摘要:

A prominent feature of the solar cycle is the rise and fall of the number of sunspots on the surface with a timescale of approximately eleven years. The mathematical description of this behavior is complicated by the interruption of the cycle for 75 years starting around 1650. Similar previous intermissions of this kind are implied by the available data. We explore the possibility of modeling such temporal variations of the sunspot number with a deterministic dynamical system of relatively low order. The system we propose manifests on/off intermittency in which the cyclic variations of the solar activity switch off almost completely for extended periods. We also offer an explanation of the variation of the fluctuating part of the sunspot number over the cycle.

ISSN:0309-1929    

DOI:10.1080/03091929308203626

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A simple numerical model of the self-excitation of the magnetic field by chaotic motion of a highly conductive fluid is being developed. It is based on the following approach to simulating the turbulent dynamo generation of magnetic fields: the fluid is divided into cells and each cell acts as a machine that can randomly amplify or destroy a given magnetic field. The random amplification models the effects of a chaotic fast dynamo and the random destruction models the effects of reconnection. Uncorrelated and correlated processes are considered. Effects of non-linearity, diffusion, and correlation between cells in time and space are also included. Numerical results are presented from one- and two-dimensional models and possible applications to the generation and spatial-temporal distribution of solar, planetary and interplanetary magnetic fields are discussed.

ISSN:0309-1929    

DOI:10.1080/03091929308203627

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The amplification of magnetic field frozen to a two-dimensional spatially periodic flow consisting of two distinct pulsed Beltrami waves is investigated. The period α of each pulse is long (α » 1) so that fluid particles make excursions large compared with the periodicity length. The action of the flow is reduced to a mapTof a complex vector field Z measuring the magnetic field at the end of each pulse. Attention is focused on the mean field <Z> produced. Under the assumption, <Tk+2Z>−|λ7infin;|2<TKZ>→0asK→∞ an asymptotic representation of the complex constant λ∞ is obtained, which determines the growth rate α−1In (α|λ|). The main result is the construction of a family of smooth vector fields ZNand complex constants λNwhich, for evenN, have the properties <TK+2ZN> =O(α−3(N+2)/4and λN-∞= O(for all integersK(> 0). In the case of the dissipative problem at large but finite magnetic Reynolds numberR(> α), it is argued that the fastest growing mode Z with amplification factor λ is approximated best by ZNc, whereNc ∼ frac12(InR)/(In α) and λ−λNc= O[(α/R⅜].

ISSN:0309-1929    

DOI:10.1080/03091929308203628

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

General features of Beltrami vector fields in a sphere are discussed. Numerical solutions of the kinematic dynamo problem of magnetic fields generation by a Beltrami flow of conducting fluid in a sphere are presented. The Beltrami flow chosen for simulations is chaotic. Maximal temporal growth rates of magnetic field are obtained for magnetic Reynolds numbersRmup to 200, together with associated magnetic eigenmodes forRm100. Their behavior suggests that the dynamo under consideration is fast.

ISSN:0309-1929    

DOI:10.1080/03091929308203629

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor