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On the multi-scale nature of large geomagnetic storms: an empirical mode decomposition analysis

Wed, 31 Oct 2012 23:00:00 GMT

Title: On the multi-scale nature of large geomagnetic storms: an empirical mode decomposition analysis Authors: De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Consolini, G.; INAF – Istituto di Astrofisica e Planetologia Spaziali, 00133 Roma, Italy; Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Complexity and multi-scale are very common properties of several geomagnetic time series. On the other hand, it is amply demonstrated that scaling properties of geomagnetic time series show significant changes depending on the geomagnetic activity level. Here, we study the multiscale features of some large geomagnetic storms by applying the empirical mode decomposition technique. This method, which is alternative to traditional data analysis and is designed specifically for analyzing nonlinear and nonstationary data, is applied to long time series of Sym-H index relative to periods including large geomagnetic disturbances. The spectral and scaling features of the intrinsic mode functions(IMFs) into which Sym-H time series can be decomposed, as well as those of the Sym-H time series itself, are studied considering different geomagnetic activity levels. The results suggest an increase of dynamical complexity and multi-scale properties for intermediate geomagnetic activity levels.

An information theory approach to the storm‐substorm relationship

Fri, 26 Aug 2011 22:00:00 GMT

Title: An information theory approach to the storm‐substorm relationship Authors: De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Consolini, G.; Istituto Nazionale di Astrofisica–Istituto di Fisica dello Spazio Interplanetario, Rome, Italy; Materassi, M.; Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, Sesto Fiorentino, Italy; Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: One of the most interesting aspects of the global magnetospheric response to solar wind changes is the relationship between storms and substorms. Here we present new results on the relationship between these two different classes of magnetospheric phenomena by approaching the problem on the side of information theory. Using the Auroral Electrojet AL and SYM‐H indices as representative proxies of magnetic substorms and storms, we investigate the transfer of information by means of transfer entropy analysis (Schreiber, 2000). The obtained results seem, on average, to indicate the presence of a net transfer of information from AL to SYM‐H on time scales shorter than 10 h. On the basis of this result, geomagnetic substorms may act as a driver for the occurrence of geomagnetic storms. However, carrying out a more careful analysis which takes into account the global geomagnetic daily activity, we suggest that the direction of information flow between substorms and storms depends on the global activity level. Indeed, if it is true that a sequence of magnetospheric substorms may drive a moderate storm, it is also true that very large storms may dominate and drive the occurrence of magnetospheric substorms.

Rank ordering multifractal analysis of the auroral electrojet index

Thu, 05 May 2011 22:00:00 GMT

Title: Rank ordering multifractal analysis of the auroral electrojet index Authors: Consolini, G.; INAF-Istituto di Fisica dello Spazio Interplanetario, 00133 Roma, Italy; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: In the second half of the 90s interest grew on the complex features of the magnetospheric dynamics in response to solar wind changes. An important series of papers were published on the occurrence of chaos, turbulence and complexity. Among them, particularly interesting was the study of the bursty and fractal/multifractal character of the high latitude energy release during geomagnetic storms, which was evidenced by analyzing the features of the Auroral Electrojet (AE) indices. Recently, the multifractal features of the small time-scale increments of AE-indices have been criticized in favor of a more simple fractal behavior. This is particularly true for the scaling features of the probability density functions (PDFs) of the AE index increments. Here, after a brief review of the nature of the fractal/multifractal features of the magnetospheric response to solar wind changes, we investigate the multifractal nature of the scaling features of the AE index increments PDFs using the Rank Ordering Multifractal Analysis (ROMA) technique. The ROMA results clearly demonstrate the existence of a hierarchy of scaling indices, depending on the increment amplitude, for the data collapsing of PDFs relative to increments at different time scales. Our results confirm the previous results by Consolini et al. (1996) and the more recent results by Rypdal and Rypdal (2010).

