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

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, Correspondence to: K. Unnikrishnan (kaleekkalunni@gmail.com) 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.

The comparative study of chaoticity and dynamical complexity of the low-latitude ionosphere, over Nigeria, during quiet and disturbed days

“…The presence of chaos is indicated by the positive values of the Lyapunov exponent found in all the computations for all the TEC values obtained for the selected days for all the measuring stations used in this work. This can be expected, as it agrees with results from previous works that show that there is a reasonable presence of chaos in the ionosphere, even in the midst of the influence of stochastic drivers like solar winds (Bhattacharyya, 1990;Wernik and Yeh, 1994;Kumar et al, 2004;Unnikrishnan et al, 2006a, b;Unnikrishnan, 2010).…”

“…The major explanation for this is the fact that Tsallis entropy is based on non-extensive statistical mechanics (Balasis et al, 2009). The ionosphere is a system that can also be described by similar dynamical processes as the magnetosphere, as both systems are also coupled (Unnikrishnan, 2010). Some of the investigations carried out on the chaoticity of both the ionosphere and the magnetosphere have yielded similar results for storm and quiet periods (Unnikrishnan, 2008(Unnikrishnan, , 2010.…”

“…2. This method is similar to that used by Unnikrishnan et al (2006a, b); Unnikrishnan (2010). Further explanations of the dynamical results can be found in Kumar et al (2004).…”

“…Likewise, the minimal embedding dimension, which corresponds to the minimum number of the nearest false neighbors as shown in Fig. 4, can be treated as the optimum value of the embedding dimension in Unnikrishnan et al (2006a, b) and Unnikrishnan (2010). It was observed that for all the daily detrended TEC time series the choice of τ ≥ 25 and m = 3 values of delay and embedding dimension above these values are suitable for analysis of data for all stations.…”

“…The uplifted plasma over the Equator moves along the magnetic field lines in response to gravity, diffusion and pressure gradients and hence, the fountain effect. The fountain effect being controlled by the EXB drift shows the dynamics of the diurnal variation equatorial anomaly (Abdu, 1997;Unnikrishnan, 2010). There is a reduction in the F region ionization density at the magnetic Equator and much enhanced ionization density at the two anomaly crests within ±15 • of the magnetic latitude north and south of the Equator (Rama Rao et al, 2006).…”