The access of 1.2-40 MeV protons and 0.4-1.0 MeV electrons frominterplanetary space to the polar cap regions has been investigated withan experiment on board a low altitude, polar orbiting satellite (OG0-4).
A total of 333 quiet time observations of the electron polar capboundary give a mapping of the boundary between open and closed geomagneticfield lines which is an order of magnitude more comprehensive thanpreviously available.
Persistent features (north/south asymmetries) in the polar cap protonflux, which are established as normal during solar proton events,are shown to be associated with different flux levels on open geomagneticfield lines than on closed field lines. The pole in which these persistentfeatures are observed is strongly correlated to the sector structureof the interplanetary magnetic field and uncorrelated to the north/southcomponent of this field. The features were observed in the north (south)pole during a negative (positive) sector 91% of the time, while thesolar field had a southward component only 54% of the time. In addition,changes in the north/south component have no observable effect on thepersistent features.
Observations of events associated with co-rotating regions of enhancedproton flux in interplanetary space are used to establish thecharacteristics of the 1.2 - 40 MeV proton access windows: the access windowfor low polar latitudes is near the earth, that for one high polarlatitude region is ~250 R⊕ behind the earth, while that for the otherhigh polar latitude region is ~1750 R⊕ behind the earth. All of theaccess windows are of approximately the same extent (~120 R⊕). The followingphenomena contribute to persistent polar cap features: limitedinterplanetary regions of enhanced flux propagating past the earth,radial gradients in the interplanetary flux, and anisotropies in theinterplanetary flux.
These results are compared to the particle access predictions ofthe distant geomagnetic tail configurations proposed by Michel and Dessler,Dungey, and Frank. The data are consistent with neither the model ofMichel and Dessler nor that of Dungey. The model of Frank can yield aconsistent access window configuration provided the following constraintsare satisfied: the merging rate for open field lines at one polar neutralpoint must be ~5 times that at the other polar neutral point, relatedto the solar magnetic field configuration in a consistent fashion,the migration time for open field lines to move across the polar capregion must be the same in both poles, and the open field line mergingrate at one of the polar neutral points must be at least as large asthat required for almost all the open field lines to have merged in0 (one hour).The possibility of satisfying these constraints is investigatedin some detail.
The role played by interplanetary anisotropies in the observationof persistent polar cap features is discussed. Special emphasis is givento the problem of non-adiabatic particle entry through regions where themagnetic field is changing direction. The degree to which such particleentry can be assumed to be nearly adiabatic is related to the particlerigidity, the angle through which the field turns, and the rate at whichthe field changes direction; this relationship is established for thecase of polar cap observations.
