the near-inertial response is shifted toward more energetic frequencies that enhance vertical shear and mixing. TC-induced temperature anomalies in QG vortices propagate westward with time, deforming the cold wake. Therefore, to accurately simulate the impact of TC-induced OML cooling and feedback mechanisms on storm intensity, coupled ocean–atmosphere TC models must resolve geostrophic ocean eddy location as well as thermal, density, and velocity structures.
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Haller, G., A. Hadjighasem, M. Farazmand, and F. Huhn. "Defining coherent vortices objectively from the vorticity." Journal of Fluid Mechanics 795 (April 13, 2016): 136–73. http://dx.doi.org/10.1017/jfm.2016.151.
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Rotationally coherent Lagrangian vortices are formed by tubes of deforming fluid elements that complete equal bulk material rotation relative to the mean rotation of the deforming fluid volume. We show that the initial positions of such tubes coincide with tubular level surfaces of the Lagrangian-averaged vorticity deviation (LAVD), the trajectory integral of the normed difference of the vorticity from its spatial mean. The LAVD-based vortices are objective, i.e. remain unchanged under time-dependent rotations and translations of the coordinate frame. In the limit of vanishing Rossby numbers in geostrophic flows, cyclonic LAVD vortex centres are precisely the observed attractors for light particles. A similar result holds for heavy particles in anticyclonic LAVD vortices. We also establish a relationship between rotationally coherent Lagrangian vortices and their instantaneous Eulerian counterparts. The latter are formed by tubular surfaces of equal material rotation rate, objectively measured by the instantaneous vorticity deviation (IVD). We illustrate the use of the LAVD and the IVD to detect rotationally coherent Lagrangian and Eulerian vortices objectively in several two- and three-dimensional flows.
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Henderson, D. M., J. M. Lopez, and D. L. Stewart. "Vortex evolution in non-axisymmetric impulsive spin-up from rest." Journal of Fluid Mechanics 324 (October 10, 1996): 109–34. http://dx.doi.org/10.1017/s0022112096007859.
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The flow evolution of water in a completely filled rectangular container, impulsively rotated from rest to a steady angular speed, is investigated experimentally and numerically. The pathlines of the fluid from rest to solid-body rotation primarily follow one of two possible configurations that have been described previously in the literature. The first, consisting of two cyclones that form following the separation and roll-up of the sidewall boundary layers and an anticyclone that forms subsequently, results in a pattern on the path to spin-up of cyclonic–anticyclonic–cyclonic vorticity. In the second configuration the cyclones migrate into the interior of the container and merge, resulting in a pattern on the path to spin-up of anticyclonic–cyclonic–anticyclonic vorticity. The experiments provide a parameterization of the possible evolutionary configurations as a function of horizontal and vertical aspect ratios and Reynolds numbers. Critical Reynolds numbers for vortex merger are determined experimentally. Evolutionary configurations in addition to the primary two are observed; in particular symmetry breaking occurs at high Reynolds numbers causing complicated patterns of flow evolution. For some flow conditions at high Reynolds numbers, more than one evolutionary pattern is observed for the same external parameters. The experiments are conducted with a rigid lid showing that a free surface is not required for vortex merger. Numerical integrations of the two-dimensional Navier–Stokes equations (a situation corresponding to the limiting case of a container of infinite depth, where there are no effects from the top and bottom and all flow is horizontal) reproduce qualitatively many of the features of the experimental observations, in particular the merger events. The numerical results show that neither vertical flow due to Ekman boundary layers at the top and bottom nor a free surface are necessary for the observed vortex merger.
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Jolivet, S., F. Chane-Ming, D. Barbary, and F. Roux. "A numerical study of orographic forcing on TC Dina (2002) in South West Indian Ocean." Annales Geophysicae 31, no. 1 (2013): 107–25. http://dx.doi.org/10.5194/angeo-31-107-2013.
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Abstract. Using the French non-hydrostatic mesoscale numerical model Méso-NH, intense tropical cyclone (TC) Dina (2002) is simulated to investigate the forcing caused by the steep orography of Réunion island (20.8° S, 55.5° E) in the southwest Indian Ocean. The model initialised by a bogus vortex derived from Doppler radar observations reproduces quite well the dynamical characteristics of TC Dina approaching the island and provides some clues on the orographic influence on the structure and the evolution of the TC. The presence of the island is observed to stabilise the cyclonic circulation by damping the natural elliptical eyewall rotation and forcing the flow circulation. Initially, the cyclonic flow is blocked upwind of the orography which induces a convergence associated with upward vertical velocities, intense precipitation and maximum horizontal winds along the upwind slopes of the island. A mountain wave, generated over the highest terrains, is associated with downward motions on the lee side. When the strongest winds reach the island, the flow changes its behaviour from passing around to over the island. Non-dimensional flow parameters in agreement with recent theories are calculated to explain TC track.
