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1
Seo, Kyong-Hwan, and Seok-Woo Son. "The Global Atmospheric Circulation Response to Tropical Diabatic Heating Associated with the Madden–Julian Oscillation during Northern Winter." Journal of the Atmospheric Sciences 69, no. 1 (January 1, 2012): 79–96. http://dx.doi.org/10.1175/2011jas3686.1.
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Abstract The detailed dynamical mechanisms of the upper-tropospheric circulation response to the Madden–Julian oscillation (MJO) convection are examined by integrating a primitive equation model. A series of initial-value calculations with the climatological boreal winter background flow forced by the MJO-like thermal forcing successfully capture the key aspects of the observed circulation response to the MJO convection. This suggests that a large fraction of MJO-related circulation anomalies are direct responses to tropical heating in both the tropics and extratropics and can be largely explained by linear dynamics. It is found that MJO-like dipole heatings not only intensify tropical upper-tropospheric anomalies but also weaken them at certain regions because of the interaction between equatorial Kelvin and Rossby waves. The Rossby wave train primarily excited by horizontal divergence of upper-level perturbation flow propagates northeastward and then heads back to the equator. In this way, Rossby wave activity once generated over the subtropical Indian Ocean tends to enhance the equatorial upper-tropospheric anomalies over the tropical Atlantic and West Africa that have already been created by the zonally propagating equatorial Rossby and Kelvin waves. A ray path tracing reveals that a successive downstream development of Rossby wave train mostly results from the large-scale waves with zonal wavenumbers 2–3 in the Northern Hemisphere and 3–5 in the Southern Hemisphere. The sensitivity tests show that the overall results are quite robust. It is found, however, that the detailed circulation response to the MJO-like forcing is somewhat sensitive to the background flow. This suggests that MJO-related circulation anomalies may have nonnegligible long-term variability and change as background flow varies.
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Takaya, Koutarou, and Hisashi Nakamura. "Mechanisms of Intraseasonal Amplification of the Cold Siberian High." Journal of the Atmospheric Sciences 62, no. 12 (December 1, 2005): 4423–40. http://dx.doi.org/10.1175/jas3629.1.
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Abstract Mechanisms of intraseasonal amplification of the Siberian high are investigated on the basis of composite anomaly evolution for its strongest events at each of the grid points over Siberia. At each location, the amplification of the surface high is associated with formation of a blocking ridge in the upper troposphere. Over central and western Siberia, what may be called “wave-train (Atlantic-origin)” type is common, where a blocking ridge forms as a component of a quasi-stationary Rossby wave train propagating across the Eurasian continent. A cold air outbreak follows once anomalous surface cold air reaches the northeastern slope of the Tibetan Plateau. It is found through the potential vorticity (PV) inversion technique that interaction between the upper-level stationary Rossby wave train and preexisting surface cold anomalies is essential for the strong amplification of the surface high. Upper-level PV anomalies associated with the wave train reinforce the cold anticyclonic anomalies at the surface by inducing anomalous cold advection that counteracts the tendency of the thermal anomalies themselves to migrate eastward as surface thermal Rossby waves. The surface cold anomalies thus intensified, in turn, act to induce anomalous vorticity advection aloft that reinforces the blocking ridge and cyclonic anomalies downstream of it that constitute the propagating wave train. The baroclinic development of the anomalies through this vertical coupling is manifested as a significant upward flux of wave activity emanating from the surface cold anomalies, which may be interpreted as dissipative destabilization of the incoming external Rossby waves.
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Page, Michael A. "Separation and free-streamline flows in a rotating fluid at low Rossby number." Journal of Fluid Mechanics 179 (June 1987): 155–77. http://dx.doi.org/10.1017/s0022112087001472.
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The flow past a circular cylinder in a rotating frame is examined when the Rossby number Ro is O(E½), where E is the Ekman number. Previous studies of the configuration have shown that, provided the ratio Ro/E½ is less than a certain critical value, the flow around the cylinder is determined by the classical potential-flow solution. However, once Ro/E½ is greater than that critical value the E1/4 layer on the surface of the cylinder, which is rather like a boundary layer in a high-Reynolds-number non-rotating fluid, can separate from the cylinder and distort the potential flow. In this study the form of the flow once separation has occurred is examined using a method analogous to the Kirchhoff free-streamline theory in a non-rotating fluid. The results are compared with published experimental and numerical data on the flow for various values of Ro/E½.
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David, Trevor J., Ruth Angus, Jason L. Curtis, Jennifer L. van Saders, Isabel L. Colman, Gabriella Contardo, Yuxi Lu, and Joel C. Zinn. "Further Evidence of Modified Spin-down in Sun-like Stars: Pileups in the Temperature–Period Distribution." Astrophysical Journal 933, no. 1 (July 1, 2022): 114. http://dx.doi.org/10.3847/1538-4357/ac6dd3.
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Abstract We combine stellar surface rotation periods determined from NASA’s Kepler mission with spectroscopic temperatures to demonstrate the existence of pileups at the long-period and short-period edges of the temperature–period distribution for main-sequence stars with temperatures exceeding ∼5500 K. The long-period pileup is well described by a curve of constant Rossby number, with a critical value of Rocrit ≲ Ro⊙. The long-period pileup was predicted by van Saders et al. as a consequence of weakened magnetic braking, in which wind-driven angular momentum losses cease once stars reach a critical Rossby number. Stars in the long-period pileup are found to have a wide range of ages (∼2–6 Gyr), meaning that, along the pileup, rotation period is strongly predictive of a star’s surface temperature but weakly predictive of its age. The short-period pileup, which is also well described by a curve of constant Rossby number, is not a prediction of the weakened magnetic braking hypothesis but may instead be related to a phase of slowed surface spin-down due to core-envelope coupling. The same mechanism was proposed by Curtis et al. to explain the overlapping rotation sequences of low-mass members of differently aged open clusters. The relative dearth of stars with intermediate rotation periods between the short- and long-period pileups is also well described by a curve of constant Rossby number, which aligns with the period gap initially discovered by McQuillan et al. in M-type stars. These observations provide further support for the hypothesis that the period gap is due to stellar astrophysics, rather than a nonuniform star formation history in the Kepler field.
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Shaman, Jeffrey, and Eli Tziperman. "The Effect of ENSO on Tibetan Plateau Snow Depth: A Stationary Wave Teleconnection Mechanism and Implications for the South Asian Monsoons." Journal of Climate 18, no. 12 (June 15, 2005): 2067–79. http://dx.doi.org/10.1175/jcli3391.1.
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Abstract An atmospheric stationary wave teleconnection mechanism is proposed to explain how ENSO may affect the Tibetan Plateau snow depth and thereby the south Asian monsoons. Using statistical analysis, the short available record of satellite estimates of snow depth, and ray tracing, it is shown that wintertime ENSO conditions in the central Pacific may produce stationary barotropic Rossby waves in the troposphere with a northeastward group velocity. These waves reflect off the North American jet, turning equatorward, and enter the North African–Asian jet over the eastern Atlantic Ocean. Once there, the waves move with the jet across North Africa, South Asia, the Himalayas, and China. Anomalous increases in upper-tropospheric potential vorticity and increased wintertime snowfall over the Tibetan Plateau are speculated to be associated with these Rossby waves. The increased snowfall produces a larger Tibetan Plateau snowpack, which persists through the spring and summer, and weakens the intensity of the south Asian summer monsoons.
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Mittag, M., J. H. M. M. Schmitt, and K. P. Schröder. "Revisiting the connection between magnetic activity, rotation period, and convective turnover time for main-sequence stars." Astronomy & Astrophysics 618 (October 2018): A48. http://dx.doi.org/10.1051/0004-6361/201833498.
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The connection between stellar rotation, stellar activity, and convective turnover time is revisited with a focus on the sole contribution of magnetic activity to the Ca II H&K emission, the so-called excess flux, and its dimensionless indicator R+HK in relation to other stellar parameters and activity indicators. Our study is based on a sample of 169 main-sequence stars with directly measured Mount Wilson S-indices and rotation periods. The R+HK values are derived from the respective S-indices and related to the rotation periods in various B–V-colour intervals. First, we show that stars with vanishing magnetic activity, i.e. stars whose excess flux index R+HK approaches zero, have a well-defined, colour-dependent rotation period distribution; we also show that this rotation period distribution applies to large samples of cool stars for which rotation periods have recently become available. Second, we use empirical arguments to equate this rotation period distribution with the global convective turnover time, which is an approach that allows us to obtain clear relations between the magnetic activity related excess flux index R+HK, rotation periods, and Rossby numbers. Third, we show that the activity versus Rossby number relations are very similar in the different activity indicators. As a consequence of our study, we emphasize that our Rossby number based on the global convective turnover time approaches but does not exceed unity even for entirely inactive stars. Furthermore, the rotation-activity relations might be universal for different activity indicators once the proper scalings are used.
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Karami, K., P. Braesicke, M. Kunze, U. Langematz, M. Sinnhuber, and S. Versick. "Modelled thermal and dynamical responses of the middle atmosphere to EPP-induced ozone changes." Atmospheric Chemistry and Physics Discussions 15, no. 22 (November 25, 2015): 33283–329. http://dx.doi.org/10.5194/acpd-15-33283-2015.
