University of Oulu

McKay, D., Partamies, N., and Vierinen, J.: Pulsating aurora and cosmic noise absorption associated with growth-phase arcs, Ann. Geophys., 36, 59-69,, 2018

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

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Author: McKay, Derek1,2; Partamies, Noora3,4; Vierinen, Juha1
Organizations: 1Department of Physics and Technology, University of Tromsø, Tromsø, Norway
2Sodankylä Geophysical Observatory, University of Oulu, Oulu, Finland
3UNIS University Centre in Svalbard, Svalbard, Norway
4Birkeland Centre for Space Science, Bergen, Norway
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 0.9 MB)
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Language: English
Published: Copernicus Publications, 2018
Publish Date: 2018-03-14


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- (< 10  keV) and high- (>  10 keV) energy electrons, respectively. The observations indicate that growth-phase arcs have the following characteristics:

1. The 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. Optical 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. There is no evidence of pulsations in the CNA.

4. Once the equatorward drift starts, it proceeds at constant speed, with uniform separation between the growth-phase arc and CNA of 40 ± 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.

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Series: Annales geophysicae
ISSN: 0992-7689
ISSN-E: 1432-0576
ISSN-L: 0992-7689
Volume: 36
Pages: 59 - 69
DOI: 10.5194/angeo-36-59-2018
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: KAIRA was funded by the University of Oulu and the FP7 European Regional Development Fund and is operated by Sodankylä Geophysical Observatory with assistance from the University of Tromsø, Norway. Derek McKay and Juha Vierienen are supported by the Tromsø Research Foundation. Noora Partamies is supported by the Research Council of Norway under CoE contract 223252.
EU Grant Number: (261967) EISCAT_3D_2 - EISCAT_3D: A European three-dimensional imaging radar for atmospheric and geospace research (Preparatory Phase)
Copyright information: © Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License.