摘要:

We study nonlinear waves in polytropic slabs under the joint influence of both self-gravitational and externally imposed gravitational fields. In the long wavelength limit, these obey nonlinear evolution equations akin to the Boussinesq and the KdV equations, with modifications resulting from the effects of self-gravity, or autogravity. We present pole solutions of these equations, including, in particular, a travelling solitary wave. These are surface gravity waves that we call autogravity waves because they are excited by selfgravity.

ISSN:0309-1929    

DOI:10.1080/03091929408203640

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

TheNonuniform Magnetic Reconnectionmodel presented by Priest and Lee (1990) was the first to incorporate several features observed in previous numerical models, in particular the highly curved field in the inflow region, which relaxes one of the key assumptions of the classicalAlmost-Uniformreconnection model of Petschek (1964). Also present is a strong jet of plasma emerging from the reconnection region along the separatrix and a negative current spike at the outflow from the central diffusion region. In this paper we present a generalisation of the Priest-Lee model to include pressure gradients in the inflow region, so relaxing the other main assumption of the Petschek and Priest-Lee models, namely that the inflow is current-free or potential. This produces several reconnection regimes similar to those described by Priest and Forbes (1986) in theirUnified Almost-Uniformsolutions, where significant pressure gradients are included, but their inflow, like Petschek's, is almost-uniform with slightly curved field lines. We investigate the behaviour of the inflow magnetic field without linearising about a uniform field. We study both a shockless, incompressible outflow and one containing weak shocks, where the type of reconnection is dictated by both the inflow and outflow boundary conditions. In order to introduce a pressure gradient into the Priest-Lee model an extra non-potential field in thex-direction is added. This field has a uniform current and does not alter theY-point nature of the neutral points at the ends of the diffusion region but does alter the position of the separatrix, where the flow becomes singular, and hence the position of the Alfvénic discontinuity and the strength of the plasma jet. The maximum reconnection rate given by the model scales as (1 +c)3/2Rme−½, where the parametercis a measure of the current and is such thatc>0 gives fast- or slow-mode expansions andc< 0 gives slow-mode compressions. These regimes are also found in theUnified Almost-Uniformmodel. Fast reconnection with a reconnection rate in excess of the pure Sweet-Parker scaling is therefore possible in the flux pile-up regimes withc> 0. For a given large magnetic Reynolds number, a fast reconnection rate of, say, 0.1 times the Alfvén speed is possible providedcis large enough (e.g.c> 10 forRme= 105).

ISSN:0309-1929    

DOI:10.1080/03091929408203641

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

DEEP CONVECTION AND DEEP WATER FORMATION IN THE OCEANS, edited by P. C. Chu and J. C. Gascard, Elsevier Oceanography Series, 57,1991,382 pp., US $110.50, DFL 215.00 (ISBN 0-444-88764-4).

ISSN:0309-1929    

DOI:10.1080/03091929408203642

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor