On the local Hurst exponent of geomagnetic field fluctuations: Spatial distribution for different geomagnetic activity levels

Michelis, Paola De; Consolini, Giuseppe

doi:10.1002/2014ja020685

Cited by 17 publications

(21 citation statements)

References 38 publications

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“…Last but not the least, we notice that our results on the latitudinal dependence of permutation entropy and complexity measure confirm previous findings obtained on a single magnetic storm and using a different technique [ De Michelis and Consolini , ]. Consequently, the observed results have a general character and are independent from the method of analysis.…”

Section: Discussionsupporting

confidence: 91%

Latitudinal dependence of short timescale fluctuations during intense geomagnetic storms: A permutation entropy approach

2015

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The present study is focused on the analysis of the latitudinal dependence of complexity degree of the short timescale geomagnetic field fluctuations during four intense geomagnetic storms occurring between 2000 and 2003. The aim is that of investigating the qualitative and quantitative changes in the dynamical properties of the magnetospheric system during magnetically disturbed periods. We analyze the short timescale fluctuations (<120 min) of the horizontal component of the Earth's magnetic field at nine different geomagnetic observatories from 49°N magnetic latitude (MLat) to 87°N MLat, by filtering the signal via empirical mode decomposition and successively by applying the permutation entropy analysis to the filtered time series. We show that some properties of the geomagnetic fluctuations during the selected periods are the result of dynamical changes in the magnetospheric system response to the solar wind changes and that these geomagnetic fluctuations display a complex character during the geomagnetic storm development. This evidence supports the idea that the geomagnetic storm nature may be the result of a cooperative and collective dynamics. We also find that the permutation entropy values change with latitude suggesting a latitudinal dependence of the complexity degree of the signals.

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Section: Discussionsupporting

confidence: 91%

Latitudinal dependence of short timescale fluctuations during intense geomagnetic storms: A permutation entropy approach

2015

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“…An alternative method to unveil the characteristic timescales of nonstationary signals is the empirical mode decomposition (EMD) technique, introduced by Huang et al [] [see also Wu and Huang , ], as a preconditioning method for the application of the Hilbert transform. EMD is an adaptive method based on the local characteristics of the data, useful to analyze natural signals [ Vecchio et al , , , ; Alberti et al , ; Vecchio et al , ], also including geomagnetic time series [ De Michelis et al , ; De Michelis and Consolini , ]. Particularly, the EMD does not require to have any “a priori” assumption on the functional form of the basis of the decomposition.…”

Section: Methodsmentioning

confidence: 99%

“…In particular, the characteristic mean frequency f n of all the IMFs is estimated by means of the associated Fourier power spectral density S n ( f ) as

f_{n} = \frac{\int_{0}^{\infty} f S_{n} (f) normald f}{\int_{0}^{\infty} S_{n} (f) normald f}

This allows us to obtain the characteristic timescale oscillation of each mode as

τ_{n} = f_{n}^{- 1}

. Moreover, since the decomposition is local, complete, and orthogonal, the EMD can be used as a filter by reconstructing partial sums of equation in a chosen frequency range [ Laurenza et al , ; Vecchio et al , ; Alberti et al , ; De Michelis and Consolini , ].…”

Section: Methodsmentioning

confidence: 99%

Timescale separation in the solar wind‐magnetosphere coupling during St. Patrick's Day storms in 2013 and 2015

et al. 2017

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In this work, we present a case study of the relevant timescales responsible for coupling between the changes of the solar wind and interplanetary magnetic field (IMF) conditions and the magnetospheric dynamics during the St. Patrick's Day Geomagnetic Storms in 2013 and 2015. We investigate the behavior of the interplanetary magnetic field (IMF) component Bz, the Perreault‐Akasofu coupling function and the AE, AL, AU, SYM‐H, and ASY‐H geomagnetic indices at different timescales by using the empirical mode decomposition (EMD) method and the delayed mutual information (DMI). The EMD, indeed, allows to extract the intrinsic oscillations (modes) present into the different data sets, while the DMI, which provides a measure of the total amount of the linear and nonlinear shared information (correlation degree), allows to investigate the relevance of the different timescales in the solar wind‐magnetosphere coupling. The results clearly indicate the existence of a relevant timescale separation in the solar wind‐magnetosphere coupling. Indeed, while fluctuations at long timescales (τ > 200 min) show a large degree of correlation between solar wind parameters and magnetospheric dynamics proxies, at short timescales (τ < 200 min) this direct link is missing. This result suggests that fluctuations at timescales lower than 200 min, although triggered by changes of the interplanetary conditions, are mainly dominated by internal processes and are not directly driven by solar wind/IMF. Conversely, the magnetospheric dynamics in response to the solar wind/IMF driver at timescales longer than 200 min resembles the changes observed in the solar wind/IMF features. Finally, these results can be useful for Space Weather forecasting.

