THEMIS observations of double-onset substorms and their association with IMF variations

Cheng, C.; Russell, C. T.; Angelopoulos, V.; Mann, I. R.; Glaßmeier, Karl‐Heinz; Baumjohann, W.

doi:10.5194/angeo-29-591-2011

Cited by 5 publications

(10 citation statements)

References 45 publications

(65 reference statements)

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“…But as the IMF turned north after the C2 onset from south at the C1 onset, both had decreasing magnitude in the IMF clock angle. This shows the orientation change of the IMF to south from north and then north again that is the same as those found by Cheng et al (2011). Moreover, Vsw and Dp stayed around 650 km/s and 1.8 nPa, respectively.…”

Section: Solar Wind Observations and Geomagnetic Indicessupporting

confidence: 83%

Characteristic study of double substorm onsets in response to IMF variations

Cheng

Russell

Mann

et al. 2018

Preprint

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Abstract. A study of the characteristics of double substorm onsets in response to variations of the interplanetary magnetic field (IMF) is undertaken with magnetotail and ground observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission on 18 March 2009 and 3 April 2009 (Kp ~ 0), and on 16 February 2008 and 24 February 2010 (Kp ~ 2–3). During the time of interest, THEMIS probes at −8RE > XGSM > −20RE and 5RE > YGSM > −5RE observed earth-bound flow bursts accompanied by magnetic dipolarizations varying in two stages. The keograms and all sky images close to their footprints showed two consecutive auroral breakups of which the first appeared at lower latitudes than the second. The ground-based magnetometers sensed magnetic bays and perturbations resulting from the formation of substorm current wedge. Two consecutive pulsations in the Pi2-Ps6 band period occurred simultaneously from high to low and very low latitudes. They appeared in the same cycle of growth and then decline in Kyoto-AL. The onset timing of ground pulsations mapped to the solar wind observation just in front of Earth’s magnetopause shows their occurrence under an IMF variation cycle of north-to-south and then north. Their dynamic spectrums have the spectral features of double substorm onsets triggered by northward IMF turning. Hence in response to IMF variations, double substorm onsets can be characterized with two-stage magnetic dipolarizations in the magnetotail, two auroral breakups of which the first occurring at lower latitudes than the second, and two consecutive Pi2-Ps6 band pulsations.

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Section: Solar Wind Observations and Geomagnetic Indicessupporting

confidence: 83%

Characteristic study of double substorm onsets in response to IMF variations

Cheng

Russell

Mann

et al. 2018

Preprint

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“…Considering that the DF is measured on average at X GSM ≈ −15 R E [ Fu et al , 2012a], and the IMF Bz , provided by OMNI, is measured at the subsolar point of the bow shock (X GSM ≈ 14 R E ), the 10‐min interval corresponds to a solar wind velocity of ∼500 km/s, a reconnection site at X GSM ≈ −25 R E , and a BBF velocity of ∼500 km/s, which are reasonable for most of the cases. This 10‐min interval was also suggested as the time delay from the turning of IMF Bz at the magnetopause to the substorm onset [e.g., Lyons et al , 1997; Cheng et al , 2011]. Positive 〈 Bz 〉 represents the northward IMF, while negative 〈 Bz 〉 the southward IMF.…”

Section: Methods and Statistical Resultsmentioning

confidence: 99%

Pitch angle distribution of suprathermal electrons behind dipolarization fronts: A statistical overview

Fu¹,

Khotyaintsev²,

Vaivads³

et al. 2012

J. Geophys. Res.

152

201

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We examine the pitch angle distribution (PAD) of suprathermal electrons (>40 keV) inside the flux pileup regions (FPRs) that are located behind the dipolarization fronts (DFs), in order to better understand the particle energization mechanisms operating therein. The 303 earthward‐propagating DFs observed during 9 years (2001–2009) by Cluster 1 have been analyzed and divided into two groups according to the differential fluxes of the >40 keV electrons inside the FPR. One group, characterized by the low flux (F < 500/cm2 · s · sr · keV), consists of 153 events and corresponds to a broad distribution of IMF Bz components. The other group, characterized by the high flux (F ≥ 500/cm2 · s · sr · keV), consists of 150 events and corresponds to southward IMF Bzcomponents. Only the high‐flux group is considered to investigate the PAD of the >40 keV electrons as the low‐flux situation may lead to large uncertainties in computing the anisotropy factor that is defined asA = F⊥/F∥ − 1 for F⊥ > F∥, and A = −F∥/F⊥ + 1 for F⊥ < F∥. We find that, among the 150 events, 46 events have isotropic distribution (|A| ≤ 0.5); 60 events have perpendicular distribution (A > 0.5), and 44 events have field‐aligned distribution inside the FPR (A < −0.5). The perpendicular distribution appears mainly inside the growing FPR, where the flow velocity is increasing and the local flux tube is compressed. The field‐aligned distribution occurs mainly inside the decaying FPR, where the flow velocity is decreasing and the local flux tube is expanding. Inside the steady FPR, we observed primarily the isotropic distribution of suprathermal electrons. This statistical result confirms the previous case study and gives an overview of the PAD of suprathermal electrons behind DFs.

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“…Pi2 pulsations are the impulsive and damped geomagnetic oscillations with a period 40–150 s (corresponding to a frequency band of 6–25 mHz) [ Baumjohann and Glassmeier , ; Yumoto , ; Olson , , and references therein]. In addition, they can successively occur in a sequence [ Saito , ; Clauer and McPherron , ] and in association with the variations of the interplanetary magnetic field (IMF) as well [e.g., Cheng et al , , , , ].…”

Section: Introductionmentioning

confidence: 99%

Association of consecutive Pi2‐Ps6 band pulsations with earthward fast flows in the plasma sheet in response to IMF variations

2014

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On 11 March 2009, the H component had four consecutive bay-like variations accompanied by positive and negative deflections in the D component across the Atlantic like those affected by the substorm current wedge formation. A train of pulsations with a frequency range 2-10 mHz (referred to as Pi2-Ps6 band), sensed by Time History of Events and Macroscale Interactions during Substorms (THEMIS)/Canadian Array for Real-time Investigations of Magnetic Activity (CARISMA) magnetometers, had clearly three consecutive Pi2s followed by a Ps6 at low latitudes, but first Pi2 and then Ps6 at high latitudes mixed with large-amplitude Ps6 at midlatitudes. The geostationary orbit magnetometers sensed similar magnetic perturbations. THEMIS probes first observed earthward fast flows, magnetic dipolarizations, and modulated energetic particle fluxes at~XGSM À9.2 R E , then at~XGSM À7.5 R E for Pi2 and at~XGSM À18.0 R E only for Ps6. They appeared during a very quiet period for northward interplanetary magnetic field (IMF) with a clock angle variation of low to high and then low. The H spectrum shows two harmonic frequencies~2-4 mHz and~8-10 mHz but the D spectrum one dominant frequency~2-4 mHz. Pi2 can result from a combination of fast magnetospheric and plasmaspheric cavity resonances and Ps6 from a fast magnetospheric cavity resonance. The surface waves at the interface separating braking earthward fast flows from the ambient plasma convection region could lead to large-amplitude Ps6 at midlatitudes. Hence, consecutive Pi2-Ps6 band pulsations can be associated with earthward fast flows in the plasma sheet, expectedly driven by magnetotail reconnection, respectively, in the near-Earth region and the distant Earth one in response to IMF variations as in the two-neutral-point model.

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THEMIS observations of double-onset substorms and their association with IMF variations

Cited by 5 publications

References 45 publications

Characteristic study of double substorm onsets in response to IMF variations

Characteristic study of double substorm onsets in response to IMF variations

Pitch angle distribution of suprathermal electrons behind dipolarization fronts: A statistical overview

Association of consecutive Pi2‐Ps6 band pulsations with earthward fast flows in the plasma sheet in response to IMF variations

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