ULF Waves above the Nightside Auroral Oval during Substorm Onset

Rae, I. J.; Watt, Clare E. J.

doi:10.1002/9781119055006.ch7

Cited by 12 publications

(12 citation statements)

References 83 publications

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“…The Earth's magnetosphere, whose field strength varies from about 60 000 nT in polar low-Earth orbit to about 100 nT at geosynchronous orbit, has different wave populations present with frequencies ranging from a few mHz to a few Hz on both the day-and nightside (e.g., Sakurai et al, 1999;Rae and Watt, 2016). Traditionally, the continuous pulsations which are denoted by Pc1-5 can be divided into categories that are characterized by a given frequency range as summarized in Table 1 (e.g., Jacobs et al, 1964;Fraser, 2007;Menk, 2011).…”

Section: Ulf Waves In the Magnetospherementioning

confidence: 99%

Investigation of a low-cost magneto-inductive magnetometer for space science applications

Regoli¹,

Moldwin²,

Pellioni³

et al. 2018

Geosci. Instrum. Method. Data Syst.

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Abstract.A new sensor for measuring low-amplitude magnetic fields that is ideal for small spacecraft is presented. The novel measurement principle enables the fabrication of a low-cost sensor with low power consumption and with measuring capabilities that are comparable to recent developments for CubeSat applications. The current magnetometer, a software-modified version of a commercial sensor, is capable of detecting fields with amplitudes as low as 8.7 nT at 40 Hz and 2.7 nT at 1 Hz, with a noise floor of 4 pT/ √ Hz at 1 Hz. The sensor has a linear response to less than 3 % over a range of ±100 000 nT. All of these features make the magneto-inductive principle a promising technology for the development of magnetic sensors for both space-borne and ground-based applications to study geomagnetic activity.

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Section: Ulf Waves In the Magnetospherementioning

confidence: 99%

Investigation of a low-cost magneto-inductive magnetometer for space science applications

Regoli¹,

Moldwin²,

Pellioni³

et al. 2018

Geosci. Instrum. Method. Data Syst.

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“…We note that our four band‐pass filters are close to the Pc 1–3 bands and Pi 1 band [ Jacobs et al ., ]. Given that Pc 1 waves occurrence peaks close to 60° magnetic latitude [ Park et al ., ] and Pi 1 waves are closely linked with auroral activity (see review by Rae and Watt []), it is perhaps unsurprising that wave activity disrupts the calculation of FACs on these scales. However, according to Park et al .…”

Section: Impact On Exploitation Of Swarm Fac Datamentioning

confidence: 99%

Identifying intervals of temporally invariant field‐aligned currents from Swarm: Assessing the validity of single‐spacecraft methods

et al. 2017

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Field‐aligned currents (FACs) are a fundamental component of coupled solar wind‐magnetosphere‐ionosphere. By assuming that FACs can be approximated by stationary infinite current sheets that do not change on the spacecraft crossing time, single‐spacecraft magnetic field measurements can be used to estimate the currents flowing in space. By combining data from multiple spacecraft on similar orbits, these stationarity assumptions can be tested. In this technical report, we present a new technique that combines cross correlation and linear fitting of multiple spacecraft measurements to determine the reliability of the FAC estimates. We show that this technique can identify those intervals in which the currents estimated from single‐spacecraft techniques are both well correlated and have similar amplitudes, thus meeting the spatial and temporal stationarity requirements. Using data from European Space Agency's Swarm mission from 2014 to 2015, we show that larger‐scale currents (>450 km) are well correlated and have a one‐to‐one fit up to 50% of the time, whereas small‐scale (<50 km) currents show similar amplitudes only ~1% of the time despite there being a good correlation 18% of the time. It is thus imperative to examine both the correlation and amplitude of the calculated FACs in order to assess both the validity of the underlying assumptions and hence ultimately the reliability of such single‐spacecraft FAC estimates.

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“…Finally, it has been shown that both the ULF wave amplitudes and auroral brightness grow exponentially at the location of ionospheric substorm onset (Rae et al 2012;Kalmoni et al 2015Kalmoni et al , 2017. Although the relationship between the enhancement of ULF waves and auroral brightness is no longer in doubt (see review by Rae and Watt 2016), the relative timing and localisation of Pi1, Pi1-2 and Pi2 waves across the auroral zone at substorm onset have not yet been investigated.…”

Section: Introductionmentioning

confidence: 99%

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

et al. 2017

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Substorm onset is marked in the ionosphere by the sudden brightening of an existing auroral arc or the creation of a new auroral arc. Also present is the formation of auroral beads, proposed to play a key role in the detonation of the substorm, as well as the development of the large-scale substorm current wedge (SCW), invoked to carry the current diversion. Both these phenomena, auroral beads and the SCW, have been intimately related to ultra-low frequency (ULF) waves of specific frequencies as observed by ground-based magnetometers. We present a case study of the absolute and relative timing of Pi1 and Pi2 ULF wave bands with regard to a small substorm expansion phase onset. We find that there is both a location and frequency dependence for the onset of ULF waves. A clear epicentre is observed in specific wave frequencies concurrent with the brightening of the substorm onset arc and the presence of "auroral beads". At higher and lower wave frequencies, different epicentre patterns are revealed, which we conclude demonstrate different characteristics of the onset process; at higher frequencies, this epicentre may demonstrate phase mixing, and at intermediate and lower frequencies these epicentres are characteristic of auroral beads and cold plasma approximation of the "Tamao travel time" from near-earth neutral line reconnection and formation of the SCW.

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ULF Waves above the Nightside Auroral Oval during Substorm Onset

Cited by 12 publications

References 83 publications

Investigation of a low-cost magneto-inductive magnetometer for space science applications

Investigation of a low-cost magneto-inductive magnetometer for space science applications

Identifying intervals of temporally invariant field‐aligned currents from Swarm: Assessing the validity of single‐spacecraft methods

Using ultra-low frequency waves and their characteristics to diagnose key physics of substorm onset

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