Observations of high-latitude geomagnetic field fluctuations during St. Patrick’s Day storm: Swarm and SuperDARN measurements

Abstract

The aim of this work is to study the properties of the magnetic field's fluctuations produced by ionospheric and magnetospheric electric currents during the St. Patrick's Day geomagnetic storm (17 March 2015). We analyse the scaling features of the external contribution to the horizontal geomagnetic field recorded simultaneously by the three satellites of the Swarm constellation during a period of 13 days (13-25 March 2015). We examine the different latitudinal structure of the geomagnetic field fluctuations and analyse the dynamical changes in the magnetic field scaling features during the development of the geomagnetic storm. Analysis reveals consistent patterns in the scaling properties of magnetic fluctuations and striking changes between the situation before the storm, during the main phase and recovery phase. We discuss these dynamical changes in relation to those of the overall ionospheric polar convection and potential structures as reconstructed using SuperDARN data. Our findings suggest that distinct turbulent regimes characterised the mesoscale magnetic field's fluctuations and that some factors, which are known to influence large-scale fluctuations, have also an influence on mesoscale fluctuations. The obtained results are an example of the capability of geomagnetic field fluctuations data to provide new insights about ionospheric dynamics and ionosphere-magnetosphere coupling. At the same time, these results could open doors for development of new applications where the dynamical changes in the scaling features of the magnetic fluctuations are used as local indicators of magnetospheric conditions.

Scaling Features of High‐Latitude Geomagnetic Field Fluctuations at Swarm Altitude: Impact of IMF Orientation

“…To estimate ξ (1) and ξ (2) for the geomagnetic field fluctuations, we use the detrended structure function method (De Michelis et al, , ). We take into consideration a moving window of 400 s, and in each time window we construct a detrended time series x ( t ) obtained by subtracting to the original time series, which is in our case the intensity of the horizontal component of the Earth's magnetic field with a time resolution of 1 s, its average long‐term trend.…”

“…Recently, using measurements of the Earth's magnetic field recorded on board of Swarm satellites, the local scale index of the first‐order structure function of the geomagnetic field fluctuations has been evaluated (De Michelis et al, , ), showing its capability both to give new insights about the ionosphere‐magnetosphere coupling and to use it as local indicator of the overall magnetospheric‐ionospheric coupling conditions and turbulence. Indeed, the scaling properties of the first‐order structure function of the geomagnetic field fluctuations permit us to evaluate the associated scale index (also named as Hurst exponent) and consequently to characterize their degree of persistence.…”

“…Indeed, the scaling properties of the first-order structure function of the geomagnetic field fluctuations permit us to evaluate the associated scale index (also named as Hurst exponent) and consequently to characterize their degree of persistence. Evidences suggest that the spatiotemporal persistence character of the geomagnetic field fluctuations may be used to localize ionospheric structures caused by different physical processes (De Michelis et al, 2015) and that the knowledge of the Hurst exponent can provide a global and/or local characterization of the nature and level of ionospheric turbulence, which can be displayed along a single satellite orbit (De Michelis et al, 2016) or through average maps over the region of interest (De Michelis et al, 2015). This paper analyzes the impact of the different IMF orientations on the spatial distribution of the degree of persistence of the geomagnetic field fluctuations recorded by Swarm A satellite for 1 year (from 15 April 2014 to 15 April 2015) with particular attention to the northern high-latitude region.…”

Characterising the electron density fluctuations in the high-latitude ionosphere at Swarm altitude in response to the geomagnetic activity

“…In recent literature, the Hurst exponent has been successfully used to characterise the correlations and the persistent features inherent to magnetic field fluc− tuations observed from the ground [Balasis et al, 2006[Balasis et al, , 2008[Balasis et al, , 2009De Michelis et al, 2015a] and via in situ ionospheric measurements performed by the Swarm mission [De Michelis et al, 2015b;De Michelis et al, 2016;De Michelis et al, 2017]. In this work, we applied the Hurst exponent technique to the electron density fluctuations measured by Swarm in the ionospheric F− layer by performing the same approach of the detrended structure function analysis (DSFA) used by De Michelis et al [2015a] and consisting in the following steps.…”

Variation of atmospheric electric field measured at Vostok, Antarctica, during St. Patrick's Day storms on 24th solar cycle

“…During this period, IMF components are not stable and they highly fluctuate because of turbulent motion of plasma, which ultimately controls the convection pattern between dawn and dusk. It is understood, the ionospheric plasma convection pattern is well established for IMF southward, but not well known for a sudden change in the orientation of IMF [De Michelis et al, 2016]. Hence, the synoptic snapshot of convection map from SuperDARN is essential to explain the convection pattern changes.…”