Simultaneous ground-based optical and SuperDARN observations of the shock aurora at MLT noon

Jianjun Liu,Desheng Han,Huigen Yang,Hongqiao Hu,Mark Lester

doi:10.1186/s40623-015-0291-2

Abstract

Using ground-based high temporal and spatial optical aurora observations, we investigated one fortuitous event to illustrate the direct responses of the fine structure auroral emission to interplanetary shock on 7 January 2005. During the shock impact to the magnetosphere, the Chinese Arctic Yellow River Station (YRS) equipped with all-sky imagers (ASIs) was situated at the magnetic local noon region (~1210 MLT) in the Northern Hemisphere, while the SuperDARN CUTLASS Finland HF radar covering the field of view (FOV) of the ASIs at YRS had fine ionospheric plasma convection measurement. We observed that an intensified red aurora manifesting as a discrete emission band at a higher latitude responds to the shock impact gradually, which results in a distinct broadening of the dayside auroral oval due to the equatorward shifting of its lower latitude boundary after the shock arrival. In contrast, the green diffuse aurora, manifesting as a relatively uniform luminosity structure, reacts immediately to the shock compression, displaying prompt appearance in the southern edge of the FOV and subsequent poleward propagation of its higher latitude boundary. Simultaneously, the CUTLASS Finland radar monitored enhanced backscatter echo power and increased echo number, which coincided with intensified discrete aurora in approximately the same latitudinal region. Doppler velocity measurement showed moving ionospheric irregularities with generally enhanced line-of-sight (LOS) speed, but with prominent sunward flow in the polar cap and antisunward flow in both the eastern and western regions. The SuperDARN global ionospheric convection pattern clearly presented a large-scale plasma flow divided in four circulation cells, with two reversed flow cells nested in the noon sector of the polar cap. These direct observations strongly suggest that the prompt shock compression intensified the wave-particle interaction in the inner magnetosphere and enhanced the lobe magnetic reconnection rate at magnetospheric high latitude.

Highlights

The large-scale auroral feature associated with interplanetary shock has been investigated widely over the last two decades mainly using satellite onboard imager observations (Sibeck et al 1999; Zhou and Tsurutani 1999; Zhou et al 2003; Meurant et al 2003; Meurant et al 2005)
Zhou et al (2009) studied dayside shock auroral forms and their variations when Svalbard was at ~1120 magnetic local time (MLT), and they found that both green and red auroral emissions intensified by a factor larger than 2 within 5 min after the shock arrival to the magnetosphere, equatorward and eastward expanding diffuse aurora on closed-field lines and doubled the cusp meridional width due to equatorward motion of the low latitude boundary of the cusp
We concentrate on the detailed evolution of the diffuse and discrete aurora by using high temporal and spatial ground-based optical observation and simultaneous ionospheric plasma drift determined with the SuperDARN radar located at Hankasalmi during the interval following the IP shock compression of the magnetosphere

Summary

Introduction

The large-scale auroral feature associated with interplanetary shock (i.e., shock aurora) has been investigated widely over the last two decades mainly using satellite onboard imager observations (Sibeck et al 1999; Zhou and Tsurutani 1999; Zhou et al 2003; Meurant et al 2003; Meurant et al 2005). Previous studies on shock aurora were mainly concentrated on the measurements of large-scale auroral emissions from satellite imager observations and characteristics of energetic particle precipitation, but with few works using ground-based medium and small-scale optical aurora and simultaneous related ionospheric plasma drift measurements (Zhou and Tsurutani 1999; Zhou et al 2003; Meurant et al 2003; Zhou et al 2009; Motoba et al 2009; Liu et al 2011). Intensified auroral arc with a lifetime of ~14 min and periodical oscillation in the ionospheric plasma flow were detected by ASI and SuperDARN caused by the shock impact (Liu et al 2013) All of these works mentioned above demonstrated that more features of shock aurora and related ionospheric response have not been unveiled yet. A general direct relationship between dayside aurora and IP shock has been observed, but more exact response time and certain auroral forms have been elusive because of low temporal and spatial resolution observation

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Conclusion