Observational properties of dayside throat aurora and implications on the possible generation mechanisms

Abstract

Observational properties of throat aurora are investigated in detail by using 7 year continuous auroral observations obtained at Yellow River Station (magnetic latitude 76.24°N). From our inspection, throat aurora is often observed under the condition of stripy diffuse aurora contacting with the persistent discrete auroral oval, and the long‐period throat aurora observations generally consist of intermittent subsequences of throat aurora brightening followed by poleward moving auroral form and throat aurora dimming. We also noticed that the orientation of throat aurora is aligned along the ionospheric convection flow, and its local time distribution shows clear dependence on the interplanetary magnetic field (IMF) By component. These observational results indicate that factors inside the magnetosphere may play important role on occurrence of throat aurora. We thus suggest that throat aurora may present the ionospheric signature of redistribution of reconnection rate on the magnetopause by cold magnetospheric plasma flowing into the reconnection site. In addition, we also found that the occurrence rate of throat aurora clearly decreases with increase of the IMF cone angle (arccos(|Bx|/B)), which is very similar with the occurrence rate of high‐speed jet (HSJ) observed in magnetosheath depending on the IMF cone angle. This is suggested as that the HSJs occurred outside the magnetosphere may also play important role for generation of throat aurora by triggering magnetopause reconnection or by direct impacting. Although further studies are needed to clarify how the throat auroras are generated in detail, the relevant observations about throat aurora have presented important implications on a variety open questions, such as distribution and generation of cold plasma structures in the outer magnetosphere, magnetopause deformation, and possible relation between HSJ and reconnection.

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

“…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, ). All of these results provide strong evidence that throat auroras are definite ground signatures for the magnetopause transients that are all correspondent to magnetopause indentations.…”

Jets Downstream of Collisionless Shocks

“…(ii) They may change the shear angle between the magnetospheric and magnetosheath magnetic field The equatorward boundary of the discrete aurora oval and the throat aurora are outlined by the red and black dots. Adapted from Han et al (2017) lines, hence affecting the β-shear relation (Swisdak et al 2010) which states whether or not asymmetric reconnection is suppressed by diamagnetic drift. The change in shear can be due to the magnetic field orientation within the jets (i.e., on the magnetosheath side).…”

“…Are there specific solar wind conditions that lead to jets that trigger reconnection, so that it could be forecasted? Possible Connection Between Jets and Dayside 'Throat Aurora' Recently, Han et al (2015Han et al ( , 2016Han et al ( , 2017 found that dayside diffuse auroras observed near magnetic local noon often show discrete north-south aligned arcs extending from low latitudes towards the equatoward edge of the main auroral oval (Fig. 42).…”

Plasma flow patterns in and around magnetosheath jets

“…In the magnetosphere, the radiation belt electron population may be modified by magnetopause shadowing (Elkington et al, 2003;Turner et al, 2012). Consequences may even be seen on the ground, in the form of increased ionospheric convection, geomagnetic field variations, and possibly "throat" aurora observations (Hietala et al, 2012;Dmitriev and Suvorova, 2012;Archer et al, 2013b;Han et al, 2017).…”