Relationship between Plasma Density Gradients and Swarm GPS Data

GPS signals are subject to disturbances in the polar regions, caused in part by clouds of high density plasma (polar cap patches). For the Swarm satellites, this noise results in positioning errors in the order of centimeters. In this study, we use data from the GPS receiver and compare it to in situ density gradient data from the Langmuir probes. 65 We find that when GPS satellites are in front (azimuth φ=0±20°) of the Swarm, there is a direct proportionality between the density gradient dn/ds and the GPS observable dL4/dt. The same is true for when GPS satellites are positioned behind the Swarm satellite (azimuth φ=180±20°).Our results suggest that dL4/dt measurements from any satellite can be used to extrapolate the distribution of the plasma density gradient in the surrounding volume of the satellite, so that plasma density gradients can be detected from GPS receiver data alone.