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Markowski, Paul, Mario Majcen, Yvette Richardson, Jim Marquis, and Joshua Wurman. "Characteristics of the Wind Field in Three Nontornadic Low-Level Mesocyclones Observed by the Doppler On Wheels Radars." E-Journal of Severe Storms Meteorology 6, no. 3 (2021): 1–48. http://dx.doi.org/10.55599/ejssm.v6i3.30.
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The three-dimensional wind fields within three nontornadic supercell thunderstorms are retrieved from dual-Doppler radar observations obtained by a pair of Doppler on Wheels (DOW) radars. The observations focus on the low-level mesocyclone regions of the storms near the time of strongest low-level rotation. All three storms display strong low-level rotation (e.g., the vertical vorticity maxima exceed 0.05 s-1 in the lowest 1000 m AGL in each storm). A principal finding is that the nontornadic mesocyclones possess many of the same signatures found in tornadic supercells, even those viewed in similarly fine resolution; e.g., rear-flank gust fronts wrapping around the circulation centers, multiple cyclonic vertical vorticity maxima along the gust front that spiral inward toward the circulation center, and arching vortex lines joining the cyclonic vorticity maxima to regions of anticyclonic vertical vorticity on the opposite side of the hook echo. The nontornadic mesocyclones possess less circulation than most of the tornadic mesocyclones that have been observed by the DOW radars, particularly within 1 km of the axis of rotation. Another finding is that the trajectories of air parcels passing through the near-surface vertical vorticity maxima have relatively shallow upward vertical excursions, suggesting that these parcels do not enter the overlying midlevel updraft and mesocyclone.
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KUNNEN, R. P. J., B. J. GEURTS, and H. J. H. CLERCX. "Experimental and numerical investigation of turbulent convection in a rotating cylinder." Journal of Fluid Mechanics 642 (December 23, 2009): 445–76. http://dx.doi.org/10.1017/s002211200999190x.
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The effects of an axial rotation on the turbulent convective flow because of an adverse temperature gradient in a water-filled upright cylindrical vessel are investigated. Both direct numerical simulations and experiments applying stereoscopic particle image velocimetry are performed. The focus is on the gathering of turbulence statistics that describe the effects of rotation on turbulent Rayleigh–Bénard convection. Rotation is an important addition, which is relevant in many geophysical and astrophysical flow phenomena.A constant Rayleigh number (dimensionless strength of the destabilizing temperature gradient) Ra = 109 and Prandtl number (describing the diffusive fluid properties) σ = 6.4 are applied. The rotation rate, given by the convective Rossby number Ro (ratio of buoyancy and Coriolis force), takes values in the range 0.045 ≤ Ro ≤ ∞, i.e. between rotation-dominated flow and zero rotation. Generally, rotation attenuates the intensity of the turbulence and promotes the formation of slender vertical tube-like vortices rather than the global circulation cell observed without rotation. Above Ro ≈ 3 there is hardly any effect of the rotation on the flow. The root-mean-square (r.m.s.) values of vertical velocity and vertical vorticity show an increase when Ro is lowered below Ro ≈ 3, which may be an indication of the activation of the Ekman pumping mechanism in the boundary layers at the bottom and top plates. The r.m.s. fluctuations of horizontal and vertical velocity, in both experiment and simulation, decrease with decreasing Ro and show an approximate power-law behaviour of the shape Ro0.2 in the range 0.1 ≲ Ro ≲ 2. In the same Ro range the temperature r.m.s. fluctuations show an opposite trend, with an approximate negative power-law exponent Ro−0.32. In this Rossby number range the r.m.s. vorticity has hardly any dependence on Ro, apart from an increase close to the plates for Ro approaching 0.1. Below Ro ≈ 0.1 there is strong damping of turbulence by rotation, as the r.m.s. velocities and vorticities as well as the turbulent heat transfer are strongly diminished. The active Ekman boundary layers near the bottom and top plates cause a bias towards cyclonic vorticity in the flow, as is shown with probability density functions of vorticity. Rotation induces a correlation between vertical vorticity and vertical velocity close to the top and bottom plates: near the top plate downward velocity is correlated with positive/cyclonic vorticity and vice versa (close to the bottom plate upward velocity is correlated with positive vorticity), pointing to the vortical plumes. In contrast with the well-mixed mean isothermal bulk of non-rotating convection, rotation causes a mean bulk temperature gradient. The viscous boundary layers scale as the theoretical Ekman and Stewartson layers with rotation, while the thermal boundary layer is unaffected by rotation. Rotation enhances differences in local anisotropy, quantified using the invariants of the anisotropy tensor: under rotation there is strong turbulence anisotropy in the centre, while near the plates a near-isotropic state is found.
