[PEM11-P17] Variations of cosmic noise absorption (CNA) by energetic electron precipitation (EEP) and changes of the auroral morphology
Keywords:Ionosphere, Aurora, Energetic Electron Precipitation (EEP)
Some previous studies have presented changes in morphology from pulsating aurora to patch structures [e.g., Shiokawa et al., 2014] and temporal variations of energetic electron precipitation [e.g., Hosokawa and Ogawa, 2015]. As mentioned above, the wave-particle interaction has been widely accepted with experimental evidences to support generation of pulsating aurora and energetic electron precipitation. However, our understanding has not yet reached its maturity of presenting spatiotemporal evolutions of auroral morphology and associated electron precipitation. Oyama et al.  presented enhancements of CNA (cosmic noise absorption) coinciding with appearance of the patch structure but with only two events. Furthermore, due to measurements with intensive diagnostic instruments, the result was based on information of a part of the auroral ionosphere. In this study, we conducted observations to capture simultaneously time evolutions and spatial distributions of auroral morphology and energetic electron precipitation by utilizing a network of EMCCD (Electron Multiplying Charge Coupled Device) cameras and riometers deployed in Northern Europe.
This study will present three events (February 19-20, 2018, March 6-7, 2017, and March 29-30, 2017). On the way of all events, after substorm onsets twice near Northern Europe, another onset occurred again at more west side (near Iceland or Greenland area) but at dawn in the Northern Europe. In this study, we have focused on the aurora and CNA associated with the latter onset, and at that time, the aurora spatially and temporally shifted from diffuse to pulsation and patch structures. This suggests that substorm activities occurred in the distance can induce these auroral morphological changes seen in the Northern Europe. CNA at that time is characterized by gradual variations with time scale of several hours. This trend cannot be seen at substorm onset near the Northern Europe. Moreover, in the latitude distribution, the feature was confirmed that CNA increases at the latitude where patch structure is seen, and CNA keeps constant value at the latitude where patch structure is not seen. In the presentation, based on these observations, we will discuss physical mechanisms to cause changes in the auroral morphology and energetic electron precipitation, which can be seen as increases of CNA.