Small scale Alfvénic structures in the Earth's magnetosphere

• Project Objectives
• Summary of the first Working Team meeting held in Bern 24-28 March 1998.
• Results of the second Working Team meeting held in Bern 12-17 October 1998.
• Directory of Team Members.

Thin auroral arcs 100-1000 m width (possibly related to Alfvenic structures) pictured by Trond Trondsen.

Project Objectives:
High time resolution measurements performed in ionospheric/magnetospheric plasma provide growing evidence that thin auroral forms with thickness of ~1 km are related to solitary electromagnetic structures of similar thickness. These structures are most clearly observed  in data from medium altitude satellites, as for example Freja at  h~1500 km, and are associated with strong electric fields, field-aligned currents,  large electron energy fluxes, density depletions, and a wealth of high frequency waves. The electromagnetic structures are being explained in the literature  by a number of  competing theoretical models as for example:
    (1) dispersive field line resonances
    (2) solitary kinetic Alfven waves
    (3) nonlinear Alfven solitons
    (4) magnetic field line fractures
    (5) vortex street structures
    (6) Alfvenic shocks
    (7) drift Alfven waves
    (8) Alfven resonance cones.
This indicates great uncertainty and insufficient understanding of the fundamentals of the ionosphere-magnetosphere coupling. The measurements gathered on satellites Viking, Freja, Polar, and Fast combined with high resolution ground based optical imagery, as for example ALIS facility in northern Scandinavia, portable auroral imager in Canada, provide invaluable experimental base for resolving some fundamental problems in auroral electrodynamics and the coupling between the magnetosphere and the ionosphere. In addition, a number of  laboratory plasma devices, as for example LAPD facility in Los Angeles are being used in the parameter regime encountered in space, and provide important clues for understanding the plasma phenomena in space. The importance of Alfven waves for laboratory physics, space physics and astrophysics is that they represent a fundamental mode of transmitting information and electromagnetic energy througth magnetized plasmas.