Pulsating aurora and cosmic noise absorption associated with growth-phase arcs

McKay, Derek; Partamies, Noora; Vierinen, Juha

The initial stage of a magnetospheric substorm is the growth phase, which typically lasts 1–2 h. During the growth phase, an equatorward moving, east–west extended, optical auroral arc is observed. This is called a growth-phase arc. This work aims to characterize the optical emission and riometer absorption signatures associated with growth-phase arcs of isolated substorms. This is done using simultaneous all-sky camera and imaging riometer observations. The optical and riometric observations allow determination of the location of the precipitation within growth-phase arcs of low- (inline-formula<10  keV) and high- (inline-formula> 10 keV) energy electrons, respectively. The observations indicate that growth-phase arcs have the following characteristics:

  1. d1e140The peak of the cosmic noise absorption (CNA) arc is equatorward of the optical emission arc. This CNA is contained within the region of diffuse aurora on the equatorward side.

  2. d1e144Optical pulsating aurora are seen in the border region between the diffuse emission region on the equatorward side and the bright growth-phase arc on the poleward side. CNA is detected in the same region.

  3. d1e148There is no evidence of pulsations in the CNA.

  4. d1e152Once the equatorward drift starts, it proceeds at constant speed, with uniform separation between the growth-phase arc and CNA of inline-formula40±10 km.

Optical pulsating aurora are known to be prominent in the post-onset phase of a substorm. The fact that pulsations are also seen in a fairly localized region during the growth phase shows that the substorm expansion-phase dynamics are not required to closely precede the pulsating aurora.

keywordsKeywords. Ionosphere (auroral ionosphere)

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McKay, Derek / Partamies, Noora / Vierinen, Juha: Pulsating aurora and cosmic noise absorption associated with growth-phase arcs. 2018. Copernicus Publications.

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