We employ multi-instrumental data to investigate the behavior of equatorial and low latitude ionosphere during the geomagnetic storm of November 3-6, 2021. We used TEC data obtained from GPS receiver stations located in the equatorial and low-latitudes of the Asian, African, and American sectors. It is found that the storm-time ionization level varies significantly in the trough and crest of EIA region over the three longitudes. ROTI is used to estimate the occurrence of ionospheric plasma irregularities during the storm. Usually, the main phase of the geomagnetic storm triggers the equatorial plasma irregularities and the recovery phase suppresses the occurrence of them. Here, we observed inhibition of the plasma irregularities over the three sectors during the main phase of the storm. We suspect this may be due to the injection of the PEFs which occur between local midnight and around noon during the main phase. The PEFs restrict the diffusion of plasma and therefore, suppress the occurrence of plasma irregularities during the main phase. During the recovery phase, moderate ionospheric irregularities occurred at local midnight in the American sector. In the African sector, the occurrence of weak irregularities can be seen before midnight on November 5 and 6. However, the Asian sector does not exhibit noticeable ionospheric irregularities during the storm. We conclude that the longitudinal variation in the development of ionospheric irregularities can be influenced by factors such as local time occurrence of maximum ring current, PPEF, disturbance wind dynamo electric field, and shielding electric field.

Thermospheric mass density (TMD) measurements are invaluable to accurately estimate and predict the position and velocity of orbiting objects in Low Earth Orbit (LEO). Existing observational methods and empirical models fail to describe and predict, with enough accuracy and resolution, the actual air-drag variations required for practical applications. With the increasing number of LEO satellites equipped with high-precision Global Navigation Satellite System (GNSS) receivers, precise orbit technology can be used to obtain non-gravitational accelerations, and therefore estimate accurate TMD variations. In this work, TMD is estimated from CASSIOPE precise orbits, and data from the February 2014 geomagnetic storm can be investigated to high accuracy and resolution. Using this method, a more accurate description than previous methods and empirical models, that are unable to describe short-term TMD variations, during geomagnetic storm conditions is given.

In this paper, we study the variations of the solar-wind parameters (solar wind velocity, plasma density, and IMF-Bz component) and the Earth’s disturbance storm-time index (Dst), in relation to cosmic ray flux measurements from 8 neutron monitor stations distributed over Canada, Russia, Finland, and Greenland, during 3 intense geomagnetic storms occurred during the 24th solar cycle (March 16-18, 2015, June 21-23, 2015, and September 7-9, 2017). The wavelet analysis of the Forbush decrease seen in the cosmic ray intensity reveals the clear evolution of the classical two-step process, and with a peak period of approximately 2.1 h. The correlation-delay analyses show a very strong correlation (~0.9) between the relative count rate changes cosmic ray intensity and the indices of solar wind velocity and Dst. We obtain similar time-delay responses to the solar wind velocity for all the cases (~4 hours), but large discrepancies are seen for the Dst index between the storms. We therefore recommend not using the Dst index for predicting Forbush decreases. Finally, we employ the resulting delay-times to parameterize the Forbush decreases in terms of solar wind, and we obtain a predictive model with R2 parameter of an approximate value of 0.8. Moreover, we observe a possible dependence on solar wind proton density which modulates the magnitude of Forbush decreases under similar solar wind velocity conditions. Our results verify the suitability of using solar wind parameters to predict Forbush decreases in the cosmic ray flux.