Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes

Unnikrishnan, K. P.; Saito, Akinori; Otsuka, Yuichi; Yamamoto, M.; Fukao, S.

doi:10.5194/angeo-23-3439-2005

Cited by 11 publications

(4 citation statements)

References 36 publications

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“…Various studies suggested that the ionospheric electron content perturbations were also caused by the penetration of magnetospheric electric fields, which were controlled or modulated by the oscillations in the IMF/solar wind pressure (Borovsky, et al, 1993;Fejer and Scherliess, 1998;Sobral et al, 1997;Huang et al, 2002;Unnikrishnan, et al, 2005). The energy and particle injection that takes place during magnetospheric disturbances produce multiple changes to the Earth's high latitude ionosphere-thermosphere system (Pincheira et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Comparison of chaotic aspects of magnetosphere under various physical conditions using AE index time series

Unnikrishnan

2008

Ann. Geophys.

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Abstract. The deterministic chaotic behaviour of magnetosphere was analyzed, using AE index time series. The significant chaotic quantifiers like, Lyapunov exponent, spatiotemporal entropy and nonlinear prediction error for AE index time series under various physical conditions were estimated and compared. During high solar activity (1991), the values of Lyapunov exponent for AE index time series representing quiet conditions (yearly mean = 0.5±0.1 min −1 ) have no significant difference from those values for corresponding storm conditions (yearly mean = 0.5±0.17 min −1 ). This implies that, for the cases considered here, geomagnetic storms may not be an additional source to increase or decrease the deterministic chaotic aspects of magnetosphere, especially during high solar activity. During solar minimum period (1994), the seasonal mean value of Lyapunov exponent for AE index time series belong to quiet periods in winter (0.7±0.11 min −1 ) is higher compared to corresponding value of storm periods in winter (0.36±0.09 min −1 ). This may be due to the fact that, stochastic part, which is D st dependent could be more prominent during storms, thereby increasing fluctuations/stochasticity and reducing determinism in AE index time series during storms. It is observed that, during low solar active period (1994), the seasonal mean value of entropy for time series representing storm periods of equinox is greater than that for quiet periods. However, significant difference is not observed between storm and quiet time values of entropy during high solar activity (1991), which is also true for nonlinear prediction error for both low and high solar activities. In the case of both high and low solar activities, the higher standard deviations of yearly mean Lyapunov exponent values for AE index time series for storm periods compared to those for quiet periods might be due to the strong interplay between stochasticity and determinism during storms.Correspondence to: K. Unnikrishnan (kaleekkal unni@yahoo.com) It is inferred that, the external driving forces, mainly due to solar wind, make the solar-magnetosphere-ionosphere coupling more complex, which generates many active degrees of freedom with various levels of coupling among them, under various physical conditions. Hence, the superposition of a large number of active degrees of freedom can modify the stability/instability conditions of magnetosphere.

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Section: Discussionmentioning

confidence: 99%

Comparison of chaotic aspects of magnetosphere under various physical conditions using AE index time series

Unnikrishnan

2008

Ann. Geophys.

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“…Therefore it is suggested that, the nighttime TIDs play an important role to generate the 3‐m‐scale irregularity in the mid latitude F region ionosphere [ Saito et al , 2002]. Also, the TEC perturbations observed on storm days exhibit interesting transitions characterized by decreasing magnitude of perturbation component, at the region 39°–34°N (30°–25°N geomagnetically), due to the interaction with higher background content of expanded anomaly crest [ Unnikrishnan et al , 2005].…”

Section: Comparison Of Nonlinear Aspects Of Ionosphere Under Various mentioning

confidence: 99%

Differences in magnetic storm and quiet ionospheric deterministic chaotic behavior: GPS total electron content analyses

Unnikrishnan¹,

Saito²,

Fukao³

2006

J. Geophys. Res.

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1] In the present study we have investigated whether deterministic chaotic behavior is exhibited by the GPS total electron content (TEC) fluctuations at midlatitude ionosphere, under various geophysical conditions, using nonlinear aspects. Local slopes of the logarithms of correlation sum for the time series of TEC representing the winter storm and quiet periods exhibit a clear plateau, indicating a fractal dimension of the attractor of the system (5.86 ± 0.09 for quiet time and 4.15 ± 0.03 for storm time, at 35°N). The observed positive values of the Lyapunov exponent (for quiet and storm times at 35.1°N, the values are 0.1695 Â 10 À2 s À1 and 0.1167 Â 10 À2 s À1 , respectively) are another important criterion for chaoticity of the system during the above periods. To further confirm this, we have employed the surrogate data test. 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. Also, we compared the chaotic behavior of TEC during disturbed and quiet periods, under different seasons and latitudes. For all seasons, the values of the Lyapunov exponent during quiet times are greater than those during storm periods for the latitude sector, 35°-41°N. The nonlinear aspects presented here imply that geomagnetic disturbances influence the stability/instability conditions of ionosphere due to the superposition of various active degrees of freedom generated by an external stochastic driver (solar wind), and could alter the inherent dynamics of the system, if the coupling is powerful. Citation: Unnikrishnan, K., A. Saito, and S. Fukao (2006), Differences in magnetic storm and quiet ionospheric deterministic chaotic behavior: GPS total electron content analyses,

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“…The storm‐associated disturbance electric field, which is active at equatorial/low latitudes, the associated poleward expansion of equatorial ionization anomaly (EIA), and the storm‐driven disturbance neutral wind system originating at the high‐latitude regime will produce unpredictable TEC perturbations over the midlatitude region. TEC perturbations propagating through this region suffer severe damping and undergo interesting transitions due to the ionization gradients of expanded anomaly crest [ Unnikrishnan et al , 2005]. Hence the latitude sector of the present study, 32–44°N, and the five locations, i.e., 32.1, 35.1, 38.1, 41.1, and 44.1°N, are very sensitive to ionospheric disturbances and irregularities, and nonlinear analysis may reveal more about the underlying dynamics.…”

Section: Comparison Of Nonlinear and Chaotic Aspects Of Daytime And Nmentioning

confidence: 99%

Differences in daytime and nighttime ionospheric deterministic chaotic behavior: GPS total electron content analyses

Unnikrishnan¹,

Saito²,

Fukao³

2006

J. Geophys. Res.

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[1] A study on the differences in deterministic chaotic behavior of midlatitude ionosphere during local daytime and nighttime, using GPS total electron content (TEC), under various geophysical conditions, is conducted. The noninteger value of correlation dimension, the positive value of Lyapunov exponent, the power spectra in broadband, etc., and the implementation of surrogate data test strongly indicate the chaoticity of the underlying dynamics of ionosphere. The values of correlation dimension obtained for daytime and nighttime TEC of a major storm period in winter measured at 35.1°N are 3.25 ± 0.03 and 2.35 ± 0.05, respectively, which indicate the fractal dimension of the attractor. The values of Lyapunov exponent are estimated as 0.1387 Â 10 À2 s À1 and 0.0979 Â 10 À2 s À1 for the above time series during daytime and nighttime, respectively. It is observed that at the lower sector (32.1-38.1°N), Lyapunov exponents of daytime are higher than those of nighttime, during a major storm period. The values of nonlinear prediction error during nighttime are higher than those of daytime for all the latitudes, except at 32.1°N, where the trend is opposite. During winter quiet times, the values of Lyapunov exponent of nighttime at the lower sector (32.1-38.1°N) have higher values than those of daytime, where as at the upper section (41.1-44.1°N), both have the same values. During equinoctial quiet times also, the above trend exists, by exhibiting higher values of Lyapunov exponent for nighttime compared to those of daytime, especially at the upper latitude sector (38.1-44.1°N) of the present study. The values of nonlinear prediction error, during quiet times in winter and equinox, generally show higher values at daytimes, compared to those at nighttimes. However, during summer, the opposite trend is observed, with higher values of the above parameter at daytime compared to those at nighttime, except at 32.1°N. This is a case study in a broad sense and the results presented here are based on the observations made for each event. The possible causes of chaotic aspects of ionosphere, based on the values of above quantifiers under various geophysical conditions, are discussed.Citation: Unnikrishnan, K., A. Saito, and S. Fukao (2006), Differences in daytime and nighttime ionospheric deterministic chaotic behavior: GPS total electron content analyses,

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Transition region of TEC enhancement phenomena during geomagnetically disturbed periods at mid-latitudes

Abstract: Abstract. Large-scale TEC perturbations/enhancements observed during the day sectors of major storm periods, 12-

Cited by 11 publications

References 36 publications

Comparison of chaotic aspects of magnetosphere under various physical conditions using AE index time series

Comparison of chaotic aspects of magnetosphere under various physical conditions using AE index time series

Differences in magnetic storm and quiet ionospheric deterministic chaotic behavior: GPS total electron content analyses

Differences in daytime and nighttime ionospheric deterministic chaotic behavior: GPS total electron content analyses

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