This study introduces five linear regression models developed to accurately predict proton intensities in the critical energy range of 92.2 keV to 159.7 keV. To achieve this task we utilized 14 years of data sourced from the Cluster’s RAPID experiment and NASA’s OMNI database. This data was then aligned with the Solar wind-Magnetosphere-Ionosphere Link Explorer (SMILE) mission’s trajectory, to increase model accuracy in the relevant regions. Our approach diverges from existing methodologies by offering a user-friendly model that doesn’t require specialized software, making it accessible for broader applications in satellite mission planning and risk assessment. The research segregates the dataset into four distinct regions, each analyzed for proton intensity dynamics. In the outer regions (|YGSE| ≥ 6 Re) there is a pronounced dependence on radial distance and solar wind speed. In contrast, the inner regions (|YGSE| ≤ 6 Re) demonstrate a significant dependence of proton intensities on the absolute value of the z-coordinate and the magnetic field line topology. Our models achieved a Spearman correlation ranging from 0.57 to 0.72 on the test set, indicating good predictive capabilities. The findings emphasize the role of regional characteristics in space weather prediction and underscore the potential for tailored approaches in future research.

The information on plasma pressures in the outer part of the inner magnetosphere is important for simulations of the inner magnetosphere and the better understanding of its dynamics. Based on 17-year observations from both CIS and RAPID instruments onboard the Cluster mission, we used machine- learning-based models to predict proton plasma pressures at energies from ~40eV to 4MeV in the outer part of the inner magnetosphere (L*=5-9). The location in the magnetosphere, and parameters of solar, solar wind, and geomagnetic activity from the OMNI database are used as predictors. We trained several different machine-learning-based models and compared their performances with observations. The results demonstrate that the Extra-Trees Regressor has the best predicting performance. The Spearman correlation between the observations and predictions by the model data is about 68%. The most important parameter for predicting proton pressures in our model is the L* value, which is related to the location. The most important predictor of solar and geomagnetic activity is the solar wind dynamic pressure. Based on the observations and predictions by our model, we find that no matter under quiet or disturbed geomagnetic conditions, both the dusk-dawn asymmetry at the dayside with higher pressures at the duskside and the day-night asymmetry with higher pressures at the nightside occur. Our results have direct practical applications, for instance, inputs for simulations of the inner magnetosphere or the reconstruction of the 3-D magnetospheric electric current system based on the magnetostatic equilibrium, and can also provide valuable guidance to the space weather forecast.

Energetic charged particles ~>40 keV can affect the plasma temperature and pressure and as a consequence the whole dynamics of the magnetosphere. How do particles get to such energies is a fundamental science question. Energetic particles are also potentially hazardous for the space observations. It is, therefore, necessary to study the origin of energetic plasma, its acceleration, distribution and consequences on the magnetospheric dynamics. In this work we review the related results based on observations from the Cluster/RAPID energetic charged particle detector. These results represent new insights in plasma acceleration, unexpected features in its distributions, effects on substorm and geomagnetic storm dynamics and remediated observations in the radiation belts during approximately 1.5 solar cycles.

The radiation belts of the Earth, filled with energetic electrons, comprise complex and dynamic systems that pose a significant threat to a variety of satellite systems. While various models of the relativistic electron flux have been developed for geostationary orbit (GEO), the behaviour of the medium energy (120-600 keV) electrons below GEO remains poorly quantified. In this paper we present a Medium Energy electRon flux In Earth’s outer radiatioN belt (MERLIN) model based on the Light Gradient Boosting (LightGBM) machine learning algorithm. The MERLIN model takes as input the satellite position, a combination of geomagnetic indices and solar wind parameters including the time history of velocity, and does not use persistence. MERLIN is trained and validated on $>$15 years of the GPS electron flux data, and tested on more than $1.5$ years of measurements. 10-fold cross validation (CV) yields that the model predicts the MEO radiation environment well, both in terms of dynamics and amplitudes of flux. Evaluation on the test set yields high correlation between the predicted and observed electron flux (0.8) and low values of absolute error. The MERLIN model can have wide Space Weather applications, providing information for the scientific community in the form of radiation belts reconstructions, as well as industry for satellite mission design, nowcast of the MEO environment and surface charging analysis.

We study acceleration of energetic electrons in an earthward plasma jet due to magnetic reconnection in the Earth magnetotail for one case observed by Cluster. The case has been selected due to the presence of high fluxes of energetic electrons, Cluster being in the burst mode and Cluster separation being around 1000\,km that is optimal for studies of ion scale physics. We show that two characteristic acceleration mechanisms are operating during this event. First, significant acceleration is achieved inside the magnetic flux pile-up of the jet, the acceleration mechanism being consistent with betatron acceleration. Second, strong energetic electron acceleration occurs in magnetic flux rope like structure forming in front of the magnetic flux pile-up region. Energetic electrons inside the magnetic flux rope are accelerated predominantly in the field-aligned direction and the acceleration can be due to Fermi acceleration in a contracting flux rope.

