EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

Aikio, Anita; Pitkänen, Timo; Fontaine, Dominique; Dandouras, I.; Amm, O.; Kozlovsky, Alexander; Vaivdas, A.; Fazakerley, A. N.

doi:10.5194/angeo-26-87-2008

Cited by 14 publications

(32 citation statements)

References 40 publications

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“…By itself, this is not a determination of the PCB location, nor of the OCB location. However, this boundary depends on the ionospheric current system and on the ionization produced by the auroral precipitation, so that the motion of this boundary can be expected to mimic that of the OCB, and in some circumstances, the boundaries may well match each other (Amm et al, 2003;Aikio et al, 2006Aikio et al, , 2008.…”

Section: Methodsmentioning

confidence: 99%

Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Hubert¹,

Aikio

Amm

et al. 2010

Ann. Geophys.

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Abstract.We compare the location of the polar cap boundary (PCB) determined using two different techniques, and use them as proxies for the open-closed field line boundary (OCB). Electron temperatures from observations of the EIS-CAT radar facility are used to estimate the latitude of the PCB along the meridian of the EISCAT VHF beam. The second method utilizes global images of proton aurora obtained by the IMAGE satellite FUV SI12 instrument. These methods are applied to three different intervals. In two events, the agreement between the methods is good and the mean of the difference is within the resolution of the observations. In a third event, the PCB estimated from EISCAT data is located several degrees poleward of that obtained from the IMAGE FUV SI12 instrument. Comparison of the reconnection electric field estimated from the two methods shows that highresolution measurements both in time and space are needed to capture the variations in reconnection electric field during substorm expansion. In addition to the two techniques introduced above to determine the PCB location, we also use a search for the location of the reversal of the east-west component of the equivalent current known as the magnetic convection reversal boundary (MCRB). The MCRB from the MIR-ACLE magnetometer chain mainly follows the motion of the polar cap boundary during different substorm phases, but differences arise near the Harang discontinuity.

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Section: Methodsmentioning

confidence: 99%

Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Hubert¹,

Aikio

Amm

et al. 2010

Ann. Geophys.

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“…The current understanding of auroral acceleration regions has, for the most part, kept quasistatic systems separate from time-varying systems, as noted by Paschmann et al [2002, and references therein]. There are a few notable observational exceptions [e.g., Marklund et al, 2001Marklund et al, , 2004Aikio et al, 2004Aikio et al, , 2008Hull et al, 2010], and no theoretical models of this evolution. In this paper we look at the details of the flight with an overview of the event, consider specific observations to address the goals of this study, and discuss interpretations of the data and how they relate to other studies.…”

Section: Introductionmentioning

confidence: 99%

Sounding rocket study of two sequential auroral poleward boundary intensifications

et al. 2011

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“…After 18:00 UT, the polar cap boundary is located close to the poleward edge of the westward electrojet, a feature that is typical to the nightside region of the westward electrojet (e.g. Aikio et al, 2006Aikio et al, , 2008.…”

Section: Overviewmentioning

confidence: 99%

EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere

et al. 2011

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Abstract. We report observations of a sequence of quiettime Earthward bursty bulk flows (BBFs) measured by the Cluster spacecraft in the near-tail plasma sheet (XGSM ∼ −12 to −14 R E ) in the evening sector, and by simultaneous highresolution measurements in the northern conjugate ionosphere by the EISCAT radars, a MIRACLE all-sky camera and magnetometers, as well as a meridian-scanning photometer (MSP) in the Scandinavian sector on 17 October 2005.The BBFs at Cluster show signatures that are consistent with the plasma "bubble" model Wolf, 1993, 1999), e.g. deflection and compression of the ambient plasma in front of the Earthward moving bubble, magnetic signatures of a flow shear region, and the proper flows inside the bubble. In addition, clear signatures of tailward return flows around the edges of the bubble can be identified. The duskside return flows are associated with significant decrease in plasma density, giving support to the recent suggestion by Walsh et al. (2009) of formation of a depleted wake. However, the same feature is not seen for the dawnside return flows, but rather an increase in density.In the ionosphere, EISCAT and optical measurements show that each of the studied BBFs is associated with an auroral streamer that starts from the vicinity of the polar cap boundary, intrudes equatorward, brakes at 68-70 • aacgm MLAT and drifts westward along the proton oval. Within the streamer itself and poleward of it, the ionospheric plasma flow has an equatorward component, which is the ionospheric manifestation of the Earthward BBF channel. A sharp velocity shear appears at the equatorward edge of a streamer. We suggest that each BBF creates a local velocity shear in the ionosphere, in which the plasma flow poleward of and inside the streamer is in the direction of the Correspondence to: T. Pitkänen (timo.pitkanen@oulu.fi) streamer and southeastward. A northwestward return flow is located on the equatorward side. The return flow is associated with decreased plasma densities both in the ionosphere and in the magnetosphere as measured by EISCAT and Cluster, respectively. In summary, we present the first simultaneous high-resolution observations of BBF return flows both in the plasma sheet and in the ionosphere, and those are in accordance with the bubble model. The results apply for the duskside return flows, but the manifestation of dawnside return flows in the ionosphere requires further studies.Finally, EISCAT measurements indicate increased nightside reconnection rate during the ∼35-min period of BBFs. We suggest that the observed temporal event of IMF rotation to a more southward direction produces enhanced open flux transport to the nightside magnetotail, and consequently, the nightside reconnection rate is increased.

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EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary

Cited by 14 publications

References 40 publications

Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Comparison of the open-closed field line boundary location inferred using IMAGE-FUV SI12 images and EISCAT radar observations

Sounding rocket study of two sequential auroral poleward boundary intensifications

EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere

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