Review of Data Analysis Techniques for Estimating Ionospheric Currents Based on MIRACLE and Satellite Observations

Vanhamäki, Heikki; Juusola, Liisa

doi:10.1002/9781119324522.ch24

Cited by 7 publications

(5 citation statements)

References 79 publications

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“…Figure 2a shows the ionospheric equivalent current density (J , arrows) and corresponding horizontal ground magnetic field magnitude (| H |, color), calculated by fitting the superposed magnetic field of a layer of 2D SECSs at 90 km altitude to the measured B x and B y . B z cannot be included in the fitting because it cannot be represented in terms of ionospheric equivalent currents only (Untiedt and Baumjohann, 1993;Vanhamäki and Juusola, 2018). Fig.…”

Section: Field Separation and Equivalent Currentsmentioning

confidence: 99%

Drivers of rapid geomagnetic variations at high latitudes

et al. 2023

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Abstract. We have examined the most intense external (magnetospheric and ionospheric) and internal (induced) |dH/dt| (amplitude of the 10 s time derivative of the horizontal geomagnetic field) events observed by the high-latitude International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers between 1994 and 2018. While the most intense external |dH/dt| events at adjacent stations typically occurred simultaneously, the most intense internal (and total) |dH/dt| events were more scattered in time, most likely due to the complexity of induction in the conducting ground. The most intense external |dH/dt| events occurred during geomagnetic storms, among which the Halloween storm in October 2003 featured prominently, and drove intense geomagnetically induced currents (GICs). Events in the prenoon local time sector were associated with sudden commencements (SCs) and pulsations, and the most intense |dH/dt| values were driven by abrupt changes in the eastward electrojet due to solar wind dynamic pressure increase or decrease. Events in the premidnight and dawn local time sectors were associated with substorm activity, and the most intense |dH/dt| values were driven by abrupt changes in the westward electrojet, such as weakening and poleward retreat (premidnight) or undulation (dawn). Despite being associated with various event types and occurring at different local time sectors, there were common features among the drivers of most intense external |dH/dt| values: preexisting intense ionospheric currents (SC events were an exception) that were abruptly modified by sudden changes in the magnetospheric magnetic field configuration. Our results contribute towards the ultimate goal of reliable forecasts of dH/dt and GICs.

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Section: Field Separation and Equivalent Currentsmentioning

confidence: 99%

Drivers of rapid geomagnetic variations at high latitudes

et al. 2023

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“…The magnitude, spatial distribution, and temporal variations of the horizontal currents and FAC can be estimated from the magnetic field they produce. Over the years, several techniques have been developed for this task, as discussed in various Chapters of this book (see also Vanhamäki and Juusola 2018, and reference therein). The present chapter gives an overall introduction to the The original version of this chapter was revised.…”

Section: Introductionmentioning

confidence: 99%

Introduction to Spherical Elementary Current Systems

Vanhamäki

Juusola

2019

Ionospheric Multi-Spacecraft Analysis Tools

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This is a review of the Spherical Elementary Current System or SECS method, and its various applications to studying ionospheric current systems. In this chapter, the discussion is more general, and applications where both ground-based and/or satellite observations are used as the input data are discussed. Application of the SECS method to analyzing electric and magnetic field data provided by the Swarm satellites will be discussed in more detail in the next chapter.

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“…A key factor in the separation of internal and external magnetic field contributions is to use all three components of the measured magnetic field. While either the horizontal components or the vertical component can be fully described by either 125 the equivalent current sheet placed below or above the ground, reconstruction of all three component requires both equivalent current layers (Untiedt and Baumjohann, 1993;Vanhamäki and Juusola, 2018), and thus makes the separation possible.…”

Section: Image Magnetometer Network 2002mentioning

confidence: 99%

Three principal components describe the spatiotemporal development of meso-scale ionospheric equivalent currents around substorm onsets

Juusola¹,

Viljanen²,

Partamies³

et al. 2023

Preprint

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Abstract. Substorms are a commonly occurring but insufficiently understood form of dynamics in the coupled magnetosphere-ionosphere system, associated with space weather disturbances and auroras. We have used Principal Component Analysis (PCA) to characterize the spatiotemporal development of ionospheric equivalent currents as observed by the International Monitor for Auroral Geomagnetic Effects (IMAGE) magnetometers during 28 substorm onsets identified by Frey et al. (2004). Auroral observations were provided by all-sky cameras. We found that the equivalent currents can typically be described by three components: a channel of poleward equivalent current (wedgelet), a westward electrojet (WEJ) associated with an auroral arc, and a vortex. The WEJ and vortex are located at the equatorward end of the channel, which has been associated with Bursty Bulk Flows (BBFs) by previous studies. Depending on its polarity, the vortex either indents the WEJ and arc equatorward, or bulges the WEJ poleward while winding the arc into an auroral spiral. In addition, there may be a background current system associated with the large-scale convection. The dynamics of the WEJ, vortex, and channel can describe up to 95 % of the variance of the time derivative of the equivalent currents during the examined 20 min interval. Rapid geomagnetic variations at the substorm onset location, which can drive Geomagnetically Induced Currents (GIC) in technological conductor networks, are mainly associated with the oscillations of the WEJ, which may be driven by oscillations of the transition region between dipolar and tail-like field lines in the magnetotail due to the BBF impact. The results contribute to the understanding of substorm physics and to the understanding of processes that drive intense GIC.

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Review of Data Analysis Techniques for Estimating Ionospheric Currents Based on MIRACLE and Satellite Observations

Cited by 7 publications

References 79 publications

Drivers of rapid geomagnetic variations at high latitudes

Drivers of rapid geomagnetic variations at high latitudes

Introduction to Spherical Elementary Current Systems

Three principal components describe the spatiotemporal development of meso-scale ionospheric equivalent currents around substorm onsets

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