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Abstract. Energetic particles including protons, electrons and heavier ions, enter the Earth's atmosphere over the polar regions of both hemispheres, where they can greatly disturb the chemical composition of the upper and middle atmosphere and contribute to ozone depletion in the stratosphere and mesosphere. The chemistry–climate general circulation model EMAC is used to investigate the impact of changed ozone concentration due to Energetic Particle Precipitation (EPP) on temperature and wind fields. The results of our simulations show that ozone perturbation is a starting point for a chain of processes resulting in temperature and circulation changes over a wide range of latitudes and altitudes. In both hemispheres, as winter progresses the temperature and wind anomalies move downward with time from the mesosphere/upper stratosphere to the lower stratosphere. In the Northern Hemisphere (NH), once anomalies of temperature and zonal wind reach the lower stratosphere, another signal develops in mesospheric heights and moves downward. Analyses of Eliassen and Palm (EP) flux divergence show that accelerating or decelerating of the stratospheric zonal flow is in harmony with positive and negative anomalies of the EP flux divergences, respectively. This results suggest that the oscillatory mode in the downwelling signal of temperature and zonal wind in our simulations are the consequence of interaction between the resolved waves in the model and the mean stratospheric flow. Therefore, any changes in the EP flux divergence lead to anomalies in the zonal mean zonal wind which in turn feed back on the propagation of Rossby waves from the troposphere to higher altitudes. The analyses of Rossby waves refractive index show that the EPP-induced ozone anomalies are capable of altering the propagation condition of the planetary-scale Rossby waves in both hemispheres. It is also found that while ozone depletion was confined to mesospheric and stratospheric heights, but it is capable to alter Rossby wave propagation down to tropospheric heights. In response to an accelerated polar vortex in the Southern Hemisphere (SH) late wintertime, we found almost two weeks delay in the occurrence of mean dates of Stratospheric Final Warming (SFW). These results suggest that the stratosphere is not merely a passive sink of wave activity from below, but it plays an active role in determining its own budget of wave activity.
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Nakamura, Noboru, Jonathan Falk, and Sandro W. Lubis. "Why Are Stratospheric Sudden Warmings Sudden (and Intermittent)?" Journal of the Atmospheric Sciences 77, no. 3 (February 25, 2020): 943–64. http://dx.doi.org/10.1175/jas-d-19-0249.1.
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Abstract This paper examines the role of wave–mean flow interaction in the onset and suddenness of stratospheric sudden warmings (SSWs). Evidence is presented that SSWs are, on average, a threshold behavior of finite-amplitude Rossby waves arising from the competition between an increasing wave activity A and a decreasing zonal-mean zonal wind u¯. The competition puts a limit to the wave activity flux that a stationary Rossby wave can transmit upward. A rapid, spontaneous vortex breakdown occurs once the upwelling wave activity flux reaches the limit, or equivalently, once u¯ drops below a certain fraction of uREF, a wave-free, reference-state wind inverted from the zonalized quasigeostrophic potential vorticity. This fraction is 0.5 in theory and about 0.3 in reanalyses. We propose r≡u¯/uREF as a local, instantaneous measure of the proximity to vortex breakdown (i.e., preconditioning). The ratio r generally stays above the threshold during strong-vortex winters until a pronounced final warming, whereas during weak-vortex winters it approaches the threshold early in the season, culminating in a precipitous drop in midwinter as SSWs form. The essence of the threshold behavior is captured by a semiempirical 1D model of SSWs, similar to the “traffic jam” model of Nakamura and Huang for atmospheric blocking. This model predicts salient features of SSWs including rapid vortex breakdown and downward migration of the wave activity/zonal wind anomalies, with analytical expressions for the respective time scales. The model’s response to a variety of transient wave forcing and damping is discussed.
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CENEDESE, C., and P. F. LINDEN. "Stability of a buoyancy-driven coastal current at the shelf break." Journal of Fluid Mechanics 452 (February 10, 2002): 97–121. http://dx.doi.org/10.1017/s0022112001006668.
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Buoyancy-driven surface currents were generated in the laboratory by releasing buoyant fluid from a source adjacent to a vertical boundary in a rotating container. Different bottom topographies that simulate both a continental slope and a continental ridge were introduced in the container. The topography modified the flow in comparison with the at bottom case where the current grew in width and depth until it became unstable once to non-axisymmetric disturbances. However, when topography was introduced a second instability of the buoyancy-driven current was observed. The most important parameter describing the flow is the ratio of continental shelf width W to the width L* of the current at the onset of the instability. The values of L* for the first instability, and L*−W for the second instability were not influenced by the topography and were 2–6 times the Rossby radius. Thus, the parameter describing the flow can be expressed as the ratio of the width of the continental shelf to the Rossby radius. When this ratio is larger than 2–6 the second instability was observed on the current front. A continental ridge allowed the disturbance to grow to larger amplitude with formation of eddies and fronts, while a gentle continental slope reduced the growth rate and amplitude of the most unstable mode, when compared to the continental ridge topography. When present, eddies did not separate from the main current, and remained near the shelf break. On the other hand, for the largest values of the Rossby radius the first instability was suppressed and the flow was observed to remain stable. A small but significant variation was found in the wavelength of the first instability, which was smaller for a current over topography than over a flat bottom.
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Parés-Sierra, A. "Remote and local forcing of Rossby wave variability in the midlatitude Pacific Ocean." Geofísica Internacional 30, no. 3 (July 1, 1991): 121–34. http://dx.doi.org/10.22201/igeof.00167169p.1991.30.3.598.
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Un modelo de gravedad reducida se utilizó para investigar la variabilidad de baja frecuencia en el Pacífico Nororiental. El dominio del modelo abarca desde los 18°N hasta los 50°N y desde 155°O hasta la costa oeste de Norteamérica. En un primer experimento, el modelo es forzado por el esfuerzo del viento (COADS). Un segundo experimento consiste en forzar el modelo a través de su frontera austral usando los resultados de un modelo ecuatorial de gravedad reducida. Encontrarnos que los espectros de número de onda-frecuencia calculados a partir de los resultados de nuestro modelo son congruentes con los calculados a partir de observaciones. La mayor parte de la energía de baja frecuencia en el interior del océano modelado consiste en ondas de Rossby propagándose hacia el oeste. El análisis de la respuesta del modelo a los dos forzamientos (forzamiento local por el viento y forzamiento remoto a través de la frontera) nos muestra que ambos mecanismos son capaces de generar el tipo de ondas que determina la variabilidad en el interior del océano. En los resultados del modelo forzado por el viento se observa la existencia de una latitud crítica alrededor de los 35° N. La respuesta del modelo al norte y sur de esta latitud es marcadamente diferente, principalmente en cuanto a las características de propagación de las ondas predominantes: se observa un fuerte componente de decaimiento al norte y de propagación al sur de dicha latitud.
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Müller, Gabriela V., Simone E. T. Ferraz, and Tércio Ambrizzi. "Propagacão das ondas de rossby nos invernos de máxima freqüência de ocorrência de geadas na pampa úmida." Revista Brasileira de Meteorologia 24, no. 1 (March 2009): 56–62. http://dx.doi.org/10.1590/s0102-77862009000100006.
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Neste trabalho estudou-se a influência dos padrões de onda extratropicais, que favorecem o desenvolvimento de eventos extremos frios no sudeste Sul-Americano, e em particular na região conhecida como Pampa Úmida. O aquecimento anômalo observado na região do oceano Pacífico tropical ocidental a nordeste da Austrália, durante os invernos de máxima freqüência de ocorrência de Geadas Generalizadas (GG) no centro-leste da Argentina, (região conhecida como Pampa Úmida - PU), atua como disparador de ondas de Rossby, as quais se propagam até o continente, favorecendo assim a ocorrência daqueles eventos. O padrão de propagação obtido nas simulações numéricas com um modelo baroclínico global, mostra o predomínio de um número de onda 3. Adicionalmente, foram analisadas as correlações do vento meridional em altos e baixos níveis observados para os eventos de GG, selecionados dentro dos invernos de máxima freqüência de ocorrência desses eventos. O vento meridional global em 250hPa apresenta regiões com correlação estatisticamente significativa com o vento meridional médio na PU. A configuração obtida no caso do vento meridional global em 250hPa, correlacionado com o vento meridional na PU, pode estar associada ao padrão de propagação das ondas simuladas numericamente a partir da forçante tropical. Igualmente importantes e significativos são os valores de correlação do vento sul nos baixos níveis, em particular para toda região da PU. O padrão de ondas simulado está bem representado pelas significativas correlações entre o vento meridional hemisférico em altos níveis e a temperatura no dia de evento de GG.
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Herrera Cervantes, Hugo, and Alejandro Parés Sierra. "Propagación de variaciones de baja frecuencia en la temperatura superficial del Pacífico nor-oriental." Geofísica Internacional 33, no. 3 (July 1, 1994): 469–86. http://dx.doi.org/10.22201/igeof.00167169p.1994.33.3.1184.
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Se estudia la propagación de señales de baja frecuencia en ocho años de datos (1982-1989) de Temperatura Superficial del Mar (TSM) en el noreste del Océano Pacífico. El análisis de las observaciones muestra que la variabilidad interanual de la TSM está asociada con la presencia de El Niño. Este se manifiesta como un frente paralelo a la costa así como una intrusión de agua más caliente que el promedio proveniente del océano interior. La primera eigenfunción (61%) está asociada con la presencia de El Niño en la costa en su fase madura y con su decaimiento en forma de señal que se propaga hacia el oeste en bajas latitudes. La segunda eigenfunción (29%) está asociada con la intrusión proveniente del océano interior, posiblemente inducida por advección de gran escala provocada por una intensificación de los vientos en el Pacífico central. Esta señal está desfasada en el tiempo aproximadamente año y medio con respecto al frente costero. La rapidez de propagación hacia el oeste de la señal detectada inicialmente en la costa, se estimó de 3.4 a 1.7 km/día en latitudes menores de 25°N. La posición de la fase teórica de una onda de Rossby se ajusta a los desplazamientos de la señal costera observada, identificando el posible mecanismo de esta propagación en la TSM. PALABRAS CLAVE: Variabilidad de baja frecuencia, ondas de Rossby, temperatura superficial.
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Wolfe, Christopher L., and Claudia Cenedese. "Laboratory Experiments on Eddy Generation by a Buoyant Coastal Current Flowing over Variable Bathymetry*." Journal of Physical Oceanography 36, no. 3 (March 1, 2006): 395–411. http://dx.doi.org/10.1175/jpo2857.1.
