摘要:

In this paper the main problems of the theory of the short-period geomagnetic secular variation are described. An approximate analytical representation of the observational data on both the geomagnetic field variations and the associated variations in the length of the day, the kinematics of the generation of geomagnetic variations in the skin-layer at the core-mantle boundary and the influence of the electrical conductivity of the mantle on the geomagnetic variations are considered. A theory of torsional oscillations in the Earth's core is developed and an attempt is made to evaluate the associated geomagnetic variations. Magnetohydrodynamic effects in a possible thin layer of stably stratified fluid near the core-mantle boundary are investigated.

ISSN:0309-1929    

DOI:10.1080/03091928408210077

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The Cauchy-Schwarz inequality is employed to find geometry-independent limits on the magnetic helicity dissipation rate in a resistive plasma. These limits only depend upon the total energy of the plasma, the energy dissipation rate, and a mean diffusion coefficient. For plasmas isolated from external energy sources, limits can also be set on the minimum time necessary to dissipate a net amount of helicity ΔH. As evaluated in the context of a solar coronal loop, these limits strongly suggest that helicity decay occurs on a diffusion timescale which is far too great to be relevant to most coronal processes. Furthermore, rapid reconnection is likely to approximately conserve magnetic helicity. The dilliculties involved in determining the free energy residing in a magnetic structure (given the constraint of magnetic helicity conservation) are discussed.

ISSN:0309-1929    

DOI:10.1080/03091928408210078

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

Negative energy perturbations may be linked to the instability of fronts and gravity currents, for instance when the latter have uniform potential vorticity (in thef-plane). The equatorial Gaussian jet ũ(y) = ũ(0) exp (−y1/L2), in a one-layer, reduced-gravity, β-plane model may also be unstable to negative energy perturbations, particularly when the meridional gradient of potential vorticity does not change sign.

ISSN:0309-1929    

DOI:10.1080/03091928408210079

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor

摘要:

The analytical form of equivalent modons in spherical geometry is derived along with the dispersion relationship relating the modon frequency, spatial extent and interior wavenumber. The structure of equivalent modons in spherical geometry is more asymmetric as the geographic pole is approached, thus giving improved kinematic agreement with atmospheric blocking patterns than beta-plane modons. Numerical experiments demonstrating the robustness of spherical modons to background vorticity perturbations and structural augmentations of the governing equation are performed. Lastly, speculations concerning the applicability of spherical modons as models of blocking situations with preferential poleward geographic formation mechanisms are given.

ISSN:0309-1929    

DOI:10.1080/03091928408210080

出版商:Taylor & Francis Group    

年代:1984

数据来源: Taylor