The TROPOMAG project investigates the possible effects of changes of the Earth’s magnetic field on the atmosphere and weather conditions with the aim to better quantify the natural sources of the atmospheric variability. This need raises to assess the observed climate trends more correctly, with a consequent better understanding of manmade effects on climate. Specifically, this work explores possible connections between atmospheric pressure anomalies and the occurrence of geomagnetic storms. To accomplish this task pressure data, recorded over some Italian volcanic areas, are analysed according to different methods and considering geomagnetic indexes. This work describes and discusses corresponding preliminary results.

In Italy, the MARGE initiative, an abbreviation for Geoelectromagnetic Risk Map for Central Italy, strives to create an extensive map of subsurface electrical conductivity by analyzing natural electric and magnetic fields.Led by the National Institute of Geophysics and Volcanology in collaboration with the University of Bari and the Institute of Environmental Analysis Methodologies at CNR, his project involves establishing measurement points distributed on a grid spaced approximately 50 km apart.However, this endeavor faces significant challenges in the central region of the Italian peninsula due to extensive urbanization, numerous electromagnetic disturbances from railways and high-voltage power lines, and challenging topography, making finding suitable land parcels a complex task.The MARGE project aims to gather broad-band and long-term magnetotelluric data, focusing on two primary objectives: utilizing magnetotelluric data to outline large-scale lithospheric structures in the Central Apennines and developing maps of the geoelectric field in Central Italy to support Space Weather modeling and critical infrastructure vulnerability analysis.Presenting our initial findings, we discuss encountered challenges and potential solutions identified in this ongoing project.

This study focuses on the open question of the electron temperature (Te) variation with solar activity in the topside ionosphere at mid- and high latitudes. It takes advantage of in situ observations taken over a decade (2014–2023) from Langmuir probes on board the low-Earth-orbit Swarm B satellite and spanning an altitude range of 500–530 km. The study also includes a comparison with Te values modeled using the International Reference Ionosphere (IRI) model and with Millstone Hill (42.6° N. 71.5° W) incoherent scatter radar observations. The largest Te variation with solar activity was found at high latitudes in the winter season, where Te shows a marked decreasing trend with solar activity in the polar cusp and auroral regions and, more importantly, at sub-auroral latitudes in the nightside sector. Differently, in the summer season, Te increases with solar activity in the polar cusp and auroral regions, while for equinoxes, variations are smaller and less clear. Mid-latitudes generally show negligible Te variations with solar activity, which are mostly within the natural dispersion of Te observations. The comparison between measured and modeled values highlighted that future implementations of the IRI model would benefit from an improved description of the Te dependence on solar activity, especially at high latitudes.

Electron density (Ne) and electron temperature (Te) observations collected by Langmuir Probes on board the European Space Agency (ESA) Swarm B satellite are used to characterize their correlation in the topside ionosphere at an altitude of about 500 km. Spearman correlation coefficient values (RSpearman) are calculated on joint probability distributions between Ne and Te for selected conditions. The large data set of Swarm B observations at 2-Hz rate, covering the years 2014-2022, allowed investigating the correlation properties of the topside ionospheric plasma on a global scale, for different diurnal and seasonal conditions, with both a coverage and a detail never reached before. Results are given as maps of RSpearman as a function of the Quasi-Dipole (QD) magnetic latitude and magnetic local time (MLT) coordinates. The characterization of the correlation at high latitudes, along with the description of the diurnal trend at all latitudes, are the new findings of this study. The main correlation features point out a negative correlation at the morning overshoot, during daytime at mid latitudes, and during nighttime at the ionospheric trough and subauroral latitudes. Conversely, a positive correlation dominates the nighttime hours at mid and low latitudes and, to a minor extent, the low latitudes from 09 MLT onwards. A seasonal dependence of the correlation is noticeable only at very high latitudes where the general pattern of the negative correlation does not hold around +/- 75 degrees QD latitude in the summer season. Results from Swarm B have been statistically compared and discussed with observations from the Arecibo, Jicamarca, and Millstone Hill incoherent scatter radars. The correlation between the electron density and temperature in the topside ionosphere has been investigated through 9 years of Swarm B in-situ observations The latitudinal, diurnal, and seasonal variations of the correlation have been studied on a global scale at an unprecedented spatial and temporal resolution First ever study of the correlation at high latitudes, which highlighted a general pattern of negative correlation except for the summer season at the polar cusp