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Abstract Irminger rings are warm-core eddies formed off the west coast of Greenland. Recent studies suggest that these eddies, which are implicated in the rapid springtime restratification of the Labrador Sea, are formed by an internal instability of the West Greenland Current (WGC), triggered by bathymetric variations. This study seeks to explore the effect of the magnitude and downstream length scale of bathymetric variations on the stability of a simple model of the WGC in a series of laboratory experiments in which a buoyant coastal current was allowed to flow over bathymetry consisting of piecewise constant slopes of varying magnitude. The currents did not form eddies over gently sloping bathymetry and only formed eddies over steep bathymetry if the current width exceeded the width of the sloping bathymetry. Eddying currents were immediately stabilized if they flowed onto gently sloping topography. Bathymetric variations that persisted only a short distance downstream perturbed the flow locally but did not lead to eddy formation. Eddies formed only once the downstream length of the bathymetric variations exceeded a critical scale of about 8 Rossby radii. These results are consistent with the observed behavior of the WGC, which begins to form Irminger rings after entering a region where the continental slope abruptly steepens and becomes narrower than the WGC itself in a region spanning about 20–80 Rossby radii of downstream distance.
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Cai, Ming, and Bohua Huang. "A New Look at the Physics of Rossby Waves: A Mechanical–Coriolis Oscillation." Journal of the Atmospheric Sciences 70, no. 1 (January 1, 2013): 303–16. http://dx.doi.org/10.1175/jas-d-12-094.1.
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Abstract The presence of the latitudinal variation of the Coriolis parameter serves as a mechanical barrier that causes a mass convergence for the poleward geostrophic flow and divergence for the equatorward flow, just as a sloped bottom terrain does to a crossover flow. Part of the mass convergence causes pressure to rise along the uphill pathway, while the remaining part is detoured to cross isobars out of the pathway. This mechanically excited cross-isobar flow, being unbalanced geostrophically, is subject to a “half-cycle” Coriolis force that only turns it to the direction parallel to isobars without continuing to turn it farther back to its opposite direction because the geostrophic balance is reestablished once the flow becomes parallel to isobars. Such oscillation, involving a barrier-induced mass convergence, a mechanical deflection, and a half-cycle Coriolis deflection, is referred to as a mechanical–Coriolis oscillation with a “barrier-induced half-cycle Coriolis force” as its restoring force. Through a complete cycle of the mechanical–Coriolis oscillation, a new geostrophically balanced flow pattern emerges to the left of the existing flow when facing the uphill (downhill) direction of the barrier in the Northern (Southern) Hemisphere. The β barrier is always sloped toward the pole in both hemispheres, responsible for the westward propagation of Rossby waves. The β-induced mechanical–Coriolis oscillation frequency can be succinctly expressed as , where , and λ is the angle of a sloped surface along which the unbalanced flow crosses isobars, α is the angle of isobars with the barrier’s slope, and k is the wavenumber along the direction of the barrier’s contours.
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Yano, Jun-Ichi, and Glenn R. Flierl. "Jupiter's Great Red Spot: compactness condition and stability." Annales Geophysicae 12, no. 1 (January 31, 1994): 1–18. http://dx.doi.org/10.1007/s00585-994-0001-z.
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Abstract. Linear Rossby wave dispersion relationships suggest that Jupiter's Great Red Spot (GRS) is a baroclinic structure embedded in a barotropic shearing zonal flow. Quasi-geostrophic (QG) two-layer simulations support the theory, as long as an infinitely deep zonal flow is assumed. However, once a finite depth of the lower layer is assumed, a self-interaction of the baroclinic eddy component produces a barotropic radiating field, so that the GRS-like eddy can no longer remain compact. Compactness is recovered by explicitly introducing a deep dynamics of the interior for the lower layer, instead of the shallow QG formulation. An implication of the result is a strong coupling of the GRS to a convectively active interior.
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Chametla, Raúl O., Ondřej Chrenko, Wladimir Lyra, and Neal J. Turner. "On Wave Interference in Planet Migration: Dead Zone Torques Modified by Active Zone Forcing." Astrophysical Journal 951, no. 1 (July 1, 2023): 81. http://dx.doi.org/10.3847/1538-4357/acd1ee.
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Abstract We investigate planetary migration in the dead zone of a protoplanetary disk where there is a set of spiral waves propagating inward due to the turbulence in the active zone and the Rossby wave instability, which occurs at the transition between the dead and active zones. We perform global 3D unstratified magnetohydrodynamical simulations of a gaseous disk with the FARGO3D code, using weak gradients in the static resistivity profiles that trigger the formation of a vortex at the outer edge of the dead zone. We find that once the Rossby vortex develops, spiral waves in the dead zone emerge and interact with embedded, migrating planets by wave interference, which notably changes their migration. The inward migration becomes faster depending on the mass of the planet, due mostly to the constructive (destructive) interference between the outer (inner) spiral arm of the planet and the destruction of the dynamics of the horseshoe region by means of the set of background spiral waves propagating inward. The constructive wave interference produces a more negative Lindblad differential torque, which inevitably leads to an inward migration. Lastly, for massive planets embedded in the dead zone, we find that the spiral waves can create an asymmetric, wider, and deeper gap than in the case of α-disks and can prevent the formation of vortices at the outer edge of the gap. The latter could generate a faster or slower migration compared to the standard type-II migration.
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Masunaga, Hirohiko. "Seasonality and Regionality of the Madden–Julian Oscillation, Kelvin Wave, and Equatorial Rossby Wave." Journal of the Atmospheric Sciences 64, no. 12 (December 1, 2007): 4400–4416. http://dx.doi.org/10.1175/2007jas2179.1.
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Abstract The Madden–Julian oscillation (MJO), Kelvin wave, and equatorial Rossby (ER) wave—collectively called intraseasonal oscillations (ISOs)—are investigated using a 25-yr record of outgoing longwave radiation (OLR) measurements as well as the associated dynamical fields. The ISO modes are detected by applying bandpass filters to the OLR data in the frequency–wavenumber space. An automated wave-tracking algorithm is applied to each ISO mode so that convection centers accompanied with the ISOs are traced in space and time in an objective fashion. The identified paths of the individual ISO modes are first examined and found strongly modulated regionally and seasonally. The dynamical structure is composited with respect to the convection centers of each ISO mode. A baroclinic mode of the combined Rossby and Kelvin structure is prominent for the MJO, consistent with existing work. The Kelvin wave exhibits a low-level wind field resembling the shallow-water solution, while a slight lead of low-level convergence over convection suggests the impact of frictional boundary layer convergence on Kelvin wave dynamics. A lagged composite analysis reveals that the MJO is accompanied with a Kelvin wave approaching from the west preceding the MJO convective maximum in austral summer. MJO activity then peaks as the Kelvin and ER waves constructively interfere to enhance off-equatorial boundary layer convergence. The MJO leaves a Kelvin wave emanating to the east once the peak phase is passed. The approaching Kelvin wave prior to the development of MJO convection is absent in boreal summer and fall. The composite ER wave, loosely concentrated around the MJO, is nearly stationary throughout. A possible scenario to physically translate the observed result is also discussed.
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Chemke, Rei, and Yohai Kaspi. "The Effect of Eddy–Eddy Interactions on Jet Formation and Macroturbulent Scales." Journal of the Atmospheric Sciences 73, no. 5 (April 25, 2016): 2049–59. http://dx.doi.org/10.1175/jas-d-15-0375.1.
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Abstract The effect of eddy–eddy interactions on zonal and meridional macroturbulent scales is investigated over a wide range of eddy scales, using high-resolution idealized GCM simulations with and without eddy–eddy interactions. The wide range of eddy scales is achieved through systematic variation of the planetary rotation rate and thus multiple-jet planets. It is found that not only are eddy–eddy interactions not essential for the formation of jets, but the existence of eddy–eddy interactions decreases the number of eddy-driven jets in the atmosphere. The eddy–eddy interactions have little effect on the jet scale, which in both types of simulations coincides with the Rhines scale through all latitudes. The decrease in the number of jets in the presence of eddy–eddy interactions occurs because of the narrowing of the latitudinal region where zonal jets appear. This narrowing occurs because eddy–eddy interactions are mostly important at latitudes poleward of where the Rhines scale is equal to the Rossby deformation radius. Thus, once eddy–eddy interactions are removed, the conversion from baroclinic to barotropic eddy kinetic energy increases, and eddy–mean flow interactions intrude into these latitudes and maintain additional jets there. The eddy–eddy interactions are found to increase the energy-containing zonal scale so it coincides with the jets’ scale and thus make the flow more isotropic. While the conversion scale coincides with the most unstable scale, the Rossby deformation radius does not provide a good indication to these scales in both types of simulations.
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Lelong, M.-Pascale, and Miles A. Sundermeyer. "Geostrophic Adjustment of an Isolated Diapycnal Mixing Event and Its Implications for Small-Scale Lateral Dispersion." Journal of Physical Oceanography 35, no. 12 (December 1, 2005): 2352–67. http://dx.doi.org/10.1175/jpo2835.1.
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Abstract In this first of two companion papers, the time-dependent relaxation of an isolated diapycnal mixing event is examined in detail by means of numerical simulations, with an emphasis on the energy budget, particle displacements, and their implications for submesoscale oceanic lateral dispersion. The adjustment and dispersion characteristics are examined as a function of the lateral extent of the event L relative to the Rossby radius of deformation R. The strongest circulations and horizontal displacements occur in the regime R/L ≈ O(1). For short times, less than an inertial period, horizontal displacements are radial. Once the adjustment is completed, displacements become primarily azimuthal and continue to stir fluid over several to tens of inertial periods. The cumulative effect of many such events in terms of the effective lateral dispersion that they induce is examined in the companion paper.
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Ge, Xuyang, Ziyu Yan, Melinda Peng, Mingyu Bi, and Tim Li. "Sensitivity of Tropical Cyclone Track to the Vertical Structure of a Nearby Monsoon Gyre." Journal of the Atmospheric Sciences 75, no. 6 (June 1, 2018): 2017–28. http://dx.doi.org/10.1175/jas-d-17-0201.1.
