A comparative study on chaoticity of equatorial/low latitude ionosphere over Indian subcontinent during geomagnetically quiet and disturbed periods

K. Unnikrishnan

doi:10.5194/npg-17-765-2010

Abstract

Abstract. In the present study, the latitudinal aspect of chaotic behaviour of ionosphere during quiet and storm periods are analyzed and compared by using GPS TEC time series measured at equatorial trough, crest and outside crest stations over Indian subcontinent, by employing the chaotic quantifiers like Lyapunov exponent (LE), correlation dimension (CD), entropy and nonlinear prediction error (NPE). It is observed that the values of LE are low for storm periods compared to those of quiet periods for all the stations considered here. The lowest value of LE is observed at the trough station, Agatti (2.38° N, Geomagnetically), and highest at crest station, Mumbai (10.09° N, Geomagnetically) for both quiet and storm periods. The values of correlation dimension computed for TEC time series are in the range 2.23–2.74 for quiet period, which indicate that equatorial ionosphere may be described with three variables during quiet period. But the crest station Mumbai shows a higher value of CD (3.373) during storm time, which asserts that four variables are necessary to describe the system during storm period. The values of non linear prediction error (NPE) are lower for Agatti (2.38° N, Geomagnetically) and Jodhpur (18.3° N, Geomagnetically), during storm period, compared to those of quiet period, mainly because of the predominance of non linear aspects during storm periods The surrogate data test is carried out and on the basis of the significance of difference of the original data and surrogates for various aspects, the surrogate data test rejects the null hypothesis that the time series of TEC during storm and quiet times represent a linear stochastic process. It is also observed that using state space model, detrended TEC can be predicted, which reasonably reproduces the observed data. Based on the values of the above quantifiers, the features of chaotic behaviour of equatorial trough crest and outside the crest regions of ionosphere during geomagnetically quiet and disturbed periods are briefly discussed.

Highlights

In the real world system, pure determinism is rather unlikely to be realised, since all systems somehow interact with their surroundings and deterministic picture may be regarded only as a limiting case of a more general framework involving fluctuations in the environment and in the system itself (Hegger et al, 1999)
A time series, Sn is the sequence of scalar measurements of some quantity, which depends on the current state of a system, taken at multiples of a fixed sampling time ( t), and Fig. 1a represents the typical time series of Geo Augmented Navigation (GAGAN)-TEC measured at Agatti
We are interested in the nonlinear TEC variabilities, it is essential to minimize the influence of diurnal variations observed in the data

Summary

Introduction

In the real world system, pure determinism is rather unlikely to be realised, since all systems somehow interact with their surroundings and deterministic picture may be regarded only as a limiting case of a more general framework involving fluctuations in the environment and in the system itself (Hegger et al, 1999). Several interesting studies and modeling efforts on magnetospheric dynamics based on theories of nonlinearity, chaos and stochasticity were successfully carried out. Bhattacharyya (1990) had studied the chaotic behaviour of ionospheric density fluctuations, using amplitude and phase scintillation data, and found the existence of low- dimensional chaos. Wernik and Yeh (1994) have studied chaotic behaviour of ionospheric turbulence using scintillation data and numerical modeling of scintillation at high latitude. Kumar et al (2004) reported the evidence of low dimensional chaos in a set of TEC data, obtained by Faraday rotation technique, measured at a high-latitude station, Goose Bay (47◦ N, 286◦ E). Unnikrishnan et al (2006) have analyzed the deterministic chaotic behaviour of GPS TEC fluctuations at mid-latitude.

Results

Discussion

Conclusion