The 6 April 2009 earthquake at L’Aquila: a preliminary analysis of magnetic field measurements

Mon, 08 Feb 2010 23:00:00 GMT

Title: The 6 April 2009 earthquake at L’Aquila: a preliminary analysis of magnetic field measurements Authors: Villante, U.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; De Lauretis, M.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; De Paulis, C.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Francia, P.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Piancatelli, A.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Piancatelli, A.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Pietropaolo, E.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Vellante, M.; Dipartimento di Fisica, Universit`a L’Aquila, L’Aquila, Italy; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Palangio, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Schwingenschuh, K.; Institut f¨ur Weltraumforschung, Graz, Austria; Prattes, G.; Institut f¨ur Weltraumforschung, Graz, Austria; Magnes, W.; Institut f¨ur Weltraumforschung, Graz, Austria; Nenovski, P.; Geophysical Institute, Sofia, Bulgaria Abstract: Several investigations reported the possible identification of anomalous geomagnetic field signals prior to earthquake occurrence. In the ULF frequency range, candidates for precursory signatures have been proposed in the increase in the noise background and polarization parameter (i.e. the ratio between the amplitude/power of the vertical component and that one of the horizontal component), in the changing characteristics of the slope of the power spectrum and fractal dimension, in the possible occurrence of short duration pulses. We conducted, with conventional techniques of data processing, a preliminary analysis of the magnetic field observations performed at L’Aquila during three months preceding the 6 April 2009 earthquake, focusing attention on the possible occurrence of features similar to those identified in previous events. Within the limits of this analysis, we do not find compelling evidence for any of the features which have been proposed as earthquake precursors: indeed, most of aspects of our observations (which, in some cases, appear consistent with previous findings) might be interpreted in terms of the general magnetospheric conditions and/or of different sources.

Monitoring the Dynamics of the Ionosphere–Plasmasphere System by Ground-Based ULF Wave Observations

Tue, 31 Mar 2009 22:00:00 GMT

Title: Monitoring the Dynamics of the Ionosphere–Plasmasphere System by Ground-Based ULF Wave Observations Authors: Vellante, M.; Dipartimento di Fisica, Università dell’Aquila, L’Aquila, Italy; Förster, M.; GeoForschungsZentrum, Potsdam, Germany; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Jakowski, N.; Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Kommunikation und Navigation, Neustrelitz, Germany; Zhang, T. L.; Institut für Weltraumforschung, Graz, Austria; Villante, U.; Dipartimento di Fisica, Università dell’Aquila, L’Aquila, Italy; De Lauretis, M.; Dipartimento di Fisica, Università dell’Aquila, L’Aquila, Italy; Zolesi, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Magnes, W.; Institut für Weltraumforschung, Graz, Austria Abstract: Cross-spectral analysis of ULF wave measurements recorded at ground magnetometer stations closely spaced in latitude allows accurate determinations of magnetospheric field line resonance (FLR) frequencies. This is a useful tool for remote sensing temporal and spatial variations of the magnetospheric plasma mass density. The spatial configuration of the South European GeoMagnetic Array (SEGMA, 1.56 < L < 1.89) offers the possibility to perform such studies at low latitudes allowing to monitor the dynamical coupling between the ionosphere and the inner plasmasphere. As an example of this capability we present the results of a cross-correlation analysis between FLR frequencies and solar EUV irradiance (as monitored by the 10.7-cm solar radio flux F10.7) suggesting that changes in the inner plasmasphere density follow the short-term (27-day) variations of the solar irradiance with a time delay of 1–2 days. As an additional example we present the results of a comparative analysis of FLR measurements, ionospheric vertical soundings and vertical TEC measurements during the development of a geomagnetic storm.

A Revised Forest Fire Model Non-Quasistatically Driven for the Sporadic Activity of the Earth’s Magnetotail

Thu, 31 Jan 2002 23:00:00 GMT

Title: A Revised Forest Fire Model Non-Quasistatically Driven for the Sporadic Activity of the Earth’s Magnetotail Authors: De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Consolini, G.; Istituto di Fisica dello Spazio Interplanetario, CNR, Via Fosso del Cavaliere 100, 00133 Roma, Italy Editors: Sawaya-Lacoste, H.; ESA Publications Division Abstract: The energy release during magnetospheric substorms in response to solar wind changes consists of two main physical processes: the directly-driven and the unloading processes. Recent analysis on the sporadic activity related to the unloading process seems to indicate that the magnetospheric response to solar wind changes might resemble the behaviour of an out-of-equilibrium system near a marginally stable point (critical point). Here, we present a modified version of the well-known forest-fire cellular automaton (FFM) not quasistatically driven for the sporadic activity of the energy release in the geotail regions as revealed by the auroral electrojet index.