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Abstract The impact of different vertical structures of a nearby monsoon gyre (MG) on a tropical cyclone (TC) track is investigated using idealized numerical simulations. In the experiment with a relatively deeper MG, the TC experiences a sharp northward turn at a critical point when its zonal westward-moving speed slows down to zero. At the same time, the total vorticity tendency for the TC wavenumber-1 component nearly vanishes as the vorticity advection by the MG cancels the vorticity advection by the TC. At this point, the TC motion is dominated by the beta effect, as in a no-mean-flow environment, and takes a sharp northward turn. In contrast, the TC does not exhibit a sharp northward turn with a shallower MG nearby. In the case with a deeper MG, a greater relative vorticity gradient of the MG promotes a quicker attraction between the TC and MG through the vorticity segregation process. In addition, a larger outer size of the TC also favors a faster westward propagation from its initial position, thus having more potential to collocate with the MG. Once the coalescence is in place, the Rossby wave energy dispersion associated with the TC and MG together is enhanced and rapidly strengthens the southwesterly flow on the eastern flank of both systems. The steering flow from both the beta gyre and the Rossby wave dispersion leads the TC to take a sharp northward track when the total vorticity tendency is at its minimum. This study indicates the importance of good representations of the TC structure and its nearby environmental flows in order to accurately predict TC motions.
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McIntyre, M. E. "Potential-vorticity inversion and the wave-turbulence jigsaw: some recent clarifications." Advances in Geosciences 15 (June 25, 2008): 47–56. http://dx.doi.org/10.5194/adgeo-15-47-2008.
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Abstract. Two key ideas stand out as crucial to understanding atmosphere-ocean dynamics, and the dynamics of other planets including the gas giants. The first key idea is the invertibility principle for potential vorticity (PV). Without it, one can hardly give a coherent account of even so important and elementary a process as Rossby-wave propagation, going beyond the simplest textbook cases. Still less can one fully understand nonlinear processes like the self-sharpening or narrowing of jets – the once-mysterious "negative viscosity" phenomenon. The second key idea, also crucial to understanding jets, might be summarized in the phrase "there is no such thing as turbulence without waves", meaning Rossby waves especially. Without this idea one cannot begin to make sense of, for instance, momentum budgets and eddy momentum transports in complex large-scale flows. Like the invertibility principle the idea has long been recognized, or at least adumbrated. However, it is worth articulating explicitly if only because it can be forgotten when, in the usual way, we speak of "turbulence" and "turbulence theory" as if they were autonomous concepts. In many cases of interest, such as the well-studied terrestrial stratosphere, reality is more accurately described as a highly inhomogeneous "wave-turbulence jigsaw puzzle" in which wavelike and turbulent regions fit together and crucially affect each other's evolution. This modifies, for instance, formulae for the Rhines scale interpreted as indicating the comparable importance of wavelike and turbulent dynamics. Also, weakly inhomogeneous turbulence theory is altogether inapplicable. For instance there is no scale separation. Eddy scales are not much smaller than the sizes of the individual turbulent regions in the jigsaw. Here I review some recent progress in clarifying these ideas and their implications.
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Rolf, C., A. Afchine, H. Bozem, B. Buchholz, V. Ebert, T. Guggenmoser, P. Hoor, et al. "Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012." Atmospheric Chemistry and Physics 15, no. 16 (August 18, 2015): 9143–58. http://dx.doi.org/10.5194/acp-15-9143-2015.
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Abstract. Dehydration in the Antarctic winter stratosphere is a well-known phenomenon that is annually observed by satellites and occasionally observed by balloon-borne measurements. However, in situ measurements of dehydrated air masses in the Antarctic vortex are very rare. Here, we present detailed observations with the in situ and GLORIA remote sensing instrument payload aboard the German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv of water vapor were observed as far north as 47° S in an altitude between 12 and 13 km in the lowermost stratosphere. The dehydration can be traced back to individual ice formation events above the Antarctic Peninsula and Plateau, where ice crystals sedimented out and water vapor was irreversibly removed. Within these dehydrated stratospheric air masses, filaments of moister air reaching down to the tropopause are detected with the high-resolution limb sounder, GLORIA. Furthermore, dehydrated air masses are observed with GLORIA in the Antarctic lowermost stratosphere down to 7 km. With the help of a backward trajectory analysis, a midlatitude origin of the moist filaments in the vortex can be identified, while the dry air masses down to 7 km have stratospheric origins. Antarctic stratosphere–troposphere exchange (STE) and transport of dehydrated air masses into the troposphere are investigated. Further, it is shown that the exchange process can be attributed to several successive Rossby wave events in combination with an isentropic exchange of air masses across the thermal tropopause. The transport into the troposphere is caused by air masses that are detached from the potential vorticity (PV) structure by Rossby wave breaking events and subsequently transported diabatically across the dynamical tropopause. Once transported to the troposphere, air masses with stratospheric origin can reach near-surface levels within several days.
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Auad, Guillermo, and Alejandro Parés Sierra. "Mean flow stability in a model of the eastern North Pacific Ocean." Geofísica Internacional 37, no. 2 (April 1, 1998): 113–26. http://dx.doi.org/10.22201/igeof.00167169p.1998.37.2.400.
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Datos de estratificación y corriente media de un modelo cuasigeostrófico de ocho capas de la Corriente de California son usados para resolver el problema de estabilidad lineal asociado. Se obtiene, al resolver un problema de autovalores complejos la frecuencia, rapidez de fase, velocidad de grupo, razón de crecimiento y estructura vertical. Se corren siete experimentos para estudiar la influencia de las diferentes condiciones de frontera (fondo plano o inclinado), dirección media de la corriente, amplitud, latitud y mecanismos de fricción en las características de las ondas de Rossby. Usando valores de la frecuencia de flotabilidad características del Pacífico Nororiental encontramos que la resolución vertical es crucial para determinar los efectos de la topografía y fricción de fondo en la estabilidad del flujo básico. La estructura vertical del flujo medio tiene un efecto importante en la escala de decaimiento exponencial. Esta escala de decaimiento de las diferentes áreas de la región de la Corriente de California varía entre 144 y 374 días para las ondas más inestables. La estructura vertical de nuestra solución de onda (amplitud y fase) es afectada perceptiblemente por la disipación usada en el modelo. Las características del primer modo baroclínico de la onda estable son cualitativamente y cuantitativamente similares a las obtenidas por Kang et al. (1982) usando datos hidrográficos de la Corriente de California. La inclusión de topografía de fondo lleva a una moderada redistribución de frecuencias en el espacio de número de onda y a más altas velocidades de grupo.
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Takaya, Koutarou, and Hisashi Nakamura. "Geographical Dependence of Upper-Level Blocking Formation Associated with Intraseasonal Amplification of the Siberian High." Journal of the Atmospheric Sciences 62, no. 12 (December 1, 2005): 4441–49. http://dx.doi.org/10.1175/jas3628.1.
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Abstract Intraseasonal amplification events of the surface Siberian high in winter are generally associated with blocking ridge formation in the upper troposphere. Composite analysis applied to the 20 strongest intraseasonal events of upper-level anticyclonic anomalies at every grid point over Siberia reveals that the blocking formation differs fundamentally between the east and west of the climatological upper-level trough over the Far East. To the west, what can be called “wave-train (Atlantic-origin)” type is common, where a blocking ridge develops from anomalies as a component of a quasi-stationary Rossby wave train propagating across the Eurasian continent under modest feedback forcing from transient eddies. To the east of the trough, what can be called “Pacific-origin” type dominates, where a blocking ridge forms in association with westward development of anticyclonic anomalies from the North Pacific under stronger feedback forcing from the Pacific storm track. Regardless of a particular type of blocking formation in the upper troposphere, a cold air outbreak tends to occur once anomalously cold air reaches the northeastern slope of the Tibetan Plateau.
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MCQUISTON, KATE. "Brian Wilson Reimagined: The Reparative Portrait in Love & Mercy." Journal of the Society for American Music 13, no. 03 (August 2019): 359–78. http://dx.doi.org/10.1017/s1752196319000233.
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AbstractThe 50-year anniversary of the Beach Boys’ seminal album Pet Sounds and Brian Wilson's corresponding world concert tour have once again brought attention to Wilson and his creative work with the Beach Boys. These events have brought about new recording releases and publications about the band and Wilson, including the first feature-length biopic on Wilson, Love & Mercy. The following essay investigates Atticus Ross's reimaginative approach to Brian Wilson's music for the soundtrack of this film, directed by Bill Pohlad and released in 2014. The film expands recent trends in music biopics of the last couple of decades regarding the mobilization and activation of music to afford new interpretations of their subjects and new ways to hear their work. Ross's approach is distinct for its extensive recomposition of Brian Wilson's music in the film's original score, which allows director Bill Pohlad to show Wilson in a new light.Ross incorporates Beach Boys recordings (studio sessions and released tracks) into new pieces that highlight processes of manipulation, layering, and repetition, which point to the studio as a major site of Wilson's creativity. These processes furthermore portray the psychic life of the film's characters. Ross's compositions dramatize the subjectivity of hearing and rogue behaviors of auditory recollection and hallucination that characterize both Wilson's creativity and mental illness. In the context of the story of Brian Wilson and Melinda Ledbetter, Ross's compositions take on palliative associations that have direct implications for the reception of the film's original soundtrack.
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Shadpour, Pejman, and Behkam Rezaimehr. "“Rosary of Testes”: Splenogonadal Fusion in Association with Bilateral Abdominal Testes Presenting as Polyorchidism." Case Reports in Urology 2015 (2015): 1–3. http://dx.doi.org/10.1155/2015/317189.
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Polyorchidism is a rare anomaly where early segmentation in the gonadal ridge can lead to the development of three or less commonly four testes in one individual. Just over 150 reports of this phenomenon exist in English medical literature. However, once confronted by the clinical finding of supernumerary gonads, one must remain mindful of other likely diagnoses involving nontesticular origin. We report on a male patient with bilaterally impalpable testes in whom splenogonadal fusion mimicked polyorchidism. By keeping such differential diagnoses in mind, surgeons are more liable to take the appropriate intraoperative course of action.
