Characteristics of consecutive bursts of Pi2 pulsations observed at the SMALL array: A new implication

Cheng, C.; Russell, C. T.; Yumoto, K.; Gao, Yingjie; J., P.

doi:10.1186/bf03352513

Cited by 8 publications

(9 citation statements)

References 32 publications

(58 reference statements)

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“…This fact is consistent with previous results about BBEs by Shiokawa et al [1996Shiokawa et al [ , 1997Shiokawa et al [ , 1999. The fact that the second Pi 2 corresponds to the global substorm onset with positive and negative H bays is consistent with the idea of consecutive Pi 2 bursts by Cheng et al [2002Cheng et al [ , 2004.…”

Section: Ground-based Observationssupporting

confidence: 93%

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm

et al. 2007

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[1] Broadband electrons (BBEs) are remarkable flux enhancements (>10 13 eV cm À2 s À1 ) of precipitating electrons over a broad energy range (0.03-30 keV) near the equatorward edge of the auroral oval during geomagnetic storms. We show characteristics of particles (energy spectra and pitch angle distribution) and fields (electric field, magnetic field, and wave spectra) during a BBE event observed by the Fast Auroral SnapshoT (FAST) satellite. The BBEs were observed at an altitude of $2000 km at 59°-61°i nvariant latitudes (ILATs) and 21 h magnetic local time (MLT). The event was observed at $7 min after the onset of a substorm during the main phase of the Bastille Day geomagnetic storm (minimum Dst = À301 nT) on 15 July 2000. The precipitation region of the BBEs corresponded to a localized intensification of auroral emission, lasting $14 min, observed by the Polar UVI images at 50°-60°geomagnetic latitudes (MLATs) and 20-21 MLTs. These results suggest that rapid particle acceleration was occurring in the inner magnetosphere associated with a storm-time substorm. The pitch angle distribution of BBEs was isotropic except for a loss cone feature around the field-aligned upward direction at a higher energy range above $1 keV, while field-aligned electron fluxes were larger than the perpendicular fluxes below $1 keV. These results imply that a higher energy part of the BBEs originated from higher altitudes in the inner magnetosphere and that a lower energy part was accelerated parallel to the local magnetic field at lower altitudes near the satellite. Intense fluctuations of electric and magnetic fields were observed during this BBE event. From these results, we discuss possible acceleration of the lower energy part of BBEs through wave-particle interaction.

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Section: Ground-based Observationssupporting

confidence: 93%

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm

et al. 2007

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“…Moreover, the amplitude of Pi2 burst at CLK (L = 3.10) is largest in contrast to those at JAX (L = 1.80) and other three available MEASURE stations not shown in this study. Like those events studied by Cheng et al [1998Cheng et al [ , 2004, this may be due to the coupling of a magnetospheric cavity (resonance) mode to field line resonances and/or a surface wave at the plasmapause driven by the impulsive source in the magnetotail after substorm onset. In this study, the first Pi2 pair associated with the first substorm are denoted as #F1 and #F2, respectively.…”

Section: Ground Observationsmentioning

confidence: 93%

On the relationships between double‐onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event

et al. 2005

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[1] The relationships between double-onset substorm, pseudobreakup, and IMF variation were investigated with magnetic, auroral, and particle observations from space to the ground during 0200-0600 UT on 4 September 1999. There were five consecutive bursts of Pi2 pulsations on the ground during the time of interest. The onset time of ground Pi2s maps to the same variation sequence in the IMF structure seen propagating to the Earth in multiple satellite observations in the upstream region. The comparison of auroral and energetic particle data with IMF observations shows that a sequence of two doubleonset substorms intervened by a pseudobreakup appears in two distinct cycles of southward IMF followed by a northward interval. For the first substorm, the first onset begins when the B y magnitude declines after the IMF turns southward for about 90 min, and the second onset occurs after northward turning of the IMF accompanied by an increasing B y magnitude. The pseudobreakup appears while the IMF turns southward and the B y magnitude slightly decreases. For the second substorm, the first onset commences while the IMF remains southward with a steady B y magnitude, and the second onset occurs after the IMF becomes strongly northward and the B y magnitude decreases instead. These observations can be explained with the two-neutral-point model. The first onset occurs when the IMF turns southward. Reconnection at the near-Earth neutral point first begins on closed field lines within the plasma sheet, and the second onset occurs when the IMF turns northward and reconnection at the distant neutral point ceases and reconnection at the near-Earth neutral point may reach the open flux of the tail lobes. In addition, a decrease in the B y magnitude may help reduce magnetotail convection and release all the built-up flux to allow the onset to commence after northward turning of the IMF. If the IMF remains southward, the reduction of magnetotail convection due to a decreasing B y would lead to a pseudobreakup instead. In contrast, an increasing B y magnitude would increase magnetotail convection and weaken magnetospheric substorm after the IMF turns northward. Consequently, for the occurrence of double-onset substorms and pseudobreakups, not only the first onset begins spontaneously during steady southward IMF and the second onset appears after northward turning of the IMF but the B y change also affects magnetotail convection which may evoke (or abate) the substorm-related activation while the IMF turns southward (or northward).

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“…It is well known that nightside Pi2 waves excited by the impulsive source in the magnetotail can propagate across the magnetospheric cavity in fast modes and along the geomagnetic field lines to the ground in shear Alfvén modes (e.g. Cheng et al, 2004Cheng et al, , 2009a. Hence, the dominant frequency of ground Pi2s depends on their source location and traveling path that is determined by the cavity size, the length of the field lines and the plasma density in the magnetosphere.…”

Section: Spectral Analysismentioning

confidence: 99%

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

et al. 2011

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Abstract. On 16 July 2008, two pairs of consecutive bursts of Pi2 pulsations were recorded simultaneously across the THEMIS ground-based observatory system. Wavelet transformation reveals that for each high-latitude pair, the dominant frequency of the first burst is higher than that of the second. But at low latitudes, the dominant frequency does not change. It is suggested that both pairs result from fast magnetospheric cavity waves with the second burst also containing shear Alfvén waves. INTERMAGNET magnetograms at auroral latitudes showed magnetic variations affected by two recurrent electrojets for each pair. The ground-based magnetometers and those at geostationary orbit sensed magnetic perturbations consistent with the formation of the substorm current wedge. Four consecutive enhancements of energetic electron and ion fluxes detected by the THEMIS probes in the dayside magnetosphere appeared in the later afternoon and then in the early afternoon. The horizontal magnetic variation vectors had vortex patterns similar to those induced by the upward and downward field-aligned currents during substorm times. The hodogram at mid-L stations had a polarization pattern similar to the one induced by the substorm current wedge for each Pi2 burst. The mapping of ground Pi2 onset timing to the interplanetary magnetic field (IMF) observations shows that they appear under two cycles of north-to-south and then north variation. CLUSTER 4 in the south lobe observed wave-like magnetic fluctuations, probably driven by near-Earth reconnection, similar to those on the ground. These two observations are consistent with the link of double-onset substorms to magnetotail reconnection externally triggered by IMF variations.

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Characteristics of consecutive bursts of Pi2 pulsations observed at the SMALL array: A new implication

Cited by 8 publications

References 32 publications

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm

Particle and field characteristics of broadband electrons observed by the FAST satellite during a geomagnetic storm

On the relationships between double‐onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event

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

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