A Physical Model for Nonlinear, Supersonic Equatorial Bubbles

  • W. J. Burke
  • T. L. Aggson
Part of the Springer Series in Nonlinear Dynamics book series (SSNONLINEAR)


After sunset the bottomside of the equatorial F layer is Rayleigh-Taylor unstable with buoyancy provided by g x B drifting ions that accumulate space charge on the walls of depleted flux tubes. The nonlinear equations for bubble motions are those of incompressible fluidsl. Assuming that buoyancy forces are balanced by drag from shedding vortices into the wake plasma, the model predicts bubbles of radius R have terminal speeds \(U \approx 0.5\sqrt {(Rg)}\). Measurements from DE-2 show a plasma bubble updrafting at ~ 2 km/s, well above model predictions and even accelerating upward at ~ 0.5 g. Magnetic perturbations of ~150 nT were detected on the western wall of the deepest plasma depletion. The electromagnetic variations carry downward Poynting flux, too large for shunting of the g x B current. The perturbation is Alfvénic, radiating from a generator located near the depleted flux tube’s equatorial apex in the plasma at the bubble’s leading edge. We model depleted flux tubes of circular cross sections moving upward through the background plasma. The electric field is uniform inside and a 2-D dipole outside the bubble. Without drag, bubbles accelerate at large fractions of g. The generator current is driven by inertial forces acting on plasma in thin layer at the bubble’s leading edge. Consequent, radiated Alfvén wings2 act as counter-buoyancy drag forces.


Flux Tube Bubble Wall Alfven Wave Magnetic Perturbation Plasma Bubble 
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Copyright information

© Springer-Verlag Berlin Heidelberg 1993

Authors and Affiliations

  • W. J. Burke
    • 1
  • T. L. Aggson
    • 2
  1. 1.Geophysics DirectoratePL/OL-AA, Hanscom AFBUSA
  2. 2.NASA: Goddard Space Flight CenterGreenbeltUSA

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