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Perfect, B., N. Kumar, and J. J. Riley. "Energetics of Seamount Wakes. Part II: Wave Fluxes." Journal of Physical Oceanography 50, no. 5 (May 2020): 1383–98. http://dx.doi.org/10.1175/jpo-d-19-0104.1.
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AbstractSeamounts are thought to facilitate ocean mixing through unsteady wake processes, and through the generation of internal waves, which propagate away from the seamount and later break. The relative importance of these processes is examined for idealized, isolated seamounts (with characteristic width D and height H) in uniform barotropic flow U. A range of Coriolis parameters f and buoyancy frequencies N are used such that a broad parameter space of low Froude numbers (U/NH) and low Rossby numbers (U/fD) is considered. Results indicate that eddy processes energetically dominate the internal wave energy flux in this range of parameter space. The internal wave field is specifically examined and partitioned into steady lee waves and unsteady, wake-generated waves. It is found that the lee wave energy flux cannot be explained by existing analytical theories. A lee wave model by Smith is then extended into the low-Froude-number regime and the effect of rotation is included. While strongly stratified experiments have previously indicated that only the top U/N of an obstacle generates internal waves, the effect of rotation appears to modify this wavemaking height. Once the U/N height is revised to account for rotation, the lee wave energy flux can be reasonably accurately reproduced by the extended Smith model.
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Moraes da Silva, Ana Carolina. "Figurações do duplo em Dona flor e seus dois maridos (1966) de Jorge Amado." Brumal. Revista de investigación sobre lo Fantástico 11, no. 1 (June 15, 2023): 313–28. http://dx.doi.org/10.5565/rev/brumal.893.
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O duplo há muito tempo está presente na literatura, passando a ser mais recorrente a partir do século XVIII, no Romantismo. E, por estar na literatura das mais variadas formas, trazendo os mais diversos significados, o duplo proporcionou e proporciona, consequentemente, inúmeros estudos. Este artigo é resultado de uma pesquisa que teve por objetivo principal a realização da análise interpretativa do duplo, sob a perspectiva da literatura fantástica, na obra do escritor Jorge Amado, Dona Flor e seus dois maridos (1966). Como fundamentação teórica, citamos: Juan Herrero Cecília (2000, 2011), Sigmund Freud (1976), Otto Rank (1939) e Clément Rosset (2008). Das considerações finais do trabalho, destacamos a constante presença do duplo como ideia de completude por meio do personagem de Vadinho, buscando destacar o seu caráter antitético. Nesse contexto, Amado nos mostra como prevalece o duplo subjetivo, onde parte da narrativa está relacionada à questão da identidade associado ao fantástico.
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Tamarin, Talia, James R. Maddison, Eyal Heifetz, and David P. Marshall. "A Geometric Interpretation of Eddy Reynolds Stresses in Barotropic Ocean Jets." Journal of Physical Oceanography 46, no. 8 (August 2016): 2285–307. http://dx.doi.org/10.1175/jpo-d-15-0139.1.
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AbstractBarotropic eddy fluxes are analyzed through a geometric decomposition of the eddy stress tensor. Specifically, the geometry of the eddy variance ellipse, a two-dimensional visualization of the stress tensor describing the mean eddy shape and tilt, is used to elucidate eddy propagation and eddy feedback on the mean flow. Linear shear and jet profiles are analyzed and theoretical results are compared against fully nonlinear simulations. For flows with zero planetary vorticity gradient, analytic solutions for the eddy ellipse tilt and anisotropy are obtained that provide a direct relationship between the eddy tilt and the phase difference of a normal-mode solution. This allows a straightforward interpretation of the eddy–mean flow interaction in terms of classical stability theory: the initially unstable jet gives rise to eddies that are tilted “against the shear” and extract energy from the mean flow; once the jet stabilizes, eddies become tilted “with the shear” and return their energy to the mean flow. For a nonzero planetary vorticity gradient, ray-tracing theory is used to predict ellipse geometry and its impact on eddy propagation within a jet. An analytic solution for the eddy tilt is found for a Rossby wave on a constant background shear. The ray-tracing results broadly agree with the eddy tilt diagnosed from a fully nonlinear simulation.
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Noraz, Q., A. S. Brun, A. Strugarek, and G. Depambour. "Impact of anti-solar differential rotation in mean-field solar-type dynamos." Astronomy & Astrophysics 658 (February 2022): A144. http://dx.doi.org/10.1051/0004-6361/202141946.
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Context. Over the course of their lifetimes, the rotation of solar-type stars goes through different phases. Once they reach the zero-age main sequence, their global rotation rate decreases during the main sequence until at least the solar age, approximately following the empirical Skumanich’s law and enabling gyrochronology. Older solar-type stars might then reach a point of transition when they stop braking, according to recent results of asteroseismology. Additionally, recent 3D numerical simulations of solar-type stars show that different regimes of differential rotation can be characterized with the Rossby number. In particular, anti-solar differential rotation (fast poles, slow equator) may exist for high Rossby number (slow rotators). If this regime occurs during the main sequence and, in general, for slow rotators, we may consider how magnetic generation through the dynamo process might be impacted. In particular, we consider whether slowly rotating stars are indeed subject to magnetic cycles. Aims. We aim to understand the magnetic field generation of solar-type stars possessing an anti-solar differential rotation and we focus on the possible existence of magnetic cycles in such stars. Methods. We modeled mean-field kinematic dynamos in solar (fast equator, slow poles) and anti-solar (slow equator, fast poles) differential rotation, using the STELEM code. We consider two types of mean field dynamo mechanisms along with the Ω-effect: the standard α-effect distributed at various locations in the convective envelope and the Babcock-Leighton effect. Results. We find that kinematic αΩ dynamos allow for the presence of magnetic cycles and global polarity reversals for both rotation regimes, but only if the α-effect is saddled on the tachocline. If it is distributed in the convection zone, solar-type cases still possess a cycle and anti-solar cases do not. Conversely, we have not found any possibility for sustaining a magnetic cycle with the traditional Babcock-Leighton flux-transport dynamos in the anti-solar differential rotation regime due to flux addition. Graphic interpretations are proposed in order to illustrate these cases. However, we find that hybrid models containing both prescriptions can still sustain local polarity reversals at some latitudes. Conclusions. We conclude that stars in the anti-solar differential rotation regime can sustain magnetic cycles only for very specific dynamo processes. The detection of a magnetic cycle for such a star would therefore be a particularly interesting constraint in working to decipher what type of dynamo is actually at work in solar-type stars.
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Wang, Tao, Roy Barkan, James C. McWilliams, and M. Jeroen Molemaker. "Structure of Submesoscale Fronts of the Mississippi River Plume." Journal of Physical Oceanography 51, no. 4 (April 2021): 1113–31. http://dx.doi.org/10.1175/jpo-d-20-0191.1.
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AbstractSubmesoscale currents (SMCs), in the forms of fronts, filaments, and vortices, are studied using a high-resolution (~150 m) Regional Oceanic Modeling System (ROMS) simulation in the Mississippi River plume system. Fronts and filaments are identified by large horizontal velocity and buoyancy gradients, surface convergence, and cyclonic vertical vorticity with along-coast fronts and along-plume-edge filaments notably evident. Frontogenesis and arrest/destruction are two fundamental phases in the life cycle of fronts and filaments. In the Mississippi River plume region, the horizontal advective tendency induced by confluence and convergence plays a primary role in frontogenesis. Confluent currents sharpen preexisting horizontal buoyancy gradients and initiate frontogenesis. Once the fronts and filaments are formed and the Rossby number reaches O(1), they further evolve frontogenetically mainly by convergent secondary circulations, which can be maintained by different cross-front momentum balance regimes. Confluent motions and preexisting horizontal buoyancy gradients depend on the interaction between wind-induced Ekman transport and the spreading plume water. Consequently, the direction of wind has a significant effect on the temporal variability of SMCs, with more active SMCs generated during a coastally downwelling-favorable wind and fewer SMCs during an upwelling-favorable wind. Submesoscale instabilities (~1–3 km) play a primary role in the arrest and fragmentation of most fronts and filaments. These instabilities propagate along the fronts and filaments, and their energy conversion is a mixed barotropic–baroclinic type with horizontal-shear instabilities dominating.
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Maiorino, Fabiana Tavolaro. "O contemporâneo através do Cinema: o ilusório pelo duplo." Revista Educação, Artes e Inclusão 19, no. 1 (May 29, 2023): e0037. http://dx.doi.org/10.5965/198431781820231e0037.
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Na interface temática entre o campo da educação e dos estudos fílmicos, o objetivo desse artigo é trazer o tema do duplo pelo cinema, como um dos modos de vida do contemporâneo, onde há a duplicação do eu como tentativa de relacionar-se com o real. Como metodologia, usou-se a cartografia deleuziana e a analítica da hermenêutica trágica. Analisou-se para isso a película “O Duplo” (2013, Ayoade). Notou-se pelo gesto cartográfico, que o filme ao enfocar o recurso ontológico da criação de uma duplicação do real, pelo surgimento do duplo do protagonista, acaba tornando-se uma tentativa de elaboração existencial diante o mal estar contemporâneo, atravessado pelo niilismo e pela decadência social. Nesse sentido, o artigo explicita esse modo de vida como ilusório, baseado na leitura pertinente de Clement Rosset, que caracteriza essa saída como frágil do ser contemporâneo, por explicitar a incapacidade desse homem existente em lidar com a atmosfera niilista dos tempos atuais, que escapa pelo recurso da duplicação seja do real ou de si mesmo.
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Wagner, Patrick, Markus Scheinert, and Claus W. Böning. "Contribution of buoyancy fluxes to tropical Pacific sea level variability." Ocean Science 17, no. 4 (August 20, 2021): 1103–13. http://dx.doi.org/10.5194/os-17-1103-2021.
