Accession Number:

ADA199255

Title:

A Model of the Westward Traveling Surge and the Generation of Pi 2 Pulsations

Descriptive Note:

Corporate Author:

AIR FORCE GEOPHYSICS LAB HANSCOM AFB MA

Report Date:

1988-08-01

Pagination or Media Count:

13.0

Abstract:

A model of the westward traveling surge WTS and the generation of Pi 2 pulsations is presented here. Previous work concentrated on the motion of the WTS as a function of the precipitating electron energy and the concurrent generation of Pi 2 pulsations via feedback instability. Now one examines the physical assumptions used in deriving the present model and the relations between the zero-order and the first-order solutions. Constraints are placed on the electron temperature asymmetry in the plasma sheet by requiring the Pi 2 pulsations to be bounded. It is found that the electron temperature anisotropy in the plasma sheet plays a major role in determining the direction in which the surge will propagate. Narrower surges require greater electron heating parallel to the magnetic field for poleward motion. More energetic electron precipitation is predicted to produce high-frequency Pi 2 pulsations. Pulsations occur in multiple bursts with the time interval between bursts being shorter for shorter field lines. Initial amplitude and phase conditions are crucial in determining the pulse shape. The dominant period of the Pi 2 pulsation is found to be equal to twice the north-south dimension of the surge divided by a term which is proportional to the poleward velocity of the boundary. The poleward surge velocities and Pi 2 pulsation periods, as measured during the magnetospheric substorm of June 23, 1979, are consistent with our model. By noting the direction of the surge motion, one can use the model to estimate the magnitude of the polarization electric field. It is consistent with zero for the onsets considered.

Subject Categories:

  • Atmospheric Physics
  • Radiofrequency Wave Propagation

Distribution Statement:

APPROVED FOR PUBLIC RELEASE