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LEBLANC, STÉPHANE, and CLAUDE CAMBON. "Effects of the Coriolis force on the stability of Stuart vortices." Journal of Fluid Mechanics 356 (February 10, 1998): 353–79. http://dx.doi.org/10.1017/s0022112097007982.
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A detailed investigation of the effects of the Coriolis force on the three-dimensional linear instabilities of Stuart vortices is proposed. This exact inviscid solution describes an array of co-rotating vortices embedded in a shear flow. When the axis of rotation is perpendicular to the plane of the basic flow, the stability analysis consists of an eigenvalue problem for non-parallel versions of the coupled Orr–Sommerfeld and Squire equations, which is solved numerically by a spectral method. The Coriolis force acts on instabilities as a ‘tuner’, when compared to the non-rotating case. A weak anticyclonic rotation is destabilizing: three-dimensional Floquet modes are promoted, and at large spanwise wavenumber their behaviour is predicted by a ‘pressureless’ analysis. This latter analysis, which has been extensively discussed for simple flows in a recent paper (Leblanc & Cambon 1997) is shown to be relevant to the present study. The basic mechanism of short-wave breakdown is a competition between instabilities generated by the elliptical cores of the vortices and by the hyperbolic stagnation points in the braids, in accordance with predictions from the ‘geometrical optics’ stability theory. On the other hand, cyclonic or stronger anticyclonic rotation kills three-dimensional instabilities by a cut-off in the spanwise wavenumber. Under rapid rotation, the Stuart vortices are stabilized, whereas inertial waves propagate.
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Xu, Shuai, Junlin Xie, Shuxia Mei, et al. "Numerical Simulation of Gas-Solid Two-Phase Heat Transfer in a Kaolin Cyclone Cooling System." Energies 16, no. 9 (2023): 3744. http://dx.doi.org/10.3390/en16093744.
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The kaolin suspension calcination technology is currently gaining attention as a new process of calcining kaolin. In this paper, the cooling system of the kaolin suspension calcination process designed by CBMI Construction Co., Ltd. is simulated using ANSYS Fluent software to analyze the velocity field and temperature field of the gas–solid two-phase flow using the Eulerian model. A compiled UDF (User-Defined Function) is used to simulate the transfer of mass and heat from the downcomer tube to the different elements. The gas, coming from the gas outlet of the cyclone, enters the next level twin-cylinder cyclone in a spiral state. The results show that the airflow in the cyclone consists of an external spiral flow from the top to the bottom and an internal spiral flow from the bottom to the top. During the downward movement of the airflow, the outer spiral flow is continuously transformed into an inner cyclonic flow. The part of the airflow that rotates close to the inner cylinder is likely to become a ‘short circuit flow’, which largely affects the separation efficiency and cooling effect of the cyclone. There is evident temperature deviation and flow deviation in the twin-cylinder cyclone, which is primarily due to the high cooling air volume and high rotation of air flow coming from the gas outlet of the previous level’s cyclone. The rotation of the air flow is the main cause of the bias temperature and bias flow phenomenon in the twin-cylinder cyclone.
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Arobone, Eric, and Sutanu Sarkar. "Evolution of a stratified rotating shear layer with horizontal shear. Part 2. Nonlinear evolution." Journal of Fluid Mechanics 732 (September 6, 2013): 373–400. http://dx.doi.org/10.1017/jfm.2013.383.