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Abstract. Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean–atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air–sea buoyancy fluxes is less clear. We use a global, eddy-permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around a 10∘ latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy-flux-forced anomalies are correlated with variations driven by wind stress changes, but their effect on the prevailing anomalies and the importance of heat and freshwater fluxes vary locally. In the eastern tropical basin, interannual sea level variability is amplified by anomalous heat fluxes, while the importance of freshwater fluxes is small, and neither has any impact on decadal timescales. In the western tropical Pacific, the variability on interannual and decadal timescales is dampened by both heat and freshwater fluxes. The mechanism involves westward-propagating Rossby waves that are triggered during El Niño–Southern Oscillation (ENSO) events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.
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Cecelski, Stefan F., and Da-Lin Zhang. "Genesis of Hurricane Julia (2010) within an African Easterly Wave: Low-Level Vortices and Upper-Level Warming." Journal of the Atmospheric Sciences 70, no. 12 (November 22, 2013): 3799–817. http://dx.doi.org/10.1175/jas-d-13-043.1.
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Abstract While a robust theoretical framework for tropical cyclogenesis (TCG) within African easterly waves (AEWs) has recently been developed, little work explores the development of low-level meso-β-scale vortices (LLVs) and a meso-α-scale surface low in relation to deep convection and upper-tropospheric warming. In this study, the development of an LLV into Hurricane Julia (2010) is shown through a high-resolution model simulation with the finest grid size of 1 km. The results presented expand upon the connections between LLVs and the AEW presented in previous studies while demonstrating the importance of upper-tropospheric warming for TCG. It is found that the significant intensification phase of Hurricane Julia is triggered by the pronounced upper-tropospheric warming associated with organized deep convection. The warming is able to intensify and expand during TCG owing to formation of a storm-scale outflow beyond the Rossby radius of deformation. Results confirm previous ideas by demonstrating that the intersection of the AEW's trough axis and critical latitude is a preferred location for TCG, while supplementing such work by illustrating the importance of upper-tropospheric warming and meso-α-scale surface pressure falls during TCG. It is shown that the meso-β-scale surface low enhances boundary layer convergence and aids in the bottom-up vorticity development of the meso-β-scale LLV. The upper-level warming is attributed to heating within convective bursts at earlier TCG stages while compensating subsidence warming becomes more prevalent once a mesoscale convective system develops.
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Yadav, Navneet K., and Arnab Samanta. "The stability of compressible swirling pipe flows with density stratification." Journal of Fluid Mechanics 823 (June 23, 2017): 689–715. http://dx.doi.org/10.1017/jfm.2017.335.
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We investigate the spatial stability of compressible, viscous pipe flows with radius-dependent mean density profiles, subjected to solid body rotations. For a fixed Rossby number $\unicode[STIX]{x1D716}$ (inverse of the rotational speed), as the Reynolds number $Re$ is increased, the flow transitions from being stable to convectively unstable, usually leading to absolute instability. If flow compressibility is unimportant and $Re$ is held constant, there appears to be a maximum $Re$ below which the flow remains stable irrespective of any rotational speed, or a minimum azimuthal Reynolds number $Re_{\unicode[STIX]{x1D703}}$ $(=Re/\unicode[STIX]{x1D716})$ is required for any occurrence of absolute instabilities. Once compressible forces are significant, the effect of pressure–density coupling is found to be more severe below a critical $Re$, where as rotational speeds are raised, a stable flow almost directly transitions to an absolutely unstable state. This happens at a critical $Re_{\unicode[STIX]{x1D703}}$ which reduces with increased flow Mach number, pointing to compressibility aiding in the instability at these lower Reynolds numbers. However, at higher $Re$, above the critical value, the traditional stabilizing role of compressibility is recovered if mean density stratification exists, where the gradients of density play an equally important role, more so at the higher azimuthal modes. A total disturbance energy-based formulation is used to obtain mechanistic understanding at these stability states, where we find the entropic energy perturbations to dominate as the primary instability mechanism, in sharp contrast to the energy due to axial shear, known to play a leading role in incompressible swirling flows.
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DeAngelis, Anthony M., Hailan Wang, Randal D. Koster, Siegfried D. Schubert, Yehui Chang, and Jelena Marshak. "Prediction Skill of the 2012 U.S. Great Plains Flash Drought in Subseasonal Experiment (SubX) Models." Journal of Climate 33, no. 14 (July 15, 2020): 6229–53. http://dx.doi.org/10.1175/jcli-d-19-0863.1.
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AbstractRapid-onset droughts, known as flash droughts, can have devastating impacts on agriculture, water resources, and ecosystems. The ability to predict flash droughts in advance would greatly enhance our preparation for them and potentially mitigate their impacts. Here, we investigate the prediction skill of the extreme 2012 flash drought over the U.S. Great Plains at subseasonal lead times (3 weeks or more in advance) in global forecast systems participating in the Subseasonal Experiment (SubX). An additional comprehensive set of subseasonal hindcasts with NASA’s GEOS model, a SubX model with relatively high prediction skill, was performed to investigate the separate contributions of atmospheric and land initial conditions to flash drought prediction skill. The results show that the prediction skill of the SubX models is quite variable. While skillful predictions are restricted to within the first two forecast weeks in most models, skill is considerably better (3–4 weeks or more) for certain models and initialization dates. The enhanced prediction skill is found to originate from two robust sources: 1) accurate soil moisture initialization once dry soil conditions are established, and 2) the satisfactory representation of quasi-stationary cross-Pacific Rossby wave trains that lead to the rapid intensification of flash droughts. Evidence is provided that the importance of soil moisture initialization applies more generally to central U.S. summer flash droughts. Our results corroborate earlier findings that accurate soil moisture initialization is important for skillful subseasonal forecasts and highlight the need for additional research on the sources and predictability of drought-inducing quasi-stationary atmospheric circulation anomalies.
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Laurila, Terhi K., Victoria A. Sinclair, and Hilppa Gregow. "The Extratropical Transition of Hurricane Debby (1982) and the Subsequent Development of an Intense Windstorm over Finland." Monthly Weather Review 148, no. 1 (December 27, 2019): 377–401. http://dx.doi.org/10.1175/mwr-d-19-0035.1.
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Abstract On 22 September 1982, an intense windstorm caused considerable damage in northern Finland. Local forecasters noted that this windstorm potentially was related to Hurricane Debby, a category 4 hurricane that occurred just 5 days earlier. Due to the unique nature of the event and lack of prior research, our aim is to document the synoptic sequence of events related to this storm using ERA-Interim reanalysis data, best track data, and output from OpenIFS simulations. During extratropical transition, the outflow from Debby resulted in a ridge building and an acceleration of the jet. Debby did not reintensify immediately in the midlatitudes despite the presence of an upper-level trough. Instead, ex-Debby propagated rapidly across the Atlantic as a diabatic Rossby wave–like feature. Simultaneously, an upper-level trough approached from the northeast and once ex-Debby moved ahead of this feature near the United Kingdom, rapid reintensification began. All OpenIFS forecasts diverged from reanalysis after only 2 days indicating intrinsic low predictability and strong sensitivities. Phasing between Hurricane Debby and the weak trough, and phasing of the upper- and lower-level potential vorticity anomalies near the United Kingdom was important in the evolution of ex-Debby. In the only OpenIFS simulation to correctly capture the phasing over the United Kingdom, stronger wind gusts were simulated over northern Finland than in any other simulation. Turbulent mixing behind the cold front, and convectively driven downdrafts in the warm sector, enhanced the wind gusts over Finland. To further improve understanding of this case, we suggest conducting research using an ensemble approach.
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Irving, Zackery A., Steven H. Saar, Bradford J. Wargelin, and José-Dias do Nascimento. "Stellar Cycles in Fully Convective Stars and a New Interpretation of Dynamo Evolution." Astrophysical Journal 949, no. 2 (June 1, 2023): 51. http://dx.doi.org/10.3847/1538-4357/acc468.
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Abstract An αΩ dynamo, combining shear and cyclonic convection in the tachocline, is believed to generate the solar cycle. However, this model cannot explain cycles in fast rotators (with minimal shear) or in fully convective stars (no tachocline); an analysis of these stars could therefore provide key insights into how these cycles work. We reexamine ASAS data for 15 M dwarfs, 11 of which are presumed fully convective; the addition of newer ASAS-SN data confirms cycles in roughly 12 of them, while presenting new or revised rotation periods for 5 stars. The amplitudes and periods of these cycles follow A cyc ∝ P cyc 0.94 ± 0.11 , with P cyc/P rot ∝ Ro −1.02±0.06 (where Ro is the Rossby number), very similar to P cyc/P rot ∝ Ro −0.81±0.17 that we find for 40 previously studied FGK stars, although P cyc/P rot and α are a factor of ∼20 smaller in the M stars. The very different P cyc/P rot–Ro relation seen here compared to previous work suggests that two types of dynamo, with opposite Ro dependences, operate in cool stars. Initially, a (likely α 2 or α 2Ω) dynamo operates throughout the convective zone in mid- to late-M and fast-rotating FGK stars, but once magnetic breaking decouples the core and convective envelope, a tachocline αΩ dynamo begins and eventually dominates in older FGK stars. A change in α in the tachocline dynamo generates the fundamentally different P cyc/P rot–Ro relation.
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Zhang, Ruijie, Buwen Dong, Zhiping Wen, Yuanyuan Guo, and Xiaodan Chen. "Relationship between the AMOC and the Multidecadal Variability of the Midlatitude Southern Indian Ocean." Journal of Climate 36, no. 24 (December 15, 2023): 8761–81. http://dx.doi.org/10.1175/jcli-d-23-0198.1.
