FG: Kinetic Plasma Processes in the Magnetotail during Substorm Dynamics

Dates: 2024 – 2028
Leaders: Harry Arnold, Jason Derr, Akhtar Ardakani, Anton Artemyev
Research Area: Primary – MPS, Secondary – GSM

Topic Description

The Earth’s magnetotail is where magnetic field energy is stored during a substorm growth phase and finally released during the expansion phase, either through magnetic reconnection or some other kinetic instability, resulting in charged particle acceleration and plasma heating. Being less accessible in comparison with the inner Earth’s magnetosphere for monitoring with ground-based facilities and having a much more dynamic magnetic field configuration, this region is mostly investigated via in-situ spacecraft measurements and remote sensing. Ambiguity of spatial and temporal structures is an intrinsic property of such measurements, that together with mapping/projection problems in highly non-dipolar and dynamic magnetic fields complicates the investigation of the magnetotail. Thus, the optimal approach for determination of the dominant magnetotail current sheet modes and dynamical characteristics consists in combining global numerical simulations, modern theoretical/analytical approaches, and multi-spacecraft observations organized via classical statistical approaches and modern machine learning and/or data mining (ML/DM) approaches. The magnetotail current sheet is a principally important element of the magnetosphere, where the substorm grows and its onset is finally triggered by external drivers and/or internal plasma instabilities. A several hour long substorm growth phase with clear memory effects preconditions the magnetotail and determines the location and timing of substorm onset. Plasma transport from the distant tail and ionospheric outflow can significantly alter properties of the magnetotail and cross-magnetopause plasma transport and convective plasma heating affects the magnetotail dawn-dusk asymmetry. Similar global processes significantly alter magnetotail dynamics: plasma transport by fast plasma flows may contribute to both adiabatic (controlled by magnetic field dynamics) and nonadiabatic (determined by local plasma kinetics) charged particle acceleration. All of the aforementioned processes are also influenced by ionospheric outflow of heavy ions such as oxygen and field-aligned anisotropic electron and ion populations that are frequently detected in the near-Earth and mid-tail. This group is focused on various cross-scale couplings and processes (e.g., reconnection, buoyancy, dipolarization fronts, thin current sheets, etc.) which can occur prior to substorm onset, at the onset, and throughout the expansion phase. The primary focus is on the magnetotail current sheet embedded within the plasma sheet, its formation by plasma populations of different origins and its dynamics affecting pre-onset stability and post-onset magnetotail reconfiguration associated with energy transfer and, in particular, charged particle acceleration. The following topics are largely motivated by recent results about the principal role which non-ideal plasma processes play in substorm dynamics from pre-onset through expansion phase. Combining modern global magnetosphere models, including dynamical ionospheric feedback and test particles, ML/DM techniques of reconstructing the magnetic field configuration and plasma parameters, theory and multiple spacecraft observational datasets, we plan to address the following outstanding questions:

  • Magnetotail plasma populations: origins and role in substorm dynamics.
    • What is the role played by ionospheric outflow, transport across the flank magnetopause, and convection from the distant magnetotail in populating the near-Earth tail?
    • What are the dynamics of different plasma sources before and after substorm onset?
  • Thin current sheet dynamics (including formation, stability, and destruction).
    • Which non-ideal effects due to ions (including heaving ions) and electrons play a role in thin current sheet formation?
    • What determines the location and dynamics of substorm onset in the magnetotail?
    • How do thin current sheets interact with mesoscale plasma sheet structures?
  • Role of fast plasma flows in charged particle transport and acceleration.
    • What is the dominant mechanism(s) of charged particle acceleration in the magnetotail, prior to injection into the inner magnetosphere?
    • Are plasma kinetics (parallel electric fields, wave-particle resonant interactions, nonadiabatic dynamics) important for charged particle acceleration in the magnetotail?

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