Visualizing sporadic E using aeronautical navigation signals at VHF frequencies Keisuke Hosokawa, Kotaku Kimura, Jun Sakai, Susumu Saito, Ichiro Tomizawa, Michi Nishioka, Takuya Tsugawa and Mamoru Ishii J. Space Weather Space Clim., 11 (2021) 6 Published online: 22 January 2021 DOI: 10.1051/swsc/2020075