Observed geomagnetic induction effect on Dst-related magnetic observations under different disturbance intensities of the magnetospheric ring current

Abstract

Based on the spherical harmonic expansion of geomagnetic disturbance observed on the mid-latitude surface of the Earth, external and internal field separation is conducted in which the external component is magnetic disturbance caused by the magnetospheric ring current and the internal component is that raised by the correspondingly induced currents within the Earth. The objectives are to evaluate the influences of the induced internal field on the surface magnetic observations and to reveal the response performance of internal geomagnetic induction under different strengths of magnetospheric ring current fluctuations for better understanding of the disturbance storm time (Dst) index variations. The results show that the ratio of the internal component to surface observation does not remain constant in storm time. During the main phase of the storm, the ratio variation follows the pattern of logarithmic growth with storm evolution up to the top value at the Dst-minimum; then, the ratio slowly decreases in the long recovery phase. Multiple small logarithmic growths are superimposed on the traces of internal ratios, corresponding to temporary ring current intensification during the storm main phase and amplifying the effect of this intensification on surface magnetic observations. With the intensification of magnetospheric storms from the level of (−200 nT, − 100 nT) to (−300 nT, − 200 nT) and (−500 nT, − 300 nT) classified with the Dst-minimum, the top value of the ratio averaged for each storm group in the superposed epoch analysis method increases from the value of 0.295 ± 0.014 to 0.300 ± 0.016 and 0.308 ± 0.015, respectively. It is demonstrated that the geomagnetic induction exceeds the linear relation with the intensification of the external field, which is physically reasonable and coincident with the Faraday's law of induction. Due to the effects of high induction of the oceans and lateral heterogeneity of electric conductivity distribution in the upper mantle of the Earth, the geomagnetic induction and its contribution to surface geomagnetic disturbance vary significantly among observatories. This factor should be considered in the research of magnetospheric current systems.

Data Agreement Analysis And Correction of Comparative Geomagnetic Vector Observations

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Extremely severe space weather and geomagnetically induced currents in regions with locally heterogeneous ground resistivity

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Core surface sub-centennial magnetic flux patches: characteristics and evolution

“…The "decadal, " 11-year oscillation is considered as solar-cycle-related, contaminating the observatory annual means, while the ~ 22, ~ 80 year, and steady constituents are of internal origin. We are aware that a decadal signal could also have a partial internal origin, if only the induced response to external variations, the amplitude of which is assessed to ~ 1/3 of the inducing one (Price 1967;Xu et al 2015), was considered. Also, decadal and shorter signals originating in the Earth's core have been recently studied (Gillet et al 2010;Silva et al 2012;Holme and de Viron 2013;Cox et al 2016); however, additional effort is needed to decide on the origin and degree of overlapping.…”