While dual frequency GPS receivers can mitigate the effects of group delay due to the ionosphere quite effectively, both single and dual frequency GPS systems are adversely impacted by scintillation due to ionospheric irregularities. Amplitude fluctuations cause intermittent signal fades and enhancements that result in errors decoding the GPS data messages and also in estimating the range. The deepest fades result in a loss of lock on the signal, which makes the satellite temporarily unavailable for use in the position solution, increasing the dilusion of precision and degrading overall positioning accuracy. Phase fluctuations stress the ability of the receiver to maintain lock and cause “cycle slips” or breaks in the measured phase that can preclude its use in precise positioning applications. When the receiver is no longer able to maintain lock on four or more GPS satellites, a complete loss of positioning service results. The duration of these service “outages” depends on the duration and severity of the disturbances, the geometry of the satellites in view, and the recovery time of the equipment. Ionospheric scintillation occurs primarily in the equatorial and polar regions of the globe, and the effects are most prevalent during periods of high solar activity. In this paper we report on the morphology of ionospheric scintillation and the GPS positioning errors they induce as a function of local time, latitude, longitude, season, and solar activity based on measurements from the AFRL-SCINDA global network of UHF and GPS scintillation monitoring instruments.