View Full Version : STEVE is not an aurora

2018-Aug-21, 02:16 PM
From spaceweather.com (https://spaceweatherarchive.com/2018/08/21/a-new-type-of-aurora-is-not-an-aurora-at-all/)

A new type of aurora nicknamed "STEVE" may not be an aurora at all, according to a new paper published August 20th in the Geophysical Research Letters. A group of researchers combined satellite data with ground-based imagery of STEVE during a geomagnetic storm to investigate how STEVE is formed. "Our main conclusion is that STEVE is not an aurora," said Bea Gallardo-Lacourt, a space physicist at the University of Calgary in Canada and lead author of the new study.

STEVE is a purple ribbon of light that amateur astronomers in Canada have been photographing for decades, belatedly catching the attention of the scientific community in 2016. It doesn't look exactly like an aurora, but it often appears alongside auroras during geomagnetic storms. Is it an aurora -- or not? That's what Gallardo-Lacourt's team wanted to find out.

Auroras appear when energetic particles from space rain down on Earth's atmosphere during geomagnetic storms. If STEVE is an aurora, they reasoned, it should form in much the same way. On March 28, 2008, STEVE appeared over eastern Canada just as NOAA's Polar Orbiting Environmental Satellite 17 (POES-17) passed overhead. The satellite, which can measure the rain of charged particles that causes auroras, went directly above the purple ribbon. Gallardo-Lacourt's team looked carefully at the old data and found ... no rain at all.

"Our results verify that this STEVE event is clearly distinct from the aurora borealis since it is characterized by the absence of particle precipitation," say the researchers. "Interestingly, its skyglow could be generated by a new and fundamentally different mechanism in Earth's ionosphere."
Earlier story from spaceweather about STEVE (https://spaceweatherarchive.com/2018/05/06/steve-visits-the-usa/)

Link to paper (https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2018GL078509)

Abstract One of the recent developments in ionospheric research was the introduction of a subauroral spectacle called STEVE (Strong Thermal Emission Velocity Enhancement). Although STEVE has been documented by amateur night sky watchers for decades, it is an exciting new upper atmospheric phenomenon for the scientific community. Observed first by amateur auroral photographers, STEVE appeared as a narrow luminous structure across the night sky. Currently, only one scientific study has focused on STEVE, revealing that it corresponds to a narrow (tens of kilometers in north-south extent) and long (thousands of kilometers in east-west direction) structure located in the subauroral region. An important and fundamental question that arises from this study is the origin of STEVE; more specifically, does STEVE correspond to a new ionospheric phenomenon or is it due to particle precipitation? In this letter, we analyze a STEVE event on 28 March 2008 observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) ground-based All-Sky Imagers and a Polar Orbiting Environmental Satellite (POES). The POES-17 satellite crossed STEVE at the center of the All-Sky Imager field-of-view, allowing us to collect particle data simultaneously. These concurrent measurements show that STEVE might not be associated with particle precipitation (electrons or ions). Therefore, this event suggests that STEVE’s skyglow (which we defined to be unrelated to aurora or airglow) could be generated in the ionosphere.