Research On The Quasi-Biannual Oscillation Of Solar Wind Based On Irregularity Index

As the only star in the solar system,the sun is very closely related to humans and the earth.Since the discovery of the solar wind in the middle of the last century,the long-term evolution characteristics of solar wind activity,the solar cycle behavior of the solar wind,especially the high-frequency quasi-periodic behavior of 1-3 years(the quasi-biennial oscillation)has always been the key topic of solar physics and space physics research.And it is of great significance to help us further understand the relationship between the origin region of the solar wind and its acceleration mechanism.At present,the research on the quasi-biennial oscillation phenomenon in solar activity mainly focuses on the relatively regular and clearer solar activity indicators such as the international sunspot number and polar light spot,while the research on solar wind speed is rarely concerned.In this dissertation,the irregularity index proposed by Shapoval(2013)is used to study the solar wind speed sequence.By analyzing the regular and irregular characteristics in the long-term evolution of the solar wind,the hidden nonlinear change information is mined.This helps us to further explore the time distribution characteristics of quasi-biennial oscillations in solar wind activities.The work done by this article is as follows:Firstly,a phase-space reconstruction of the daily solar wind speed series from November 1963 to March 2018,so that the dynamic characteristics existing in the data can be displayed in the high-dimensional phase space in the form of phase trajectories,and the overall characteristics of dynamical systems can be explored.It was found that there seems to be an attraction domain in the reconstructed trajectory of the solar wind speed,and there is still a certain cyclic and highly variable structure in the phase diagram,and this phenomenon is just in line with the irregularity of the solar wind speed with a large number of high-frequency oscillations but periodic and quasiperiodic activities.Secondly,the irregularity index sequence is calculated based on the reconstructed data to analyze the performance characteristics of the irregularity of solar wind activity in different solar activity cycles.Since the irregularity index can reflect the nonlinear variation characteristics of the original sequence,it helps us to understand the variation characteristics of the internal mechanism of solar activity more clearly from the perspective of nonlinear dynamics.The research results show that in each solar activity cycle lasting about 11 years,its irregularity index will roughly experience two quasi-5.5-year periodic oscillations,based on this,we construct a quantitative index to measure the strength of this new cycle,and discuss in detail whether the evolution law of the 5.5-year quasi-periodic phenomenon is modulated by the quasi-biennial oscillation.Finally,the solar wind has a relatively complex periodicity.In this paper,a statespace model that can handle complex seasonal patterns is used to fit the daily solar wind speed data,so as to explore the temporal distribution characteristics of quasi-biennial oscillations in its activities.By constructing four different cases of the seasonal cycle in the fitting model,the evolution law of the irregularity degree of the fitting data in the two periods before and after the change of the internal activity mechanism of the sun in1996 was observed,and compare it with the results obtained from the original solar wind speed sequence,so as to obtain a quasi-bi-annual oscillation cycle pattern reflecting the irregularity of the solar wind speed.We can draw these conclusions from the work just done:(1)The solar wind activity mechanism changed significantly around 1996,and its irregularity increased rapidly since this period;(2)During the period from 1963 to 1996,the 1.3-year cycle oscillation in solar wind activity was relatively weak,and there may be a relatively significant 1.7-year quasi-biennial oscillation,that is,the quasi-biennial shock during this period is mainly dominated by 1.7-year cycle activities;(3)After 1996,the solar activity has entered a new round of quiet period,and its internal activity mechanism has also undergone significant changes.During the same period,the quasi-bi-annual oscillation in solar wind activity also manifested as the result of co-modulation with a 1.3-year cycle and a 1.7-year cycle;(4)The state change of solar activity around 1996 may be closely related to the gradual strengthening of the 1.3-year quasi-biennial oscillation during this period.