Quasi-periodic variations of a few to several days are observed in the energetic plasma and magnetic dipolarization in Jupiter’s magnetosphere. Variation in the plasma mass flux related to Io’s volcanic activity is proposed as a candidate of the variety of the period. Using a long-term monitoring of Jupiter by the Earth-orbiting space telescope Hisaki, we analyzed the quasi-periodic variation seen in the auroral power integrated over the northern pole for 2014–2016, which included monitoring Io’s volcanically active period in 2015 and the solar wind near Jupiter during Juno’s approach in 2016. Quasi-periodic variation with periods of 0.8–8 days was detected. The difference between the periodicities during volcanically active and quiet periods is not significant. Our dataset suggests that a difference of period between this volcanically active and quiet conditions is below 1.25 days. This is consistent with the expected difference estimated from a proposed relationship based on a theoretical model applied to the plasma variation of this volcanic event. The periodicity does not show a clear correlation with the auroral power, central meridional longitude, or Io phase angle. The periodic variation is continuously observed in addition to the auroral modulation due to solar wind variation. Furthermore, Hisaki auroral data sometimes shows particularly intense auroral bursts of emissions lasting <10h. We find that these bursts coincide with peaks of the periodic variations. Moreover, the occurrence of these bursts increases during the volcanically active period. This auroral observation links parts of previous observations to give a global view of Jupiter’s magnetospheric dynamics.

The Kelvin-Helmholtz instability (KHI) and its effects relating to the transfer of energy and mass from the solar wind into the magnetosphere remain an important focus of magnetospheric physics. One such effect is the generation of Pc4-Pc5 ultra low frequency (ULF) waves (periods of 45-600 s). On 3 July 2007 at $\sim$ 0500 magnetic local time (MLT) the Cluster space mission encountered Pc4 frequency Kelvin-Helmholtz waves (KHWs) at the magnetopause with signatures of persistent vortices. Such signatures included bipolar fluctuations of the magnetic field normal component associated with a total pressure increase and rapid change in density at the vortex edges, oscillations of magnetosheath and magnetospheric plasma populations, wave frequencies within the expected range of the fastest growing KH mode, and magnetopause conditions favorable to the onset of the KHI. The event occurred during a period of southward polarity of the interplanetary magnetic field. Most of the KHI vortices were associated with reconnection indicated by the Walén relation, the presence of deHoffman-Teller frames and field-aligned ion beams. Global magnetohydrodynamic (MHD) simulation of the event also resulted in KHWs at the magnetopause. The observed KHWs associated with reconnection coincided with recorded ULF waves at the ground whose properties suggest that they were driven by the KHWs. Such properties were the location of Cluster’s magnetic foot point, the Pc4 frequency, and the solar wind conditions.

The present paper demonstrates the first observations by the Magnetospheric Multiscale (MMS) mission of the counter-streaming energetic electrons and trapped energetic protons, localized in the magnetic field depressions between the mirror mode peaks, in the Earth’s dusk sector high-latitude magnetosphere. This region is characterized by high plasma beta, strong ion temperature anisotropy and intermediate plasma density between magnetospheric and magnetosheath plasma. We show that these plasma conditions are unstable for the drift mirror instability. The counter-streaming electron feature resembles those of the previously reported energetic electron microinjections, but without the energy-time dispersion signature. This suggests that MMS is passing through one of the potential microinjection source regions. The energetic ion data in the present study is mainly used to estimate the scale size of the mirror mode structures.

Charge exchange between hot ions and cold neutral atoms is an important effect in ring current loss processes on magnetized planets. In this letter, we investigate the spatial distribution of charge exchange loss contributions to terrestrial ring current decay using data from the Van Allen Probes. These contributions were calculated by dividing local energetic neutral atom energy density escape rates by local ring current energy density decay rates. The results exhibit clear MLT and L dependence, with larger contributions observed nightside during the recovery phase of geomagnetic storms. The contribution of H+; peaked at L~4 during early recovery phases and was stronger at higher L shells during late recovery phases, while O+; decreased slightly with L shell. Possible explanations for this inhomogeneous distribution are also discussed. The asymmetric exospheric hydrogen density distribution may cause the inhomogeneous distribution in the MLT, while the L dependence may be related to the charge exchange cross-section and the ion energy flux. These results provide the first spatial distribution of charge exchange contributions, which is helpful for understanding local terrestrial ring current evolution.