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AbstractDirect numerical simulation is used to investigate the nonlinear evolution of a horizontally oriented mixing layer with uniform stable stratification and coordinate system rotation about the vertical axis. The important dimensional parameters governing inviscid dynamics are maximum shear $S(t)$, buoyancy frequency $N$, angular velocity of rotation $\Omega $ and characteristic shear thickness $L(t)$. The effect of rotation rate, $\Omega $, on the development of fluctuations in the shear layer is systematically studied in a regime of strong stratification. An instability mechanism, qualitatively distinct from the inertial instability, is found to deform columnar vortex cores in vertical planes for a strongly stratified rotating mixing layer. This mechanism emerges when centreline absolute vertical vorticity, $\langle {\omega }_{3} \rangle (t)+ 2\Omega $, is nearly zero as predicted by the linear stability analysis in Part 1 (J. Fluid. Mech., vol. 703, 2012, pp. 29–48). When the initial rotation rate is moderately anticyclonic, strong destabilization and a cascade to small scales is observed, consistent with prior studies involving horizontally sheared flow in the presence of rotation. Examination of enstrophy budgets in cases which are initially inertially unstable reveal the importance of baroclinic torque in maintaining lateral enstrophy fluctuations substantially beyond the time when the flow becomes inertially stable. The cyclonic stratified cases show weak nonlinearity in vortex dynamics. At high Reynolds number, despite the strong stratification, the flow exhibits three-dimensional, nonlinear dynamics and significant vertical mixing except for cases where the rotation is stabilizing.
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Tritton, D. J. "Stabilization and destabilization of turbulent shear flow in a rotating fluid." Journal of Fluid Mechanics 241 (August 1992): 503–23. http://dx.doi.org/10.1017/s0022112092002131.
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We consider turbulent shear flows in a rotating fluid, with the rotation axis parallel or antiparallel to the mean flow vorticity. It is already known that rotation such that the shear becomes cyclonic is stabilizing (with reference to the non-rotating case), whereas the opposite rotation is destabilizing for low rotation rates and restabilizing for higher. The arguments leading to and quantifying these statement are heuristic. Their status and limitations require clarification. Also, it is useful to formulate them in ways that permit direct comparison of the underlying concepts with experimental data.An extension of a displaced particle analysis, given by Tritton & Davies (1981) indicates changes with the rotation rate of the orientation of the motion directly generated by the shear/Coriolis instability occurring in the destabilized range.The ‘simplified Reynolds stress equations scheme’, proposed by Johnston, Halleen & Lezius (1972), has been reformulated in terms of two angles, representing the orientation of the principal axes of the Reynolds stress tensor (αa) and the orientation of the Reynolds stress generating processes (αb), that are approximately equal according to the scheme. The scheme necessarily fails at large rotation rates because of internal inconsistency, additional to the fact that it is inapplicable to two-dimensional turbulence. However, it has a wide range of potential applicability, which may be tested with experimental data. αa and αb have been evaluated from numerical data for homogeneous shear flow (Bertoglio 1982) and laboratory data for a wake (Witt & Joubert 1985) and a free shear layer (Bidokhti & Tritton 1992). The trends with varying rotation rate are notably similar for the three cases. There is a significant range of near equality of αa and αb. An extension of the scheme, allowing for evolution of the flow, relates to the observation of energy transfer from the turbulence to the mean flow.
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Liu, F., S. Tang, and C. Chen. "Satellite observations of the small-scale cyclonic eddies in the western South China Sea." Biogeosciences 12, no. 2 (2015): 299–305. http://dx.doi.org/10.5194/bg-12-299-2015.
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Abstract. High-resolution ocean color observations offer an opportunity to investigate the oceanic small-scale processes. In this study, the Medium Resolution Imaging Spectrometer (MERIS) daily 300 m data were used to study small-scale processes in the western South China Sea. It is indicated that the cyclonic eddies with horizontal scales of 10 km are frequently observed during the upwelling season of each year over the 2004–2009 period. These small-scale eddies were generated in the vicinity of the southern front of the cold tongue, and then propagated eastward with a speed of approximately 12 cm s−1. This propagation speed was consistent with the velocity of the western boundary current. As a result, the small-scale eddies kept the high levels of phytoplankton rotating away from the coastal areas, resulting in the accumulation of phytoplankton in the interior of the eddies. The generation of the small-scale eddies may be associated with strengthening of the relative movement between the rotation speed of the anticyclonic mesoscale eddies and the offshore transport. With the increases of the normalized rotation speed of the anticyclonic mesoscale eddies relative to the offshore transport, the offshore current became a meander under the impacts of the anticyclonic mesoscale eddies. The meandered cold tongue and instability front may stimulate the generation of the small-scale eddies. Unidirectional uniform wind along the cold tongue may also contribute to the formation of the small-scale eddies.
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Liu, F., S. Tang, and C. Chen. "Satellite observations of the small-scale cyclonic eddies in the western South China Sea." Biogeosciences Discussions 11, no. 9 (2014): 13515–32. http://dx.doi.org/10.5194/bgd-11-13515-2014.
