During the year 2015 two great geomagnetic storms (Dst < −200 nT) occurred on 17 March and 22 June. These two geomagnetic storms have similarities. They occurred during the same decreasing phase of the sunspot cycle 24. The interplanetary and magnetospheric environments were calm before the beginning of the storms. Both events were due to Coronal Mass Ejections and High‐Speed Solar Wind. Variations of the solar wind velocity and the Bz component of the interplanetary magnetic field were also similar. Two key features that are different for these storms are UT time of the beginning (04:45 UT for 17 March and 18:33 UT for 22 June) and season (equinox and solstice). The comparison of the impact of the storms on the Earth ionosphere and magnetosphere has been performed using diverse parameters including global ionospheric maps of vertical total electron content, data from individual Global Navigation Satellite System receivers, ionosondes, magnetometers, and instruments from different space missions. Visualizing global ionospheric map data as the difference of vertical total electron content between consecutive days allowed understanding better the effect of the storms as a function of time of the beginning of the storm and of the season. It is shown that the presence or absence of scintillations in Global Navigation Satellite System signals during these two storms in African longitude sector is clearly related to the local time at a given station at the beginning of the storm.

Modelling the Earth’s ionosphere is a big challenge, due to the complexity of the system. Different first principle models have been developed over the last 50 years, based on ionospheric physics and chemistry, mostly controlled by Space Weather conditions. However, it is not understood in depth if the residual or mismodelled component of the ionosphere’s behaviour is predictable in principle as a simple dynamical system, or is conversely so chaotic to be practically stochastic. Working on an ionospheric quantity very popular in aeronomy, we here suggest data analysis techniques to deal with the question of how chaotic and how predictable the local ionosphere’s behaviour is. In particular, we calculate the correlation dimension $D_2$ and the Kolmogorov entropy rate $K_2$ for two one-year long time series of data of vertical total electron content (vTEC), collected on the top of the mid-latitude GNSS station of Matera (Italy), one for the year of Solar Maximum 2001 and one for the year of Solar Minimum 2008. The quantity $D_2$ is a proxy of the degree of chaos and dynamical complexity. $K_2$ measures the speed of destruction of the time-shifted self-mutual information of the signal, so that $K_2^{-1}$ is a sort of maximum time horizon for predictability. The analysis of the $D_2$ and $K_2$ for the vTEC time series allows to give a measure of chaos and predictability of the Earth’s ionosphere, expected to limit any claim of prediction capacity of any model. The results reported here are preliminary, and must be intended only to demonstrate how the application of the analysis of these quantities to the ionospheric variability is feasible, and with a reasonable output.

Low latitude ionospheric effects of two major geomagnetic storms are analysed using TOPEX TEC data for specific satellite passes. The storms are the one that started on 15 July 2000 and the one that started on 8 November 2004. The variation of vertical TEC as a function of latitude along the satellite passes during day-time mostly in the region of the Pacific Ocean have been analysed comparing the storm period with quiet conditions. It has to be noted that for obvious reasons the TEC behaviour over this region cannot be observed using ground-based instruments but TOPEX data give a reasonable overall view of the region covered by the Equatorial Anomaly, just as the storms were developing. The performance of vertical TEC obtained from GPS derived TEC of global ionospheric maps (GIMs) are compared with the TOPEX data in order to determine their accuracy when storms of this type take place. The results show that the Equatorial Anomaly TEC peaks move towards the poles by several degrees and increase their intensity with respect to the quiet conditions behaviour for both storms that occurred at different seasons and solar activity level. This behaviour is not well represented by the maps of the different GIMs used in this study. The rate of change obtained from TOPEX TEC were computed to look for vertical TEC spatial gradients variations.

Spacecraft‐to‐spacecraft radio occultations experiments are being conducted at Mars between Mars Express (MEX) and Trace Gas Orbiter (TGO), the first ever extensive inter‐spacecraft occultations at a planet other than Earth. Here we present results from the first 83 such occultations, conducted between 2 Nov 2020 and 5th of July 2023. Of these, 44 observations have to‐date resulted in the extraction of vertical electron density profiles. These observations are the successful results of a major feasibility study conducted by the European Space Agency to use pre‐existing relay communication equipment for radio science purposes. Mutual radio occultations have numerous advantages over traditional spacecraft‐to‐ground station occultations. In this work, we demonstrate how raw data are transformed into electron density values and validated with models and other instruments.

Studies on the irregularities of the ionosphere during disturbed geomagnetic conditions are fundamental to understanding the complex dynamics taking place in the upper atmosphere. In this work, different data sources are used to study the ionosphere effects of two moderate geomagnetic storms, 26–27 February 2014 and 17–18 September 2021, over the Iberian Peninsula. Data are obtained from digital ionosondes in Spain, Italy and Greece; the Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) and Rate Of TEC Index (ROTI) from several receiver stations in Spain, Portugal and Morocco; and the UPC Quarter-of-an-hour time resolution Rapid GIM (UQRG), vertical TEC global ionosphere maps (GIMs), produced at 15 min intervals by the Universitat Politecnica de Catalunya (UPC, Spain). This analysis showed that, during the two moderate storms, spread-F and high values of ROTI, indicating the presence of irregularities, are found in a very localized area (Southern Iberian Peninsula and northwest Africa) and local times (night-time). However, no irregularities are found eastwards and northwards of the location indicated. We propose some possible explanations for these observations for both the storms, one of them related to the position of the Equatorial Ionosphere Anomaly (EIA) and the other one attributed to the Perkins’ instabilities.