Polar cap convection/precipitation states during Earth passage of two ICMEs at solar minimum

Sandholt, P. E.; Andalsvik, Yngvild Linnea; Farrugia, C. J.

doi:10.5194/angeo-28-1023-2010

Cited by 13 publications

(24 citation statements)

References 46 publications

(59 reference statements)

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“…This demonstrates that flow channel FC 2 is formed by the ionospheric Pedersen current closure of Birkeland currents C1-C2. The C1-C2 Birkeland current configurations corresponding to the different FC 2 flow channels appearing during IMF B y < 0 conditions are indicated in Sandholt et al (2010).…”

Section: Discussionmentioning

confidence: 99%

“…In Sandholt et al (2010) we reported one case showing the presence of a series of 5-10-min-long negative X-component magnetic deflections detected at ground stations located underneath the FC 2 flow channel of type NH-dusk/B y < 0. This led us to speculate that the ionospheric ion flow was also pulsed in this case and possibly related to flux transfer events (FTEs), i.e., momentum transfer in a later stage of the evolution of field lines previously opened by pulsed magnetopause reconnection.…”

Section: Introductionmentioning

confidence: 99%

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Polar cap flow channel events: spontaneous and driven responses

2010

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Abstract. We present two case studies of specific flow channel events appearing at the dusk and/or dawn polar cap boundary during passage at Earth of interplanetary (IP) coronal mass ejections (ICMEs) on 10 January and 25 July 2004. The channels of enhanced (>1 km/s) antisunward convection are documented by SuperDARN radars and dawn-dusk crossings of the polar cap by the DMSP F13 satellite. The relationship with Birkeland currents (C1-C2) located poleward of the traditional R1-R2 currents is demonstrated. The convection events are manifest in ground magnetic deflections obtained from the IMAGE (International Monitor for Auroral Geomagnetic Effects) Svalbard chain of ground magnetometer stations located within 71-76 • MLAT. By combining the ionospheric convection data and the ground magnetograms we are able to study the temporal behaviour of the convection events. In the two ICME case studies the convection events belong to two different categories, i.e., directly driven and spontaneous events. In the 10 January case two sharp southward turnings of the ICME magnetic field excited corresponding convection events as detected by IMAGE and SuperDARN. We use this case to determine the ground magnetic signature of enhanced flow channel events (the NHdusk/B y < 0 variant). In the 25 July case a several-hour-long interval of steady southwest ICME field (B z < 0; B y < 0) gave rise to a long series of spontaneous convection events as detected by IMAGE when the ground stations swept through the 12:00-18:00 MLT sector. From the ground-satellite conjunction on 25 July we infer the pulsed nature of the polar cap ionospheric flow channel events in this case. The typical duration of these convection enhancements in the polar cap is 10 min.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Polar cap flow channel events: spontaneous and driven responses

2010

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“…The dayside source is shown in the variant of negative IMF B y conditions (southwest-directed IMF) with E-field coupling along old open magnetic field lines (OOFLs), giving rise to a prenoon versus postnoon convection asymmetry (see e.g. Heppner and Maynard, 1987), i.e., E-field concentration in the postnoon sector via ionospheric Pedersen current closure of FACs marked R1-C1 (our FC 2 flow channel), as described by Sandholt and Farrugia (2009) and Sandholt et al (2010). The ground magnetic signature of this dayside convection source is demonstrated in Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Crooker et al, 1991). For documentations of associations between auroral, magnetic and convection signatures of pulsed magnetopause reconnection in the postnoon sector we refer to Sandholt et al (1986), Sandholt and Farrugia (2007) and Sandholt et al (2010).…”

