Event Details

Space and Planetary Physics seminar

Abstract: The flux of energetic electrons in the terrestrial Van Allen Belts can vary by orders of magnitude during a magnetic storm. Depending upon the magnetic storm, a range of belt responses spanning from depletion, to recovery, or enhancement can result, previous works arguing that this occurs as a result of an often delicate balance between competing acceleration and loss processes. Here, we show instead how the dynamics of Van Allen belt electrons are clearly separated by energy into two distinct populations, which are governed by different storm time behaviour. We reveal how self-limiting processes, described theoretically over 50 years ago by Kennel and Petschek (1966), govern the energy-dependent dynamics of the electrons. For terrestrial magnetic storms, accelerated electrons with energies below ~850 keV quickly reach and are capped at a maximum energy-dependent differential flux level and which is almost identical in every storm. Higher energy electrons typically do not reach a limiting flux, except in the most extreme events. In general, electron fluxes saturate at the Kennel-Petschek limit first at lower energies, impacting higher energies later in the storm. For the most intense storms, the maximum energy at which the fluxes are capped can also increase. Significantly, throughout the seven years of the operation of the NASA Van Allen Probes mission electrons with energies >2.6 MeV never reached the Kennel-Petschek limit. In recent work, we are also assessing the implications of this for affecting the intensity of storm-time chorus plasma waves, which are an integral element of the Kennel-Petschek flux limiting process. Overall, our work shows that the terrestrial Van Allen belts appear to have an energy dependent absolute maximum, which caps the severity of the electron space radiation and strongly impacts the chorus wave populations, which have been further implicated as a crucial element of relativistic belt dynamics. The results are of significant importance for specifying the worst-case electron radiation. They also have wide implications for both more accurate modelling and forecasting of belt dynamics, and for the development of worst-case radiation specification models for the design of radiation resilient satellites.

If someone from outside of the SPP group would like to join the webinar, please send a request to n.rogers1@lancaster.ac.uk