The interaction between plasma of solar origin and the Earth’s magnetosphere-ionosphere (MI) system is at the base of several phenomena relevant to Space Weather. Among them, the MI coupling plays a fundamental role, as it allows energy and momentum to be exchanged between magnetosphere and ionosphere, and thus provides a mechanism able to modify the energy budget of the ionosphere. In fact, part of the energy injected into the ionosphere may be converted into mechanical energy and dissipated via Joule heating. Such a dissipation may significantly affect temperature, density, and the composition of the upper ionosphere, resulting, for instance, in an increased atmospheric drag affecting the satellite orbits. The MI coupling is mainly realized by means of field-aligned currents (FACs) that connect the magnetosphere with the high-latitude ionosphere. Thus, understanding the dissipation of these currents in the ionosphere may help to clarify their contribution to the energetic budget and to shed light on some physical processes still unclear. Generally speaking, the work done by electromagnetic fields on a charge distribution is given by the dot product of current density, J, and the electric field, E, which describes the conversion of electromagnetic energy into mechanical energy. In the direction parallel to the geomagnetic field, under the reasonable assumptions of quasi-neutrality and neglecting higher order terms, the only relevant contribution to the conversion term is given by Ohmic dissipation and the consequent Joule heating. This quantity can be computed by using Swarm data instead of models. Here, for the first time, we show statistical maps of power density features dissipated by FACs via Joule heating at Swarm A altitudes (about 460 km). This is realised by using six-year time series of electron density and temperature data acquired by the Langmuir Probes onboard the Swarm A satellite at 1 s cadence together with the field-aligned current density product provided by the ESA’s Swarm Team at the same cadence. Maps of the same quantity under different levels of geomagnetic activity are also shown and discussed in light of the previous literature.

This work is partially supported by the Italian National Program for Antarctic Research under contract N. PNRA18 00289-SPIRiT and by the Italian MIUR-PRIN grant 2017APKP7T on "Circumterrestrial Environment: Impact of Sun-Earth Interaction".

Height-integrated ionospheric Pedersen and Hall conductances play a major role in ionospheric electrodynamics and Magnetosphere-Ionosphere (MI) coupling. Especially the Pedersen conductance is a crucial parameter in estimating ionospheric Joule heating, which is an important energy sink of the whole MI-system. Increased Joule heating during geomagnetic storms and substorms has large impact on the thermospheric chemical composition and circulation, and can also affect the atmospheric drag experianced by satellites at low Earth orbits. Unfortunately, the conductances are rather difficult to measure directly in extended regions, so statistical models and various proxies are often used.

We discuss a method for estimating the Pedersen Conductance from magnetic and electric field data provided by the Swarm satellites. We need to assume that the height-integrated Pedersen current is identical to the curl-free part of the height integrated ionospheric horizontal current density, which is strictly valid only if the conductance gradients are parallel to the electric field. This may not be a valid assumption in individual cases but could be a good approximation in a statistical sense. Further assuming that the cross-track magnetic disturbance measured by Swarm is mostly produced by field-aligned currents and not affected by ionospheric electrojets, we can use the cross-track ion velocity and the magnetic perturbation to directly estimate the height-integrated Pedersen conductance. The same relationship is valid both in the case of quasi-static MI-coupling and idealized Alfven wave reflection at the ionospheric boundary.

We present results of a statistical study utilizing 7 years of ion velocity and magnetic field data from the Swarm-A and Swarm-B satellites. Carefull selection and filtering of the data are required, which tends to limit the analysis to regions where the ion velocity and magnetic disturbances are reasonably strong, i.e. close to the auroral ovals. Statistical Pedersen conductance maps are derived for the Northern and Southern auroral regions during different seasons and levels of geomagnetic activity. We discuss possible applications of the results and possible limitations of the method.

Extreme lightning activity can cause electromagnetic fluctuations that propagate from the lower atmosphere up to the ionosphere. This process requires conversion of the electromagnetic perturbation propagating in the neutral atmosphere into an ionospheric plasma wave, which for ultralow frequencies (ULF) can attenuate strongly the wave amplitude. Additionally, thunderstorms have an observable effect on the ionosphere, which is manifested by small scale irregularities in the ionospheric plasma.

The ESA Swarm mission has been designed to provide high-precision registrations of the Earth's magnetic field. Since its launch in November 2013, the constellation, consisting of three LEO satellites, measures the magnetic signals that stem from Earth's core, mantle,
crust, oceans, ionosphere, and magnetosphere. However instruments onboard Swarm allow to expand main goals of the mission and give capabilities to capture signals originating from strong lightning events. In particular Swarm occurred to be quite effective in detection of transient luminous events (TLEs). In contrast to previous and on-going satellite missions fully dedicated to TLE, it is not a straightforward task for Swarm to capture such signals on a regular basis and 20 ms time resolution is the main limitation. However, Swarm allows for detection of continuing currents following the most intense +CG strokes. Having simultaneous registrations of ionospheric plasma parameters and magnetic field scintillations we are able to conduct systematic study to answer the question whether TLEs trigger perturbations in ionospheric plasma parameters in the thunderstorm active region?

The study concentrates on the longitudinal sector of both Americas, spanning through regions which belong to areas of most frequent occurrence of ionospheric scintillations, as well as lightning hotspots. In the joint analysis of in-situ registration of plasma parameters and magnetic field components from the ESA Swarm mission together with lightning observations derived from the GLM instrument on-board the meteorological GOES-R satellite, we provide classification of two types of ionospheric responses to the intensified thunderstorm activity. We reveal links between lightning and ionospheric wave properties that suggest a real causality relationship between the two phenomena.
Finally, in the context of upcoming launch of the Meteosat Third Generation (MTG): Lightning Imager, analysis shows, that synergy between in-situ ionospheric observations from the low-Earth orbit satellite and lightning imager will be beneficial for better understanding of upper ionospheric irregularities developing in the African thunderstorm cells as well as for detection of severe thunderstorms in the European region.

