13 May 2022
13 May 2022
Status: this preprint is open for discussion.

The Morphology of Poleward Moving Auroral Forms

Anton Oscar Goertz1,2,3, Noora Partamies2,3, Daniel Whiter4, and Lisa Baddeley2,3 Anton Oscar Goertz et al.
  • 1Intelligence and Space Research, Los Alamos National Laboratory, Los Alamos, NM, USA
  • 2Department of Arctic Geophysics, University Centre of Svalbard, Longyearbyen, Norway
  • 3Birkeland Centre for Space Science, University of Bergen, Norway
  • 4School of Physics and Astronomy, University of Southampton, UK

Abstract. We investigated the morphology of poleward moving auroral forms (PMAFs) qualitatively by visual inspection of all sky camera (ASC) images and quantitatively using the arciness index. The PMAFs in this study were initially identified with a meridian scanning photometer located at Kjell Henriksen Observatory (KHO), Svalbard, and analyzed using ASC images taken by cameras at KHO and in Ny-Ålesund, Svalbard. We present a detailed six-step evolution of PMAF morphology in two dimensions. This evolution includes (1) an equatorward expansion of the auroral oval and an intensification of auroral brightness at the open-closed boundary, (2) the appearance of an arc-like structure in the oval, (3) poleward and possible west/eastward propagation, (4) azimuthal expansion events, (5) rebrightening of the PMAF and eventual (6) fading away. While there have been previous studies commenting on PMAF morphology this is the first work dedicated to the morphological evolution of PMAFs and it includes more detailed discussion and novel aspects, such as the observation of initial merging of 557.7 nm auroral patches to form a PMAF. Moreover, the morphology of PMAFs is quantified using the arciness index, which is a number describing how arc-like auroral forms appear in ASC images. We present the results of a superposed epoch analysis of arciness in relation to PMAF occurrence. This analysis uncovered that arciness increases suddenly during the onset of a PMAF event and decreases over the PMAF lifetime to return to its baseline value once the event has concluded. This behavior may be understood based on changes in the morphology of PMAFs and the auroral oval and furthermore may be used to identify PMAFs from arciness data.

Anton Oscar Goertz et al.

Status: open (until 24 Jun 2022)

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Anton Oscar Goertz et al.

Anton Oscar Goertz et al.


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Short summary
Poleward moving auroral forms (PMAFs) are specific types of aurora that are believed to be the signature of the connection of Earth's magnetic field to that of the sun. In this paper we discuss the evolution of PMAFs in regards to their auroral morphology as observed in all-sky camera images. We interpret different aspects of this evolution in terms of the connection dynamics between Earth's and the sun's magnetic fields. This sheds more light on the magnetic interaction between sun and Earth.