A KINETIC-MODEL OF THE FORMATION OF THE HOT OXYGEN GEOCORONA .1. QUIET GEOMAGNETIC CONDITIONS

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the non linear Boltzmann equation for hot oxygen atoms produced by chemical pr ocesses usually considered as a source of hot oxygen (photodissociatio n of O-2 and dissociative recombination of O-2(+) and NO+ ions). The e volution of the system is described stochastically as a series of rand om Markovian processes. The energy distribution function of the therma l and non-thermal O(P-3) atoms and of the nonthermal O(D-1) atoms is c alculated from the thermospheric collision-dominated region to the exo sphere where the gas flow is virtually collisionless. The model is app lied to equatorial latitudes for conditions of low solar and geomagnet ic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly, perturbed by collisions with the h ot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudes. The number density and tem perature of the nonthermal oxygen atoms are derived from their microsc opic distribution function and found to be in qualitative agreement wi th previous theoretical and experimental estimates.