Bursty bulk flow intrusion to the inner plasma sheet as inferred from auroral observations

Abstract

[1] The physics of the interaction of bursty bulk flows (BBFs) with the near-Earth plasma is not yet known in detail. We address this issue with comprehensive observations made with the MIRACLE network during a well-documented streamer event. In this case an equatorward intruding auroral streamer inclined from northwest (NW) to southeast (SE) reached the region of the proton oval of 486 nm (H b ) luminosity. This H b band is assumed to map poleward of the !30 keV proton isotropic boundary, which is at geocentric distances $7-8 R E according to the appropriate magnetic field models. A significant enhancement (30%) in the H b luminosity was recorded just at the time and in the location where the equatorward end of the streamer reached the H b band. This enhancement implies a corresponding pressure enhancement in the equatorial magnetosphere. The simultaneous poleward shift of the H b emission suggests that also a magnetic field dipolarization took place in the same region. An NW-aligned electrojet (300-400 km in width) accompanied the equatorward development of the streamer (with streamer locating at the dusk flank of this electrojet), and it produced a sharp negative magnetic bay ($300 nT) resembling a substorm onset. Both auroral and equivalent current observations suggest that the plasma jet was not completely dissolved or stopped during this interaction, but rather diverted in the azimuthal direction. Equivalent currents reconstructed from ground magnetic field observations indicate that a R1-type field-aligned current system (upward current $0.5 MA) accompanied the streamer development. However, our observations do not show any signatures of a R2-type current system expected to build up during the flow braking and diversion according to previously published simulation studies.

EISCAT-Cluster observations of quiet-time near-Earth magnetotail fast flows and their signatures in the ionosphere

“…Figs. 8c-f show that the streamer braked and then drifted westward along the poleward boundary of the proton oval, which is consistent with the observations by Kauristie et al (2003). In this case, the streamer tip stayed a rather long time in the vicinity of the proton oval, which is related to rather long-lived positive δB y perturbation at C3 and C4 (panels e and f in Fig.…”

“…Figure 10a-d shows that the tip of streamer 3a turned duskward forming a hook-like structure on the equatorward end of the most intense emissions. This is a similar feature that was seen by Kauristie et al (2003) and it suggests that the flows at the Earthward end of the BBF flow channel were diverted towards dusk in the inner magnetosphere. During the westward motion of the merged streamer started to fade from Earthward end, which again indicates that the flows started to decay starting from the Earthward.…”

“…Figure 1 shows solar wind and geomagnetic conditions for the period of 16:00-21:00 UT. Top panel shows the IMF components measured by the Magnetic Field Investigation (MFI) instrument (Lepping et al, 1995) onboard the WIND spacecraft (XGSM ∼ 197 R E ). The data are 1-min OMNI data, so the solar wind parameters have been propagated to the magnetospheric bow shock nose (XGSM ∼ 14 R E ).…”

“…The equatorward boundary of the oval can be taken as a proxy for the isotropic boundary for these protons which means that equatorward of the boundary the field lines are dipolar enough for the ions to move adiabatically with empty loss cone (e.g. Kauristie et al, 2003, and references therein). The location of the proton oval stayed stable in the KIL MSP during the period of the BBF-streamer events.…”

The Behaviors of Ionospheric Scintillations Around Different Types of Nightside Auroral Boundaries Seen at the Chinese Yellow River Station, Svalbard

“…At ∼23:00 UT we observe sudden enhancement in the ionospheric current (see Figure 1G) and the auroral emission band intensity appears fragmented. The enhanced ionospheric current in the auroral oval may be associated with flow burst in the ionosphere (Sergeev et al, 1990;de la Beaujardière et al, 1994;Kauristie et al, 2003). There is a possibility that the fragmented poleward moving auroral structures may be associated with the flow burst (Zou et al, 2009), which causes significant enhancement in the phase scintillation.…”