## LSU Historical Dissertations and Theses

#### Title

Global Zones of Particle Precipitation.

1988

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

John P. Wefel

#### Abstract

Magnetospheric particles are precipitated at low altitude all over the globe. The study of the physics of the equatorial global zone is important for geospace environment modeling, for knowing the loss processes of radiation belt particles and for the Space Station Project. The equatorial global zone was investigated by the Phoenix-1 experiment on board the S81-1 mission in May through November, 1982. The global profile of the peak flux of quasi-trapped protons follows the line of minimum magnetic field strength, with a FWHM of $\sim$13$\sp\circ$ in latitude. The pitch angle distribution anisotropy index is found to be 19 $\pm$ 2, and the protons show no statistically significant longitude dependence. Contrary to an earlier observation (Moritz, 1972), we find a strong altitude dependence. Within the altitude range of observation ($\sim$160-285 km) the proton flux varies as the fifth power of altitude. This altitude gradient indicates a strong depletion of source neutrals, coupled with charge exchange loss and ionization loss of protons. A power law fit to the flux values of the previous observations, yields an energy spectral index of $-$2.55 $\pm$ 0.11, implying that the mean energy of the protons observed by Phoenix-1 is 1.3 MeV. For comparison of the observed proton population with the earlier observation, the response functions of both instruments--the monitor telescope on the S81-1 mission, and the EI-92 telescope on the Azur mission--have been calculated as a function of the satellite orbital parameters and instrument geometry, both in the dipole and real magnetic field models. The undepleted source model (altitude dependent power law valid up to 450 km) predicts a population enhancement by an order of magnitude, while the depleted source model (altitude dependence turns over beyond 300 km) predicts an enhancement by $\sim$1.5, both indicating a possible temporal variation of the flux. The enhanced flux indicates either a local time effect, in which case the night time flux exceeds the daytime flux, or different solar conditions which cause an increased generation of energetic neutral hydrogen, or, possibly, some of both effects.

288

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