Ingmar Sandberg

The first Norwegian Radiation Monitor (NORM) sensor unit, flying aboard the Arctic Satellite Broadband Mission (ASBM), provides critical information on the space radiation environment along its three-apogee (TAP), 16-hour highly elliptical orbit (HEO). This work reviews the first year of NORM measurements, presenting the first detailed evaluation, analysis, and validation of radiation environment measurements along the TAP orbit, specifically focusing on trapped electrons and solar particle radiation. A series of validation studies demonstrate the inter-consistency of NORM measurements relative to the unit’s on-ground and numerical calibration, as well as with measurements from other radiation monitors. In addition, comparisons between NORM flux measurements and electron radiation belt specification models are presented. The results show that NORM provides high-quality and high-resolution measurements of varying electron differential fluxes within the 0.7–5.3 MeV energy range. Furthermore, NORM provides high-quality differential flux measurements of solar energetic protons within the 12–88 MeV energy range. ASBM/NORM datasets are available to EU users and collaborators, providing an invaluable asset for developing and validating space radiation environment models.

Specification models for radiation belts are essential for the design of radiation resistant, long-lasting spacecraft. Using the available in-situ measurements allows these models to virtually describe the average space radiation environment. However, their dependence on observations will make them suffer from data gaps which may lead to poor assessment of degradation risks. To counter this problem, one can have access to continuous descriptions of the radiation belt dynamics on long time periods through climate reanalysis. This operation consists in the assimilation of historical measurements in radiation belt simulations over solar-cycle-long periods, allowing for a physics-based filling of data gaps and the re-calibration of the radiation belt codes on long simulations. The obtained database of continuous historical distributions may serve later in the elaboration of space climatology models and a new generation of physics-based specification models. Yet, the success of climate reanalysis operation is strongly dependent on the numerical stability of the data assimilation procedure that can be deteriorated in the low earth orbit region for instance. Hence, we present in this paper, the climate reanalysis of the trapped electron dynamics using the Salammbô code for the 2014–2022 period, with promising results when compared to standard specification models. We also present the methodology followed to stabilize the assimilation in the low earth orbit.

Context. A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, and the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of this specific process.Aims. In this paper, we investigate in depth the proton polytropic behaviour in interplanetary coronal mass ejections (ICMEs). Moreover, for the first time (to our knowledge and at such an extent) we further investigate the behaviour of both the total and partial polytropic indices within ICMEs with various magnetic field configurations inside the magnetic obstacles.Methods. To that end we used a list of 401 ICMEs identified from Wind measurements during more than two solar cycles (1995–2001), during which we derived the distributions of the polytropic index in the near-Earth space (L1).Results. Our results show that sheaths are sub-adiabatic, indicating turbulent plasma, while the value of γ further depends on the existence of a shock. Furthermore, the polytropic behaviour of the protons inside the ICME magnetic obstacles is dependent on the magnetic field configuration, with flux ropes with rotation above 90 deg exhibiting sub-adiabatic γ, while ejecta with no clear rotation exhibiting super-adiabatic γ, supporting the scenario that changes during the interplanetary evolution might affect the magnetic field configuration inside the magnetic obstacle.

In this paper, we present the SafeSpace prototype for a safety warning system, dedicated to the electron radiation-belt-induced internal charging hazard aboard spacecraft. The space weather tool relies on a synergy of physical models associated in a chain that covers the whole Sun–interplanetary-space–Earth's inner magnetosphere medium. With the propagation of uncertainties along the modelling pipeline, the safety prototype provides a global nowcast and forecast (within a 4 d lead time) of the electron radiation belt dynamic as well as tailored indicators for space industry operators. They are meant to inform the users about the severity of the electron space environment via a three-coloured alarm system, which sorts the index intensity according to a representative historical distribution of in situ data. The system was tested during the challenging 2015 St Patrick's Day storm in order to assess its performance. It showed overall good nowcasting and forecasting capabilities due to its broad physics-driven pipeline.

The outer Van Allen radiation belt stands out for its intense variability, due to the complex mechanisms that take place due to the Sun – Earth coupling. One fundamentally important effect is the acceleration of seed electrons to relativistic and ultra – relativistic energies, through different mechanisms, namely radial diffusion and local acceleration.In our work, we examine 46 events from the Van Allen Probes era (2012 – 2018), which we categorize according to the interplanetary driver of the geomagnetic disturbance. In particular, we study 16 events caused by Interplanetary Coronal Mass Ejections (ICMEs) and 30 events caused by High Speed Streams (HSS), following Stream Interaction Regions (SIRs), for which we calculate the electron Phase Space Density (PSD) for distinct values of the first adiabatic invariant (μ = 100, 1000, 5000 MeV/G) corresponding to seed, relativistic and ultra – relativistic electrons in the outer radiation belt. Furthermore, we perform a Superposed Epoch Analysis (SEA) of the geomagnetic disturbance events, which lead to either enhancements or depletions of the electron PSD, taking into consideration the parameters of solar wind activity, the state of the magnetosphere and the values of the second adiabatic invariant (K = 0.03, 0.09, 0.15 G1/2RE). We discuss the effects of the drivers on the variability of the outer radiation belt and how the different electron populations are affected, by comparing the time and radial profiles of the PSD. Our results lead to a clear difference between the two drivers, as far as it concerns the acceleration mechanisms.

