Concurrent observations of the ionospheric response following an intense geomagnetic storm from the equator and the auroral zones

The equatorial/low latitudes and the polar regions of the Earth experience the most challenges in terms of maintaining high levels of performance of radio signal-based systems and services. It is important to note that while the geomagnetic field lines are parallel to the surface of the Earth in the low latitudes, they are nearly perpendicular in the polar latitudes. Hence, the interaction between the radar transmitted signal and the geomagnetic field lines will be determined by their relative orientation. While the high latitude ionospheric irregularity generation is closely associated with adverse Space Weather conditions and intense geomagnetic storms, the equatorial and low- latitude ionosphere seriously jeopardizes the performance of any transionospheric radio signals even under geomagnetic benign conditions. The Plasmasphere Ionosphere Thermosphere Integrated Research Environment and Access services: a Network of Research Facilities (PITHIA-NRF) is an EU project funded through the Horizon 2020 Research and Innovation Programme (grant agreement No 101007599), aimed at creating a European distributed network that integrates observing facilities, data processing tools and prediction models dedicated to the ionosphere, thermosphere and plasmasphere research (https://www.pithia-nrf.eu/). Under the framework of PITHIA TNA program of the EU, a novel experiment was conducted on September 18-19, 2024 during 13-17 UT combining active and passive ionospheric sensing instruments operated in a coordinated manner from the high and low latitudes to understand the ionospheric impact following an intense geomagnetic storm during September 12-16 and a 2nd storm for which the Dst was restored on September 18, 2024. This study used the EISCAT VHF radar at Tromso (69.58°N 19.23°E geographic; magnetic dip: 78.19°N) and the University of Calcutta VHF Radar (CUVR) (22.93°N 88.37°E geographic; magnetic dip 35°N) under varying geomagnetic conditions. Fluctuations in electron density were found around 16:30-17:00 UT associated with positive ion drift velocities on September 18, 2024 using the EISCAT Tromso VHF radar with the radar transmitted beam nearly parallel to the geomagnetic field lines. On September 19, 2024, the EISCAT radar was operated in the wide latitude scan mode which showed presence of the auroral oval. On the other hand, observations from the CUVR exhibited prominent irregularity signatures on September 18, 2024 around 14:00-15:00 UT at altitudes of 300-400 km. GPS observations near CUVR exhibited significant amplitude scintillations on a number of satellite links on both September 18 and 19, 2024. GPS observations from the Madrigal database revealed substantial decrease in TEC and ionization density on September 19th compared to September 18th near EISCAT as well as CUVR which may be attributed to the poleward movement of thermospheric O/N2 depletions poleward during an extension of the recovery phase of the second storm.