Tracking patchy pulsating aurora through all-sky images

Abstract

Abstract. Pulsating aurora is frequently observed in the evening and morning sector auroral oval. While the precipitating electrons span a wide range of energies, there is increasing evidence that the shape of pulsating auroral patches is controlled by structures in near-equatorial cold plasma; these patches appear to move with convection, for example. Given the tremendous and rapidly increasing amount of auroral image data from which the velocity of these patches can be inferred, it is timely to develop and implement techniques for the automatic identification of pulsating auroral patch events in these data and for the automatic determination of the velocity of individual patches from that data. As a first step towards this, we have implemented an automatic technique for determining patch velocities from sequences of images from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) all-sky imager (ASI) and applied it to many pulsating aurora events. Here we demonstrate the use of this technique and present the initial results, including a comparison between ewograms (eastwest keograms) and time series of patch position as determined by the algorithm. We discuss the implications of this technique for remote sensing convection in the inner magnetosphere.

Differentiating diffuse auroras based on phenomenology

“…This network has been operating for over 10 years and has amassed tens of millions of images. As demonstrated by Grono et al (2017), it can be extrapolated from Jones et al (2011) that on the order of 10 % of THEMIS ASI images contain pulsating aurora.…”

“…Pulsating auroral patches appear to be controlled by structures in the near-equatorial cold plasma (Rae, 2014) whose motion is almost entirely determined by E ×B drifting. Consequently, these patches appear to move with ionospheric convection and could be used to create automatically generated two-dimensional maps of convection (Yang et al, 2015;Grono et al, 2017).…”

“…This property is dependent on the cadence of the camera and it is likely that all patches exhibit some amount of streaming while pulsating. Grono et al (2017) noted that all structures that would be considered to be a pulsating auroral patch did not move with convection. They identified a type of patch whose motion was more dynamic and whose morphology was visually distinct from those that followed convection.…”

Surveying pulsating auroras

“…Pulsating auroras are a type of diffuse aurora characterized by quasi-periodic pulsations and precipitating electron energies between a few kiloelectron volts and hundreds of kiloelectron volts (Johnstone, 1978). They generally have an irregular, patchy structure (Royrvik and Davis, 1977) which constantly evolves in time (Shiokawa et al, 2010).…”

Inferring the source regions of pulsating auroras

“…The THEMIS ASIs image the aurora in "white light" at a 3 second cadence on a 256 × 256 pixel CCD and have been operating continually for over 10 years to amass tens of millions of images. Following observations of Jones et al (2011), it can be surmised that pulsating aurora has been observed within on the order 10 % of these images (Grono et al, 2017).…”