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Abstract. High-resolution ocean color observation offers an opportunity to investigate the oceanic small-scale processes. In this study, The Medium Resolution Imaging Spectrometer (MERIS) daily 300 m data are used to study small-scale processes in the western South China Sea. It is indicated that the cyclonic eddies with horizontal scales of the order of 10 km are frequently observed during upwelling season of each year over 2004–2009. These small-scale eddies are generated in the vicinity of the southern front of the cold tongue, and then propagate eastward with a speed of approximately 12 cm s−1. This propagation speed is consistent with the velocity of the western boundary current. As a result, the small-scale eddies keep rotating high levels of the phytoplankton away from the coastal areas, resulting in the accumulation of phytoplankton in the interior of the eddies. The generation of the small-scale eddies may be associated with strengthening of the relative movement between the rotation speed of the anticylconic mesoscale eddies and the offshore transport. With the increases of the normalized rotation speed of the anticyclonic mesoscale eddies relative to the offshore transport, the offshore current become meander under the impacts of the anticyclonic mesoscale eddies. The meandered cold tongue and instability front may stimulate the generation of the small-scale eddies. Unidirectional uniform wind along cold tongue may also contribute to the formation of the small-scale eddies.
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Zhao, Zhuangming, Yu Yan, Shibin Qi, Shuaishuai Liu, Zhonghan Chen, and Jing Yang. "Cyclonic and Anticyclonic Asymmetry of Reef and Atoll Wakes in the Xisha Archipelago." Atmosphere 13, no. 10 (2022): 1740. http://dx.doi.org/10.3390/atmos13101740.
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A high-resolution (∼500 m) numerical model was used to study the reef and atoll wakes in the Xisha Archipelago (XA) during 2009. Statistical analyses of simulation data indicated strong cyclonic dominance in the mixing layer (above ∼35 m) and weak anticyclonic dominance in the subsurface layer (35∼160 m) for both eddies and filaments in the XA. The intrinsic dynamical properties of the flow, such as the vertical stratification and velocity magnitude, and the terrain of reefs and atolls had a significant effect on the asymmetry. Without considering the existence of reefs and atolls, the “background cyclonic dominance” generated under local planetary rotation (f≈4.1×10−5 s−1) and vertical stratification (with mean Brunt–Väisälä frequency N = 0.02 s−1 at 75 m) was stronger for filaments than eddies in the upper layer from 0∼200 m, and the larger vorticity amplitude in the cyclonic filaments could greatly enhance the cyclonic wake eddies. Furthermore, inertial–centrifugal instability induced selective destabilization of anticyclonic wake eddies in different water layers. As the Rossby number (Ro) and core vorticity (Burger number, Bu) decreased (increased) with the water depth, a more stable state was achieved for the anticyclonic wake eddies in the deeper layer. The stratification and slipping reefs and atolls also led to vertical decoupled shedding, which intensified the asymmetry.
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MAHPEYKAR, Omid, LARKI Amir ASHTARI, and Mohammad Akbarinansab. "Automatic detection of eddies and influence of warm eddy on sound propagation in the Persian Gulf." Marine Reports 3, no. 1 (2024): 1–20. https://doi.org/10.5281/zenodo.12335495.
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Eddies are among the most complex phenomena in marine environments, with significant impacts on hydrodynamic parameters. Various intelligent algorithms are utilized to identify and analyze these eddies. In this study, a vector geometry algorithm based on the rotation of velocity vectors was employed to detect and extract eddies in the Persian Gulf. The algorithm utilizes horizontal velocity components from numerical modeling as inputs. Following eddy extraction, their characteristics were thoroughly examined. A total of 4308 cyclonic and 2860 anticyclonic eddies were identified at the surface, with 617 cyclonic and 329 anticyclonic eddies detected at a depth of 50 meters for daily data over one year. Additionally, an investigation into the impact of eddies on sound propagation revealed that warm eddies create areas of severe transmission loss at their centers, leading to divergence in sound rays.
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Castaño, D., M. C. Navarro, and H. Herrero. "Cyclonic and anticyclonic rotation in a cylinder cooled inhomogeneously on the top." Chaos: An Interdisciplinary Journal of Nonlinear Science 31, no. 9 (2021): 093108. http://dx.doi.org/10.1063/5.0061312.
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Williams, M. E., L. O. Amoudry, J. M. Brown, and C. E. L. Thompson. "Fine particle retention and deposition in regions of cyclonic tidal current rotation." Marine Geology 410 (April 2019): 122–34. http://dx.doi.org/10.1016/j.margeo.2019.01.006.
