A document by Riley N Troyer. Click on the document to view its contents.

This paper uses energy flux data from the DMSP F6 thru F19 satellites to construct a new equatorward auroral boundary model. This method of processing the data allows one to easily extend boundary detections to different instrument generations because it is based on a standard deviation value instead of hard thresholds. Using this method, the paper provides statistics from just under 1 million auroral boundaries between 1986 and 2014. These statistics are based on normal distribution fits for each Kp/Hp and MLT bin, which allows one to specify the boundary for an arbitrary distribution percentile. The paper compares how the model performs for driving by Hp30, Hp60, and Kp and finds that Hp30 is the best representation of the data. Finally, the paper provides specifications to recreate the model for the 50th and 95th percentiles for Kp and Hp30.

Energetic electron precipitation (EEP) associated with pulsating aurora can transfer greater than 30 keV electrons from the outer radiation belt region into the upper atmosphere and can deplete atmospheric ozone via collisions that produce NOx and HOx molecules. Our knowledge of exactly how EEP occurs is incomplete. Previous studies have shown that pitch angle scattering between electrons and lower-band chorus waves can cause pulsating aurora associated with EEP and that substorms play an important role. In this work, we quantify the timescale of chorus wave decay following substorms and compare that to previously determined timescales. We find that the chorus decay e-folding time varies based on magnetic local time (MLT), magnetic latitude, and wave frequency. The fastest decay occurs for lower-band chorus in the 21 to 9 MLT region and compares well to the timescale of Troyer et al. (2022) for energetic pulsating aurora. We are able to further support this connection by modelling our findings in a quasi-linear diffusion simulation. These results provide observations of how chorus waves behave after substorms and add additional statistical evidence linking energetic pulsating aurora to substorm driven lower-band chorus waves.

Pulsating aurora are common diffuse-like aurora. Studies have suggested that they contain higher energy particles than other types and are possibly linked to substorm activity. There has yet to be a quantitative statistical study of pulsating aurora energy content. We analyzed the inverted energy content from 53 events using the Poker Flat Incoherent Scatter Radar. We compared this to magnetic local time (MLT), AE index, and temporal proximity to substorm onset. There was a slight trend in MLT, but a much stronger one in relation to both substorm onset and AE index. For higher AE and closer to onset the total energy flux and flux above 30 keV increased. In addition, this higher energy remained enhanced for an hour after substorm onset. Our results confirm the high energy nature of pulsating aurora, demonstrate the connection to substorms, and imply their importance to coupling between the magnetosphere and atmosphere.

The source of diffuse aurora has been widely studied and linked to electron cyclotron harmonic (ECH) and upper-band chorus (UBC) waves. It is known that these waves scatter 100s of eV to 10s of keV electrons from the plasma sheet, but the relative contribution of each wave type is still an open question. In this paper, we report on a new structured diffuse aurora feature observed on March 15, 2002 that could help further our understanding. This feature is characterized by four phases: (1) the initial phase exhibiting regular diffuse aurora, (2) the brightening phase, where a stripe of diffuse aurora rapidly brightens, (3) the eraser phase, where the stripe dims to below its initial state, and (4) the recovery phase, where the diffuse aurora returns to its original brightness. Using a superposed epoch analysis of 22 events, we calculate the average recovery phase time to be 20 seconds, although this varies widely between events. We hypothesize that the process responsible for these auroral eraser events could be an interaction between ECH and chorus waves.