Plasmasphere effects for GPS TEC measurements in North America

Plasmasphere effects on total electron content (TEC) measurements conducted using Global Positioning System (GPS) receivers are typically neglected for the North American region, because of the relatively high magnetic latitudes there, but model and measurement cases for this region are presented here to demonstrate the magnitude of the effects for GPS TEC measurements away from vertical and for the associated equivalent vertical TEC values. For high solar flux conditions, the effects of high, distant electron content can range up to 25 TEC units for equivalent vertical TEC, or up to 65 TEC units for slant TEC determinations derived from vertical TEC measurements. The effects of the plasmasphere for TEC calibrations conducted in North America include systematic overestimation of the equivalent vertical TEC and excessive latitudinal gradients, especially at night. These may not be readily evident in the calibration results, and some alternatives for addressing these circumstances are considered.