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Hettipathirana, Terrance D., and David E. Davey. "Analytical Performance in Flow Injection—Simultaneous Multielement—Inductively Coupled Plasma—Optical Emission Spectrometry Employing a Cyclonic Spray Chamber." Applied Spectroscopy 50, no. 8 (1996): 1015–22. http://dx.doi.org/10.1366/0003702963905286.
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Simultaneous multielement–inductively coupled plasma–optical emission spectrometry (ICP-OES) with flow injection (FI) and a small-volume cyclonic spray chamber is described. Analytical performance of FI-ICP-OES was studied with the use of a concentric nebulizer and the cyclonic spray chamber for carrier nebulization. A noise study using Fourier transformation analysis was also carried out to identify the factors that affect the analytical figures of merit of FI-ICP-OES. At a carrier flow rate of 1.0 mL/min, the major source of noise, between 0 and 15 Hz, was the peristaltic pump's roller rotation; this pump noise disappeared at a flow rate of 3.5 mL/min. A number of other discrete low-frequency noise sources were also observed at flow rates below 2.5 mL/min, with resultant degradation of precision and detection limit.
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Sokolovskiy, Mikhail A., Xavier J. Carton, and Boris N. Filyushkin. "Mathematical Modeling of Vortex Interaction Using a Three-Layer Quasigeostrophic Model. Part 2: Finite-Core-Vortex Approach and Oceanographic Application." Mathematics 8, no. 8 (2020): 1267. http://dx.doi.org/10.3390/math8081267.
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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.
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Novotryasov, V. V., V. B. Lobanov, and A. F. Sergeev. "THE FEATURES OF INERTIAL OSCILLATIONS IN THE CURRENT VELOCITIES IN THE PETER THE GREAT BAY CAUSED BY EXTREME ATMOSPHERIC FORCING (ON THE EXAMPLE OF TYPHOON LIONROCK)." DEDICATED TO THE 90TH ANNIVERSARY OF PROF. K.N. FEDOROV OCEAN PHYSICS 47, no. 3 (2019): 92–103. http://dx.doi.org/10.29006/1564-2291.jor-2019.47(3).8.
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We conducted a study of the inertial oscillations of the speed of currents in Peter the Great Bay, induced by typhoon Lionrock. The study is based on the measurements of the moored acoustic Doppler current profiler. Data analysis showed that under the action of the typhoon a field of currents with inertial oscillations (IO) of anomalous characteristics was formed in the bay. It is found that the spectral energy of the IO of currents with left and right rotation are of the same order while the major axis of the hodograph of the speed of these currents exceeds its small axis by an order of magnitude. A change of the inertial frequencies of the currents with cyclonic rotation, as well as the “red shift” of this frequency in the bottom and the “blue shift” in the surface layer of the inertial currents with anticyclonic rotation were found. Parametric IO interaction with anticyclonic rotation and the synoptic component of the currents with the same direction of rotation was detected. It has been suggested that the anomalous characteristics of inertial currents with two types of rotation are due to their interaction with the low-frequency component of the stream of Primorsky Current induced by the typhoon.
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Helfrich, Karl R. "Thermals with background rotation and stratification." Journal of Fluid Mechanics 259 (January 25, 1994): 265–80. http://dx.doi.org/10.1017/s0022112094000121.
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Scaling analysis and experiments are used to study the evolution of thermals in the presence of background rotation. When the ambient environment is homogeneous, the thermal rises and expands until it reaches a critical height where the Rossby number becomes ∼ 1. The thermal then stops expanding and rises in a column. Both the critical height and column radius scale with (F0f-2)1/4. F0 is the initial thermal buoyancy and f is the Coriolis frequency. The thermal vertical velocity is independent of f. When the background is stratified with buoyancy frequency N, the thermal rises to a neutral buoyancy level which scales with (F0N-2)1/4. For N/f [Lt ] 0.6 column formation occurs before the thermal reaches the neutral level. For N/f [Gt ] 0.6 the thermal reaches the neutral level before rotation is important. In both regimes, geostrophic adjustment eventually causes the formation of a baroclinic vortex consisting of an anticyclonic lens of thermal fluid at the neutral level and cyclonic circulation below. The lens has Nh/fl ∼ 1. The lens thickness 2h and the radius l obey relations of the form (F0N-2)1/4 (N/f)m. However, the exponents m are different in the two regimes. The relevance of these results to deep-ocean convection and hydrothermal venting is discussed.
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Mordvinov, Vladimir, Elena Devyatova, and Vladimir Tomozov. "Influence of the magnetic field and the mean flow configuration on spatial structure and growth rate of normal modes." Solar-Terrestrial Physics 9, no. 4 (2023): 123–35. http://dx.doi.org/10.12737/stp-94202315.
