Simultaneous Global Positioning System observations of equatorial scintillations and total electron content fluctuations

One aspect of the Global Positioning System (GPS) is the potential to condu ct geophysical research, and worldwide networks of GPS receivers have been established to exploit this potential. Several research groups have begun u sing this global GPS data to study ionospheric total electron content (TEC) variations, also referred to as GPS phase fluctuations, as surrogates for ionospheric scintillations. This paper investigates the relationship betwee n GPS amplitude scintillations and TEC variations for the same line of sigh t using observations from Ancon, Peru. These observations were taken under equatorial spread F conditions for three nights in April 1997. As expected, only when the spectrum of TEC fluctuations includes significant power at t he Fresnel scale do scintillations appear. We also find that when the TEC f luctuation spectrum includes the Fresnel scale, the Sq scintillation index is roughly proportional to measures of TEC fluctuation for the weak scintil lations observed. The proportionality constant varies from night to night, however, casting doubt on the ability to predict GPS Sq successfully from T EC fluctuation data alone. We also present a simple theoretical phase scree n model and show that if a relationship between TEC fluctuation measures an d Sq exists, that relationship depends on the power spectrum of phase varia tions at the screen. Unfortunately, the available TEC data, at 30 s per sam ple (with some aliasing apparently permitted), offer limited spectral infor mation. A preliminary comparison of 1 s/sample data with the same data deci mated to a 30 s/sample interval suggests, however, that the level of succes sful Sq prediction, based on TEC fluctuation measures alone, is comparable at either sample rate.