Research On The Spectrum Characterization Method Of Sunspot Number And Geomagnetic Index Based On Synchronous Compression Transform

Sunspots number is an important index describing the level of solar activity;the geomagnetic Ap index is an index of the global full-time geomagnetic disturbance intensity,describing the level of global geomagnetic activity.Studying the activity characteristics of the sunspot and the Ap index can be used to understand the solar activity,the changes in the Earth's magnetic field,and the effects of the Sun on the Earth's magnetic field.Most of the current analysis is to use the spectrum analysis method to characterize the activity cycle of sunspots number and the Ap index to obtain the activity characteristics of the two indices.However,the spectrum analysis methods for sunspots number and the Ap index are mostly Fourier transforms or wavelet transforms.These spectrum analysis methods have problems such as frequency broadening,inaccurate positioning,and noise pollution in the spectral representation of non-stationary signals and noise-containing sunspots and Ap indices.The synchrosqueezed transforms method can compress and rearrange the instantaneous frequency of the wavelet transform to improve the resolution of the spectrogram,and the frequency positioning is accurate and robust to noise interference.This method has been widely used in oil and gas detection and microseismic signal extraction.Applying the synchrosqueezed transforms to the spectral representation of the black number and the Ap index can solve the problems in the spectral representation of the two indices.Accurately characterize the activity cycle of the Ap index and sunspots number.The research content of this paper includes:(1)Improvements to synchrosqueezed transforms.Synchrosqueezed transforms are inaccurate in high frequency positioning and can be contaminated by noise.For the problem of noise pollution,adaptive threshold denoising is performed;for the problem of inaccurate frequency localization in the high frequency part,the filtering method and the greedy algorithm are combined to extract the wavelet ridges of the high frequency part.(2)Applying the improved synchrosqueezed transforms to the spectral representation of the Ap index and the black number.A multi-scale activity cycle of sunspots number and the Ap index is obtained.In the spectrogram,the activity periods of each scale are clearly expressed,the positioning is accurate,and the time-varying characteristics are obvious.The multi-scale period of the sunspot and the Ap index was compared.(3)The 1.3-1.7 year activity cycle of the Ap index and the sunspot number was studied.The results show that the 1.3-1.7 years of the Ap index and sunspots number change with time;the Ap index changes significantly during different solar activity weeks,and the odd solar activity week is the periodic component of the adjacent even solar activity week.It is high and shows the characteristics of up and down fluctuations;the activity period Ap index lags behind sunspots number,and the sun affects geomagnetic activity.In this paper,the improved synchrosqueezed transforms is applied to the geomagnetic Ap index and the sunspot number.The experimental results show that the spectral characterization results of the method used in this paper are better than the current spectrum characterization method,and the activity of Ap index and black number is obtained.The periodic and time-varying properties can be further used in scientific research to contribute to the study of the formation and evolution of the sunspot oscillation law and the influence of sunspots on the Earth's magnetic field.