East-West Coast Differences in Ionospheric Electron Density over the Continental US

This paper reports on a new finding of pronounced longitudinal variations in midlatitude electron density in the F region over the continental US manifested as an east-west coast difference, based on observations by a dense network of ground-based GPS receivers and extra-wide coverage experiments by the incoherent scatter radar at Millstone Hill. We find that the evening TEC is substantially higher on the US east coast than on the west, and vice versa for the morning TEC; the longitudinal difference displays a clear diurnal variation. Through an analysis of morning-evening variability in the east-west TEC difference, minimum variability is found to coincide with the longitudes of zero magnetic declination over the continental US. We suggest that these new findings of longitudinal differences in ionospheric electron density at midlatitudes are caused by the longitudinal difference in magnetic declination combined with the effects of thermospheric zonal winds which are subject to directional reversal over the course of a day. This study indicates that longitudinal variations in TEC measurements contain critical information on thermospheric zonal winds. The proposed declination-zonal wind mechanism may also provide a new insight into longitude/UT changes at midlatitudes on a global scale, as well as on some geospace disturbances.