A source of very energetic oxygen located in Jupiter’s inner radiation belts

A local charged particle source in Jupiter’s inner radiation belts generates oxygen ions of cosmic ray energies.

An operational approach to forecast the Earth’s radiation belts dynamics

The Ca index is a time-integrated geomagnetic index that correlates well with the dynamics of high-energy electron fluxes in the outer radiation belts. Therefore Ca can be used as an indicator for the state of filling of the radiation belts for those electrons. Ca also has the advantage of being a ground-based measurement with extensive historical records. In this work, we propose a data-driven model to forecast Ca up to 24 hours in advance from near-Earth solar wind parameters. Our model relies mainly on a recurrent neural network architecture called Long Short Term Memory that has shown good performances in forecasting other geomagnetic indices in previous papers. Most implementation choices in this study were arbitrated from the point of view of a space system operator, including the data selection and split, the definition of a binary classification threshold, and the evaluation methodology. We evaluate our model (against a linear baseline) using both classical and novel (in the space weather field) measures. In particular, we use the Temporal Distortion Mix (TDM) to assess the propensity of two time series to exhibit time lags. We also evaluate the ability of our model to detect storm onsets during quiet periods. It is shown that our model has high overall accuracy, with evaluation measures deteriorating in a smooth and slow trend over time. However, using the TDM and binary classification forecast evaluation metrics, we show that the forecasts lose some of their usefulness in an operational context even for time horizons shorter than 6 hours. This behaviour was not observable when evaluating the model only with metrics such as the root-mean-square error or the Pearson linear correlation. Considering the physics of the problem, this result is not surprising and suggests that the use of more spatially remote data (such as solar imaging) could improve space weather forecasts.

Charged Particles in Near-Earth Space

In this chapter we discuss the concepts that govern the motion of charged particles in the geomagnetic field and the principles how they stay trapped in the radiation belts. The basic particle orbit theory can be found in most plasma physics textbooks. We partly follow the presentation in Koskinen (Physics of space storms, from solar surface to the earth. Springer-Praxis, Heidelberg, 2011). A more detailed discussion can be found in Roederer and Zhang (Dynamics of magnetically trapped particles. Springer, Heidelberg, 2014). A classic treatment of adiabatic motion of charged particles is Northrop (The adiabatic motion of charged particles. Interscience Publishers, Wiley, New York, 1963).

Dynamics of the Electron Belts

In this chapter we discuss the overall structure and dynamics of the electron belts and some of their peculiar features. We also consider the large-scale solar wind structures that drive geomagnetic storms and detail the specific responses of radiation belts on them. Numerous satellite observations have highlighted the strong variability of the outer electron belt and the slot region during the storms, and the energy and L-shell dependence of these variations. The belts can also experience great variations when interplanetary shocks or pressure pulses impact the Earth, even without a following storm sequence.

Radiation Belts and Their Environment

The Van Allen radiation belts of high-energy electrons and ions, mostly protons, are embedded in the Earth’s inner magnetosphere where the geomagnetic field is close to that of a magnetic dipole. Understanding of the belts requires a thorough knowledge of the inner magnetosphere and its dynamics, the coupling of the solar wind to the magnetosphere, and wave–particle interactions in different temporal and spatial scales. In this introductory chapter we briefly describe the basic structure of the inner magnetosphere, its different plasma regions and the basics of magnetospheric activity.

Particle Source and Loss Processes

The main sources of charged particles in the Earth’s inner magnetosphere are the Sun and the Earth’s ionosphere. Furthermore, the Galactic cosmic radiation is an important source of protons in the inner radiation belt, and roughly every 13 years, when the Earth and Jupiter are connected via the interplanetary magnetic field, a small number of electrons originating from the magnetosphere of Jupiter are observed in the near-Earth space. The energies of solar wind and ionospheric plasma particles are much smaller than the particle energies in radiation belts. A major scientific task is to understand the transport and acceleration processes leading to the observed populations up to relativistic energies. Equally important is to understand the losses of the charged particles. The great variability of the outer electron belt is a manifestation of the continuously changing balance between source and loss mechanisms, whereas the inner belt is much more stable.