Abstract
AbstractFlux transfer events (FTEs) are the manifestation of bursty and/or patchy magnetic reconnection at the magnetopause. We compare two sequences of the ionospheric signatures of flux transfer events observed in global auroral imagery and coherent ionospheric radar measurements. Both sequences were observed during very similar seasonal and interplanetary magnetic field (IMF) conditions, though with differing solar wind speed. A key observation is that the signatures differed considerably in their local time extent. The two periods are 26 August 1998, when the IMF had components BZ≈−10 nT and BY≈9 nT and the solar wind speed was VX≈650 km s−1, and 31 August 2005, IMF BZ≈−7 nT, BY≈17 nT, and VX≈380 km s−1. In the first case, the reconnection rate was estimated to be near 160 kV, and the FTE signatures extended across at least 7 h of magnetic local time (MLT) of the dayside polar cap boundary. In the second, a reconnection rate close to 80 kV was estimated, and the FTEs had a MLT extent of roughly 2 h. We discuss the ramifications of these differences for solar wind‐magnetosphere coupling.
Highlights
Magnetic reconnection occurring at the low-latitude magnetopause when the interplanetary magnetic field (IMF) has a southward component is the primary mechanism by which dynamics are driven within the magnetosphere-ionosphere system [e.g., Dungey, 1961; Cowley and Lockwood, 1992; Milan et al, 2007]
In this paper we investigate the width of the ionospheric convection throat in the ionosphere, which is related to the extent of the reconnection X line on the magnetopause, and the factors which may control this
We have presented new observations of the Southern Hemisphere dayside auroral dynamics and the Northern Hemisphere ionospheric convection flows during a period of southward IMF, BZ ≈ −7 nT, around 12 UT on 31 August 2005, when significant low-latitude magnetopause reconnection is ongoing
Summary
Magnetic reconnection occurring at the low-latitude magnetopause when the interplanetary magnetic field (IMF) has a southward component is the primary mechanism by which dynamics are driven within the magnetosphere-ionosphere system [e.g., Dungey, 1961; Cowley and Lockwood, 1992; Milan et al, 2007]. Studies of the distribution of FTE signatures in the ionosphere [e.g., Lockwood and Davis, 1996; Provan et al, 1999; Milan et al, 2000; Wild et al, 2005; Fear et al, 2008, 2009, 2012; Carter et al, 2015] have demonstrated that reconnection signatures can be observed over a wide range of magnetic local times (MLT) and that there appears to be an IMF BY control of the location. We investigate the possible reasons for the observed differences between the two intervals and discuss the ramifications for solar wind-magnetosphere coupling
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