DSpace Collection:

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

2012-10-31T23:00:00Z

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

2011-08-26T22:00:00Z

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.

Application of Autoscala to ionograms recorded by the AIS-Parus ionosonde

2010-04-30T22:00:00Z

Title: Application of Autoscala to ionograms recorded by the AIS-Parus ionosonde Authors: Krasheninnikov, I.; Pushkov InstituteofTerrestrialMagnetism,IonosphereandRadiowavePropagation,Russia; Pezzopane, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Scotto, C.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Autoscala was applied to ionograms recorded by the digital AIS-Parus ionosonde, built at the Pushkov Institute of Terrestrial Magnetism,Ionosphere and Radiowave Propagation, Russia, and installed in Moscow (55.5N,37.5E). Some results in regard to the reliability of the foF2, foF1, and ftEs autoscaled characteristics are presented and discussed. The flexibility of Autoscala is illustrated based on its modular structure.

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

2008-08-20T22:00:00Z

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.

Pc3 pulsations during variable IMF conditions

1998-12-31T23:00:00Z

Title: Pc3 pulsations during variable IMF conditions Authors: Villante, U.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Lepidi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Francia, P.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Vellante, M.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Lepping, R. P.; Laboratory for Extraterrestrial Physics, NASA/GSFC, Greenbelt, USA; Mariani, F.; Dipartimento di Fisica, Università di Roma-Tor Vergata, Italy Abstract: Pc3 geomagnetic field fluctuations detected at low latitude (L'Aquila, Italy) during the passage of a high velocity solar wind stream, characterized by variable interplanetary magnetic field conditions, are analyzed. Higher frequency resonant fluctuations and lower frequency phenomena are simultaneously observed; the intermittent appearance and the variable frequency of the longer period modes can be well interpreted in terms of the variable IMF elements; moreover their polarization characteristics are consistent with an origin related to external waves propagating in antisunward direction. A comparison with simultaneous observations performed at Terra Nova Bay (Antarctica) provides additional evidence for a clear relationship between the IMF and Pc3 pulsations also at very high latitudes.

Geomagnetic field variations at low and high latitude during the January 10-11, 1997 magnetic cloud

1998-07-14T22:00:00Z

Title: Geomagnetic field variations at low and high latitude during the January 10-11, 1997 magnetic cloud Authors: Villante, U.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Francia, P.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Lepidi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; De Lauretis, M.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Pietropaolo, E.; Dipartimento di Fisica, Università dell'Aquila, L'Aquila, Italy; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Lazarus, A. J.; Center for Space Research, MIT, Cambridge, USA; Lepping, R. P.; Lab. for Extraterrestrial Physics, NASA/GSFC, Greenbelt, USA; Mariani, F.; Dipartimento di Fisica, Università di Roma-Tor Vergata, Italy Abstract: On Jan. 10-11, 1997 a wide magnetic cloud reached the Earth triggering intense geomagnetic activity. Observations performed at low and very high latitude show that the same features appear simultaneously in correspondence to different changes in the solar wind conditions. In particular, highly polarized modes are simultaneously observed at the same discrete frequencies after the passage of the high density solar wind region following the cloud. SI's and ULF waves polarization are also examined in a wide latitudinal and longitudinal extent.

Geomagnetic storms, dependence on solar and interplanetary phenomena: a review

2004-12-31T23:00:00Z

Title: Geomagnetic storms, dependence on solar and interplanetary phenomena: a review Authors: Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; 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: Geomagnetic storms are probably the most intensively measured perturbations of the Earth’s magnetic field. They are multi-faceted phenomena that result as a final element of a chain of processes that starts on the Sun, a ects the solar wind and the interplanetary medium, and ends on the Earth. At present, one of the key questions in the scientific community is the ability to predict the occurrence of geomagnetic storms on the basis of solar and interplanetary space observations. For these reasons, in recent years a number of investigations have been carried out to understand the solar-terrestrial relationships and to ascertain those factors that are ultimately responsible for geomagnetic storms. Here a brief review of published results on the geomagnetic storm e ectiveness from CMEs, solar flares, as well as interplanetary event observations, is presented.

Imaging of fast moving electron-density structures in the polar cap

2007-05-31T22:00:00Z

Title: Imaging of fast moving electron-density structures in the polar cap Authors: Spencer, P. S. J.; Department of Electronic and Electrical Engineering, University of Bath, U.K.; Mitchell, C. N.; Department of Electronic and Electrical Engineering, University of Bath, U.K. Abstract: The imaging of fast-moving electron-density structures in the polar cap presents a unique set of challenges that are not encountered in other ionospheric imaging problems. GPS observations of total electron content in the polar cap are sparse compared to other regions in the Northern Hemisphere. Furthermore, the slow relative motion of the satellites across the sky complicates the problem since the velocity of the plasma can be large in comparison and traditional approaches could result in image blurring. This paper presents a Kalman-filter based method that incorporates a forward projection of the solution based on a model plasma drift velocity field. This is the first time that the plasma motion, rather than just integrations of electron density, has been used in an ionospheric imaging algorithm. The motion is derived from the Weimer model of the electric field. It is shown that this novel approach to the implementation of a Kalman filter provides a detailed view of the polar cap ionosphere under severe storm conditions. A case study is given for the October 2003 Halloween storm where verification is provided by incoherent scatter radars.

Tempeste, sottotempeste e baie magnetiche

1992-12-31T23:00:00Z

Title: Tempeste, sottotempeste e baie magnetiche Authors: De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia

Interplanetary magnetic field and its possible effects on the mid-latitude ionosphere II

1994-04-30T22:00:00Z

Title: Interplanetary magnetic field and its possible effects on the mid-latitude ionosphere II Authors: Tulunay, Y.; Middle East Technical University, Department of Aeronautical Engineering, Ankara, Turkey Abstract: Using criticaI frequencies, f0F2 from the Uppsala, Lannion and Dourbes ionosonde stations, the possible effects of the orientation of the IMF on mid-latitude ionosphere are further investigated. For this purpose, the regular diurnal, seasonal and solar cycle variations in the f0F2 data were removed by subtracting the mean of f0F2 for the same UT on all the magnetically quiet days (Ap< 6) within 15 days around the IMF Bz turnings. This yields the deviation from the average quiet-time value ?f0F2. The data are sorted according to the polarity of the IMF Bz and the effects of the southward turnings are discussed. Hapgood et al. (1991), Tulunay et al. (1991), Tulunay and Rahman (1992) investigated the possible effects of the IMF on mid-latitude ionosphere by employing the Slough and Argentine Islands f0F2 data. In order to facilitate a comparison the same method of analysis is being adopted again. However, in the present work the southward polarity changes in IMF Bz with no consideration of the IMF sector structure were considered only.