On multifractality of high-latitude geomagnetic fluctuations

Abstract

Abstract. In order to contribute to the understanding of solar wind±magnetosphere interactions the multifractal scaling properties of high-latitude geomagnetic uctuations observed at the Thule observatory have been studied. Using the local observatory data and the present experimental knowledge only it seems hard to characterize directly the, presumably intermittent, mesoscale energy accumulation and dissipation processes taking place at the magnetotail, auroral region, etc. Instead a positive probability measure, describing the accumulated local geomagnetic signal energy content at the given time scales has been introduced and its scaling properties have been studied. There is evidence for the multifractal nature of the so de®ned intermittent ®eld , a result obtained by using the recently introduced technique of large deviation multifractal spectra. This technique allows us to describe the geomagnetic¯uctuations locally in time by means of singularity exponents a, which represent a generalization of the local degree of di erentiability and characterize the power-law scaling dependence of the introduced measure on resolution. A global description of the geomagnetic¯uctuations is insured by the spectrum of exponents f a which represents a rate function quantifying the deviations of the observed singularities a from the expected value. The results show that there exists a multifractal counterpart of the previously reported spectral break and di erent types of f a spectra describe thē uctuations in direct dissipation or loading-unloading regimes of the solar wind±magnetosphere interaction. On the time scale of substorms and storms the multifractal structure of the loading±unloading mode¯uc-tuations seems to be analogous to the simple multiplicative P-model, while the f a spectra in direct dissipation regime are close but not equal to the features of a uniform distribution. Larger deviations from the multiplicative model are observed when the in¯uence of the solar wind¯uctuations is examined. On this basis it is expected that an extended multifractal analysis of the singularity structure of nearEarth plasma system¯uctuations would lead to improved geomagnetic diagnosis of the magnetospheric dynamics.

Similarities between the dynamics of geomagnetic signal and of heartbeat intervals

“…3b). This result is consistent with recent studies that also suggest the presence of multifractality in other geomagnetic data [41,42]. We also perform a test with shuffled time series in order to investigate the origin of the multifractal behavior.…”

Global geomagnetic responses to the IMF <i>B</i><sub>z</sub> fluctuations during the September/October 2003 high-speed stream intervals

“…This is because of the largely disparate physical character of these domains and the nonlinearities in the magnetospheric response to the solar wind input (Pulkkinen et al, 2007). Vörös (2000), using the multi-fractal approach on highlatitude geomagnetic fluctuations time series, found an important timescale around 60 min. According to (Benzi and Biferale, 2009), the multi-fractal approach to turbulence is based on the hypotheses that the statistical properties of the turbulent time series do exhibit scaling properties.…”

Latitudinal variation of stochastic properties of the geomagnetic field

“…Ground-based geomagnetic indices (Takalo et al, 1999;Wanliss, 2004Wanliss, , 2005Balasis et al, 2011) and individual magnetometer stations (Vörös, 2000;Wanliss and Reynolds, 2003) provide excellent signals of the fractal nature of space weather energy dissipation. Part of the reason for this is the property of the earth's magnetic field lines to focus and converge when approaching the earth.…”