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Abstract Air–sea coupling system in the southwestern Indian Ocean (SWIO; 35°–55°S, 40°–75°E) exhibits predominant multidecadal variability that is the strongest during austral summer. It is characterized by an equivalent barotropic atmospheric high (low) pressure over warm (cold) sea surface temperature (SST) anomalies and a poleward (equatorward) shift of the westerlies during the positive (negative) phase. In this study, physical processes of this multidecadal variability are investigated by using observations/reanalysis and CMIP6 model simulations. Results suggest that the multidecadal fluctuation can be explained by the modulation of the Atlantic meridional overturning circulation (AMOC) and the local air–sea positive feedback in the SWIO. In both observations/reanalysis and CMIP6 model simulations, the AMOC fluctuation presents a significantly negative correlation with the multidecadal SST variation in the SWIO when the AMOC is leading by about a decade. The mechanisms are that the preceding AMOC variation can cause an interhemispheric dipolar pattern of SST anomalies in the Atlantic Ocean. Subsequently, the SST anomalies in the midlatitudes of the South Atlantic can propagate to the SWIO by the oceanic Rossby wave under the influence of the Antarctic Circumpolar Current (ACC). Once the SST anomalies reach the SWIO, these SST anomalies in the oceanic front can affect the baroclinicity in the lower troposphere to influence the synoptic transient eddy and then cause the atmospheric circulation anomaly via the eddy–mean flow interaction. Subsequently, the anomalous atmospheric circulation over the SWIO can significantly strengthen the SST anomalies through modifying the oceanic meridional temperature advection and latent and sensible heat flux.
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Rolf, C., A. Afchine, H. Bozem, B. Buchholz, V. Ebert, T. Guggenmoser, P. Hoor, et al. "Transport of Antarctic stratospheric strongly dehydrated air into the troposphere observed during the HALO-ESMVal campaign 2012." Atmospheric Chemistry and Physics Discussions 15, no. 6 (March 16, 2015): 7895–932. http://dx.doi.org/10.5194/acpd-15-7895-2015.
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Abstract. Dehydration in the Antarctic winter stratosphere is a well-known phenomenon that is occasionally observed by balloon-borne and satellite measurements. However, in-situ measurements of dehydration in the Antarctic vortex are very rare. Here, we present detailed observations with the in-situ and GLORIA remote sensing instrument payload aboard the new German aircraft HALO. Strongly dehydrated air masses down to 1.6 ppmv of water vapor were observed as far north as 47° S and between 12 and 13 km in altitude, which has never been observed by satellites. The dehydration can be traced back to individual ice formation events, where ice crystals sedimented out and water vapor was irreversibly removed. Within these dehydrated stratospheric air masses, filaments of moister air reaching down to the tropopause are detected with the high resolution limb sounder, GLORIA. Furthermore, dehydrated air masses are observed with GLORIA in the Antarctic troposphere down to 7 km. With the help of a backward trajectory analysis, a tropospheric origin of the moist filaments in the vortex can be identified, while the dry air masses in the troposphere have stratospheric origins. The transport pathways of Antarctic stratosphere/troposphere exchange are investigated and the irrelevant role of the Antarctic thermal tropopause as a transport barrier is confirmed. Further, it is shown that the exchange process can be attributed to several successive Rossby wave events in combination with an isentropic interchange of air masses across the weak tropopause and subsequent subsidence due to radiative cooling. Once transported to the troposphere, air masses with stratospheric origin are able to reach near-surface levels within 1–2 months.
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Khouider, Boualem, and Andrew J. Majda. "Equatorial Convectively Coupled Waves in a Simple Multicloud Model." Journal of the Atmospheric Sciences 65, no. 11 (November 1, 2008): 3376–97. http://dx.doi.org/10.1175/2008jas2752.1.
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Abstract Linear stability results for the multicloud model recently developed by the authors on an equatorial beta plane are presented here. The linearized equations, about a realistic radiative–convective equilibrium (RCE) are projected in the meridional direction via a Galerkin truncation procedure based on the parabolic cylinder functions. In a suitable parameter regime, the multicloud model exhibits convectively coupled Kelvin, M = 0 eastward (Yanai), and M = 1 westward inertia–gravity waves, unstable at the synoptic scales in agreement with the outgoing longwave radiation (OLR) spectral peaks observed by Wheeler and Kiladis. The horizontal wave structure and vertical wavenumber of the unstable waves qualitatively match those of the rotating equatorial shallow water waves but with a reduced phase speed, as in the observations. More importantly, they exhibit the same self-similar front-to-rear vertical tilt in the zonal winds, temperature, and heating fields as observed by Kiladis and colleagues. Similar to the case without rotation (from earlier work) a wave life cycle is identified, once again demonstrating the crucial role, played by congestus clouds and moisture, of preconditioning and moistening prior to deep convection and of triggering and maintaining the instability. When the troposphere is excessively dry, the convective wave instability fades out and an instability of low-frequency modes moving in both eastward and westward directions takes place. The eigenstructure of the low-frequency modes projects heavily on the congestus and moisture components and exhibits a quadruple vortex configuration reminiscent of Rossby waves with strong meridional convergence of warm and moist air toward the equatorial belt, suggesting a moistening and preconditioning role resembling the congestus standing mode seen in the case without rotation.
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Pierens, A., M.-K. Lin, and S. N. Raymond. "Vortex instabilities triggered by low-mass planets in pebble-rich, inviscid protoplanetary discs." Monthly Notices of the Royal Astronomical Society 488, no. 1 (June 28, 2019): 645–59. http://dx.doi.org/10.1093/mnras/stz1718.
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Abstract In the innermost regions of protoplanerary discs, the solid-to-gas ratio can be increased considerably by a number of processes, including photoevaporative and particle drift. Magnetohydrodynamic disc models also suggest the existence of a dead zone at R ≲ 10 au, where the regions close to the mid-plane remain laminar. In this context, we use two-fluid hydrodynamical simulations to study the interaction between a low-mass planet (∼1.7 M⊕) on a fixed orbit and an inviscid pebble-rich disc with solid-to-gas ratio ϵ ≥ 0.5. For pebbles with Stokes numbers St = 0.1, 0.5, multiple dusty vortices are formed through the Rossby wave instability at the planet separatrix. Effects due to gas drag then lead to a strong enhancement in the solid-to-gas ratio, which can increase by a factor of ∼103 for marginally coupled particles with St = 0.5. As in streaming instabilities, pebble clumps reorganize into filaments that may plausibly collapse to form planetesimals. When the planet is allowed to migrate in an Minimum Mass Solar Nebula (MMSN) disc, the vortex instability is delayed due to migration but sets in once inward migration stops due a strong positive pebble torque. Again, particle filaments evolving in a gap are formed in the disc while the planet undergoes an episode of outward migration. Our results suggest that vortex instabilities triggered by low-mass planets could play an important role in forming planetesimals in pebble-rich, inviscid discs, and may significantly modify the migration of low-mass planets. They also imply that planetary dust gaps may not necessarily contain planets if these migrated away.
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Glover, Nicola, and Paul Todd. "The myth of common intention." Legal Studies 16, no. 3 (November 1996): 325–47. http://dx.doi.org/10.1111/j.1748-121x.1996.tb00533.x.
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The leading recent authority on beneficial interests in shared homes is Lloyds Bank plc v Rosset, where the House of Lords clarified what had become rather a confused area of law. By no means all the problems were resolved, however, and the House proceeded on the basis of a now commonly-held but nevertheless fundamental misapprehension, that common intention is relevant to the creation of a trust. It is our contention that once it is clear precisely whose intention is relevant, and why, many of the conceptual difficulties in this area disappear.For the purposes of the discussion, we consider the two situations, where legal title to a home is vested in A alone, and where it is vested in A and B jointly. In each case, the question is whether B can claim a beneficial interest, and if so, what is its nature and extent.
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Herbert, Gaëlle, and Bernard Bourlès. "Impact of intraseasonal wind bursts on sea surface temperature variability in the far eastern tropical Atlantic Ocean during boreal spring 2005 and 2006: focus on the mid-May 2005 event." Ocean Science 14, no. 4 (August 27, 2018): 849–69. http://dx.doi.org/10.5194/os-14-849-2018.
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Abstract. The impact of boreal spring intraseasonal wind bursts on sea surface temperature variability in the eastern tropical Atlantic Ocean in 2005 and 2006 is investigated using numerical simulation and observations. We especially focus on the coastal region east of 5° E and between the Equator and 7° S that has not been studied in detail so far. For both years, the southerly wind anomalies induced cooling episodes through (i) upwelling processes, (ii) vertical mixing due to the vertical shear of the current, and for some particular events (iii) a decrease in incoming surface shortwave radiation. The strength of the cooling episodes was modulated by subsurface conditions affected by the arrival of Kelvin waves from the west influencing the depth of the thermocline. Once impinging the eastern boundary, the Kelvin waves excited westward-propagating Rossby waves, which combined with the effect of enhanced westward surface currents contributed to the westward extension of the cold water. A particularly strong wind event occurred in mid-May 2005 and caused an anomalous strong cooling off Cape Lopez and in the whole eastern tropical Atlantic Ocean. From the analysis of oceanic and atmospheric conditions during this particular event, it appears that anomalously strong boreal spring wind strengthening associated with anomalously strong Hadley cell activity prematurely triggered the onset of coastal rainfall in the northern Gulf of Guinea, making it the earliest over the 1998–2008 period. No similar atmospheric conditions were observed in May over the 1998–2008 period. It is also found that the anomalous oceanic and atmospheric conditions associated with the event exerted a strong influence on rainfall off northeast Brazil. This study highlights the different processes through which the wind power from the South Atlantic is brought to the ocean in the Gulf of Guinea and emphasizes the need to further document and monitor the South Atlantic region.
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Wicht, Johannes. "Flow instabilities in the wide-gap spherical Couette system." Journal of Fluid Mechanics 738 (December 5, 2013): 184–221. http://dx.doi.org/10.1017/jfm.2013.545.
