The Difference Between Isolated Flux Transfer Events and Flux Transfer Event Cascades

Abstract

This flux transfer event (FTE) study is based on 984 FTEs originally identified by Wang et al. (2005, https://doi:10.1029/2005JA011150) in Cluster data. Due to Cluster's orbit, the FTE list exclusively contains events detected at the high‐latitude dayside magnetopause and low‐latitude flanks. The focus of this study is on FTE separation time. The results show that FTEs appearing in cascades are mainly located at the northern dusk and southern dawn magnetopause, while isolated FTEs are equally spread over the region covered by Cluster. This difference may be explained by the different interplanetary magnetic field (IMF) conditions during which the subsets occur. For isolated FTEs, average IMF By is close to zero. During such conditions, FTEs are expected to form at arbitrary longitudes along an equatorial merging line. After formation, they propagate northward and southward, causing an equal distribution at higher latitudes. In contrast, FTE cascades typically occur during weakly southward IMF with a negative By component. Their asymmetric distribution at higher latitudes is consistent with both the component and the antiparallel merging model for nonzero By. In both scenarios, newly formed FTEs are expected to move to the northern dusk and southern dawn regions, as observed. Many FTE cascades appearing during northward IMF are located close to the low‐latitude flanks, confirming previous reports. We discovered that such FTEs appear during large IMF values. Another new result is that 16% of all isolated FTEs appear during small IMF cone angles, suggesting that these may form as a result of magnetosheath jets impacting on the magnetopause.

Intermittent Lobe Reconnection Under Prolonged Northward Interplanetary Magnetic Field Condition: Insights From Cusp Spot Event Observations

“…Although the cascade of FTEs may occur during a northward IMF (Kullen et al, 2019) and under stable IMF conditions, it is worth noting that the observed EMRFs during this period were not accompanied by correlated variations in solar wind and IMF conditions. This implies that the intermittent lobe reconnections were not directly driven by changes in solar wind or IMF.…”

“…This discovery holds particular significance in advancing our understanding of the solar wind-magnetosphere coupling process in the cusp region. which appear quasi-periodically in cascades of up to 10 FTEs in succession (Farrugia et al, 1987;Kullen et al, 2019). Therefore, it is puzzling why the lobe reconnection under prolonged northward IMF conditions should be always continuous.…”

“…Low‐latitude reconnection at the magnetopause has also been found to be unsteady (Lockwood et al., 2001; Wild et al., 2001; Zou et al., 2022). Intermittent reconnection typically occurs in the form of local reconnection bursts during flux transfer events (FTEs), which appear quasi‐periodically in cascades of up to 10 FTEs in succession (Farrugia et al., 1987; Kullen et al., 2019). Therefore, it is puzzling why the lobe reconnection under prolonged northward IMF conditions should be always continuous.…”

Magnetic Field in Magnetosheath Jets: A Statistical Study of BZ Near the Magnetopause

“…However, Kullen et al. (2019) studied the occurrence of two different types of flux transfer events (FTEs): FTE cascades with separation times <70 min and isolated FTEs with separation times ≥70 min. They found that while only 2–5 of FTE cascades in their data set occurred during low IMF cone angle (<30) conditions, 16 of isolated FTEs occurred during these conditions.…”

“…Thus, they concluded that these fluctuations do not cause reconnection and argued that the timescale of the fluctuations is probably too short for reconnection. However, Kullen et al (2019) studied the occurrence of two different types of flux transfer events (FTEs): FTE cascades with separation times <70 min and isolated FTEs with separation times ≥70 min. They found that while only 2-5% of FTE cascades in their data set occurred during low IMF cone angle (<30  ) conditions, 16% of isolated FTEs occurred during these conditions.…”