Physics of the Terrestrial Magnetosphere

We have long been working on satellite-measured ion data (from Prognoz-7, Viking, Freja, Atrid-1 and -2, Munin, and Cluster) related to ion acceleration along the geomagnetic field and other energization, particularly related the auroral phenomena, solar wind plasma entry to the magnetosphere, magnetosphere-ionosphere coupling, ion outflow from the ionosphere, circulation and dynamics of these ions in the magnetosphere, particularly in the  inner-magnetosphere, and ion escape from the magnetosphere. While these topics are under study, the recent focus has shifted toward at lower altitude (ionosphere, important for space weather) and heavier (molecular and metallic) ions for the satellite-related studies.

In addition to the research related to the satellite ion data, we also study the ionosphere-magnetosphere coupling system (including auroral phenomenon) using Kiruna Atmospheric and Geophysical Observatory (KAGO) data.

For example we started an auroral alert system when strong visible aurora appears in the all sky camera (ASC), by creating the ASC auroral index

During the past 5 years we have studied:

  • Ion escape and relevant energization process
  • Dynamics of ions in the inner-magnetosphere
  • Very heavy (molecular and metallic) ions in the magnetosphere (ISSI activity)
  • Preparing ESA mission proposals to study heavy ions in the magnetosphere
  • Collaborative projects involving Cluster ion data (including preparing ESA-China joint mission SMILE)

Ion escape and relevant energization process

We take advantage of ion data and its analyses on Mars and Venus, and tune our Cluster study in a planetary perspective, i.e., to compare the terrestrial ion dynamics (escape, acceleration, and circulation) on the viewpoint of comparative planetary study at both magnetized and unmagnetized planets.  The questions that we have been and are questing are, for examples,

  • Why hand how does the planetary magnetic field NOT protect the atmosphere but enhance the solar wind scavenging?
  • How different ion species (H+, He+, He++, O+, N2+) behave differently to each other beyond any theory?
  • What is the consequence of ion dynamics in geological scale?

The actual studies are:

  1. Identification and quantification the acceleration mechanisms operating on the cusp related heavy ion outflow at Earth
  2. Cause and mechanism of different behaviors between different ion species (H+, He+, He++, O+, N2+) and between different souce (dayside vs nightside, high-latitude vs low-latitude)
  3. Dependence of escaping ions (energy, direction, amount) on the external parameters (solar wind conditions).
  4. Determination of the fate of the cusp related ion outflow, whether these ions can enter the tail plasma sheet.

More recently we have started to study ion behavior in the tail (dynamics, amount, and final destination of the ion return from the tail) because only a part of ion in the tail can return to the inner magnetosphere.

Dynamics of ions in the magnetosphere

We have long been working on the low-energy (< 10 keV) ions in the inner magnetosphere. While energetic ions in the inner magnetosphere are basically adiabatically energized ions from the magnetotail, low energy ions are convolution of tail-origin ions, near-earth plasma sheet origin ions, directly supplied from the ionosphere, and locally energized ions of plasmaspheric origin or plasma sheet origin. We have recently classified all proton patterns and its temporal variation and spatial distribution.

Very heavy (molecular and metallic) ions in the magnetosphere (ISSI activity)

Molecular and metallic ions are vastly unexplored in near-Earth space.  Nevertheless, existing patchy data including those not designed for the required mass separation are capable of detecting many of these ions with available tools, although severe limitations exist. By combining these patchy and incomplete data, we found several features that indicate sources of these heavy ions.

  1. The Moon can be a substantial source for low charge-state metallic ions in the magnetosphere when the Moon is located upstream of the Earth.
  2. Upward expansion of mesospheric metal/sodium layer can be another important source of the low charge-state metallic ions in the magnetosphere during a major magnetic storm.
  3. The molecular ion can be supplied to the inner magnetosphere via low-latitude in addition to the cusp during high outflow flux period. This indicates extraordinary upward convection (or ion flow) at the sub-auroral region.
  • Yamauchi, M., et al (2022): EGU presentation

Preparing mission proposal to study heavy ions in the magnetosphere

Cluster ion instruments cannot distinguish nitrogen (N) from oxygen (O). This is not only Cluster problem but also all past magnetospheric missions at energy range 0.05-30 keV. However, nitrogen and oxygen are expected to show completely different dependency on the solar and solar wind condition, and nitrogen can escape more than oxygen for extremely large events. Furthermore, nitrogen is as important as oxygen for life because as the basic element to form amino acid. Therefore, both nitrogen behavior an oxygen behaviors against the solar and solar wind activity is the fundamental information in understanding the evolution of the Earth in terms of habitability.

To study this, we need dedicated mission to study, and this is why we have proposed NITRO and ESCAP to ESA’s call for medium-class mission (M4 and M5) and FATE for fast class mission (F1).

Similarly, ion-neutral interaction at very energy < 100 eV in the same plasma environment is not well known because low-energy ions are strongly influenced by environment (electric and magnetic fields, radiation, cosmic ray, gravity,and their gradient). These are also the important theme to study by space missions.

Collaborative projects involving Cluster ion data (including SMILE preparation)

Since we are Swedish co-investigators on the Cluster ion instrument, particularly CIS instrument, it is our responsibility to assist other groups (primarily Swedish but also SMILE community) in the use of ion data and to keep the general knowledge of the ion instruments up to date.

For example, we participate studies of energy budget in the magnetotail (collaboration with Umeå University), auroral-related ion phenomena (collaboration with Royal Institute of Technology KTH, Stockholm), and wave-related ion phenomena (collaboration with Uppsala group). In addition, we participate ISSI working groups (other than mentioned above) of both magnetotail dynamics and auroral studies, part of which are related to our study of “Ion escape and relevant
energization process”.

The ESA-China joint SMILE mission, to be launched 2024 or 2025 and stay north of the Earth where solar wind accesses the magnetosphere, studies solar wind interaction with the magnetosphere and resultant auroral activity with imagers (UV and soft X-ray) and in-situ plasma measurement (magnetometer and ion detector).  To have the highest science output with such limited and unique payload at unique orbit, we need many modelling for which our Cluser knowledge  is essential.

Solar and solar wind effect on the ionosphere-magnetosphere coupling system

Solar flares are known to enhance the ionospheric electron density and thus influence the D- and E-region electric currents in the sunlit hemisphere. The resultant geomagnetic disturbances (called “crochet”) has been expected as mainly subsolar phenomenon. However, we found that high-latitude crochet is much more significant compared to the subsolar crochet. We are making systematic study on it.

Similarly, the mass loading effect on the solar wind flow into the magnetosphere by the outflowing ions has long been ignored, but because of high mass of O+ than H+, it turned out to be significant near the cusp region.  This explains the independency of the cusp current from the dayside region 1 current or polar cap (NBZ) current.

Created by Masatoshi Yamauchi at

Last modified by Masatoshi Yamauchi at