Section: P E Sandholt Et Al: Repetitive Substorm Activity Driven Bmentioning

confidence: 99%

M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

2014

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Abstract. We study substorms from two perspectives, i.e., magnetosphere-ionosphere coupling across the auroral oval at dusk and at midnight magnetic local times. By this approach we monitor the activations/expansions of basic elements of the substorm current system (Bostrøm type I centered at midnight and Bostrøm type II maximizing at dawn and dusk) during the evolution of the substorm activity. Emphasis is placed on the R1 and R2 types of field-aligned current (FAC) coupling across the Harang reversal at dusk. We distinguish between two distinct activity levels in the substorm expansion phase, i.e., an initial transient phase and a persistent phase. These activities/phases are discussed in relation to polar cap convection which is continuously monitored by the polar cap north (PCN) index. The substorm activity we selected occurred during a long interval of continuously strong solar wind forcing at the interplanetary coronal mass ejection passage on 18 August 2003. The advantage of our scientific approach lies in the combination of (i) continuous ground observations of the ionospheric signatures within wide latitude ranges across the auroral oval at dusk and midnight by meridian chain magnetometer data, (ii) "snapshot" satellite (DMSP F13) observations of FAC/precipitation/ion drift profiles, and (iii) observations of current disruption/near-Earth magnetic field dipolarizations at geostationary altitude. Under the prevailing fortunate circumstances we are able to discriminate between the roles of the dayside and nightside sources of polar cap convection. For the nightside source we distinguish between the roles of inductive and potential electric fields in the two substages of the substorm expansion phase. According to our estimates the observed dipolarization rate (δB z /δt) and the inferred large spatial scales (in radial and azimuthal dimensions) of the dipolarization process in these strong substorm expansions may lead to 50-100 kV enhancements of the cross-polar-cap potential due to inductive electric field coupling.

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“…Such channels of pulsed antisunward flows on old open field lines (polar rain precipitation) were documented by Sandholt and Farrugia (2009) and Sandholt et al (2010). Our aim here is to study the possible contribution of these flows to the CPCP fluctuations as measured by satellites in polar orbit or by ground-based radars.…”

Section: Electrojet Deflections: Ground Magnetometer Datamentioning

confidence: 99%

Dayside and nightside contributions to cross-polar cap potential variations: the 20 March 2001 ICME case

2011

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Abstract. We investigate the association between temporalspatial structure of polar cap convection and auroral electrojet intensifications during a 5-h-long interval of strong forcing of the magnetosphere by an ICME/Magnetic cloud on 20 March 2001. We use data from coordinated ground-satellite observations in the 15:00-20:00 MLT sector. We take advantage of the good latitudinal coverage in the polar cap and in the auroral zone of the IMAGE chain of ground magnetometers in Svalbard -Scandinavia -Russia and the stable magnetic field conditions in ICMEs. The electrojet events are characterized by a sequence of 10 min-long AL excursions to −1000/−1500 nT followed by poleward expansions and auroral streamers. These events are superimposed on a high disturbance level when the AL index remains around −500 nT for several hours. These signatures are different from those appearing in classical substorms, most notably the absence of a complete recovery phase when AL usually reaches above −100 nT. We concentrate on polar cap convection in both hemispheres (DMSP F13 data) in relation to the ICME B y conditions, electrojet intensifications, and the global UV auroral configuration obtained from the IM-AGE spacecraft. The temporal evolution of convection properties such as the cross-polar cap potential (CPCP) drop and flow channels at the dawn/dusk polar cap (PC) boundaries around the time of the electrojet events are investigated. This approach allows us to distinguish between dayside (magnetopause reconnection) and nightside (magnetotail reconnection) sources of the PC convection events within the context of the expanding-contracting model of high-latitude convection in the Dungey cycle. Inter-hemispheric symmetries/asymmetries in the presence of newly-discovered convection channels at the dawn or dusk side PC boundaries are determined.

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Polar cap convection/precipitation states during Earth passage of two ICMEs at solar minimum

Cited by 13 publications

References 46 publications

Polar cap flow channel events: spontaneous and driven responses

Polar cap flow channel events: spontaneous and driven responses

M–I coupling across the auroral oval at dusk and midnight: repetitive substorm activity driven by interplanetary coronal mass ejections (CMEs)

Dayside and nightside contributions to cross-polar cap potential variations: the 20 March 2001 ICME case

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