Full textAbstract:
The first part of the work presents the results of numerical experiments with the magnetohydrodynamic model of “shallow water” to assess the degree of influence of the magnetic field on the development of instabilities conditioned by a combination of inhomogeneities in the mean flow and the mean magnetic field. Normal mode calculations have confirmed the earlier obtained result on the different influence of weak and strong magnetic fields on the instability of differential rotation. Calculations have shown that a weak magnetic field stabilizes the development of instabilities, whereas a strong magnetic field, on the contrary, enhances the instability. Azimuthal inhomogeneities of differential rotation in all cases contribute to the development of instabilities. In the second part of the work, we examine the spatial structure of normal modes and make an attempt to interpret the torsional oscillations observed in the atmospheres of Earth and the Sun. Calculations have shown that regular axisymmetric disturbances can be caused by the formation of a cyclonic vortex above the pole, which is characteristic of Earth's atmosphere and, possibly, of the Sun's atmosphere. The least damped normal mode of a stable polar cyclone has a structure of torsional oscillations. Flow anomalies and the development of an anticyclonic eddy in winter at midlatitudes destroy torsional oscillations and lead to a rapid amplification of normal modes, which are more complex in structure.
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Mordvinov, Vladimir, Elena Devyatova, and Vladimir Tomozov. "Influence of the magnetic field and the mean flow configuration on spatial structure and growth rate of normal modes." Solnechno-Zemnaya Fizika 9, no. 4 (2023): 134–46. http://dx.doi.org/10.12737/szf-94202315.
Full textAbstract:
The first part of the work presents the results of numerical experiments with the magnetohydrodynamic model of “shallow water” to assess the degree of influence of the magnetic field on the development of instabilities conditioned by a combination of inhomogeneities in the mean flow and the mean magnetic field. Numerical simulation of normal modes has confirmed the earlier obtained result on the different influence of weak and strong magnetic fields on the instability of differential rotation. Calculations have shown that a weak magnetic field stabilizes the development of instabilities, whereas a strong magnetic field, on the contrary, enhances the instability. Azimuthal inhomogeneities of differential rotation in all cases contribute to the development of instabilities. In the second part of the work, we examine the spatial structure of normal modes and make an attempt to interpret the torsional oscillations observed in the atmospheres of Earth and the Sun. Calculations have shown that regular axisymmetric disturbances (torsional oscillations) can be caused by the formation of a cyclonic vortex above the pole, which is characteristic of Earth’s atmosphere and, possibly, of the Sun’s atmosphere. The least damped normal mode of a stable polar cyclone has a structure of torsional oscillations. Flow anomalies and the development of an anticyclonic eddy in winter at midlatitudes destroy torsional oscillations and lead to a rapid amplification of normal modes, which are more complex in structure.
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Brown, S. N., and H. K. Cheng. "The response of a stratified rapidly rotating flow to a pulsating topography." Journal of Fluid Mechanics 177 (April 1987): 359–79. http://dx.doi.org/10.1017/s0022112087000995.
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A theoretical study is made of the disturbance produced by an oscillating, shallow topographical feature in horizontal relative motion in a rapidly rotating, linearly stratified, unbounded fluid. For a sinusoidal surface oscillation, an explicit solution is obtained in terms of wavenumber spectra of the topography. The oscillating far-field behaviour is shown to consist of a large-scale, cyclonic component above the topography and a system of inertial waves behind the caustics, which spreads predominantly in the downstream direction. A significant property of the flow field is its dependence on a frequency threshold familiar from classical works on internal gravity waves in the absence of rotation, determined by the Brunt-Väisälä value. When the frequency is supercritical, a prominent circle of maximum disturbance appears in the far field, which provides the transition boundary between two distinct cyclonic structures and an upstream barrier to the propagating waves ahead of the obstacle. The circle has a radius depending on the relative magnitude of the pulsating frequency and the Brunt-Väisälä value, and is distinctly marked also by a phase jump in pressure and velocities. These features are substantiated by numerical examples of the full solution at a large but finite distance above the obstacle at supercritical frequencies. The circle of maximum disturbance signifies a preferential direction for energy propagation unaccounted for by group velocity. Its relation to the classical result of Görtler in the homogeneous case and that in the classical internal-gravity-wave theory are examined.
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Park, Junho, and Paul Billant. "Radiative instability of an anticyclonic vortex in a stratified rotating fluid." Journal of Fluid Mechanics 707 (July 27, 2012): 381–92. http://dx.doi.org/10.1017/jfm.2012.286.