On the Earth’s magnetospheric dynamics: Nonequilibrium evolution and the fluctuation theorem

Wed, 20 Aug 2008 22:00:00 GMT

Title: On the Earth’s magnetospheric dynamics: Nonequilibrium evolution and the fluctuation theorem Authors: Consolini, G.; Istituto di Fisica dello Spazio Interplanetario, INAF, Rome, Italy; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Tozzi, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: The Earth’s magnetosphere evolves as an out-of-equilibrium system due to the continuous coupling with the solar wind and the Earth’s ionosphere. We test the validity of the symmetries implied in the Fluctuation Theorem for the magnetospheric dynamics by investigating the long-term evolution of the Earth’s magnetospheric ring current, as monitored by the geomagnetic Dst index. We find that the symmetries implied by the Fluctuation Theorem are all verified, thus providing a proof of the existence of a steady state far from equilibrium for the Earth’s magnetosphere. A possible link between the Dst index and the entropy production rate is also proposed and discussed.

Fractal time statistics of AE-index burst waiting times: evidence of metastability

Mon, 31 Dec 2001 23:00:00 GMT

Title: Fractal time statistics of AE-index burst waiting times: evidence of metastability Authors: Consolini, G.; Istituto di Fisica dello Spazio Interplanetario – CNR, Roma, Italy; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Recent observations and analyses evidenced that the magnetotail, as well as the magnetospheric dynamics are characterised by a scale-free behaviour and intermittence. These results, along with numerical simulations on cellular automata, suggest that the observed scale-invariance may be due to forced and/or self-organised criticality (FSOC), meaning that the magnetotail operates near a marginally stable state (Chang, 1999). On the other hand, it was underlined that a complex magnetic field topology in the geotail regions may play a relevant role in the impulsive energy relaxation (Consolini and Chang, 2001).

A revised forest-fire cellular automaton for the nonlinear dynamics of the Earth’s magnetotail

Fri, 31 Aug 2001 22:00:00 GMT

Title: A revised forest-fire cellular automaton for the nonlinear dynamics of the Earth’s magnetotail Authors: Consolini, G.; Istituto di Fisica dello Spazio Interplanetario, Consiglio Nazionale delle Ricerche-CNR, Via Fosso del Cavaliere 100, 00133 Roma, Italy; De Michelis, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Recent observations and numerical simulations seem to suggest that the Earth’s magnetotail plasma could exist in a near-criticality configuration, and that many features of the magnetospheric response to solar wind changes could be described by avalanche models displaying self-organized criticality. Further evidences of this near-criticality dynamics have been found analyzing the statistical features of the auroral electrojet (AE) index. Here, we present a cellular automaton, based on a revised version of the well-known forest-fire model, for the nonlinear dynamics of the Earth’s magnetotail. This simple model, chaotically driven using a 1-d coupled map, is able to capture many of the statistical features of the magnetospheric response to solar wind changes. The results, compared with previous analyses of the AE-index features, are discussed in the framework of a near-criticality dynamics of the magnetospheric tail plasma.

Long period geomagnetic field fluctuations at Terra Nova Bay (Antarctica)

Sat, 14 Jun 1997 22:00:00 GMT

Title: Long period geomagnetic field fluctuations at Terra Nova Bay (Antarctica) Authors: Villante, U.; Dipartimento di Fisica, Università dell'Aquila, L’Aquila, Italy; Lepidi, S.; Dipartimento di Fisica, Università dell'Aquila, L’Aquila, Italy; Francia, P.; Dipartimento di Fisica, Università dell'Aquila, L’Aquila, Italy; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Palangio, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: A statistical analysis of the power spectra (0.7 - 5 mHz) of the geomagnetic field components H and D recorded at Terra Nova Bay (Antarctica) during three austral summers close to the maximum of solar activity reveals power enhancements in the H componenta t = 3.3, 3.9 and 4.5 mHz, which become more evident during daytime intervals. During intervals characterized by higher solar wind speeds these spectral features more clearly emerge and are also accompanied by other enhancements at lower frequencies (= 1.2, 1.9 and 2.7 mHz). The observed frequencies are close to the ones detected both at auroral and low latitudes.