1,721,067 research outputs found
Some new approaches to the study of the Earth's magnetic field reversals
No full textPaleomagnetic studies clearly show that the polarity of the magnetic fi eld has been subject to reversals. It is
generally assumed that polarity intervals are exponentially distributed. Here, the geomagnetic polarity reversal
record, for the past 166 Ma, is analysed and a new approach to the study of the reversals is presented. In detail, the
occurrence of 1/f-noise in the Power Spectral Density (PSD), relative to geomagnetic fi eld reversals, the existence
of a Zipf's law behaviour for the cumulative distribution of polarity intervals, and the occurrence of punctuated
equilibrium, as shown by a sort of Devil's staircase for the reversal time series, are investigated. Our results give
a preliminary picture of the dynamical state of the geomagnetic dynamo suggesting that the geodynamo works in
a marginally stable out-of-equilibrium confi guration, and that polarity reversals are equivalent to a sort of phase
transition between two metastable states.PublishedJCR Journalope
A Local Intermittency Measure (LIM) approach to the detection of geomagnetic jerks
No full textIn the present work we investigate the temporal distributions of the geomagnetic jerks occurring in the last three decades of
the 20th century using a new method of analysis based on the wavelet transform: the Local Intermittency Measure (LIM). This
method, which allows us to single out intermittent structures within a given time series, was applied to geomagnetic monthly
means time series of the eastward magnetic field component (Y) of 44 worldwide observatories. We study the bimodal
distribution of the jerk occurrence in time for the 1978 and 1991 events and point out a local/regional jerk in South Africa and in
the Pacific Ocean which happened around 1986. The worldwide character of the 1999 geomagnetic jerk is also investigated
integrating the LIM analysis with the traditional straight-line fit.Published261-2723.4. GeomagnetismoJCR Journalreserve
Fractal time statistics of AE-index burst waiting times: evidence of metastability
No full textRecent 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).Published419-4233.9. Fisica della magnetosfera, ionosfera e meteorologia spazialeJCR Journalope
Time intermittency and spectral features of the geomagnetic field
No full textIn the field of geomagnetism a number of studies have been devoted to the investigation of turbulence and intermittency
in the outer core fluid motions. Here, in order to obtain information on such phenomena we study
the time spectral and self-similarity features of the main geomagnetic field fluctuations as measured on the
Earth’s surface. The existence of a power law spectrum, characterised by an exponent a˜-11/3, and an anomalous
scaling of q-th order structure functions on time scales longer than 5 years, suggests the occurrence of intermittent
turbulence rather than classical Kolmogorov turbulence in the fluid core motions. These results are
briefly discussed in connection with the existence of a strong magnetic field and drift-wave turbulence.PublishedJCR Journalope
Permutation entropy analysis of complex magnetospheric dynamics
No full textThe present study is focused on the emergence of dynamical complexity in the Earth's magnetospheric dynamics during magnetic storms as monitored by SYM-H index. A long time series of SYM-H index covering the period from January 2000 to December 2004 is analyzed using a quite novel technique, the permutation entropy analysis. We show that the normalized permutation entropy values of the SYM-H time series decrease during geomagnetic disturbed periods revealing a gradual increase in the temporal correlation of the fluctuations which generates a gradual increase in the complexity degree of the magnetosphere response to the solar wind magnetic field and plasma parameter changes. These large changes in the normalized permutation entropy values and complexity degree observed during the disturbed periods can be interpreted as the signature of dynamical phase transitions happening in proximity to the occurrence of geomagnetic storms and substorms confirming results previously found using different methods. The dependence of the degree of complexity on both the magnitude of the geomagnetic disturbance and the IMF ByGSM and BzGSM components is investigated and discussed.Published25-311A. Geomagnetismo e PaleomagnetismoJCR Journalrestricte
A Revised Forest Fire Model Non-Quasistatically Driven for the Sporadic Activity of the Earth’s Magnetotail
No full textThe 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.PublishedVico Equense, Italy / 24-29 September 20013.9. Fisica della magnetosfera, ionosfera e meteorologia spazialeope
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