<i>AE</i> index variability during corotating fast solar wind streams

Diego, Piero; Storini, M.; Parisi, M.; Cordaro, E. G.

doi:10.1029/2004ja010715

Cited by 19 publications

(19 citation statements)

References 52 publications

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“…[11] Our definition of high-speed streams in this paper is solar wind streams with V sw > 500 km/s that are not associated with a CME. We have confirmed the earlier result [e.g., Sheeley et al, 1977;Diego et al, 2005;Tanskanen et al, 2005] that the occurrence of high-speed streams and their accompanied Alfvén waves are not limited to the declining phase of the solar cycle but can also exist during other years, although they are less frequent and of shorter duration. We searched for high-speed streams and their associated Alfvén waves for the period 1996-2002.…”

Section: High-speed Streams Alfvénic Fluctuations Of Imf and Repetisupporting

confidence: 91%

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Repetitive substorms caused by Alfvénic waves of the interplanetary magnetic field during high‐speed solar wind streams

Lee¹,

Lyons²,

Kim³

et al. 2006

J. Geophys. Res.

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[1] Substorms sometimes occur repetitively with a period of $1-4 hours. In this paper we examine repetitive substorms, identified using particle injections and positive H bays on the nightside, that we find to occur during corotating high-speed streams associated with coronal holes. The high-speed streams often last for several days and are accompanied by large amplitude Alfvén waves of the interplanetary magnetic field (IMF). We find that repetitive substorms occur every $1-4 hours, regardless of the solar cycle phase, whenever the Earth's magnetosphere is impinged by these high-speed streams. We further find that a significant number of these substorms are associated with repetitive northward turnings of the Alfvénic IMF, each northward turning preceded by weakly-to-moderately southward IMF, i.e., B z $ À3.6 nT for $29 min on the average. We present eight example intervals where most of the repetitive substorms were associated with a northward turning. Statistically, for 63.5% of 312 substorms we are able to identify a reasonable association with a northward turning. While limitations of the Weimer-mapped IMF used here and the spatial structure of the Alfvénic IMF prevent us from estimating a precise figure for the percentage of IMF triggered substorms, our results indicate that many of the repetitive substorms are likely due to repetitive triggering by the Alfvénic IMF.

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Section: High-speed Streams Alfvénic Fluctuations Of Imf and Repetisupporting

confidence: 91%

“…These fluctuations have large amplitudes during the periods of high-speed solar wind. Other examples of similar fluctuations have been shown to be Alfvén waves [e.g., Tsurutani et al, 1995a;Diego et al, 2005]. The IMF B z fluctuates roughly between +5 and À5 nT.…”

Section: High-speed Streams Alfvénic Fluctuations Of Imf and Repetimentioning

confidence: 78%

Repetitive substorms caused by Alfvénic waves of the interplanetary magnetic field during high‐speed solar wind streams

Lee¹,

Lyons²,

Kim³

et al. 2006

J. Geophys. Res.

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“…The fluctuations of the interplanetary magnetic field during fast streams have been shown to be mostly due to Alfvén waves propagating outward from the Sun. Previous studies suggested that there is a close correlation between interplanetary Alfvén waves and AE index [ Gonzalez et al , 1999; Diego et al , 2005; Chian et al , 2006].…”

Section: Introductionmentioning

confidence: 99%

Is geomagnetic activity driven by solar wind turbulence?

D’Amicis

Bruno

Bavassano

2007

Geophysical Research Letters

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The Earth's magnetosphere is a highly dynamical system, which continuously exchanges energy, mass and momentum with the solar wind and the Earth's ionosphere. Existing literature would suggest that particular large amplitude interplanetary Alfvén wave trains might cause intense auroral activities known as High‐Intensity Long‐Duration Continuous Auroral Activity (HILDCAAs), as a result of the magnetic reconnection between the southward magnetic field z component and the magnetopause magnetic fields. This paper presents a statistical analysis concerning the role played by Alfvénic turbulence in the solar wind‐magnetosphere coupling as a function of the solar cycle. We find that Alfvénic fluctuations are geoeffective at solar minimum while at solar maximum magnetic structures play a role.

