A Caltech Library Service

Magnetospheric access of solar particles and the configuration of the distant geomagnetic field


Evans, Lawrence C. (1972) Magnetospheric access of solar particles and the configuration of the distant geomagnetic field. Dissertation (Ph.D.), California Institute of Technology.


The access of 1.2-40 MeV protons and 0.4-1.0 MeV electrons from interplanetary space to the polar cap regions has been investigated with an experiment on board a low altitude, polar orbiting satellite (OG0-4).

A total of 333 quiet time observations of the electron polar cap boundary give a mapping of the boundary between open and closed geomagnetic field lines which is an order of magnitude more comprehensive than previously available.

Persistent features (north/south asymmetries) in the polar cap proton flux, which are established as normal during solar proton events, are shown to be associated with different flux levels on open geomagnetic field lines than on closed field lines. The pole in which these persistent features are observed is strongly correlated to the sector structure of the interplanetary magnetic field and uncorrelated to the north/south component of this field. The features were observed in the north (south) pole during a negative (positive) sector 91% of the time, while the solar field had a southward component only 54% of the time. In addition, changes in the north/south component have no observable effect on the persistent features.

Observations of events associated with co-rotating regions of enhanced proton flux in interplanetary space are used to establish the characteristics of the 1.2 - 40 MeV proton access windows: the access window for low polar latitudes is near the earth, that for one high polar latitude region is ~250 R behind the earth, while that for the other high polar latitude region is ~1750 R behind the earth. All of the access windows are of approximately the same extent (~120 R). The following phenomena contribute to persistent polar cap features: limited interplanetary regions of enhanced flux propagating past the earth, radial gradients in the interplanetary flux, and anisotropies in the interplanetary flux.

These results are compared to the particle access predictions of the distant geomagnetic tail configurations proposed by Michel and Dessler, Dungey, and Frank. The data are consistent with neither the model of Michel and Dessler nor that of Dungey. The model of Frank can yield a consistent access window configuration provided the following constraints are satisfied: the merging rate for open field lines at one polar neutral point must be ~5 times that at the other polar neutral point, related to the solar magnetic field configuration in a consistent fashion, the migration time for open field lines to move across the polar cap region must be the same in both poles, and the open field line merging rate at one of the polar neutral points must be at least as large as that required for almost all the open field lines to have merged in 0 (one hour). The possibility of satisfying these constraints is investigated in some detail.

The role played by interplanetary anisotropies in the observation of persistent polar cap features is discussed. Special emphasis is given to the problem of non-adiabatic particle entry through regions where the magnetic field is changing direction. The degree to which such particle entry can be assumed to be nearly adiabatic is related to the particle rigidity, the angle through which the field turns, and the rate at which the field changes direction; this relationship is established for the case of polar cap observations.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Physics
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Thesis Availability:Restricted to Caltech community only
Research Advisor(s):
  • Stone, Edward C.
Group:Space Radiation Laboratory
Thesis Committee:
  • Unknown, Unknown
Defense Date:22 September 1971
Funding AgencyGrant Number
NASANAS 5-3095
NASANGL 05-002-007
Record Number:CaltechTHESIS:10132014-144759243
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:8691
Deposited By: Ignis Nguyen
Deposited On:14 Oct 2014 16:51
Last Modified:20 Oct 2014 17:57

Thesis Files

[img] PDF - Final Version
Restricted to Caltech community only
See Usage Policy.


Repository Staff Only: item control page