The ionospheric morphology responses to tropical cyclone passing over eastern Australia, named as Debbie in 2017, is investigated using Global Positioning System (GPS) Slant Total Electron Content (STEC), and ionospheric characteristics by ionosonde. Based on the data analysis in this study, some significant morphological characteristics of ionospheric responses to tropical cyclone Debbie are identified as follows. As the GPS satellites PRN05 and PRN20 observed on Townsville GPS station were passing near to the cyclone Debbie center at landfall time, their STEC values are obviously increased. The stronger enhancement of f0F1 and f0F2 were also observed by ionosonde at Townsville on 28th March, when the distance between Townsville and the center of tropical cyclone Debbie was shorter. Regarding the coupling mechanism between the ionospheric disturbance and the tropical cyclone, it is supposed that the electric field perturbations due to turbulent top movement from tropical cyclones might generate ionospheric irregularity and disturbance.

The inter-hemispheric difference in the impact of the geomagnetic storms of June 2015 and December 2015 is investigated with respect to quiet time seasonal asymmetry. A meridional chain of ground observatories along 95°E (GNSS receiver/Ionosonde), satellite in-situ measurements (SWARM/COSMIC/C-NOFS), Total Electron Content map and SAMI2/CTIPe model simulations are utilized. Symmetric negative (positive) effects prevailed during the main phase of June (December) storm but hemispheric asymmetry was manifested during the recovery phase. Differential VTEC and NmF2 response in addition to perturbations in VTEC by more than 30 TECU (~90-100%) were recorded. The SWARM observations confirmed that the topside density/TEC enhancement in the southern low latitude was much higher than 300%. The SWARM A/B pass of 23 June and ground TEC map showed a third latitudinal maxima around -45° dip angle in southern hemisphere low latitude in addition to the conventional EIA crests. Similarly an additional peak appeared at +45° dip in northern hemisphere in the SWARM A pass in the sunrise period of 21 December. The higher winter-side hmF2 and northward C/NOFS meridional flow velocity suggest that storm time Joule heating resulted in anomalous equator-ward winds surge in the winter hemispheres of 95°E which led to the formation of the additional storm time maxima at the pole-ward edge of the EIA region. Further modeling efforts are needed to capture this counter-intuitive feature for a better forecasting of the impact of space weather events over low latitude ionosphere.

Abstract. The ionospheric morphology responses to tropical cyclone passing over eastern Australia, named as DEBBIE in 2017, is investigated using Global Positioning System (GPS) Slant Total Electron Content (STEC), GPS ionospheric scintillation S4 index and ionospheric characteristics by High Frequency (HF) radio. Based on the data analysis in this study, some significant morphological characteristics of ionospheric responses to tropical cyclone Debbie are identified as follows: a) As the GPS satellites PRN01 and PRN11 were passing above typhoon center, their ROTI (Rate of STEC index) is obviously increased. b) The S4 intensity of the GPS ionospheric scintillation is significantly enhanced on March 27, which mostly concentrate around tropical cyclone center and distribute over the region within 18 °S-25 °S. c) The stronger enhancement of f0F1 and f0F2 was observed by High Frequency at Townsville on March 28, when the distance between Townsville and the center of tropical cyclone Debbie was shorter. Regarding the coupling mechanism between the ionospheric disturbance and the tropical cyclone, it is suspected that the electric field perturbations due to turbulent top movement from tropical cyclones might generate ionospheric irregularity and disturbance. To a certain extent, some ionospheric irregularities can further produce bubbles.