Evolution of Dynamical Complexities in Geospace as Captured by Dst Over Four Solar Cycles 1964–2008.

Abstract

AbstractThe dynamical complexities of geospace has been examined by investigating the characteristic chaotic properties of hourly Dst values obtained from the World Data Center for Geomagnetism, Kyoto, over four solar cycles (1964–2008) using nonlinear methods: sample entropy, Lyapunov exponents, correlation dimension, recurrence quantification analysis, and multifractal detrended fluctuation. Throughout the solar cycles considered, the space environment was observed to be chaotic based on Lyapunov exponents obtained. The order of increasing complexity in the solar cycles based on recurrence rate (RR) values is Cycle 21 < 22 < 23 < 20. Similar patterns and trend were observed in the correlation dimension values for the different solar cycles. The peak of each solar cycle is associated with high chaoticity. In all the analysis considered, high values of sample entropy, Lyapunov exponent, correlation dimension, correspond to increasing chaoticity. However, lower value of RR signifies more chaotic activity. The solar cycle 20 with the greatest values of mean sunspot number (651.62) and standard deviation of sunspot number (1,656.90) has the greatest chaoticity. The chaoticity in the magnetosphere increases with increasing geomagnetic activity as captured by Dst index. Similar trends were not observed in BZ and solar wind dynamic pressure which showed that the observed chaoticity is due to internal variations. The multifractal spectrum of Dst at all solar cycles considered revealed that the chaotic activities in the magnetosphere are not influenced by the local fluctuations in the region. The degree of multifractality were found to be in the order Cycle 20 > Cycle 23 > Cycle 21 > Cycle 22.