Medium-scale traveling ionospheric disturbances triggered by Super Typhoon Nepartak (2016)

Two remarkable typhoon-induced traveling ionospheric disturbances (TIDs) with concentric andnorthwest-southeast (NW-SE) alignments, respectively, associated with concentric gravity waves (CGWs) andionospheric instabilities possibly seeded by CGWs, were observed in total electron content (TEC) derived fromground-based Global Navigation Satellite System networks in Taiwan and Japan when the Category 5 SuperTyphoon Nepartak approached Taiwan on 7 July 2016. The concentric TIDs (CTIDs) first appear withhorizontal phase velocities of 161-200 m/s, horizontal wavelengths of 160-270 km, and periods of 15-22 min during 08:00-11:20 UT. Following the CTIDs, the NW-SE aligned nighttime medium-scale TIDs(MSTIDs) are formed on the west edge of the CTIDs over the Taiwan Strait during 11:30-14:00 UT. It issuggested that the MSTIDs are produced by the electrodynamical coupling of Perkins instability andCGW-induced polarization electric fields. This study proposes connections of typhoon-induced CTIDs andsubsequently occurring MSTIDs in the low-latitude ionosphere.