On 3 November 2021, an interplanetary coronal mass ejection impacted the Earth’s magnetosphere leading to a relevant geomagnetic storm (Kp = 8-), the most intense event that occurred so far during the rising phase of solar cycle 25. This work presents the state of the solar wind before and during the geomagnetic storm, as well as the response of the plasmasphere–ionosphere–thermosphere system in the European sector. To investigate the longitudinal differences, the ionosphere–thermosphere response of the American sector was also analyzed. The plasmasphere dynamics was investigated through field line resonances detected at the European quasi-Meridional Magnetometer Array, while the ionosphere was investigated through the combined use of ionospheric parameters (mainly the critical frequency of the F2 layer, foF2) from ionosondes and Total Electron Content (TEC) obtained from Global Navigation Satellite System receivers at four locations in the European sector, and at three locations in the American one. An original method was used to retrieve aeronomic parameters from observed electron concentration in the ionospheric F region. During the analyzed interval, the plasmasphere, originally in a state of saturation, was eroded up to two Earth’s radii, and only partially recovered after the main phase of the storm. The possible formation of a drainage plume is also observed. We observed variations in the ionospheric parameters with negative and positive phase and reported longitudinal and latitudinal dependence of storm features in the European sector. The relative behavior between foF2 and TEC data is also discussed in order to speculate about the possible role of the topside ionosphere and plasmasphere response at the investigated European site. The American sector analysis revealed negative storm signatures in electron concentration at the F2 region. Neutral composition and temperature changes are shown to be the main reason for the observed decrease of electron concentration in the American sector.

This paper presents how the magnetosphere–plasmasphere–ionosphere system was affected as a whole during the geomagnetic storm peaking on 27 May 2017. The interplanetary conditions, the magnetospheric response in terms of the magnetopause motion, and the ionospheric current flow pattern were investigated using data, respectively, from the WIND spacecraft, from GOES15, GOES13, THEMIS E, THEMIS D and THEMIS A satellites and from the INTERMAGNET magnetometer array. The main objective of the work is to investigate the plasmaspheric dynamics under disturbed conditions and its possible relation to the ionospheric one; to reach this goal, the equatorial plasma mass densities derived from geomagnetic field line resonance observations at the European quasi-Meridional Magnetometer Array (EMMA) and total electron content values obtained through three GPS receivers close to EMMA were jointly considered. Despite the complexity of physical mechanisms behind them, we found a similarity between the ionospheric and plasmaspheric characteristic recovery times. Specifically, the ionospheric characteristic time turned out to be ~ 1.5 days, ~ 2 days and ~ 3.1 days, respectively, at L ~ 3, L ~ 4 and L ~ 5, while the plasmaspheric one, for similar L values, ranged from ~ 1 day to more than 4 days.

On 20 December 2021, after six quiet years, the Hunga Tonga–Hunga Ha’apai volcano erupted abruptly. Then, on 15 January 2022, the largest eruption produced a plume well registered from satellites and destroyed the volcanic cone previously formed in 2015, connecting the two islands. We applied a multi-parametric and multi-layer study to investigate all the possible pre-eruption signals and effects of this volcanic activity in the lithosphere, atmosphere, and ionosphere. We focused our attention on: (a) seismological features considering the eruption in terms of an earthquake with equivalent energy released in the lithosphere; (b) atmospheric parameters, such as skin and air temperature, outgoing longwave radiation (OLR), cloud cover, relative humidity from climatological datasets; (c) varying magnetic field and electron density observed by ground magnetometers and satellites, even if the event was in the recovery phase of an intense geomagnetic storm. We found different precursors of this unique event in the lithosphere, as well as the effects due to the propagation of acoustic gravity and pressure waves and magnetic and electromagnetic coupling in the form of signals detected by ground stations and satellite data. All these parameters and their detailed investigation confirm the lithosphere–atmosphere–ionosphere coupling (LAIC) models introduced for natural hazards such as volcano eruptions and earthquakes.

This paper presents the project Comprehensive spAce wEather Studies for the ASPIS prototype Realization (CAESAR), which aims to tackle the relevant aspects of Space Weather (SWE) science and develop a prototype of the scientific data centre for Space Weather of the Italian Space Agency (ASI) called ASPIS (ASI SPace Weather InfraStructure). To this end, CAESAR involves the majority of the SWE Italian community, bringing together 10 Italian institutions as partners, and a total of 92 researchers. The CAESAR approach encompasses the whole chain of phenomena from the Sun to Earth up to planetary environments in a multidisciplinary, comprehensive, and unprecedented way. Detailed and integrated studies are being performed on a number of well-observed “target SWE events”, which exhibit noticeable SWE characteristics from several SWE perspectives. CAESAR investigations synergistically exploit a great variety of different products (datasets, codes, models), both long-standing and novel, that will be made available in the ASPIS prototype: this will consist of a relational database (DB), an interface, and a wiki-like documentation structure. The DB will be accessed through both a Web graphical interface and the ASPIS.py module, i.e., a library of functions in Python, which will be available for download and installation. The ASPIS prototype will unify multiple SWE resources through a flexible and adaptable architecture, and will integrate currently available international SWE assets to foster scientific studies and advance forecasting capabilities.

The technique for remote sensing the plasma mass density in magnetosphere by geomagnetic field line resonances detected at ground-based stations is getting more and more popular after the establishment in the last few years of extended magnetometer arrays, such as the EMMA network recently formed in the framework of the EU FP-7 PLASMON project [1]. It is important therefore to quantify the level of accuracy associated to such technique. In this study we examine the effect of using different magnetic field models. First the equatorial plasma mass density estimates obtained using the dipole approximation are compared with those obtained using the IGRF model for low-mid latitudes. It is found that the use of the centered dipole model may result in an error in the inferred density appreciably larger than what is usually assumed. In particular it has a significant longitudinal dependence being, for example, greater than +30% in the atlantic sector and ~ -30% at the opposite longitude sector for field lines extending to a geocentric distance of 2 Earth radii. This may result in an erroneous interpretation of the longitudinal variation in plasmaspheric density when comparing results from ground-based arrays located at different longitudes. Simple modifications of the technique are proposed which allow to keep using the dipole approximation but with a significant error reduction. Then the results of using the T01 Tsyganenko model [2] are compared with those based on the IGRF model. With respect to previous studies we take into account the different equatorial crossing points of the IGRF and T01 field lines traced from a given ground position by considering reasonable radial gradients of the equatorial density. For average solar wind/magnetospheric conditions, mass densities computed using the IGRF model result to be moderately overestimated (less than 20%) for L values <; 4. The uncertainty obviously increases for higher L values and the bias may become negative for steep radial variations of the equatorial density. For storm-time conditions the error dramatically increases beyond L ~ 4, but may remain within ~ 20% for L <; 4 assuming radial variations of the equatorial density which are typical for such magnetospheric conditions. We also present an analysis of a real event using measurements provided by the European magnetometer network EMMA.