PLASMON

"A new, ground based data-assimilative modeling of the Earth's plasmasphere - a critical contribution to Radiation Belt modeling for Space Weather purposes"

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 Obiettivo del progetto (Objective)

'The security of space assets are affected by the high-energy charged particle environment in the radiation belts. The controlling principal source and loss mechanisms in the radiation belts are not yet completely understood. During a geomagnetic storm the length of time during which space assets are in danger is determined by the loss mechanisms, particularly by relativistic electron precipitation. The primary mechanism for this precipitation is the interaction of several wave modes with resonant electrons which leads to scattering into the atmospheric loss cone. The nature of the wave activity and the interactions between the waves and radiation belt particles are strongly governed by the properties of the plasmasphere. At this point there are few existing and regular measurements of plasmaspheric properties, with existing plasmaspheric models lacking the structures known to exist in the real plasmasphere. There is evidence that enhanced wave activity and enhanced radiation belt losses occur due to such structures. In addition, there are large uncertainties concerning the fundamental nature of relativistic electron precipitation (REP), due to the difficulties of undertaking quality in-situ measurements. To address these uncertainties in this proposed project we will provide regular longitudinally-resolved measurements plasmaspheric electron and mass densities and hence monitor the changing composition of the plasmasphere, one of the properties which determines wave growth. This will allow us to develop a data assimilative model of the plasmasphere. At the same time, we will monitor the occurrence and properties of REP, tying the time-resolved loss of relativistic electrons to the dynamic plasmasphere observations. Our approach will primarily use ground-based networks of observing stations, operating in the ULF and VLF ranges, deployed on a worldwide level. Our proposal is made up of 6 work packages to meet these science goals.'

Introduzione (Teaser)

The near-Earth space is populated by electrically charged particles that occupy regions knows as the plasmasphere and the Van Allen radiation belts. EU-funded scientists have conducted numerous studies revealing intriguing links between these overlapping regions.

Descrizione progetto (Article)

The outer Van Allen radiation belt is much more dynamic than the inner one. It is readily affected by solar storms that impact the Earth's magnetosphere. At such times, the density of high-energy electrons and protons can vary by several orders of magnitude. During these so-called geomagnetic storms, space assets such as satellites are in danger.

The radiation belts overlap with the plasmasphere, a doughnut-shaped region of low-energy particles that co-rotates with the Earth. EU-funded scientists initiated the project PLASMON (A new, ground based data-assimilative modeling of Earth's plasmasphere - A critical contribution to radiation belt modeling for space weather purposes) to elucidate the role of the plasmasphere in the dynamics of the radiation belts.

The plasmasphere determines the growth and propagation of plasma waves that are responsible for the energisation of the radiation belts and particle loss through wave-particle interaction. PLASMON scientists attempted to identify and monitor how the two populations of particles interact through measurements by ground-based magnetometers.

The Automatic Whistler Detector and Analyzer Network (AWDANet) was extended and enhanced by whistler inversion capabilities and now it is able to provide plasmaspheric electron densities quasi real-time. In addition, the existing MM100 and SEGMA magnetometer networks were extended with new stations in Croatia, Lithuania, Namibia, Poland and Slovakia forming European Magnetometer Network (EMMA) obtaining plasma mass densities by Field Line Resonances (FLRs). Very precise and complementary data collected at the same time and in different places helped to reveal changes in the densities in the plasmasphere .

However, measurements only partly cover the plasmasphere. PLASMON scientists needed a global map of the plasma density in both time and space to determine the effect of wave-particle interactions on the radiation belts' dynamics. Data was, therefore, incorporated into a numerical model of the plasmasphere with advanced data assimilation schemes.

This physics-based model of the plasmasphere, continuously fed with new measurements, was used to identify structures inside or outside the plasmapause that are likely to result in enhanced electron losses. The PLASMON scientists monitored relativistic electron precipitation during periods of high geomagnetic activity by means of the perturbation of military VLF transmitters'.

The presence of the radiation belts is a key factor in the design and operation of all spacecraft in low Earth orbit, as well as a natural hazard for astronauts. Accurate predictions of the dynamics of the belts were one of the prime objectives of the PLASMON project, and this was achieved by better understanding the underlying physics.