Search results for "Vorticity"

Strain analysis and vorticity of flow in the Northern Sardinian Variscan Belt: Recognition of a partitioned oblique deformation event

2008

Abstract A field example of strain partitioning has been analysed along the Nurra–Asinara transect of the NW Sardinian Variscan chain (Italy). The section in the Nurra–Asinara area is in a continuous sequence of tectono-metamorphic complexes made of low- to high-grade metamorphic rocks affected by a polyphase tectonic history. The principal fabric of the area is controlled by a D2 progressive deformation phase in which the strain is partitioned into folds and shear zone domains. The D2 stretching lineation and shear sense show a clear change from south to north. The principal meso- and micro-structures, vorticity gauges and a quantitative kinematic analysis of local strain suggest that the …

Flux-flow instability and heating effects in Bi2Sr2CaCu2O8 and YBa2Cu3O7 thin films

2000

Abstract We investigated current–voltage curves of Bi 2 Sr 2 CaCu 2 O 8 and YBa 2 Cu 3 O 7 thin films. Voltage jumps due to flux-flow instabilities at high vortex-velocities were found and interpreted in the framework of the theory of Larkin and Ovchinnikov. The extensions introduced by Bezuglyj et al. account for quasiparticle heating during the measurement. While in Bi 2 Sr 2 CaCu 2 O 8 the instability is found in the vortex-liquid phase, in YBa 2 Cu 3 O 7 we observed it in the vortex-glass phase. Moreover, we studied the temporal behavior of the instability in current–voltage curves with a time resolution in the microsecond range.

A derivation of the isothermal quantum hydrodynamic equations using entropy minimization

2005

Isothermal quantum hydrodynamic equations of order O(h 2 ) using the quantum entropy minimization method recently developed by Degond and Ringhofer are derived. The equations have the form of the usual quantum hydrodynamic model including a correction term of order O(h 2 ) which involves the vorticity. If the initial vorticity is of order 0(h), the standard model is obtained up to order O(h 4 ). The derivation is based on a careful expansion of the quantum equilibrium obtained from the entropy minimization in powers of h 2 .

Life Cycle Study of a Diabatic Rossby Wave as a Precursor to Rapid Cyclogenesis in the North Atlantic—Dynamics and Forecast Performance

2011

Monthly Weather Review, 139 (6)

A composite study on the structure and formation of ozone miniholes and minihighs over central Europe

2005

[1] Two different mechanisms have been proposed to be important for the formation of extreme total ozone events in mid-latitudes, so-called miniholes: (A) far-range meridional transport of air masses from regions with different climatological ozone mixing ratios, and (B) (local) adiabatic vertical displacement of isentropes. Here, the relative importance of these two mechanisms is studied using two different ozone profile reconstruction techniques for all miniholes and minihighs (events with anomalously high ozone) during the time period 1980–1989 over Switzerland. Composites for the two types of events of their vertical potential vorticity (PV) reveal a vertical dipole structure of PV anom…

Waveguidability of idealized midlatitude jets and the limitations of ray tracing theory

2020

Abstract. Ray paths of stationary Rossby waves emanating from a local midlatitude source are usually refracted equatorward. However, this general tendency for equatorward propagation is mitigated by the presence of a midlatitude jet that acts as a zonal waveguide. This opens up the possibility of circum-global teleconnections and quasi-resonance, which suggests that the ability to guide a wave in the zonal direction is an important jet property. This paper investigates waveguidability of idealized midlatitude jets in a barotropic model on the sphere. A forced-dissipative model configuration with a local source for Rossby waves is used in order to quantify waveguidability by diagnosing the l…

Inhomogeneous space-times admitting isotropic radiation: Vorticity-free case

1992

The energy-momentum tensor of space-times admitting a vorticity-free and a shear-free timelike congruence is obtained. This result is used to write Einstein equations in a convenient way in order to get inhomogeneous space-times admitting an isotropic distribution of photons satisfying the Liouville equation. Two special cases with anisotropic pressures in the energy flow direction are considered.

Local Finite-Amplitude Wave Activity as a Diagnostic for Rossby Wave Packets

2018

AbstractUpper-tropospheric Rossby wave packets (RWPs) are important dynamical features, because they are often associated with weather systems and sometimes act as precursors to high-impact weather. The present work introduces a novel diagnostic to identify RWPs and to quantify their amplitude. It is based on the local finite-amplitude wave activity (LWA) of Huang and Nakamura, which is generalized to the primitive equations in isentropic coordinates. The new diagnostic is applied to a specific episode containing large-amplitude RWPs and compared with a more traditional diagnostic based on the envelope of the meridional wind. In this case, LWA provides a more coherent picture of the RWPs an…

A Budget Equation for the Amplitude of Rossby Wave Packets Based on Finite-Amplitude Local Wave Activity

2020

AbstractRecently, the authors proposed a novel diagnostic to quantify the amplitude of Rossby wave packets. This diagnostic extends the local finite-amplitude wave activity (LWA) of N. Nakamura and collaborators to the primitive-equations framework and combines it with a zonal filter to remove the phase dependence. In the present work, this diagnostic is used to investigate the dynamics of upper-tropospheric Rossby wave packets, with a particular focus on distinguishing between conservative dynamics and nonconservative processes. For this purpose, a budget equation for filtered LWA is derived and its utility is tested in a hierarchy of models. Idealized simulations with a barotropic and a d…

2015

The dynamics of emergent magnetic quasiparticles, such as vortices, domain walls, and bubbles are studied by scanning transmission x-ray microscopy (STXM), combining magnetic (XMCD) contrast with about 25 nm lateral resolution as well as 70 ps time resolution. Essential progress in the understanding of magnetic vortex dynamics is achieved by vortex core reversal observed by sub-GHz excitation of the vortex gyromode, either by ac magnetic fields or spin transfer torque. The basic switching scheme for this vortex core reversal is the generation of a vortex-antivortex pair. Much faster vortex core reversal is obtained by exciting azimuthal spin wave modes with (multi-GHz) rotating magnetic fie…