An extensive survey of dayside diffuse aurora based on optical observations at Yellow River Station

Abstract

By using 7 years optical auroral observations obtained at Yellow River Station (magnetic latitude 76.24°N) at Ny-Alesund, Svalbard, we performed the first extensive survey for the dayside diffuse auroras (DDAs) and acquired observational results as follows.(1) The DDAs can be classified into two broad categories, i.e., unstructured and structured DDAs. The unstructured DDAs are mainly distributed in morning and afternoon, but the structured DDAs predominantly occurred around the magnetic local noon (MLN). (2) The unstructured DDAs observed in morning and afternoon present obviously different properties. The afternoon ones are much stable and seldom show pulsating property. (3) The DDAs are more easily observed under geomagnetically quiet times. (4) The structured DDAs mainly show patchy, stripy, and irregular forms and are often pulsating and drifting. The drifting directions are mostly westward (with speed ~5 km/s), but there are cases showing eastward or poleward drifting. ( 5) The stripy DDAs are exclusively observed near the MLN and, most importantly, their alignments are confirmed to be consistent with the direction of ionospheric convection near the MLN. (6) A new auroral form, called throat aurora, is found to be developed from the stripy DDAs. Based on the observational results and previous studies, we proposed our explanations to the DDAs. We suggest that the unstructured DDAs observed in the morning are extensions of the nightside diffuse aurora to the dayside, but that observed in the afternoon are predominantly caused by proton precipitations. The structured DDAs occurred near the MLN are caused by interactions of cold plasma structures, which are supposed to be originated from the ionospheric outflows or plasmaspheric drainage plumes, with hot electrons from the plasma sheet. We suppose that the cold plasma structures for producing the patchy DDAs are in lumpy and are more likely from the plasmaspheric drainage plumes. The cold plasma structure for producing the stripy DDAs should be in wedge like and is generated by conveying the cold plasmas from lower L-shell toward higher L-shell with magnetospheric convection, and that for producing the irregular DDAs is resulted from deforming the wedge-like structure by disturbance. The throat aurora is supposed to be projection of a newly opened flux of reconnection. In addition, we also found that structured DDAs correspond to structured electron precipitations in the ionosphere, which implies that the cold plasma structures in the magnetosphere are magnetically mapped to the ionosphere and act as a duct for producing the structured DDAs. We argue that we have presented some new observational results about DDA in this paper, which will be useful for fully understanding the DDAs.

Jets Downstream of Collisionless Shocks

“…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).…”

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

“…Recently, a particular auroral form, manifested as a localized equatorward extension of the equatorward edge of the east‐west aligned persistent midday auroral oval, has been observed near the dayside convection throat region. This auroral form has been named “throat aurora” (Han et al, ). Coordinated low‐altitude satellite observations show that throat auroras are caused by magnetosheath‐like particles and are suggested to be associated with localized magnetopause deformations (Han et al, ).…”

“…throat region. This auroral form has been named "throat aurora" (Han et al, 2015). Coordinated low-altitude satellite observations show that throat auroras are caused by magnetosheath-like particles and are suggested to be associated with localized magnetopause deformations (Han et al, 2016).…”

A comparative study of auroral morphology distribution between the Northern and Southern Hemisphere based on automatic classification

“…Study of the morphology and evolution of aurora is not only helpful for revealing the solar wind-magnetosphere-ionosphere coupling processes and their internal mechanisms but also provides important physical principles for space weather forecasting (Nishimura et al, 2010;Hu et al, 2009Hu et al, , 2010Hu et al, , 2012Hu et al, , 2013Hu et al, , 2017aHan et al, 2015Han et al, , 2016Han et al, , 2017.…”