Ionospheric plasma density irregularities, which are one of the primary sources of disturbance for the Global Navigation Satellite System, significantly impact the propagation of electromagnetic signals, leading to signal degradation and potential interruptions. In the equatorial ionospheric F region after sunset, certain plasma density irregularities, identified as equatorial plasma bubbles, encounter optimal conditions for their formation and development. The energy spectra of electron density fluctuations associated with these irregularities exhibit a power-law scaling behavior qualitatively similar to the Kolmogorov power law observed in fluid turbulence theory. This intriguing similarity raises the possibility that these plasma density irregularities may possess turbulent characteristics. In this study, we analyzed electron density, temperature, and pressure data obtained from the China Seismo-Electromagnetic Satellite (CSES-01) to delve into the spectral properties of equatorial plasma depletions in the ionospheric F region at an altitude of about 500 km. This research marks the first exploration of these properties utilizing CSES-01 data and focuses on 14 semi-orbits that crossed the equator after midnight (01:00–03:00 LT), characterized by a geomagnetic quiet condition (Kp < 1). The analysis of electron temperature, density and pressure within equatorial plasma depletions revealed power-law scaling behavior for all the selected parameters. Notably, the spectral index values of these parameters are different from each other. The significance of these findings in terms of investigating plasma depletions via magnetic field signatures, as well as their relationship to the occurrence of Rayleigh–Taylor convective turbulence, is examined and discussed.

On 8 May 2024, the solar active region AR13664 started releasing a series of intense solar flares. Those of class X released between 9 and 11 May 2024 gave rise to a chain of fast Coronal Mass Ejections (CMEs) that proved to be geoeffective. The Storm Sudden Commencement (SSC) of the resulting geomagnetic storm was registered on 10 May 2024 and it is, to date, the strongest event since November 2003. The May 2024 storm, named hereafter Mother’s Day storm, peaked with a Dst of –412 nT and stands out as a “standard candle” storm affecting modern era technologies prone to Space Weather threats. Moreover, the recovery phase exhibited almost no substorm signatures, making the Mother’s Day storm as a perfect storm example. Despite the plethora of notable near Earth environment modifications that are still under investigation, in this paper we concentrate on the Space Weather effects over the Mediterranean sector, with a focus on Italy. In fact, the Istituto Nazionale di Geofisica e Vulcanologia (INGV) manages a dense network of GNSS receivers (including scintillation receivers), ionosondes and magnetometers in the Mediterranean area, which facilitated for a detailed characterization of the modifications induced by the storm. Concerning the geomagnetic field, observatories located in Italy recorded a SSC with a rise time of only 3 minutes and a maximum variation of around 600 nT. The most notable ionospheric effect following the arrival of the disturbance was a significant decrease in plasma density on 11 May, resulting in a pronounced negative ionospheric storm registered on both the critical F2-layer frequency (foF2) and the Total Electron Content (TEC). Another negative effect was recorded on 13 May, while no signatures of composition changes and, specifically, to a decrease of the [O]/[N ] ratio. The IRI UP IONORING 2 data-assimilation procedure, recently developed to nowcast foF2 over Italy, proved to be quite reliable during this extreme event, being characterised just by an overestimation during the main phase of the storm, when the electron density and the height of the F region decreased and increased, respectively. Relevant outcomes of the work relate to the Rate Of TEC change Index (ROTI), which shows unusually high spatially distributed values on the nights of 10 and 11 May. The ROTI enhancements on 10 May might be linked to Stable Auroral Red (SAR) arcs and an equatorward displacement of the main ionospheric trough. Instead, the ROTI enhancements on 11 May might be triggered by a joint action of low-latitude plasma pushed poleward by the pre-reversal enhancement (PRE) in the post-sunset hours and wave-like perturbations propagating from the North. Furthermore, the storm generated immediate attention of the general public to Space Weather effects, including mid-latitude visible phenomena like SAR arcs. This paper outlines the report of the Space Weather Monitoring Group (SWMG) of the INGV Environment Department and its effort to disseminate information about this exceptional event.

