[P-EM10] Space Weather and Space Climate

[PEM10-28] Features of ionospheric irregularities during geomagnetic storms in 25th solar maximum revealed by GNSS ROTI maps

*Iurii Cherniak^1,2, Irina Zakharenkova¹, Andrzej Krankowski^1,2 (1.Space Radio-Diagnostic Research Center, University of Warmia and Mazury, 2.University Corporation for Atmospheric Research)

Keywords:ionospheric irregularities, geomagnetic storm, GNSS, ROTI

We analyzed the ionospheric response during the severe geomagnetic storms happened around the 25 solar cycle maximum and revealed various patterns of formation of ionospheric plasma density irregularities. The plasma irregularities at mid- and high latitudes are mainly related to space weather, specifically how the ionosphere responds to the geomagnetic disturbances. During geomagnetic storms, the energy from the magnetosphere-ionosphere interaction in the form of enhanced electric fields, currents, and energetic particle precipitation perturbs the ionosphere resulting in ionospheric irregularities and enhanced plasma density gradients. The fact is that ionospheric irregularities possess a wide range of spatial and temporal scales and occur at different geographical locations. The Global Navigation Satellite Systems (GNSS) has been effectively used for study of different types of ionospheric plasma disturbances. For several decades, the GNSS ROTI has effectively been used for the monitoring and tracing of ionospheric irregularity occurrence. The application of the ROTI approach with different mapping techniques allows us to trace plasma irregularity dynamics at different temporal resolutions, on both global and regional scales. For the overall representation of the spatial evolution of plasma irregularities, we analyzed the IGS product developed and maintained in SRRC UWM - daily ROTI polar maps. Such maps are based on multi-station GPS observations and include calculation of the rate of TEC (ROT) values for every selected ground station-to-GNSS transmitter link, calculation of the ROT index (ROTI), and mapping of all the ROTI values in the magnetic latitudes–magnetic local time coordinate system. For detailed investigations of ionospheric irregularity dynamics and the ionospheric response to space weather events, we constructed and analyzed the global GNSS ROTI maps with a high spatio-temporal resolution. For this study, we utilized GNSS signals provided by the GPS, GLONASS, Galielo, and BeiDou systems. The ROTI values were computed for each GNSS satellite pass over a ground based station. The multisite ROTI values were binned into a geographic grid with 0.5° latitude and longitude spacing in order to generate global ROTI maps at 5 minute intervals.
For geomagnetic storms which we examined the ROTI maps registered an occurrence of very intense ionospheric irregularities that spread far away from the auroral region with expansion in size and moved equatorward towards midlatitudes as far as ~55–60° magnetic latitude. Evolution of the intense ionospheric irregularities and equatorward expansion of the auroral irregularities oval were well correlated with increases of geomagnetic activity and peaks of the auroral electrojet index. Apart the general irregularities pattern, we were able to trace tiny structures associated with ionospheric gradients in the main ionospheric trough, storm time enhancement density edges and tongue of ionization structures.
Combination of strong ionospheric gradients and irregularities can affect the trans-ionospheric radio links for communication and navigation systems. In particular, for the European Geostationary Navigation Overlay Service performance during the storm days, there was a noticeable increase in vertical and horizontal errors registered at RIMS sites in higher northern latitudes. Such positioning degradation effect related with direct impact of intense high-latitude irregularities occurrence due to the expansion of the auroral oval zone that receives the main part of the magnetospheric particle precipitation.