Preprints
https://doi.org/10.5194/angeo-2022-6
https://doi.org/10.5194/angeo-2022-6
 
28 Feb 2022
28 Feb 2022
Status: this preprint is currently under review for the journal ANGEO.

Local time dependence of auroral peak emission height and morphology

Noora Partamies1,2, Daniel Whiter3, Kirsti Kauristie4, and Stefano Massetti5 Noora Partamies et al.
  • 1The University Centre in Svalbard (UNIS), Longyearbyen, Norway
  • 2Birkeland Centre for Space Science, University of Bergen, Norway
  • 3University of Southampton, UK
  • 4Finnish Meteorological Institute, Helsinki, Finland
  • 5INAF-IAPS, Institute for Space Astrophysics and Planetology, Rome, Italy

Abstract. We investigate the bulk behaviour of auroral structures and peak emission height as a function of magnetic local time (MLT). These data are collected from the Fennoscandian Lapland and Svalbard latitudes from seven identical auroral all-sky cameras over about one solar cycle. The analysis focusses on green auroral emission, which is where the morphology is most clearly visible and the number of images is highest. The typical peak emission height of the green and blue aurora varies from 110 km on the nightside to about 118 km in the morning MLT over the Lapland region. It stays systematically higher (at 118–120 km) at high latitudes (Svalbard) at nighttime and reaches 140 km at around magnetic noon. During high solar wind speed (above 500 km/s) nightside emission heights appear about 5 km lower than during slow solar wind speed (below 400 km/s). The sign of the Interplanetary Magnetic Field (IMF) has nearly no effect on the emission heights in the night sector, but northward IMF causes lower emission heights in the dawn over Lapland and during the noon hours over Svalbard. While the former is interpreted as a change in the particle population within the field-of-view, the latter is rather due to the movement of the cusp location due to the IMF orientation. The morning sector heights also show a pronounced difference when previously detected pulsating aurora events have been excluded/included in the dataset, suggesting that this type of aurora is a dominant phenomenon in the morning and an important dissipation mechanism.

The morphological evolution described by an increase of complex auroral structures in the midnight hours follows the average substorm occurrence. This effect is enhanced during stronger solar wind driving and during higher geomagnetic activity (as measured by auroral electrojet index, AL). During high solar wind speed, the high latitude auroral evolution shows particularly complex morphology, which is not limited to the nightside but rather only excluding the magnetic noon hours. An increase in the geomagnetic activity further enhances the structural complexity of the aurora in the morning sector.

Noora Partamies et al.

Status: open (until 01 Jun 2022)

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  • RC1: 'Comment on angeo-2022-6', Shin-ichiro Oyama, 14 May 2022 reply

Noora Partamies et al.

Noora Partamies et al.

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Short summary
We investigate the local time behaviour of auroral structures and emission height. The data are collected from the Fennoscandian Lapland and Svalbard from 7 identical auroral all-sky cameras over about one solar cycle. The typical peak emission height of the green aurora varies from 110 km on the nightside to about 118 km in the morning over the Lapland region but stays systematically higher over Svalbard. During fast solar wind nightside emission heights are 5 km lower than during slow solar wind.