Simultaneous tracking of reconnected flux tubes: Cluster and conjugate SuperDARN observations on 1 April 2004

Abstract

Abstract. While the Cluster spacecraft were located near the high-latitude magnetopause, between 11:30-13:00 UT on 1 April 2004, a series of medium to large scale (40 nT, 0.6-1.2 Re) FTEs were observed. During this pass, simultaneous and conjugated SuperDARN measurements are available that show a global flow pattern which is consistent with the expected (mapped) north-west motion of (predominantly subsolar) reconnected, magnetic flux at the magnetopause. We focus on analysing the local response of three FTEs, tracking their magnetopause motion via the four-spacecraft measurements together with their corresponding ground mapped motions. For two of these FTEs, where the tracking is strongly coordinated with the ionospheric flow at each footprint of the implied flux tubes in the Northern Hemisphere, conditions corresponded to stable, increasing (>100 • ) clock angle, while the third event, where the correspondence is less strong, coincided with low (<100 • ) clock angle. Flux tube motion, both measured and modeled from the inferred Xline, qualitatively matches the clear velocity enhancements in ionospheric convections with northward and westward flow at each location in the Northern Hemisphere, measured simultaneously by SuperDARN, and also roughly matches the observed, south-eastward ionospheric flow in the Southern Hemisphere at the time of these events. The time periods of these velocity enhancements infer that the evolution time of the FTEs is about 4-6 min from its origin on magnetopause to its addition to the polar cap. However, the ionospheric response time in the Southern Hemisphere might be Correspondence to: Q.-H. Zhang (zhangqinghe@pric.gov.cn) 2 min longer for the 12:31 UT FTE (and 6 min longer for the 12:51 UT FTE) than the response time in the Northern Hemisphere.

Coordinated Cluster/Double Star and ground-based observations of dayside reconnection signatures on 11 February 2004

“…It is worth noting that the implied evolution time of these FTEs are different with the results reported by our previous paper (Zhang et al, 2008), but the response time of these FTEs are similar. That paper showed that the implied evolution time of the FTEs was about 4-6 min from its origin on magnetopause (at reconnection site) to its addition to the polar cap (the magnetotail lobe), and the ionospheric response time in the Southern Hemisphere were 2-6 min longer than that in the Northern Hemisphere for the events on 1 April 2004.…”

“…9a and b, respectively. It is clear from the changing IMF direction that both spacecraft may observe a variety of FTE motions depending on the different IMF conditions, which agrees well with the results of Dunlop et al (2005) and Zhang et al (2008). We show the expected velocities of the flux tubes near the spacecraft corresponding to the two FTEs observed by Cluster and the angle between the expected (Cooling) velocities and the Cluster observations in Table 1.…”

“…This might be because of the dayside magnetopause reconnection occurred at the different hemisphere and the FTEs had different speed under the different IMF and solar wind conditions (see Table 2). From Table 2, we can find that for the two FTEs on 11 February 2004, the IMF had negative B Y and B Z with a positive B X component, giving a negative elevation angle (elevation angle = (B X /|B X |)tan −1 (|B X |/B Z )) and a smaller cone angle (cone angles = cos −1 (B X /|B|)); for the two FTEs on 1 April 2004 (reported by Zhang et al, 2008), the IMF had negative B X and B Z with a positive B Y component, giving a positive elevation angle and a larger cone angle. Considering the topology of Earth magnetic field during each event, the negative (positive) elevation angle and/or smaller (larger) cone angle with a negative (positive) B Y component may suggest the reconnection site is located southward (northward) of the subsolar region.…”

“…Fear et al, 2005;Zheng et al, 2005;Hasegawa et al, 2006;Wang et al, 2005) have been combined with a variety of ground-based instruments (e.g. Lockwood et al, 2001;Wild et al, 2001Wild et al, , 2003Marchaudon et al, 2004;Zhang et al, 2008Zhang et al, , 2010.…”

On the importance of interplanetary magnetic field ∣By∣ on polar cap patch formation

“…Poleward moving plasma concentration enhancements (sometimes called “polar cap patches”) [ Davies et al , 2002] are frequently observed in the F region of the polar ionosphere during periods of southward interplanetary magnetic field (IMF), and are also thought to be associated with bursty reconnection [e.g., Lockwood and Carlson , 1992; Carlson et al , 2002, 2004]. Poleward moving regions of backscatter or enhanced backscatter power, known as “poleward moving radar auroral forms” (PMRAFs), the radar counterpart of “poleward moving auroral forms” (PMAFs), are often also observed and are widely accepted to be another ionospheric signature of FTEs [e.g., Sandholt et al , 1990; Milan et al , 2000; Wild et al , 2001; Moen et al , 1995, 2001a, 2008a; Zhang et al , 2008]. The east‐west motion of these radar auroral forms depends on IMF B y [ Sandholt et al , 1993; Karlson et al , 1996; Moen et al , 1999, 2001b].…”