The study of the physical properties of the topside ionosphere is fundamental to investigating the energy balance of the ionosphere and developing accurate models to predict relevant phenomena, which are often at the root of Space Weather effects in the near-Earth environment. One of the most important physical parameters characterising the ionospheric medium is electrical conductivity, which is crucial for the onset and amplification of ionospheric currents and for calculating the power density dissipated by such currents. We characterise, for the first time, electrical conductivity in the direction perpendicular to the geomagnetic field, namely Pedersen and Hall conductivities, in the topside ionosphere at an altitude of about 450 km. For this purpose, we use eight years of in situ simultaneous measurements of electron density, electron temperature and geomagnetic field strength acquired by the Swarm A satellite. We present global statistical maps of perpendicular electrical conductivity and study their variations depending on magnetic latitude and local time, seasons, and solar activity. Our findings indicate that the most prominent features of perpendicular electrical conductivity are located at low latitudes and are probably driven by the complex dynamics of the Equatorial Ionisation Anomaly. At higher latitudes, perpendicular conductivity is a few orders of magnitude lower than that at low latitudes. Nevertheless, conductivity features are modulated by solar activity and seasonal variations at all latitudes.

Among the effects of space weather, the degradation of air traffic communications and satellite-based navigation systems are the most notable. For this reason, it is of uttermost importance to understand the nature and origin of ionospheric irregularities that are at the base of the observed communication outages. Here we focus on polar cap patches (PCPs) that constitute a special class of ionospheric irregularities observed at very high latitudes in the F region. To this purpose we use the so-called PCP flag, a Swarm Level 2 product, that allows for identifying PCPs. We relate the presence of PCPs to the values of the first- and second-order scaling exponents and intermittency estimated from Swarm A electron density fluctuations and to the values of the Rate Of change of electron Density Index (RODI) for two different levels of geomagnetic activity, over a time span of approximately 3.5 years starting on 16 July 2014. Our findings show that values of RODI, first- and second-order scaling exponents and intermittency corresponding to measurements taken inside PCPs differ from those corresponding to measurements taken outside PCPs. Additionally, the values of the first- and second-order scaling exponents and of intermittency indicate that PCPs are in a turbulent state. Investigation of the coincidence of loss of lock (LoL) events with PCPs displayed that approximately 57.4% of LoLs in the Northern hemisphere and 45.7% in the Southern hemisphere occur in coincidence of PCPs when disturbed geomagnetic activity is considered. During quiet geomagnetic conditions these percentages decrease to 51.4% in the Northern hemisphere and to 20.1% in the Southern hemisphere.

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.

&lt;p&gt;Besides the high resolution of measurements, one feature that distinguishes ESA Swarm mission from previous ones, also aimed at monitoring the Earth&#039;s magnetic field at Low Earth Orbit altitudes, is its configuration. We here take advantage of the nine years of geomagnetic field observations from Swarm satellites, to estimate the ionospheric F region current density. Specifically, we estimate the current density between Swarm A and B satellite altitudes, of about 510 and 460 km respectively, by calculating the curl of their Earth&#039;s magnetic field components.&lt;/p&gt; &lt;p&gt;This technique was first used in 2015 on a dataset of only seven months of vector magnetic data; because it was not possible to cover the entire local time range at the time, the corresponding mapping of ionospheric current density &amp;#160;was limited to two local nighttime intervals: before and after midnight. Seven years after the first application of this technique, we now use it on a more reliable and larger dataset and map the amplitude of the radial, meridional, and zonal components, as well as the total intensity of the ionospheric current density at all local times.&lt;/p&gt;

Electron density (Ne) and electron temperature (Te) observations collected by Langmuir Probes (LPs) on board the European Space Agency’s Swarm satellites are used to characterise the Ne−Te correlation in the topside ionosphere. The large dataset of Swarm LPs in-situ observations at 2-Hz rate, covering the years 2014−2021, allowed us to investigate the correlation properties of the topside ionospheric plasma for different diurnal and seasonal conditions, with a coverage and a detail never reached before. Spearman correlation coefficients (RSpearman) are calculated on joint probability distributions between Ne and Te for specific conditions. Results are given as maps of RSpearman as a function of the Quasi-Dipole (QD) magnetic latitude and magnetic local time (MLT) coordinates, for different seasons. This study highlights, for the first time, the Ne−Te correlation at high latitudes, and provides a global description of the corresponding diurnal trend for different seasons. A negative correlation is found at the equatorial morning overshoot, during daytime at mid latitudes, and during night-time at subauroral latitudes (ionospheric trough). Conversely, a positive correlation dominates the night-time sector at mid and low latitudes, and to a minor extent the low latitudes from 09:00 MLT onwards. A seasonal dependence of the correlation is visible only at very high latitudes where the general pattern of anti-correlation is broken around ±75° QD latitude in the summer season.

