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

Abstract

Two remarkable typhoon‐induced traveling ionospheric disturbances (TIDs) with concentric and northwest‐southeast (NW‐SE) alignments, respectively, associated with concentric gravity waves (CGWs) and ionosphere instabilities possibly seeded by CGWs, were observed in total electron content (TEC) derived from ground‐based Global Navigation Satellite System networks in Taiwan and Japan when the Category 5 Super Typhoon Nepartak approached Taiwan on 7 July 2016. The concentric TIDs (CTIDs) first appear with horizontal 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 is suggested that the MSTIDs are produced by the electrodynamical coupling of Perkins instability and CGW‐induced polarization electric fields. This study proposes connections of typhoon‐induced CTIDs and subsequently occurring MSTIDs in the low‐latitude ionosphere.

Numerical Modeling of the Concentric Gravity Wave Seeding of Low‐Latitude Nighttime Medium‐Scale Traveling Ionospheric Disturbances

“…The properties and TEC amplitudes are comparable to the observations (Chou, Lin, Yue, Chang, et al, 2017) where the unique low-latitude nighttime MSTIDs on the west edge of typhoon-induced CGWs were observed. Numerical simulations demonstrate that the CGW perturbations comprising both ionospheric E and F regions could affect the ionospheric electrodynamics, leading to the ionospheric instabilities through wind dynamo.…”

“…This can explain the observational results reported by Chou, Lin, Yue, Chang, et al (2017) that the MSTIDs are mainly generated on the west edge of CGWs, and the absence of MSTIDs on the north edge of CGWs is likely due to the weaker coupling between the northward CGWs and Perkins instability. It takes a longer time to develop the MSTID structures, and the amplitude is smaller than that of Case 2.…”

“…The CGWs mainly propagate poleward, westward, and southwestward; however, the MSTIDs only organized on the west edge of CGWs suggest that the westward/southwestward propagating CGWs could be a seed to trigger the low-latitude nighttime MSTIDs in the Northern Hemisphere. These quantities are slightly smaller than the observations of~0.4 TECu and 3% of the background TEC (Chou, Lin, Yue, Chang, et al, 2017). The CGW wind effects are controlled in altitude ranges of 85-350 km, spatial extent of 1-5°E in longitude and 12-22°N in latitude.…”

“…However, later studies suggested that the MSTIDs could propagate more equatorward (Candido et al, 2008;Huang, 2016;Makela et al, 2010). Chou, Lin, Yue, Chang, et al (2017) reported nighttime MSTIDs over the Taiwan Strait when Super Typhoon Nepartak approached Taiwan. Chou, Lin, Yue, Chang, et al (2017) reported nighttime MSTIDs over the Taiwan Strait when Super Typhoon Nepartak approached Taiwan.…”

Dynamical Coupling Between Hurricane Matthew and the Middle to Upper Atmosphere via Gravity Waves

“…On 7 October, the background wind velocity is~110 m/s in the southeast direction above altitude of~300 km, meaning that the northward/westward propagating GWs have increased vertical wavelengths and can therefore propagate favorably to higher altitudes before dissipating from viscosity (e.g., Fritts & Vadas, 2008). The characteristics of the waves in the CTIDs are comparable to that of Super Typhoon Nepartak , Chou, Lin, Yue, Chang, et al, 2017) and Super Typhoon Meranti (2016, which also suggests that the CTIDs are related to the CGWs induced by Hurricane Matthew.…”