An investigation into a generalized Fisk-type heliospheric magnetic field

Abstract

The existence of a Fisk-type heliospheric magnetic field (HMF) has been contested since the Fisk field [Fisk, 1996] challenged the traditional view of the HMF first proposed by Parker [1958]. Several modifications of the original Fisk field model have been published in the past [Schwadron, 2002], of which the Fisk-Parker hybrid HMF model of Burger and Hitge [2004] is one. A detailed derivation and the uniqueness of the Fisk-Parker hybrid magnetic field expressions are shown in this study for the first time. This study also presents a divergence-free generalised Fisk HMF model to further test the existence of a Fisk-type field. The generalised Fisk field model implements a spatially dependent differential rotation rate of the photosphere by using newly developed transformations to map a magnetic field line from the solar wind source surface to the photosphere. The footpoint trajectories on the source surface as well the magnetic field line configurations are shown. The data analyses methods of Forsyth et al. [2002] are used to search for a signature of a generalised Fisk field model during solar minimum conditions using the magnetic field data from the first solar orbit of Ulysses. The generalised Fisk field agrees better with the observed magnetic field during all intervals scanned by Ulysses except during one interval. The 26-day recurrent cosmic-ray variations from data collected from the global neutron monitor network are investigated and agree well with the results of Richardson et al. [1999] and Paizis et al. [1999]. The results of this study provides further support for the existence of a Fisk-type HMF.

Die bestaan van ’n Fisk-tipe heliosferiese magneetveld (HMV) is betwis sedert the Fisk veld [Fisk, 1996] die tradisionele uitgangspunt van die eerste HMV uitgedaag het wat voorgestel is deur Parker [1958]. Verskeie veranderinge van die oorspronklike Fisk veld is gepubliseer in die verlede [Schwadron, 2002], waarvan die Fisk-Parker hibried HMV van Burger and Hitge [2004] een is. ’n Gedetailleerde afleiding en uniekheid van die Fisk-Parker hibried magneetveld vergelykings word vir die eerste keer voorgestel in hierdie studie. Hierdie studie stel ook die divergensie-vrye veralgemeende Fisk HMV model bekend om die bestaan van ’n Fisk-tipe veld verder te toets. Die veralgemeende Fisk model implementeer ’n ruimtelike afhanklike differensi¨ele rotasie tempo van die fotosfeer deur gebruik te maak van nuwe transformasies om magneetveldlyne van die sonwindbronoppervlak na die fotosfeer te spoor. Die voetpuntbane op die bronoppervlak sowel as die magneetveldlynopset word gewys. Die data-ontleding metodes van Forsyth et al. [2002] word gebruik om te soek vir ’n handtekening van die veralgemeende Fisk veld gedurende son-minimum toestande deur gebruik te maak van die magneetveld data van die eerste sonomwenteling van Ulysses. Die veralgemeende Fisk veld stem beter ooreen met die geobserweerde magneetveld gedurende al die intervalle wat geskandeer is deur Ulysses behalwe vir een interval. Die 26-dag herhalende kosmiesestraalvariasies van die data versamel deur die globale neutron monitor netwerk is ondersoek en stem baie goed ooreen met die resultate van Richardson et al. [1999] en Paizis et al. [1999] Die resultate van hierdie studie gee verdere ondersteuning vir die bestaan van ’n Fisk-tipe HMV.