Rapid increases in solar wind dynamic pressure, known as solar wind pressure pulses, compress the Earth's magnetosphere and can rapidly restructure the electrodynamics within. The propagation of pressure pulse effects into the magnetosphere is known as a geomagnetic sudden commencement (SC). SCs can be further subdivided into compressions which are rapidly followed by a geomagnetic storm (a sudden storm commencement, SSC) and those which are not (a sudden impulse, SI). In this paper, SSCs and SIs are compared and contrasted, and we examine in particular the differences between the pressure pulses that drive SSCs/SIs, and explore the physical conditions of the magnetosphere before pressure pulse arrival. Firstly, it is shown that SSCs are more likely to be driven by pressure pulses with higher magnitude and/or shorter rise time. Secondly, the magnetosphere is primed by stronger driving conditions and higher geomagnetic activity prior to SSCs than SIs. Finally, there is a solar cycle dependence in the occurrence and magnitude of solar wind pressure pulses.

In this work, we aim to characterize the effective scale height at the ionosphere F2-layer peak (H0) by using in situ electron density (Ne) observations by Langmuir Probes (LPs) onboard the China Seismo-Electromagnetic Satellite (CSES—01). CSES—01 is a sun-synchronous satellite orbiting at an altitude of ~500 km, with descending and ascending nodes at ~14:00 local time (LT) and ~02:00 LT, respectively. Calibrated CSES—01 LPs Ne observations for the years 2019–2021 provide information in the topside ionosphere, whereas the International Reference Ionosphere model (IRI) provides Ne values at the F2-layer peak altitude for the same time and geographical coordinates as CSES—01. CSES—01 and IRI Ne datasets are used as anchor points to infer H0 by assuming a linear scale height in the topside representation given by the NeQuick model. COSMIC/FORMOSAT—3 (COSMIC—1) radio occultation (RO) data are used to constrain the vertical gradient of the effective scale height in the topside ionosphere in the linear approximation. With the CSES—01 dataset, we studied the global behavior of H0 for daytime (~14:00 LT) and nighttime (~02:00 LT) conditions, different seasons, and low solar activity. Results from CSES—01 observations are compared with those obtained through Swarm B satellite Ne-calibrated measurements and validated against those from COSMIC—1 RO for similar diurnal, seasonal, and solar activity conditions. H0 values modeled by using CSES—01 and Swarm B-calibrated observations during daytime both agree with corresponding values obtained directly from COSMIC—1 RO profiles. Differently, H0 modeling for nighttime conditions deserves further investigation because values obtained from both CSES—01 and Swarm B-calibrated observations show remarkable and spatially localized differences compared to those obtained through COSMIC—1. Most of the H0 mismodeling for nighttime conditions can probably to be attributed to a sub-optimal spatial representation of the F2-layer peak density made by the underlying IRI model. For comparison, H0 values obtained with non-calibrated CSES—01 and Swarm B Ne observations are also calculated and discussed. The methodology developed in this study for the topside effective scale height modeling turns out to be applicable not only to CSES—01 satellite data but to any in situ Ne observation by low-Earth-orbit satellites orbiting in the topside ionosphere.

