Research On Propagation Of The Heliospheric Current Sheet

The heliospheric current sheet is an important structure in the slow solar wind and meaningful for space weather prediction.Occasionally,the heliospheric current sheet causes a sudden change in the polarity of the interplanetary magnetic field,the change in the polarity of the interplanetary magnetic field may produce a series of space weather events.Therefore,it is of important scientific significance and application value to study the propagation rule of the heliospheric current sheet.This paper uses multi-spacecraft observation methods,combined with case studies,statistical studies,and related model results,to study the propagation rule of the heliospheric current sheet in the slow solar wind.1.In Situ Analysis of Heliospheric Current Sheet PropagationThe heliospheric current sheet is an important structure not only for understanding the physics of interplanetary space but also for space weather prediction.We investigate the differences of the heliospheric current sheet arrival time between three spacecraft separated in heliolongitude,heliolatitude and radial distance from the Sun(STEREO A,STEREO B and ACE)to understand the key factors controlling the heliospheric current sheet propagation.By assuming that the source of the solar wind does not evolve except for the effects of solar rotation,we first test the first order approach method(ignoring latitudinal differences),using STEREO observation during the year 2007,when the Sun was quiet and the two STEREO spacecraft were separated in heliolongitude by less than 44?.The first order approach method matches well with observations for many events except for those events when the heliospheric current sheet has a small inclination angle to the heliospheric equatorial plane.The latitudinal effect is suggested to account for such discrepancies.The predictions are not improved much by considering the heliospheric current sheet inclination angle obtained from the potential field source surface(PFSS)model.However,the predictions match well with the observations when the heliospheric current sheet inclination angle at 1AU is obtained from the time differences of heliospheric current sheet arrival times between the STEREO B and ACE spacecraft.An improved model of calculating the inclination of the heliospheric current sheet other than PFSS is needed.2.The Warped Heliospheric Current SheetThe global shape of the intersection of the heliospheric current sheet with the heliospheric equatorial plane is usually considered to be an Archimedean spiral,however,so far this has not been measured directly.We used multi-spacecraft measurements to determine its global shape.The time-shifted measured locations are fitted with Archimedean spirals.In most cases,the locations are fitted very well with Archimedean spirals,in addition to the direction of heliospheric current sheet determined by the Minimum Variation Analysis.However,there is one case in which the direction of the heliospheric current sheet does not fit well with the Archimedean spiral and therefore we fit it with a sinusoidal function in addition to an Archimedean spiral.The result showed that in some cases,the heliospheric current sheet is better described with an Archimedean spiral,superposed by small-scale ripples.The Main Innovation Points in this Dissertation:· We used multi-spacecraft observations to detect the large scale of the heliosphericcurrent sheet,the Parker spiral structure of the heliospheric current sheet at an astro-nomical unit is confirmed by direct observation data;· We Studied the influence of the latitude difference and the type of the heliosphericcurrent sheet on the propagation time of the heliospheric current sheet,and clarifiedthe important role of latitude difference in the propagation of current sheet;· Based on the data of the heliospheric current sheet observed by multi-spacecraft,wediscussed the fine structure of the heliospheric current sheet and its causes.