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AbstractIn strongly stratified fluids, an axisymmetric vertical columnar vortex is unstable because of a spontaneous radiation of internal waves. The growth rate of this radiative instability is strongly reduced in the presence of a cyclonic background rotation $f/ 2$ and is smaller than the growth rate of the centrifugal instability for anticyclonic rotation, so it is generally expected to affect vortices in geophysical flows only if the Rossby number $Ro= 2\Omega / f$ is large (where $\Omega $ is the angular velocity of the vortex). However, we show here that an anticyclonic Rankine vortex with low Rossby number in the range $\ensuremath{-} 1\leq Ro\lt 0$, which is centrifugally stable, is unstable to the radiative instability when the azimuthal wavenumber $\vert m\vert $ is larger than 2. Its growth rate for $Ro= \ensuremath{-} 1$ is comparable to the values reported in non-rotating stratified fluids. In the case of continuous vortex profiles, this new radiative instability is shown to occur if the potential vorticity of the base flow has a sufficiently steep radial profile. The most unstable azimuthal wavenumber is inversely proportional to the steepness of the vorticity jump. The properties and mechanism of the instability are explained by asymptotic analyses for large wavenumbers.
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Yadav, Rakesh Kumar, Hao Cao, and Jeremy Bloxham. "A Global Simulation of the Dynamo, Zonal Jets, and Vortices on Saturn." Astrophysical Journal 940, no. 2 (2022): 185. http://dx.doi.org/10.3847/1538-4357/ac9d94.
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Abstract The fluid dynamics planet Saturn gives rise to alternating east–west jet streams, large cyclonic and anticyclonic vortices, and a dipole-dominant magnetic field that is highly axisymmetric about the planetary rotation axis. Modeling these features in a self-consistent manner is crucial for understanding the dynamics of Saturn’s interior and atmosphere. Here we report a turbulent high-resolution dynamo simulation in a spherical shell that produces these features simultaneously for the first time. A crucial model ingredient is a long-hypothesized stably stratified layer (SSL), sandwiched between a deep metallic hydrogen layer and an outer low-conductivity molecular layer, born out of the limited solubility of helium inside metallic hydrogen at certain depths. The model spontaneously produces polar cyclones and significant low-latitude and midlatitude jet stream activity in the molecular layer. The off-equatorial low-latitude jet streams partially penetrate into the SSL and interact with the magnetic field. This helps to axisymmetrize the magnetic field about the rotation axis and convert some of the poloidal magnetic field to a toroidal field, which appears as two global magnetic energy rings surrounding the deeper dynamo region. The simulation also mimics a distinctive dip in the fifth spherical harmonic in Saturn’s magnetic energy spectrum as inferred from the Cassini Grand Finale measurements. Our model highlights the role of an SSL in shaping the fluid dynamical and magnetic features of giant planets, as exemplified at Saturn.
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Sagyndykov, B. "A METHOD FOR INVESTIGATING A ONE-DIMENSIONAL CONSERVATIVE SYSTEM." Bulletin of Dulaty University 14, no. 2 (2024): 233–140. http://dx.doi.org/10.55956/obtk1024.
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The article examines the movements of systems with equal degrees of freedom in a potential, stationary external field using the laws of theoretical mechanics. In order to study the system, the following generalized form of the Lagrange function was used [1,2]: If the force F acting on a particle depends only on the x coordinate, the Lagrange function is transformed as follows [1,2]: где, , , . We have written down the Lagrange equation for plane mathematical, physical, and cyclonic pendulums as follows [3,4]: +mgl где, , +mg l The moment of inertia compared to the axis of rotation J, the distance to the center of mass with the axis of rotation l, for the case under consideration , J , . For any conservative system, the law of conservation is respected: The motion of a particle in one-dimensional space is investigated using the Lagrange function and the laws of conservation of energy.
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Reshetnyak, M., and P. Hejda. "Direct and inverse cascades in the geodynamo." Nonlinear Processes in Geophysics 15, no. 6 (2008): 873–80. http://dx.doi.org/10.5194/npg-15-873-2008.
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Abstract. The rapid rotation of planets causes cyclonic thermal turbulence in their cores which may generate the large-scale magnetic fields observed outside the planets. We investigate numerically a model based on the geodynamo equations in simplified geometry, which enables us to reproduce the main features of small-scale geostrophic flows in physical and wave vector spaces. We find fluxes of kinetic and magnetic energy as a function of the wave number and demonstrate the co-existence of forward and inverse cascades. We also explain the mechanism of magnetic field saturation at the end of the kinematic dynamo regime.