Abstract: Energetic charged particles trapped by the Earth’s magnetic field present a significant hazard for Earth-orbiting satellites and humans in space. Application of the data assimilation tools allows us to reconstruct the global state of the radiation particle environment from sparse single-point observations. The measurements from different satellites with different observational errors can be blended in an optimal way with physics-based models. The mathematical formulation on the diffusion and diffusion-advection equations for the Earth’s Van Allen radiation belts and ring current is described. We further describe several recent studies that successfully applied the data assimilation tools to the near-Earth space radiation environment. The applications to the reanalysis of the radiation belts and ring current, real-time predictions, and analysis of the missing physical processes are described and motivation for these studies is provided. We further discuss various assimilation techniques and potential topics for future research.

Surprisingly, radio observations of the planets also turned up unexpected discoveries. While testing their transit radio array using the Crab Nebula as a reference source, two scientists at the Carnegie Institution Department of Terrestrial Magnetism noticed a strange variable signal that repeated each night. First suspecting that it was ignition noise from a nearby farm vehicle, they later realized that they were detecting radio emission from powerful electrical storms on Jupiter, which was at the same declination as the Crab Nebula as it passed through their fixed telescope beam. Mercury, long thought to have one side bathed in eternal daylight, was found to be rotating. Radio observations revealed the greenhouse effect on Venus, causing surface temperatures to reach over 600 degrees Celsius, and detected intense radiation belts around Jupiter, analogous to the Earth’s van Allen belts. The other giant planets were all found to be warmer than can be explained by solar heating alone. Precise pulsar timing measurements disclosed the first known extrasolar planetary system, a precursor to the thousands of extrasolar planets later discovered by ground and space based optical studies.

Since the discovery of the magnetosphere-magnetotail system in the1950s-1960s), and the associated beginning of the satellite era, we have gained a well-informed understanding of this space plasma region permeated by the geomagnetic field and home to a variety of charged particle populations and plasma waves. Over the last six decades, IAGA has played an important role in supporting international magnetospheric research. Here we provide an overview of recent developments in energy transport from the solar wind into the Earth’s environment. Topics include, magnetosphere energy input, the role of the boundary layer. Solar wind interaction with the magnetosphere creates geomagnetic activity and the response of the region leading to sub-storms and steady magnetospheric convection are discussed. The charged particle energy (eV to MeV) inherent/contained in the magnetospheric ring current and Van Allen radiation belts establish many properties of the region, giving rise to boundary regions and waves. Results from recent state of the art and currently operating Earth orbiting satellites (Cluster, THEMIS, Van Allen Probes, Magnetosphere MultiScale), are providing exciting new results. Waves from magnetospheric scale ultra-low frequency (ULF) from a few milliHertz, up to upper hybrid waves and continuum radiation in the 1-2 MHz band. Finally, current understanding of the plasmasphere and associated boundary the plasmapause, are considered.