During the second half of 2019, the Earth’s magnetosphere was impacted by a sequence of Corotating Interaction Regions (CIRs) during four consecutive solar rotations. Based on the solar wind properties, the CIRs can be divided in four groups, with the 3rd group, which arrived on August-September 2019, resulting in significant multi-MeV electron enhancements, up to ultra-relativistic energies of 9.9 MeV.Each CIR group has a different effect on the outer radiation belt electron populations; we investigate them by exploiting combined measurements from the Van Allen Probes, THEMIS, and Arase satellites. We produce Phase Space Density (PSD) radial profiles and inspect their dependence on the values of the first and second adiabatic invariants (μ,K), ranging from seed to ultra-relativistic electrons and from near-equatorial to off equatorial mirroring populations, respectively.Focusing on the 3rd CIR group, and in order to assess the relative contribution of radial diffusion and gyro-resonant acceleration, we perform numerical simulations of the radiation belt environment, combining several relevant models: EMERALD (NKUA), GEO model (NKUA), Salammbô (ONERA), VLF model (IAP), Plasmaspheric model (BIRA-IASB), FARWEST (ONERA). We further compare the temporal evolution of the simulated electron PSD with the above observations.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870437 for the SafeSpace project.

The Environmental Monitoring Units (EMU), on-board two satellites of the EU Galileo constellation, monitor the radiation environment along the GNSS orbit providing measurements of the energetic electron fluxes in the outer Van Allen Belt. With new calibration studies that take into account more realistic shielding provided by the spacecraft and the characteristics of the encountered environment along the satellite orbit, we have derived a new version of the GSAT/EMU Level 1 dataset that provides high quality validated fluxes of trapped energetic electrons within the 0.2-4.5 MeV energy range.  In this work, we present an overview of the EMU measured electron fluxes over the last five years including recently completed validation studies with Arase [ERG] and RBSP energetic electron measurements. The new dataset, available to users from European member states registered at https://gssc.esa.int, will be used in the assimilation processes and/or the validation of the ONERA Salammbô electron radiation belt models - under the EU Safespace activity and ESA S2P RBFAN activity - leading to improved forecasts of the state of the outer belt. In addition, the quality of the time-coverage of the dataset permits their use in the development and/or evaluation of quantitative radiation environment specification models. This work has received funding from the European Union’s Horizon 2020 research and innovation programme "SafeSpace" under grant agreement No 870437, from the European Space Agency activity "Cross Calibration EMU Dataset with RBSP" under ESA Contract 4000135823/21/NL/GLC/mkn and the “SSA P3-SWE-X Space Environment Nowcast and Forecast Development” activity under ESA Contract 4000131381/20/D/CT.

The Earth’s outer radiation belt response to geospace disturbances is extremely variable spanning from a few hours to several months. In addition, the numerous physical mechanisms, which control this response, depend on the electron energy, the time-scale and the types of geospace disturbances. As a consequence, the various models that currently exist are either specialized, orbit-specific data-driven models, or sophisticated physics-based ones. In this paper we present a new approach for radiation belt modelling using Machine Learning methods driven solely by solar wind speed and pressure, Solar flux at 10.7 cm and the Russell-McPherron angle. We use Van Allen Probes data to train our model and show that it can successfully reproduce and predict the electron fluxes of the outer radiation belt in a broad energy (0.033–4.062 MeV) and L-shell (2.5–5.9) range and, moreover, it can capture the long-term modulation of the semi-annual variation. We also present validation studies of the model’s performance using data from other missions which are outside the spatio-temporal training regime such as the E>0.8 MeV electron flux measurements from GOES-15/EPEAD at geostationary orbit.This work has received funding from the European Union’s Horizon 2020 research and innovation programme "SafeSpace" under grant agreement No 870437 and from the European Space Agency under the "European Contribution to International Radiation Environment Near Earth (IRENE) Modelling System" activity under ESA Contract No 4000127282/19/NL/IB/gg.

During July-October of 2019, a sequence of Corotating Interaction Regions (VSW ≥ 600 km/s) impacted the magnetosphere, for four consecutive solar rotations. Even though the series of CIRs resulted in relatively weak geomagnetic storms (SYM-Hmin ≈ -60 nT, Kpmax ≈ 5), the net effect of the outer radiation belt during each disturbance was different, depending on the electron energy. During the August-September CIR, intense substorm activity was recorded (SMLmin ≈ - 2000 nT), as well as significant enhancement of ultra-relativistic electrons.We exploit coordinated and cross-calibrated particle measurements from the Van Allen Probes, Arase and Galileo 207, 215 satellites, to investigate the relative contribution of radial diffusion and gyro-resonant acceleration, using both electron fluxes and Phase Space Density (PSD) radial profiles, also compared with a 1D Fokker-Planck simulation.Additionally, we use chorus wave amplitude and radial diffusion coefficient (DLL) estimations, from the SafeSpace DLL database, density measurements from the GFZ-Potsdam database, as well as solar wind and geomagnetic parameters, for a detailed investigation of these events.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 870437 for the SafeSpace project.

The first two units of the ESA Next Generation Radiation Monitor (NGRM) sensor are flying onboard the European Data Relay System, Satellite-C (EDRS-C), and the Sentinel-6 Michael Freilich (S-6), providing critical information related to the space radiation environment. This work presents a first evaluation and analysis of the measurements of the unit hosted on EDRS-C during the geostationary transfer orbit (GTO) of the satellite. The evaluation studies include comprehensive comparisons with measurements from other radiation monitors and science-class experiments. NGRM datasets will become publicly available in real time from the space weather (SWE) data center through dedicated applications contributing to the monitoring of SWE and the characterization of the space radiation environment.