Sawtooth oscillations directly driven by solar wind dynamic pressure enhancements

Lee, Deuk Yong; Lyons, L. R.; Yumoto, K.

doi:10.1029/2003ja010246

Cited by 69 publications

(98 citation statements)

References 23 publications

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“…Both tests were not significant at the 5% level indicting a random occurrence in the number of events that occurred both within each hour and within the 3-h groupings. This is in line with findings by Lee et al (2004) that the solar wind pulse leads to a near simultaneous enhancement of the energetic flux at all MLT sectors at the geosynchronous orbit.…”

Section: Influence Of Local Time On Scasupporting

confidence: 80%

Observed characteristics of sudden commencement absorption

Ritchie

Honary

2009

Journal of Atmospheric and Solar-Terrestrial Physics

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a b s t r a c tIonospheric absorption at high latitudes that occurs coincidently with storm sudden commencements (SSC) is categorised as sudden commencement absorption (SCA). Having discounted any solar activity effects on the measurement of SCA this paper describes, for the first time, the basic characteristics of SCA measured over half a solar cycle.It is revealed that the measurement of SCA is not affected by Solar activity, the local time of occurrence of the SSC or the direction of B z immediately before or after the SSC event. We also show that the median value of expected SCA is best predicted by the step change in IMF magnetic field coincident with the SSC event. This strong correlation between the median value of SCA and the IMF magnitude that occurred during the shock has been formulated to aid propagation prediction.

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Section: Influence Of Local Time On Scasupporting

confidence: 80%

Observed characteristics of sudden commencement absorption

Ritchie

Honary

2009

Journal of Atmospheric and Solar-Terrestrial Physics

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“…Lee et al [2004] suggest that the sawtooth oscillations of the geosynchronous magnetic field and energetic particle fluxes are very strongly associated with semiperiodic solar wind pressure pulses. …”

Section: Summary and Discussionmentioning

confidence: 99%

Geosynchronous magnetic field response to solar wind dynamic pressure pulse

Lee

Lyons

2004

J. Geophys. Res.

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We present a study of the response of the geosynchronous magnetic field to abrupt enhancements of the solar wind dynamic pressure. Results are obtained separately for cases of northward and southward interplanetary magnetic field (IMF) prior to and after the solar wind pressure jump. For pressure enhancements with southward IMF we find that the response of the geosynchronous magnetic field on the dayside is mostly compression. However, on the nightside it can be a dipolarization‐like change that is similar to that which occurs during substorms. We report four events showing the dipolarization‐like response on the nightside. Analysis using low‐latitude geomagnetic data as well as the geosynchronous energetic particle flux data leads us to argue that this dipolarization is part of the global disturbance directly driven by the solar wind pressure enhancement. We also find that the nightside magnetosphere is remarkably sensitive to small solar wind dynamic pressure enhancements when the IMF is strongly southward (i.e., Bz is below ∼−10 nT). For northward IMF, solar wind pressure enhancements generally lead to magnetic compression, with a few cases of depression on the nightside, neither of which is a dipolarization‐like response. The compression is strongest near noon, decreases toward dawn and dusk, and increases with the amount of increase in dynamic pressure.

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“…Lee et al (2004) examined four sawtooth events and discussed that the observed signatures are unlikely to be those of substorms and rather they are directly driven by solar wind pressure increases. Lyons et al (2005) also emphasised the importance of the dynamic pressure effect; they argued that the merging of the substorm component and pressure-driven component is essential for the wide azimuthal extents of the aurora and other signatures such as the current wedge.…”

Section: Electromagnetic Field Fluctuation At Themis-cmentioning

confidence: 99%

Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

et al. 2009

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Abstract. We report multi-spacecraft and ground-based observations of a "sawtooth" event on 20 November 2007. For this event, data from three THEMIS, two GOES, and four LANL spacecraft are available as well as those from extensively distributed ground magnetometers and all-sky imagers. In the present paper we focus on the spatial extents of the electromagnetic and particle signatures of the first "tooth". In this event, auroral images and ground magnetic bays showed two activations: a pseudo onset and a major onset (we use the term pseudo onset since the former auroral brightening did not significantly expand poleward). Ground magnetic bay observations indicate that the substorm current wedge (SCW) developed after the major onset in an azimuthally wide region of ∼14-3 h MLT. Similarly, broad magnetic bay distribution was observed also for the pseudo onset prior to the major onset. Furthermore, around the pseudo onset, magnetic dipolarisations were observed from 0.5 to 5 h MLT. These observations illustrate that, during sawtooth events, activities following not only the major onset but also the pseudo onset can extend more widely than those during usual substorms. Remarkable electromagnetic field fluctuations embedded in the dipolarisation trend were seen at 0.5 and 2.5 h MLT. In particular, comprehensive plasma and field data from THEMIS showed the presence of a long-excited weak magnetosonic wave and an impulsive large-amplitude Alfvén wave with an earthward Poynting flux at around the eastward edge of the SCW; the latter was sufficiently strong for powering aurora (140 mW/m 2 Correspondence to: S. Kasahara (kshr@stp.isas.jaxa.jp) when mapped to the ionosphere). These two activations of the electromagnetic wave were identified, corresponding to the pseudo onset and the major onset. On the other hand, the dipolarisation at geosynchronous 0 h MLT was observed only after the major onset, despite its closer location to the centre of the auroral activity in terms of the MLT; this indicates that the inner radial limit of the dipolarisation region at the pseudo onset was tailward of geosynchronous altitude at 0 h MLT. The outer radial limit of the electron injection region was also found at ∼10 R E by conjunction measurements with THEMIS satellites. These radial distributions are not significantly different to those expected for usual substorms.

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Sawtooth oscillations directly driven by solar wind dynamic pressure enhancements

Cited by 69 publications

References 23 publications

Observed characteristics of sudden commencement absorption

Observed characteristics of sudden commencement absorption

Geosynchronous magnetic field response to solar wind dynamic pressure pulse

Spatial distributions of electromagnetic field variations and injection regions during the 20 November 2007 sawtooth event

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