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“…Also, the ring current effect in the storm time depression is controversial with the estimates of the symmetric ring current contribution to Dst ranging from 0 to 40%, and the contributions of the crosstail and partial ring current to Dst are very discrepant with the corresponding estimates varying from 15/25 to 80% (Maltsev, 2003). Moreover, the Physics of the associated storm-substorm relationship is presently poorly understood (e.g., Diego et al, 2005, and references therein).…”

Section: Discussionmentioning

confidence: 92%

Magnetic clouds, cosmic ray decreases, and geomagnetic storms

Ifedili

2006

Earth Planet Sp

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The relationship between magnetic clouds, cosmic ray decreases and geomagnetic storms has been investigated by using some cosmic ray hourly intensities recorded with ground-based monitors at Alert, Deep River and Mount Washington, as well as the geomagnetic activity Dst index, and the interplanetary magnetic field (IMF) and the solar wind plasma (SWP) bulk-speed, density and temperature in the near-Earth space, on 28-30 September 1978, 24-26 April 1979, 13-15 January 1967, 3-5 January 1978, and 27-29 November 1989. Due to the interplanetary coronal mass ejection (ICME) impacting on slow solar wind, there is a sheath upstream of the ICME led by a fast forward shock. And the large IMF variations in this sheath, which sustain the depressions in the cosmic ray intensity during Forbush decreases (FDs), were found not to influence the main phase storm, but rather the southward IMF in the said sheath and magnetic cloud was the major source in triggering geomagnetic storms, by allowing a strong coupling between the solar wind and the magnetosphere. It was also observed that the initial set of the main phase storm always began in the sheath where, and when, the sustained southward-oriented IMF first occurred, but ceased when the IMF was rotated to a strong northward-orientation, only to resume at subsequent sustained southward-oriented IMF within the sheath and the leading (i.e., front) region of the magnetic cloud. The front boundary of the magnetic cloud was found to be well defined by the relatively high ( 10 nT) rms of the IMF components, which prominently separates both the Lull region of the sheath and the onset of the second decrease of the two-step FD, from the magnetic cloud. There were some instances where a two-step main phase storm, caused by the combination of a sheath and cloud structure, occurred, the two steps sometimes both starting in the sheath itself. Also, in some cases, the sheath and the leading region of the magnetic cloud together produced a single-step storm. In addition, enhanced IMF south latitude and IMF intensity in the sheath and magnetic cloud during the IMF sustained southern orientation, were each observed to produce enhanced geomagnetic activity, even for intense storms. And high SWP bulk speed was found to reduce the depth of the Dst index. Therefore, it appears that when the magnetosphere is exposed to a sustained southward-oriented IMF in the magnetic cloud and the sheath preceding it, a valve (i.e., valve-like IMF direction) opens and allows direct transfer of energy between the solar wind and the magnetosphere to trigger the geomagnetic storms, such that the stronger the sustained IMF south-ward orientation, the wider the valve opens, the higher the SWP bulk speed, the narrower the opening in the valve becomes. And the more the IMF strength during the IMF southern orientation, the larger is the solar wind energy density that is available for transfer through the valve. The valve closes when the IMF is rotated to a strong northward-orientation, and the geomagnetic storms cease.

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AE index variability during corotating fast solar wind streams

Cited by 19 publications

References 52 publications

Repetitive substorms caused by Alfvénic waves of the interplanetary magnetic field during high‐speed solar wind streams

Repetitive substorms caused by Alfvénic waves of the interplanetary magnetic field during high‐speed solar wind streams

Is geomagnetic activity driven by solar wind turbulence?

Magnetic clouds, cosmic ray decreases, and geomagnetic storms

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