Shock aurora: Ground‐based imager observations

Zhou, X.; Fukui, K.; Carlson, H. C.; Moen, J.; Strangeway, R. J.

doi:10.1029/2009ja014186

Cited by 27 publications

(58 citation statements)

References 39 publications

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“…The auroral activity presented in Figure b bears strong resemblance to the shock aurora presented by Lorentzen and Moen [] and Zhou et al . [], where the diffuse aurora filled in a broad latitude region equatorward of the cusp aurora. Zhou et al .…”

Section: Observations Of Precipitating Energetic Particlesmentioning

confidence: 99%

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

et al. 2013

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[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.

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Section: Observations Of Precipitating Energetic Particlesmentioning

confidence: 99%

“…Zhou et al . [] also addressed the rayed cusp auroral signatures of Alfvénic aurora, suggesting that they were stimulated by kinetic Alfvén waves launched by magnetic reconnection [ Stasiewicz et al ., ; Chaston et al ., ].…”

Section: Observations Of Precipitating Energetic Particlesmentioning

confidence: 99%

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

et al. 2013

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“…One step is the diffuse aurora detected in 557.7 nm, and the subsequent step is the new discrete auroral forms in 557.7 and 630.0 nm. Using ground-based optical instrumentation at Ny-Ålesund of Svalbard, Zhou et al [2009] studied a shock aurora case near the local noon region, and they found that the auroral forms are presented as diffuse type in closed field lines. Up to present, all of the studies on shock aurora noticed the increase of the auroral intensity in response to a shock.…”

Section: Introductionmentioning

confidence: 99%

Decrease of auroral intensity associated with reversal of plasma convection in response to an interplanetary shock as observed over Zhongshan station in Antarctica

Liu

Han

et al. 2011

J. Geophys. Res.

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[1] We examined temporal variations of a dayside aurora and corresponding ionospheric plasma convection observed by an all-sky camera (ASC) and the Super Dual Auroral Radar Network (SuperDARN) over Zhongshan (ZHS), located at −74.5°in magnetic latitude (MLAT) in Antarctica, during a geomagnetic sudden commencement (SC) event that occurred on 27 May 2001. Simultaneous ASC observations at South Pole (SP, −74.3°MLAT) were also analyzed. During the SC time, ZHS and SP were located in the postnoon (1610 MLT) and prenoon (1100 MLT) sectors, respectively. Before the SC onset (1458UT), the ASC at ZHS observed an auroral arc with moderate intensity in the poleward direction of the field of view (FOV), and the SuperDARN radar detected sunward ionospheric plasma flow over ZHS. Just after the SC onset, the auroral intensity over ZHS decreased rapidly and the direction of the plasma flow was reversed to antisunward. Decrease of auroral intensity and reversal of the associated plasma convection in response to a sudden increase of the solar wind dynamic pressure at the early stage of a SC event has never been reported before. We suggest that these observational results were generated by a downward field-aligned current (FAC) and are consistent with a physical model of SC. The model predicts the appearance of a pair of FACs flowing downward (upward) in the postnoon (prenoon) sector at the very beginning of the SC, which is also supported by our observations. Consistence of the detailed observations with the model will be discussed in the paper, and we argue that here we present the first optical observational evidence supporting the validity of the model.

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“…Energy spectra of precipitating particles observed by DMSP on one oval crossing indicate that the major form of the auroral enhancements seen by Polar UVI is of diffuse type originating from the central plasma sheet. Previous studies from a limited number of satellite oval crossings also concluded with the same particle source from CPS (e.g., Zhou et al 2003Zhou et al , 2009Liou et al 2006Liou et al , 2007. Therefore, diffuse auroras are likely the dominant auroral form during magnetospheric compression.…”

Section: Discussionmentioning

confidence: 93%

Ionospheric Response to Solar Wind Pressure Pulses Under Northward IMF Conditions

Liou¹,

Han²,

Yang³

2013

Terr. Atmos. Ocean. Sci.

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Enhancements of aurora and auroral electrojets in response to sudden compression of the magnetosphere by shocks/ pressure pulses are well known and have been attributed by some to compression-enhanced magnetic field reconnection. To examine such a view, we analyze a fortuitous event that is comprised of a series of pressure pulses (< 20 min) on November 8, 2000. These pressure pulses were preceded by a large, northward interplanetary magnetic field (IMF) that lasted more than 15 hours such that effects from reconnection can be minimized. Auroral images acquired by ultraviolet imager on board the Polar satellite clearly show intensifications of the aurora that occurred first near local noon and progressively extended from dayside to nightside. The area-integrated global auroral power reached ~30 gigawatts (GW). It is also found that the global auroral power is well correlated with the solar wind dynamic pressure (correlation coefficient r ~0.90), rather than the change in the solar wind dynamic pressure. In-situ measurements of particle data from the Defense Meteorological Satellite Program satellite indicate that the magnetospheric source for the pressure-enhanced auroras is most likely the central plasma sheet. Other ionospheric parameters such as the auroral electrojet (AE index), magnetic storm index (Sym-H), and the cross polarcap potential drop also show a one-to-one correspondence to the pressure pulses. In one instance the auroral electrojets AE index reached more than 200 nT, the cross polar-cap potential drop (φ pc ) inferred from the SuperDARN radar network ionospheric plasma convection increased to ~60 kV. The observed increases in the auroral emissions, AE, and polar cap potential were not associated with substorms. Our result strongly suggests that solar wind pressure pulses are an important source of geomagnetic activity during northward IMF periods.

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Shock aurora: Ground‐based imager observations

Cited by 27 publications

References 39 publications

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

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

Decrease of auroral intensity associated with reversal of plasma convection in response to an interplanetary shock as observed over Zhongshan station in Antarctica

Ionospheric Response to Solar Wind Pressure Pulses Under Northward IMF Conditions

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