Multi‐instrument observations from Svalbard of a traveling convection vortex, electromagnetic ion cyclotron wave burst, and proton precipitation associated with a bow shock instability

Abstract

[1] An isolated burst of 0.35 Hz electromagnetic ion cyclotron (EMIC) waves was observed at four sites on Svalbard from 0947 to 0954 UT 2 January 2011, roughly 1 h after local noon. This burst was associated with one of a series of~50 nT magnetic impulses observed at the northernmost stations of the IMAGE magnetometer array. Hankasalmi SuperDARN radar data showed a west-to-east (antisunward) propagating vortical ionospheric flow in a region of high spectral width~1-2 north of Svalbard, confirming that this magnetic impulse was the signature of a traveling convection vortex. Ground-based observations of the H a line at Longyearbyen indicated proton precipitation at the same time as the EMIC wave burst, and NOAA-19, which passed over the west coast of Svalbard between 0951 and 0952, observed a clear enhancement of ring current protons at the same latitude. Electron precipitation from this same satellite indicated that the EMIC burst was located on closed field lines, but near to the polar cap boundary. We believe these are the first simultaneous observations of EMIC waves and precipitating energetic protons so near to the boundary of the dayside magnetosphere. Although several spacecraft upstream of Earth observed a steady solar wind and predominantly radial interplanetary magnetic field orientation before and during this event, data from Geotail (near the morning bow shock) showed large reorientations of the interplanetary magnetic field and substantial decreases in ion density several minutes before it, and data from Cluster (near the afternoon bow shock) showed an outward excursion of the bow shock simultaneous with it. These upstream perturbations suggest that a spontaneous hot flow anomaly, a bow shock related instability, may have been responsible for triggering this event, but do not provide enough information to fully characterize that instability. , et al. (2013), Multi-instrument observations from Svalbard of a traveling convection vortex, electromagnetic ion cyclotron wave burst, and proton precipitation associated with a bow shock instability, J. Geophys.

Magnetospheric response to magnetosheath pressure pulses: A low‐pass filter effect

“…The flow structures propagated westward (indicated by the arrow), seen from the relative timings at different beam directions (beam number increases toward east). Thus, SuperDARN observed a TCV (very similar to that reported by Engebretson et al []) due to a group of magnetosheath pressure pulses. While for other groups of pulses, further flow structures were observed, the data quality and coverage were often poor, and the azimuthal propagation between beam directions was not clear.…”

Simultaneous traveling convection vortex events and Pc1 wave bursts at cusp latitudes observed in Arctic Canada and Svalbard

“…Recent observations from Svalbard reported by Engebretson et al . [] showed both of these additional signatures and in addition reported both satellite and ground‐based observations of precipitating protons in association with the Pc1 waves.…”

“…[] and Engebretson et al . [] and hybrid simulations by Omidi et al . [] that bow shock instabilities that are capable of causing transient pressure increases at the dayside magnetopause can occur even in the absence of significant solar wind perturbations.…”

Impacts of spontaneous hot flow anomalies on the magnetosheath and magnetopause

“…Engebretson et al [2013] have reported the observation of electromagnetic ion cyclotron waves and precipitating energetic protons on closed magnetospheric field lines near the magnetopause during a nearly radial IMF. Engebretson et al [2013] have reported the observation of electromagnetic ion cyclotron waves and precipitating energetic protons on closed magnetospheric field lines near the magnetopause during a nearly radial IMF.…”

“…One is the magnetosheath cavities reported by Katırcıoğlu et al [2009] that are associated with drops in density, flow velocity, and magnetic field and enhancements in the flux of energetic ions. In section 4 we discuss the impacts of SHFAs on the magnetopause and how such impacts may result in the generation of ion cyclotron waves and precipitation of energetic protons in the outer magnetosphere as suggested by Engebretson et al [2013]. This paper presents results from our simulations on magnetosheath cavities in section 2 and magnetosheath jets in section 3.…”