On the Origin of STEVE: Particle Precipitation or Ionospheric Skyglow?

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. Plain Language Summary Recently, the scientific community stumbled upon a rare atmospheric phenomenon called Strong Thermal Emission Velocity Enhancement (STEVE) that has been well documented by amateur auroral photographers for decades. STEVE appears across the night sky as an extremely narrow ribbon of vibrant purple and white hues. In this letter, we address an important fundamental question: Is STEVE caused by particle precipitation like aurora or is it produced by a new ionospheric phenomenon? We analyzed a STEVE event using a network of ground‐based All‐Sky Imagers across Canada and energetic particle detectors on one of National Oceanic and Atmospheric Administration's Polar Orbiting Environmental Satellites. Our results verify that this STEVE event is clearly distinct from the aurora since it is characterized by the absence of particle precipitation. Interestingly, its skyglow could be generated by a new and fundamentally different mechanism in the ionosphere. Key Points First study of STEVE event in conjunction with POES satellite suggests ionospheric origin of STEVE This STEVE event is not aurora. Particle precipitation is not observed for this event STEVE's skyglow could be associated with protons below 50 eV or generated by a fundamentally different mechanism in the ionosphere