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AbstractThe spherical Couette system is a spherical shell filled with a viscous fluid. Flows are driven by the differential rotation between the inner and the outer boundary that rotate with $\Omega $ and $\Omega + \mathrm{\Delta} \Omega $ about a common axis. This setup has been proposed for second-generation dynamo experiments. We numerically explore the different instabilities emerging for rotation rates up to $\Omega = (1/ 3)\times 1{0}^{7} $, venturing also into the nonlinear regime where oscillatory and chaotic solutions are found. The results provide a comprehensive overview of the possible flow regimes. For low values of $\Omega $ viscosity dominates and an equatorial jet in meridional circulation and zonal flow develops that becomes unstable as the differential rotation is increased beyond a critical value. For intermediate $\Omega $ and an inner boundary rotating slower than the outer one, new double-roll and helical instabilities are found. For large $\Omega $ values Coriolis effects enforce a nearly two-dimensional fundamental flow where a Stewartson shear layer develops at the tangent cylinder. This shear layer is the source of nearly geostrophic non-axisymmetric instabilities that resemble columnar Rossby modes. At first, the instabilities differ significantly depending on whether the inner boundary rotates faster $( \mathrm{\Delta} \Omega \gt 0)$ or slower $( \mathrm{\Delta} \Omega \lt 0)$ than the outer one. For very large outer boundary rotation rates, however, both instabilities once more become comparable. Fast inertial waves similar to those observed in recent spherical Couette experiments prevail for larger $\Omega $ values and $ \mathrm{\Delta} \Omega \lt 0$ in when $ \mathrm{\Delta} \Omega $ and $\Omega $ are of comparable magnitude. For larger differential rotations $ \mathrm{\Delta} \Omega \gg \Omega $, however, the equatorial jet instability always takes over.
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Bolić, Marin. "Predlošci za slike 17. stoljeća u zbirci Pomorskog i povijesnog muzeja Hrvatskog primorja Rijeka." Ars Adriatica 9 (February 28, 2020): 75–88. http://dx.doi.org/10.15291/ars.2925.
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In 1987 the Old Masters Collection was founded at the Maritime and History Museum of the Croatian Littoral in Rijeka, comprising about one hundred and thirty paintings. It mainly consists of artworks once belonging to prominent Rijeka families that were acquired during the 19th and early 20th centuries. Only a smaller portion of the Collection came from the city’s religious institutions. These are all works of relatively modest artistic quality, thus the initial research revealed that quite a few were made after prints or more or less famous paintings. Since no systematic study of these models has hitherto been conducted, a number of questionable attributions and dates of execution concerning the paintings belonging to the Collection was proposed during the last decade of the 20th century. As far as the 17th-century paintings are concerned, the author has identified models for the paintings representing the Annunciation, Our Lady of the Rosary, the Marriage at Cana, the Adoration of the Shepherds and the Flagellation of Christ. The Annunciation was inspired by a print executed by Giovanni Jacopo Caraglio (Verona, ca. 1505 – Krakow, 1565) or its later derivation, while Our Lady of the Rosary was made after a print by Domenico Maria Canuti (Bologna, 1626-1684). The Marriage at Cana was painted after an engraving by Giovanni Battista Vanni (Florence/Pisa, 1599 – Florence, 1660) dating in 1637 or one of its later derivations. The engraving was, in its turn, made after the famous painting by Veronese (Verona, 1528 – Venice, 1588) exhibited today at the Louvre, while the Adoration of the Shepherds was made after an engraving by Jan (I) Sadeler (Brussels, 1550 – Venice, 1600). The Flagellation of Christ is a combination of a print of the same title and one depicting the Mocking of Christ. Both are work of Jan (I) Sadeler or by his copyist.
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Seabra, Elizabeth Aparecida Duque. "PIBID História: um registro da festa do Rosário em Couto de Magalhães- Minas Gerais (PIBID history: a registry of the festival of the rosary in Couto de Magalhães-Minas Gerais)." Crítica Educativa 3, no. 2 (September 13, 2017): 844. http://dx.doi.org/10.22476/revcted.v3i2.200.
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O presente trabalho se trata de uma investigação referente à Festa do Rosário em Couto de Magalhães, sendo uma manifestação cultural e religiosa que possui elementos que a caracterizam como bem cultural e patrimônio da comunidade. A ideia central do estudo é contribuir para o registro da festa na cidade, na expectativa que a mesma se torne reconhecia como patrimônio histórico e cultural da cidade de Couto de Magalhães. Buscou-se, de forma geral, na literatura as características comuns, a história e o simbolismo das festas do rosário em várias localidades. Realizamos um registro da festa nos dias 12 e 13 de setembro de 2015, onde tivemos contato de forma direta com os envolvidos na organização e figuras importantes do festejo, realizando com eles entrevistas episódicas. Nesse momento buscou-se conhecer o surgimento, a história e motivo da festa se perdurar até hoje. O texto final deste trabalho foi elaborado a partir da análise destes dados das fontes orais e das fotografias obtidas nos dias da festa. A pesquisa é de suma importância considerando a temática do patrimônio e da memória e visando contribuir para o reconhecimento acadêmico
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Meehl, Gerald A., Julie M. Arblaster, Grant Branstator, and Harry van Loon. "A Coupled Air–Sea Response Mechanism to Solar Forcing in the Pacific Region." Journal of Climate 21, no. 12 (June 15, 2008): 2883–97. http://dx.doi.org/10.1175/2007jcli1776.1.
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Abstract The 11-yr solar cycle [decadal solar oscillation (DSO)] at its peaks strengthens the climatological precipitation maxima in the tropical Pacific during northern winter. Results from two global coupled climate model ensemble simulations of twentieth-century climate that include anthropogenic (greenhouse gases, ozone, and sulfate aerosols, as well as black carbon aerosols in one of the models) and natural (volcano and solar) forcings agree with observations in the Pacific region, though the amplitude of the response in the models is about half the magnitude of the observations. These models have poorly resolved stratospheres and no 11-yr ozone variations, so the mechanism depends almost entirely on the increased solar forcing at peaks in the DSO acting on the ocean surface in clear sky areas of the equatorial and subtropical Pacific. Mainly due to geometrical considerations and cloud feedbacks, this solar forcing can be nearly an order of magnitude greater in those regions than the globally averaged solar forcing. The mechanism involves the increased solar forcing at the surface being manifested by increased latent heat flux and evaporation. The resulting moisture is carried to the convergence zones by the trade winds, thereby strengthening the intertropical convergence zone (ITCZ) and the South Pacific convergence zone (SPCZ). Once these precipitation regimes begin to intensify, an amplifying set of coupled feedbacks similar to that in cold events (or La Niña events) occurs. There is a strengthening of the trades and greater upwelling of colder water that extends the equatorial cold tongue farther west and reduces precipitation across the equatorial Pacific, while increasing precipitation even more in the ITCZ and SPCZ. Experiments with the atmosphere component from one of the coupled models are performed in which heating anomalies similar to those observed during DSO peaks are specified in the tropical Pacific. The result is an anomalous Rossby wave response in the atmosphere and consequent positive sea level pressure (SLP) anomalies in the North Pacific extending to western North America. These patterns match features that occur during DSO peak years in observations and the coupled models.
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JACOBS, P., and G. N. IVEY. "The influence of rotation on shelf convection." Journal of Fluid Mechanics 369 (August 25, 1998): 23–48. http://dx.doi.org/10.1017/s0022112098001827.
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A series of laboratory experiments was conducted to study the flows and exchange processes generated by turbulent convection in a shallow fluid with a combination of a shelf and slope topography in the presence of rotation. For convenience, heat loss at the ocean surface was modelled by heating from below with a buoyancy flux B0 applied to a circular portion (of radius R) of the base of a cylindrical tank, rotating with angular frequency f. The working volume was closed by an inverted model of a shelf and slope topography (with slope angle ϕ), creating a fluid height H between the forced surface and the shelf. After the initiation of the buoyancy forcing, the average temperature in the actively convecting region initially increases linearly with time but slows down once a lateral heat flux is generated by baroclinic instability at the edge of the convecting region. The wavelength of this instability is described by λ=(5.9±0.3) RD, with RD the Rossby radius of deformation, defined by (g′H)1/2/f, where g′ is the reduced gravity based on the density difference between the convecting and ambient fluids. A steady state is eventually reached when the lateral heat flux balances the (vertical) heat flux due to the forcing. The results differ from previous work in either unbounded or in constant-depth environments. It is shown that the steady-state density anomaly between the convecting and ambient regions is given by g′f=(1.6±0.2) (B0f)1/2 (R/H), while the time to reach this steady state is τ=(3.1±0.5) (f/B0)1/2R. The eddy velocity, characterizing the lateral exchange process, is given by vflux≈1.2 (B0/f)1/2. These results are consistent with the description of the lateral exchange process by eddy diffusion (rather than advection). Comparisons are made between the experimental results and field observations of convection events.
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Holmgren, Beth. "The Transfiguring of Context in the Work of Abram Terts." Slavic Review 50, no. 4 (1991): 965–77. http://dx.doi.org/10.2307/2500476.
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In particular, I am very interested in the problem of prose, prose as space.Andrei SiniavskiiIn 1974, soon after his expulsion from the Soviet Union, the literary scholar Andrei Siniavskii once again deferred to his created alter ego, the writer Abram Terts, to pass provocative judgment on the Soviet literary scene. The essay ascribed to Terts, “Literaturnyi protsess v Rossii,” reviews unofficial Soviet literature to highlight its artistic (rather than moral) appeal. As Terts reads it, the punitive context of this literature—established by Stalin and enforced to a less rigorous extent through the Leonid Brezhnev era—inadvertently guaranteed art and the fate of the artist richness and power: At this moment the fate of the Russian writer has become the most intriguing, the most fruitful literary topic in the whole world; he is either being imprisoned, pilloried, internally exiled, or simply kicked out. The writer nowadays is walking a knife-edge; but unlike the old days, when writers were simply eliminated one after another, he now derives pleasure and moral satisfaction from this curious pastime. The writer is now someone to be reckoned with. And all the attempts to make him see reason, to terrorize or crush him, to corrupt or liquidate him, only raise his literary achievement to higher and higher levels.