ISSN:0309-1929    

DOI:10.1080/03091929208201843

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Our discussion is concerned with the common effect of the non-uniformity of the layer rotation and stratification. We have assumed a model of the differential rotation with the upper part of the layer rotating more slowly, the bottom part more quickly. The upper part of the layer is stratified stably, the bottom part unstably. In the case of strong differential rotation the thermal instabilities are preferred and they are the most easily excited by the strong magnetic field (Λ ⋍ 102−103). The direction of its propagation is westward in the uniformly stratified layer and predominantly eastward in the non-uniformly stratified one. We have compared the stability of differently stratified layers by the adjusted Rayleigh number which represents the total amount of the thermal energy released in the layer by driving of the instability.

ISSN:0309-1929    

DOI:10.1080/03091929208201844

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The propagation properties and stability of wave motions in a spherical fluid shell, rotating uniformly in a co-rotating zonal magnetic field, are studied. Various profils of magnetic field and temperature gradient are examined. The fluid is viscous and electrically and thermally conducting. The analysis is applicable when the rotation rate is very high and the Elsasser number Λ ≪ 1. (Λ measures the ratio of Lorentz to Coriolis forces). The wave motions occur in the form of annular cylindrical cells whose thickness is determined by the rotation rate and magnetic field amplitude (Eltayeb and Kumar, 1977).

ISSN:0309-1929    

DOI:10.1080/03091929208201845

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A series of steady velocity fields at the core surface have been calculated using main field and secular variation models from the period 1900–1980 in the frozen-flux approximation. Secular variation model uncertainties have been estimated from the main field models of Bloxham and Gubbins (1986). For the period 1940–1980 it was possible to derive four consecutive flows, each assumed steady over 10 years, which fitted the spherical harmonic models to within their assumed uncertainties. For the period 1900–1940 it was found that the flows fitted the models if the SV model uncertainties were increased by a factor of one and a third for the period 1920–1940 and one and two thirds for the period 1900–1920. With the original assumed uncertainties, four consecutive flows, assumed steady over 5 years, were calculated for the period 1920–1940. For the period 1900–1920 it was only possible to derive steady flows over an interval of 2 years which fitted the SV models to within their assumed uncertainties over the periods 1900–1909 and 1917–1920. The computed flows are highly suggestive of a time-dependent flow with a dominant toroidal component which was increasing in the period 1900–1920, decelerating between 1910 and 1920 and reaching a minimum around 1930, and again increasing to a maximum in the mid-1950s. The flows computed before and after the 1969.5 secular acceleration impulse imply that the flow slowed down through the jerk event.

ISSN:0309-1929    

DOI:10.1080/03091929208201846

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Scale analysis of the MHD equations appropriate to the surface layers of the Earth's outer core is used to understand why the peak amplitude of the geomagnetic field on the core-mantle boundary (CMB),B0, is some 8 gauss, corresponding to an Alfvén speed of at least 200 km/yr in the core; and why the horizontal fluid motion just beneath the CMB reaches a typical speed, ν0, of only about 30 km/yr.

ISSN:0309-1929    

DOI:10.1080/03091929208201847

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor