Given auroral electron and ion distribution functions as observed with satellites in inverted V events, we construct a self-consistent electrostatic field distribution (both parallel and perpendicular to the earth's magnetic field). This field distribution is determined by (1) magnetic mirror forces which cause charge separation for species with different pitch angle distributions; (2) Poisson's equation, which gives the electric field in terms of the charge separation; (3) the ionospheric physics of charge and current conservation, coupled with precipitation sources and recombination losses; and (4) particle distribution functions specified at the equator (and for thermal and backscattered plasma, at the ionosphere). We assume that equatorial particle distribution functions depend on L only through the dependence of the electrostatic potential on L; and assumed factorized form for the potential allows this L dependence to be simply parameterized. These ingredients combine to yield a self-consistent latitudinal scale length of some tens of kilometers, typical for quiet arcs. A variety of particle and field data at and below S3-3 altitude are fit semiquantitatively with the model. We do not consider in this paper physical processes which act in the equatorial magnetosphere although they could well be connected to the processes we do consider through some sort of feedback.