Abstract

The geomagnetic storm is an important weather issue in the earth’s ionosphere-magnetosphere system. Many linear and nonlinear systems are involved in this earth-space environment. In order to understand the nonlinearly evolving dynamical system of magnetosphere and ionosphere, Time series analysis of foF2 data, Disturbance Storm Index Dst, Geomagnetic activity Index Ap and some other parameters during various solar cycles has been carried out in this work. The hourly data of critical frequency of F2 layer (foF2) for three ionosonde stations [Townsville (TV51R) 19.7°S, 146.9°E; Canberra (CB53N) 35.3°S, 149.1°E; Juliusruh (JR055) 54.6°N, 13.4°E] have been noted for 4 solar cycles viz., Solar Cycle 20, 21, 22 and 23. Hourly time series analysis has been performed to achieve some functional approaches such as statistical, analytical and spectral approach etc. to examine for the presence of periodicities in the data. Time Series is a sequential set of data which can be measured over time, and since the data being used for this work had been recorded as a function of time under various conditions, the appearance of missing observations in time series data is a very common issue. Different series may require different approaches to estimate these missing values. As such, to vanquish the problem of missing data we have attempted to estimate the missing value of foF2 data for various stations using the technique of Singular Value Decomposition (SVD). Another important method, Lomb Scargle Periodogram (LSP) has been performed on the Empirical Orthogonal Functions (EOFs) u1 and u2 (that has been obtained by SVD) along with the solar parameters such as solar flux f10.7, sun spot number (SSN) etc. and geomagnetic indices such as Dst index, Kp index & Ap index etc. for the four solar cycles to find the correlation, if any. For all the plots after performing LSP the power has been found out at 99% confidence level to see how much significant the generated data with respect to the parameters is. The periodicity obtained after performing LSP are divided into three terms namely:– (a) short-term periodicity, in which 27 days periodicity is found to be prominent, (b) mid-term periodicity, in which 1.3 year periodicity is found to be very common and (c) long-term periodicity, in which 11 years periodicity is very regular in almost among all the parameters and in the EOFs.

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