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“…One of the possible indication of the existence of the turbulent regime in the ionosphere is the power−law behaviour of the statistical or spectral properties of physical quantities [see, e.g., Kintner Jr., 1976;Sugiura et al, 1982;Heppner et al, 1993;Pulkkinen et al, 2006;Golovchanskaya et al, 2006;Abel et al, 2007;Kozelov et al, 2008;Golovchanskaya and Kozelov, 2010;Cousins and Shepherd, 2010;De Michelis et al, 2015a, 2015b. For this reason, in this work, we focus on the analysis of the scaling properties of the ionospheric electron density to characterize its possible turbulent state, which may play a key role in the generation and in the dynamic of ionospheric inhomogeneities.…”

Section: Methods Of Analysismentioning

confidence: 99%

“…In recent literature, the Hurst exponent has been successfully used to characterise the correlations and the persistent features inherent to magnetic field fluc− tuations observed from the ground [Balasis et al, 2006[Balasis et al, , 2008[Balasis et al, , 2009De Michelis et al, 2015a] and via in situ ionospheric measurements performed by the Swarm mission [De Michelis et al, 2015b;De Michelis et al, 2016;De Michelis et al, 2017]. In this work, we applied the Hurst exponent technique to the electron density fluctuations measured by Swarm in the ionospheric F− layer by performing the same approach of the detrended structure function analysis (DSFA) used by De Michelis et al [2015a] and consisting in the following steps.…”

Section: Methods Of Analysismentioning

confidence: 99%

Characterising the electron density fluctuations in the high-latitude ionosphere at Swarm altitude in response to the geomagnetic activity

Giannattasio

Michelis²,

Consolini³

et al. 2018

Annals of Geophysics

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The high−latitude ionosphere is characterised by plasma density irregularities with typical lengths in a wide range of scales (from ~1 m up to ~1000 km). The enhancement of these irregularities caused for instance by severe Space Weather conditions can affect trans−ionos− pheric communications between ground facilities and satellites. For this reason, an accurate characterisation of the dynamic properties of electron density and their variation with the geomagnetic activity level is of particular interest for the Space Weather especially at high latitudes. In this framework, taking advantage of high resolution in situ measurements by the recent ESA−Swarm space mission orbiting in the ionospheric F−layer, we study both the dynamical properties of the electron density and the scaling properties of the electron den− sity fluctuations at high latitudes in the Northern and Southern Hemispheres in response to changes in the geomagnetic activity levels via nonlinear techniques involving the first−order structure functions. Indeed, it has been shown that the turbulent character of the ionos− pheric plasma density plays an important role in the generation and dynamics of ionospheric plasma density irregularities and the study of the scaling properties of the electron density fluctuations permits us to characterise the possible turbulent state of the ionospheric elec− tron density. The obtained results are consistent with the turbulent character of the ionospheric dynamics, and with the presence of dif− ferent turbulent regimes that show a dependence on the geomagnetic activity levels, magnetic latitude and MLT values.

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On the local Hurst exponent of geomagnetic field fluctuations: Spatial distribution for different geomagnetic activity levels

Cited by 17 publications

References 38 publications

Latitudinal dependence of short timescale fluctuations during intense geomagnetic storms: A permutation entropy approach

Latitudinal dependence of short timescale fluctuations during intense geomagnetic storms: A permutation entropy approach

Timescale separation in the solar wind‐magnetosphere coupling during St. Patrick's Day storms in 2013 and 2015

Characterising the electron density fluctuations in the high-latitude ionosphere at Swarm altitude in response to the geomagnetic activity

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