ConceFT For Coronal Index Periodicities Analysis

The sun is the closest star to us,the most closely related to human beings,and the direct and indirect creator of almost all the energy that the earth needs.The solar activity disturbs the sun-terrestrial space and the atmosphere at the upper altitude of the earth,and affects the sun-terrestrial space environment,the earth's climate,the estimation of the life of artificial satellites,ground power and communications,etc.Therefore,the study of solar activity has extensive and important application value.Various characteristic indicators of solar activity,such as coronal index,sunspot number,solar flare index,etc.,clearly show the periodic or quasi-periodic law of solar activity.The law has not been fully understood,so there is still much room for exploration in the study of the solar activity cycle.As a widely used tool,time-frequency analysis can reveal the characteristics of non-stationary time series,such as the periodicity in the signal,in the study of solar activity cycle.Compared with traditional time-frequency analysis methods,Concentration of Frequency and Time via amultitapered synchrosqueezed transform(Conce FT)has the characteristics of high time-frequency resolution and better noise robustness,and it can capture and describe the trend of time-varying signals more accurately.In this thesis,a new time-frequency analysis method,Conce FT is used to study the period of the Modified Coronal Index(MCI),and the signal decomposition technique is added before the time-frequency analysis,so that the main activity period of the corrected corona index can be found more accurately.The main research elements include:(1)The continuous wavelet transform,synchrosqueezing wavelet transform and Conce FT are compared and analyzed by using the original data of modified coronal index.(2)The modified coronal index is decomposed by synchrosqueezing wavelet transform and singular spectrum analysis,respectively,and the main component signals that can represent the periodic activity of the MCI are obtained.(3)Use the Conce FT on the periodic signal obtained after signal decomposition,and draw the spectrum.At the same time,the maximum energy band of each periodic signal is extracted,and the maximum period and minimum period of the solar activity cycle are divided.Calculate the average period and standard deviation of the maximum energy band,describe the activity characteristics of each period signal,and explain the physical meaning of each period based on the existing literature research.The main results of this thesis are:(1)Among the spectrum of the continuous wavelet transform,the synchrosqueezing wavelet transform and the Conce FT,the spectrum of the Conce FT has higher resolution,better robustness,more accurate capture of periodic signals and more detailed description of the periodic characteristics.(2)There are 11-year Schwabe cycle and 27-day solar rotation period with the most significant solar activity in the MCI,which can strongly support the activity change of the revised coronal index and are closely related to the both.(3)Compared with the existing literature research,a new 27-year cycle is found in the MCI,which is related to the solar magnetic activity cycle.(4)Periods of other scales are also found in the MCI,15.41 years,6.75 years,5.48 years,about 3.5 years and about 1.4 years,and there are similar periods in other solar activity characteristic indexes.