Ionospheric irregularities are structures or fluctuations of plasma density in different scale sizes. These irregularities can disrupt radio waves and produce an error for space-based or ground-based technologies which depend on the GNSS/ GPS signals.
Post-sunset ionospheric plasma irregularities are a common characteristic of the equatorial ionosphere. These irregularities, associated with plasma bubbles, are defined as density depletions relative to the background plasma as determined by in situ measurements. The physical mechanism which leads to the formation of plasma bubbles has been studied extensively. A seed density perturbation leads to the nonlinear Rayleigh-Taylor instability in the bottom side of the F region ionosphere. The plasma perturbation can grow spatially and reach a higher altitude in the ionosphere. One of the main features of a plasma bubble is the existence of power-law scaling in its energy power spectrum. This feature suggests that the spatial behavior of plasma bubbles can be compared and modeled with turbulent models.

The bifurcation process is a common feature of an evolving and turbulent flow. This process has been considered in the modeling of plasma bubbles in several studies. In situ bifurcated plasma bubbles have been detected with the San Marco D satellite in the west-east direction. Some examples of bifurcation-like processes have been observed in the field-aligned plasma bubbles using the Swarm Langmuir probes. In a bifurcated plasma bubble process, we need to have information about the measured plasma density and direction of flow to understand how the topology of a plasma bubble evolves to distinguish a bifurcated plasma bubble from a shrinking or expanding bubble. We use the Swarm Electric Field Instrument data to look at the flows' direction in one of the bifurcation-like plasma bubble events. In most cases, we detect an Alfvén wave inside the walls of plasma bubbles. In this study, we compare the properties of the low-frequency fluctuations in adjacent bifurcated regions.

Most satellites are equipped with magnetometers as part of their attitude and orbit control system (AOCS).

The measurements taken by these platform or navigational magnetometers are not only useful for coarse attitude determination for satellite operation but can also be used for scientific investigations, provided they have been properly calibrated.

This contribution describes the preprocessing and calibration of platform magnetometer data collected by CryoSat-2, GRACE and other Low-Earth orbiting satellites, and how they can be used for studying the dynamics of electric current systems in Earth's environment. We will also report on experiments of calibrating magnetic data of larger satellite fleets, and how existing and future ESA LEO satellites can be used for mapping Geospace and Space-Weather applications.

As an application we show a combination of magnetic field observations from the satellites CryoSat-2, GRACE, GRACE-FO with magnetic data taken by ESA’s Swarm satellite trio, in order to obtain an improved description of the space-time structure of ionospheric and magnetospheric current systems.

Fully calibrated data from CryoSat-2 (for the years 2010 - 2019) and the GRACE satellite duo (for the years 2008 - 2017) are freely available as daily files in CDF format at https://swarm-diss.eo.esa.int/#swarm%2F%23CryoSat-2 and ftp.spacecenter.dk/data/magnetic-satellites/GRACE/.

The actual state and variability of the Earth’s ionosphere are important aspects of the space weather system. Their understanding is crucial for ionospheric modelling and building the capability of predicting and mitigating severe space weather effects. One example of such effects is the degradation of communication or positioning with the Global Navigation Satellite Systems (GNSS), which is due to ionospheric plasma irregularities impacting the propagation of radio waves. Ionospheric irregularities at various scales are a result of dynamic processes in the ionosphere.

Through the project Swarm Variability of Ionospheric Plasma (Swarm-VIP), as a part of the Swarm+ 4DIonosphere initiative, we provide spatiotemporal characteristics of ionospheric plasma at different geomagnetic latitudes and uncover coupling between various scales in response to geomagnetic conditions. The project employs data from the Swarm satellites, such as the IPIR dataset [1,2], as well as auxiliary datasets. Taking advantage of the orbital characteristics of the Swarm satellites and using complementary scale analysis techniques such as wavelets or Fast Iterative Filtering, we ascertain the dominant scales at given geomagnetic conditions. Our focus is primarily on the characteristics of ionospheric plasma, i.e., plasma density and total electron content as measured respectively by the Langmuir probes and GPS receivers onboard Swarm satellites.

The result of Swarm-VIP is a semi-empiric model for the ionosphere based on the generalized linear modeling. The model determines the probability of occurrence of different scales in ionospheric plasmas with respect to geomagnetic conditions and the magnetosphere-ionosphere coupling. It also gives insight into ionospheric structuring and coupling between scales. The model can be understood in the context of space weather effects, such as scintillations of trans-ionospheric radio signals. The Swarm-VIP model is provided globally, along the whole orbits of the Swarm satellites, and a special emphasis is put on high latitudes, Arctic and Antarctica, and the European sector, where the validation study is carried out with a network of ground-based instruments.

The Swarm VIP project is funded by the European Space Agency’s in the Swarm+ 4DIonosphere framework (Contract No. 4000130562/20/I-DT).


References

[1] A. Spicher, L.B.N. Clausen, W.J. Miloch, V. Lofstad, Y. Jin, and J.I. Moen, Interhemispheric study of polar cap patch occurrence based on Swarm in situ data, J. Geophys. Res. Space Physics, 122, (2017), pp. 3837– 3851, doi:10.1002/2016JA023750.
[2] Y. Jin, C. Xiong, L. B. N. Clausen, A. Spicher, D. Kotova, S. Brask, G. Kervalishvili, C. Stolle, W.J. Miloch, Ionospheric plasma irregularities based on in-situ measurements from the Swarm satellites. J. Geophys. Res. Space Physics, 124, (2020), e2020JA028103. https://doi.org/10.1029/2020JA028103