Dynamic properties of throat aurora revealed by simultaneous ground and satellite observations

Abstract

Throat aurora is defined as south‐north aligned auroral arcs equatorward of the dayside cusp aurora and was suggested to be the results of cold magnetospheric plasma interaction with magnetopause reconnection, but its observational properties have not yet been well established. In this paper we carefully examine a sequence of throat auroras observed over Svalbard on 27 December 2003. Observations from 630.0 nm [OI] show that poleward moving throat auroras frequently show brightening followed by dimming in auroral intensity, and sometimes, the brightening throat aurora is a precursor of poleward moving auroral forms. Simultaneous all‐sky images and HF radar backscatter observations along geomagnetic meridian show that the throat aurora brightening is drifting with ionospheric E × B convection and is colocated with enhanced spectral width poleward of the convection reversal boundary (CRB), while its dimming tends to be in the vicinity of the CRB. This leads us to propose that the throat aurora brightening and dimming may be on the open and closed field lines, respectively. Particle data from NOAA 16 confirm that the dimming throat aurora is associated with precipitation of magnetosheath‐like particles mixed with magnetospheric ions (>30 keV), which is characteristic of the low‐latitude boundary layer. For particle data from Defense Meteorological Satellite Program F16, we notice that the dimming throat aurora is associated with lower fluxes of magnetosheath‐like electrons accompanied with magnetospheric electrons, which is most likely on closed field lines. The dynamic properties of throat aurora presented in this paper are thus important to understand its generation mechanisms.

Direct Evidence for Throat Aurora Being the Ionospheric Signature of Magnetopause Transient and Reflecting Localized Magnetopause Indentations

“…Second, although FTEs have a tendency to occur predominantly during periods of southward IMF and FTE signatures are often observed during transient events, statistical studies show little tendency for the transients to occur during periods of southward IMF (Kawano et al, ). These are all comparable with the observational properties of throat aurora, because throat auroras often contain poleward moving aurora forms (PMAFs) (Chen et al, ; Han et al, ). PMAFs have been generally accepted as the ground signature of FTE (Moen et al, ) and have tendency to occur under southward IMF (Xing et al, ), whereas throat aurora show little tendency to occur during southward IMF (Han, Hietala, et al, ).…”

“…Here we show that the transients observed in Figures and are mostly associated with earthward flow enhancements, which indicates that the outside factor, such as pressure pulses proposed by Sibeck (), should be a necessary driver for producing the throat aurora, namely, the transient or the magnetopause indentation. These pressure pulses, as discussed above, are most likely associated with the HSJs generated in the magnetosheath, while observational results of throat aurora containing PMAFs (Chen et al, ; Han et al, ) strongly imply that FTEs may occur on the indented magnetopause boundary during HSJ impacting on the magnetopause. Recently, Hietala et al () provide evidence that HSJ can trigger magnetic reconnection.…”

Observational Evidence for Throat Aurora Being Associated With Magnetopause Reconnection

“…Moen et al () found one‐to‐one correspondences between upflows and PMAFs. Throat auroras are caused by soft particle precipitation from the magnetosheath (Han et al, ) and display properties similar to PMAF (Chen et al, ). So it is not surprising to observe ion upflows associated with throat aurora as shown in Figure .…”

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

“…For example, Baddeley et al (2017) used SuperDARN radar network to demonstrate that ULF waves push the auroral arcs equatorward and the wave energy is dissipated by the ionospheric joule heating / ion friction heating with the auroral particles. Chen et al (2017) studied the throat aurora using the SuperDARN radar observation and found that the throat aurora are the precursor of dayside PMAFs, and they are the auroral arcs mostly aligning in the North-South direction. Their brightening and diming is the signature of the open and closed field lines respectively.…”

“…Further, recent research studies related to the auroral emission and the polar ionospheric (e.g., Crowley et al, 2000;Zhang et al, 2013aZhang et al, , 2015Jin et al, 2015Jin et al, , 2016Jin et al, , 2017Liu et al, 2015;Lyons et al, 2015;Oksavik et al, 2015;Prikryl et al, 2015;van der Meeren et al, 2015;Hosokawa et al, 2016;Baddeley et al, 2017;Chen et al, 2017 and many others) have covered many important aspects of magnetosphere-ionosphere-thermosphere coupling, such as nightside patch related aurora and poleward edge brightening of the nightside auroral oval; nightside auroral blobs and their associated scintillations; throat aurora as the precursor of PMAFs; equatorward driven auroral arcs due to the ULF waves and their energy dissipation caused due to joule/ion frictional heating etc. Still the long time duration (3-5 h) auroral emissions neither were studied nor characterized based on their boundary movement.…”