Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements

Østgaard, Nikolai; Moen, J.; Mende, S. B.; Frey, H. U.; Immel, T. J.; Gallop, P.; Oksavik, K.; Fujimoto, M.

doi:10.5194/angeo-23-123-2005

Cited by 24 publications

(41 citation statements)

References 26 publications

(37 reference statements)

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“…In the study by Ostgaard et al (2005) the PCB was found to fluctuate at ULF frequencies (10-15 min periods) in the evening sector during substorm expansion phase. The observations occurred obviously after the initial poleward expansion.…”

Section: Discussionmentioning

confidence: 96%

“…For field-aligned currents to heat the electron gas, very small horizontal scales and very large currents are needed; those are expected at the edges of discrete arcs (Zhu et al, 2001). Increased electron temperature in the nightside ionosphere for the polar cap boundary determination has been utilised also by Ostgaard et al (2005). By using simultaneous optical measurements with the IMAGE FUV WIC camera, they searched a fixed value for the increased T e to be used as a proxy for the PCB.…”

Section: Discussionmentioning

confidence: 99%

“…They calculated the characteristic energy of precipitating electrons from the measured electron densities and compared those with the PCB determined by the all-sky images of the 630.0-nm emission. Ostgaard et al (2005) used the EISCAT VHF radar pointing at low elevation angle to a poleward direction together with the IMAGE satellite FUV WIC camera. The method was based on the measurement of the increased electron temperature T e in the nightside F region.…”

Section: Introductionmentioning

confidence: 99%

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Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

et al. 2006

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Abstract. In this paper we describe a new method to be used for the polar cap boundary (PCB) determination in the nightside ionosphere by using the EISCAT Svalbard radar (ESR) field-aligned measurements by the 42-m antenna and southward directed low-elevation measurements by the ESR 32m antenna or northward directed low-elevation measurements by the EISCAT VHF radar at Tromsø. The method is based on increased electron temperature (T e ) caused by precipitating particles on closed field lines. Since the Svalbard field-aligned measurement provides the reference polar cap T e height profile, the method can be utilised only when the PCB is located between Svalbard and the mainland. Comparison with the Polar UVI images shows that the radar-based method is generally in agreement with the PAE (poleward auroral emission) boundary from Polar UVI.The new technique to map the polar cap boundary was applied to a substorm event on 6 November 2002. Simultaneous measurements by the MIRACLE magnetometers enabled us to put the PCB location in the framework of ionospheric electrojets. During the substorm growth phase, the polar cap expands and the region of the westward electrojet shifts gradually more apart from the PCB. The substorm onset takes place deep within the region of closed magnetic field region, separated by about 6-7 • in latitude from the PCB in the ionosphere. We interpret the observations in the framework of the near-Earth neutral line (NENL) model of substorms. After the substorm onset, the reconnection at the NENL reaches within 3 min the open-closed field line boundary and then the PCB moves poleward together with the poleward boundary of the substorm current wedge. The poleward expansion occurs in the form of individual bursts, which are separated by 2-10 min, indicating that the reconnection in the magnetotail neutral line is impulsive. The poleward expansions of the PCB are followed by latitude dispersed intensifications inCorrespondence to: A. T. Aikio (anita.aikio@oulu.fi) the westward electrojet with high latitudes affected first and lower latitudes later. We suggest that reconnection bursts energize plasma and produce enhanced flows toward the Earth. While drifting earthward, part of the plasma population precipitates to the ionosphere producing latitude-dispersed enhancements in the WEJ.

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

et al. 2006

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“…Only space-borne optical imaging by satellites provides the possibility to observe the PCB globally (Baker et al, 2000;Milan et al, 2003;Hubert et al, 2006). In addition, several local methods exist, based on observations of the auroral emissions (Blanchard et al, 1995), in situ particle detection (Newell et al, 1996a,b), analysis of coherent radar backscatter (Chisham et al, 2004), or electron temperature from incoherent scatter radar (Østgaard et al, 2005;Aikio et al, 2006).…”

Section: Introductionmentioning

confidence: 99%

IMF effect on the polar cap contraction and expansion during a period of substorms

et al. 2013

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The polar cap boundary (PCB) location and motion in the nightside ionosphere has been studied by using measurements from the EISCAT radars and the MIRACLE magnetometers during a period of four substorms on 18 February 2004. The OMNI database has been used for observations of the solar wind and the Geotail satellite for magnetospheric measurements. In addition, the event was modelled by the GUMICS-4 MHD simulation. The simulation of the PCB location was in a rather good agreement with the experimental estimates at the EISCAT longitude. During the first three substorm expansion phases, neither the local observations nor the global simulation showed any poleward motions of the PCB, even though the electrojets intensified. Rapid poleward motions of the PCB took place only in the early recovery phases of the substorms. Hence, in these cases the nightside reconnection rate was locally higher in the recovery phase than in the expansion phase.

In addition, we suggest that the IMF B_z component correlated with the nightside tail inclination angle and the PCB location with about a 17-min delay from the bow shock. By taking the delay into account, the IMF northward turnings were associated with dipolarizations of the magnetotail and poleward motions of the PCB in the recovery phase. The mechanism behind this effect should be studied further

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“…Estimates of the magnetotail reconnection rate at one point of the boundary have shown that the reconnection electric field varies on time scales of minutes to tens of minutes (e.g. Østgaard et al, 2005;Pitkänen et al, 2009a, b).…”

Section: Introductionmentioning

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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Estimates of magnetotail reconnection rate based on IMAGE FUV and EISCAT measurements

Cited by 24 publications

References 26 publications

Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

Method to locate the polar cap boundary in the nightside ionosphere and application to a substorm event

IMF effect on the polar cap contraction and expansion during a period of substorms

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

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