Magnetic field orientation control of GPS occultation observations of equatorial scintillation

Abstract

We use GPS occultation measurements from three satellites in 2002 to quantify the occurrence probability of equatorial scintillation. The occultations with the highest S4 values are almost exclusively seen near the equator and in the post-sunset sector in agreement with the known MLAT and MLT distribution of equatorial scintillation. Occultations with high S4 values are much more likely to occur when the ray paths are more nearly aligned with the magnetic field. This is attributed to the geometry of the ionospheric bubbles associated with equatorial scintillation. As bubbles are distended in the magnetic field direction, a ray path that is parallel to the magnetic field incorporates a greater path length in depleted regions containing plasma density irregularities. Since scintillation strength increases with irregularity slab thickness, the scintillation occurrence increases for field-aligned conditions. Copyright 2005 by the American Geophysical Union.