Polar, Cluster and SuperDARN evidence for high-latitude merging during southward IMF: temporal/spatial evolution

Abstract

Abstract. Magnetic merging on the dayside magnetopause often occurs at high latitudes. Polar measured fluxes of accelerated ions and wave Poynting vectors while skimming the subsolar magnetopause. The measurements indicate that their source was located to the north of the spacecraft, well removed from expected component merging sites. This represents the first use of wave Poynting flux as a merging discriminator at the magnetopause. We argue that wave Poynting vectors, like accelerated particle fluxes and the Walén tests, are necessary, but not sufficient, conditions for identifying merging events. The Polar data are complemented with nearly simultaneous measurements from Cluster in the northern cusp, with correlated observations from the Super-DARN radar, to show that the locations and rates of merging vary. Magnetohydrodynamic (MHD) simulations are used to place the measurements into a global context. The MHD simulations confirm the existence of a high-latitude merging site and suggest that Polar and SuperDARN observed effects are attributable to both exhaust regions of a temporally varying X-line. A survey of 13 merging events places the location at high latitudes whenever the interplanetary magnetic field (IMF) clock angle is less than ∼150 • . While inferred highlatitude merging sites favor the antiparallel merging hypothesis, our data alone cannot exclude the possible existence of a guide field. Merging can even move away from equatorial latitudes when the IMF has a strong southward component. MHD simulations suggest that this happens when the dipole tilt angle increases or when IMF B X increases the effective dipole tilt.

Detailed dayside auroral morphology as a function of local time for southeast IMF orientation: implications for solar wind-magnetosphere coupling

“…This approach has given us important insight on the coupling of temporal features of the magnetopause reconnection process (flux transfer events; FTEs) to the ionosphere (Sandholt et al, 1990(Sandholt et al, , 1993bMilan et al, 2000;Neudegg et al, 2001;Lockwood et al, 2003). A major issue under debate in magnetospheric physics today is the magnetopause reconnection topology (Moore et al, 2002;Russell, 2003;Maynard et al, 2003). The investigation of the spatial structure of the dayside aurora is in our view very relevant to this issue.…”

A decade of the Super Dual Auroral Radar Network (SuperDARN): scientific achievements, new techniques and future directions

“…The emphasis in this paper is on studies in which SuperDARN has been the major instrument used to deliver the science. However, it Surv Geophys (2007) 28:33-109 37 should be noted that there are a large number of significant satellite, data assimilation, and modelling-centric studies in which SuperDARN data have played an important supporting role (e.g., Lu et al 2001;Maynard et al 2003;Trattner et al 2003;Farrugia et al 2004;Trattner et al 2005;Palmroth et al 2005), which are not discussed here. The code name of each radar is highlighted in red close to the radar location.…”

Characteristics of merging at the magnetopause inferred from dayside 557.7-nm all-sky images: IMF drivers of poleward moving auroral forms

“…With θ≈−135 • merging in the northern hemisphere should occur on the morning side of the cusp where the interplanetary and terrestrial fields are nearly anti-parallel (Crooker, 1979;Luhmann et al, 1984;Maynard et al, 2003). This is close to the location of Cluster.…”

“…This is an instrumental effect due the very strong central emissions. Maynard et al (2003) used Polar and Cluster data to show that merging typically occurs at high latitudes for 0<|θ|<150 • . As a result, IMF B Y bifurcates the cusp according to source regions (Maynard et al, 2001b;Coleman et al, 2001;Roger et al, 2003).…”