&lt;p&gt;The topside ionosphere embraces the region extending from the F2-layer electron density peak to the overlying plasmasphere. In this region the electron density monotonically decreases at a vertical rate driven by the plasma scale height, which in turn depends on both the plasma chemical composition and the physical state. Since an accurate and thorough knowledge of the plasma chemical and physical properties at these altitudes is not available with the required spatial and temporal coverage, an effective plasma scale height is usually inferred from topside electron density measurements and used for empirical modelling purposes.&lt;/p&gt; &lt;p&gt;In this work, we aim at characterizing the effective plasma scale height (&lt;em&gt;H&lt;/em&gt;&lt;sub&gt;0&lt;/sub&gt;) above the F2-layer peak&amp;#160; through in-situ electron density (&lt;em&gt;N&lt;/em&gt;&lt;sub&gt;e&lt;/sub&gt;) observations by Langmuir Probes (LPs) on-board the China Seismo-Electromagnetic Satellite (CSES-01). Additional information is given by the International Reference Ionosphere (IRI) model. CSES-01 is a sun-synchronous satellite flying with an orbital inclination of 97.4&amp;#176;, an altitude of ~500 km, and descending and ascending nodes are at ~14 local time (LT) and ~02 LT, respectively. Calibrated CSES-01 LPs &lt;em&gt;N&lt;/em&gt;&lt;sub&gt;e&lt;/sub&gt; data recorded in the years 2019-2021 provides the information in the topside ionosphere, while IRI provides the &lt;em&gt;N&lt;/em&gt;&lt;sub&gt;e&lt;/sub&gt; values at the F2-layer peak (&lt;em&gt;Nm&lt;/em&gt;F2) for the same time, latitude, and longitude sounded by CSES-01. These two &lt;em&gt;N&lt;/em&gt;&lt;sub&gt;e&lt;/sub&gt; set of values are used as anchor points to infer &lt;em&gt;H&lt;/em&gt;&lt;sub&gt;0&lt;/sub&gt; through the topside representation given by the NeQuick model. By exploiting the CSES-01 dataset for the years 2019-2021 we deduced the global &lt;em&gt;H&lt;/em&gt;&lt;sub&gt;0&lt;/sub&gt; behavior for daytime (~14 LT) and nighttime (~02 LT) conditions, for low solar activity conditions. Results obtained with CSES-01 observations are compared and validated with corresponding ones provided by COSMIC-1 radio occultation measurements for similar diurnal and solar activity conditions.&lt;/p&gt;

The China Seismo-Electromagnetic Satellite (CSES-01) provides in situ electron density (Ne) observations through Langmuir probes (LPs) in the topside ionosphere since February 2018. CSES-01 is a sun-synchronous satellite probing the ionosphere around two fixed local times (LTs), 14 LT in the daytime sector and 02 LT in the night-time sector, at an altitude of about 500 km. Previous studies evidenced that CSES-01 seems to underestimate Ne measurements with respect to those acquired by similar satellites or obtained from different instruments. To overcome this issue, we calibrated CSES-01 LP Ne observations through Swarm B satellite data, which flies approximately at CSES-01 altitude. As a first step, Swarm B LP Ne observations were calibrated through Faceplate (FP) Ne observations from the same satellite. Such calibration allowed solving the Ne overestimation made by Swarm LP during nighttime for low solar activity. Then, the calibrated Swarm B LP Ne observations were used to calibrate CSES-01 Ne observations on a statistical basis. Finally, the goodness of the proposed calibration procedure was statistically assessed through a comparison with Ne observations by incoherent scatter radars (ISRs) located at Jicamarca, Arecibo, and Millstone Hill. The proposed calibration procedure allowed solving the CSES-01 Ne underestimation issue for both daytime and nighttime sectors and brought CSES-01 Ne observations in agreement with corresponding ones measured by Swarm B, ISRs, and with those modelled by the International Reference Ionosphere (IRI). This is a first fundamental step towards a possible future inclusion of CSES-01 Ne observations in the dataset underlying IRI for the purpose of improving the description of the topside ionosphere made by IRI.

Complexity is a typical feature of space plasmas that may involve the formation of multiscale coherent magnetic and plasma structures. The winding features (pseudo-polarization) of magnetic field fluctuations at different spatial scales are a useful quantity in this framework for investigating complexity in space plasma. Indeed, a strong link between pseudo-polarization, magnetic/plasma structures, turbulence and dissipation exists. We present some preliminary results on the link between the polarization of the magnetic field fluctuations and the structure of field-aligned currents in the high-latitude ionosphere. This study is based on high-resolution (50 Hz) magnetic field data collected on board the European Space Agency Swarm constellation. The results show the existence of a clear link between the multiscale coarse-grained structure of pseudo-polarization and intensity of the field-aligned currents, supporting the recent findings according to which turbulence may be capable of generating multiscale filamentary current structures in the auroral ionosphere. This feature is also examined theoretically, along with its significance for the rate of energy deposition and heating in the polar regions.

