Balanced reconnection intervals: four case studies

Abstract

Abstract. During steady magnetospheric convection (SMC) events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs). This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3–4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996), while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22–23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential) than previously studied SMCs. It also has more small scale activity than the other events studied here.

Comparison of magnetotail magnetic flux estimates based on global auroral images and simultaneous solar wind—magnetotail measurements

“…Two methods of polar cap area calculation have been actively used in recent years. They are based on either electron-induced auroral emissions (thereafter referred to as F e , e.g., DeJong and Clauer, 2005;DeJong et al, 2007DeJong et al, , 2008 or protoninduced auroral emissions (thereafter referred to as F p , e.g., Hubert et al, 2006). Methods based on the electron-induced auroral emissions are expected to be more affected by dayglow contamination.…”

“…Global auroral images from DE1 and Viking made possible first individual ''measurements'' of the polar cap area and PC magnetic flux (e.g., Baker et al, 1994;Yahnin et al, 1994). Recently routine optical observation of the polar cap from the POLAR and IMAGE spacecraft during long periods became available at $ 122 min time resolution (Brittnacher et al, 1999;DeJong and Clauer, 2005;Hubert et al, 2006Hubert et al, , 2008Milan et al, 2007;DeJong et al, 2007DeJong et al, , 2008. However, these methods also have some uncertainties: the accuracy of the PC area determination depends on the accuracy of the PC boundaries identification, particularly on the chosen luminosity threshold level.…”

“…2bshows an SMC event, surrounded by substorms D and E. Solid vertical lines inFig. 2bindicate the SMC period according toDeJong et al (2008). Consider…”

On the conditions preceding sudden magnetotail magnetic flux unloading

“…The role of the magnetotail field as the main reservoir of energy dissipated during substorms have been questioned by Pulkkinen et al [2006]. Several examples of substorm onsets, not preceded by a pressure or magnetic flux increase in the magnetotail, have been presented [Petrukovich et al, 2000;Yahnin et al, 1994Yahnin et al, , 2001DeJong et al, 2008]. This has also been statistically confirmed by Dmitrieva et al [2004] who noticed that ∼1/3 out of 145 isolated substorm events in the midtail studied did not show any total pressure growth before unloading, whereas a classical growth phase was observed only in the other 1/3 of events (the remaining 1/3 showed a mixed behavior).…”

A statistical study of BRIs (SMCs), isolated substorms, and individual sawtooth injections

“…If this occurs globally and quasiperiodically then it is termed a global sawtooth oscillation, each unloading in the series is an individual sawtooth injection [ Reeves et al , 2002; Henderson , 2004]. If the energy is not stored and released, but rather continuously diverted, then convection is quasi‐steady, the dayside and nightside reconnection rates are balanced, and the magnetosphere has achieved a balanced reconnection interval (BRI), sometimes described as a steady magnetospheric convection (SMC) mode [ DeJong et al , 2008; Sergeev et al , 1996].…”