The ionospheric plasma density irregularities are known to play a role in the propagation of electromagnetic signals and to be one of the most important sources of disturbance for the Global Navigation Satellite System, being responsible for degradation and, sometimes, interruptions of the signals received by the system. In the equatorial ionospheric F region, these plasma density irregularities, known as plasma bubbles, find the suitable conditions for their development during post-sunset hours. In recent years, important features of plasma bubbles such as their dependence on latitude, longitude, and solar and geomagnetic activities have been inferred indirectly using their magnetic signatures. Here, we study the scaling properties of both the electron density and the magnetic field inside the plasma bubbles using measurements on board the Swarm A satellite from 1 April 2014 to 31 January 2016. We show that the spectral features of plasma irregularities cannot be directly inferred from their magnetic signatures. A relation more complex than the linear one is necessary to properly describe the role played by the evolution of plasma bubbles with local time and by the development of turbulent phenomena.

Swarm is the European Space Agency (ESA)'s first Earth observation constellation mission, which was launched in 2013 to study the geomagnetic field and its temporal evolution. Two Langmuir probes aboard each of the three Swarm satellites provide in situ measurements of plasma parameters, which contribute to the study of the ionospheric plasma dynamics. To maintain a high data quality for scientific and technical applications, the Swarm products are continuously monitored and validated via scienceoriented diagnostics. This paper presents an overview of the data quality of the Swarm Langmuir probes' measurements. The data quality is assessed by analysing short and long data segments, where the latter are selected to be sufficiently long enough to consider the impact of the solar activity. Langmuir probe data have been validated through comparison with numerical models, other satellite missions, and ground observations. Based on the outcomes from quality control and validation activities conducted by ESA, as well as scientific analysis and feedback provided by the user community, the Swarm products are regularly upgraded. In this paper, we discuss the data quality improvements introduced with the latest baseline, and how the data quality is influenced by the solar cycle. In particular, plasma measurements are more accurate in dayside regions during high solar activity, while electron temperature measurements are more reliable during night side at middle and low latitudes during low solar activity. The main anomalies affecting the Langmuir probe measurements are described, as well as possible improvements in the derived plasma parameters to be implemented in future baselines.

Electron density (Ne) and temperature (Te) values recorded by the Langmuir probe onboard the first satellite of the China Seismo-Electromagnetic Satellite (CSES-01) mission allow calculating quantities such as the rate of change of electron density index (RODI) and the rate of change of electron temperature index (ROTEI), which are essential to describe the ionospheric irregularities and their dynamics. These two indices depend significantly on two parameters, i.e., the measurement sampling time and the width of the sliding windows used for their computation. Ne and Te measurements from CSES-01 present two different sampling times, i.e., 3 s in the survey mode and 1.5 s in the burst mode. The purpose of this article is to understand what are the best values of these two parameters to be used when computing RODI and ROTEI based on CSES-01 data. The main results of the study show the following: The shorter the data sampling time, the higher the values of the calculated ionospheric indices, which means that it is not possible to merge values of either RODI or ROTEI calculated with a different sampling time; the wider the sliding window used to calculate the indices, the higher the indices. A reasonable compromise between the data sampling time and the satellite orbital velocity suggests that the optimal way to calculate RODI and ROTEI from CSES-01 should be done by considering data with a 3-s sampling time (i.e., in the survey mode or in the downsampled burst mode), and a 24-s wide sliding window.

Field-aligned currents (FACs) are electric currents parallel to the geomagnetic field and connecting the Earth's magnetosphere to the high-latitude ionosphere. Part of the energy injected into the ionosphere by FACs is converted into kinetic energy of the surrounding plasma. Such a current dissipation is poorly investigated, mainly due to the high electrical conductivity and the small electric field strength expected in direction parallel to the geomagnetic field. However, previous results in literature have shown that parallel electric field is not null (and may be locally not negligible), and that parallel electrical conductivity is high but finite. Thus, dissipation of FACs may occur. In this work, for the first time, we show maps of power density dissipation features associated with FACs in the topside ionosphere of the Northern hemisphere. To this aim, we use a 6-year time series of data at one second cadence acquired by the European Space Agency's "Swarm A" satellite flying at an altitude of about 460 km. In particular, we use data from the Langmuir probe together with the FAC product provided by the Swarm team. The results obtained point out that dissipation of FACs, even if small when compared to that associated with horizontal currents flowing about 350 km lower, is not null and shows evident features co-located with electron temperature at the same altitude. In particular, power density dissipation features are enhanced mainly in the ionospheric regions where intense energy injection from the magnetosphere occurs. In addition, these features depend on geomagnetic activity, which quantifies the response of the Earth's environment to energetic forcing from magnetized plasma of solar origin.