The relation between GPS loss of locks and the Interplanetary Magnetic Field orientation: Swarm observations

Swarm enabled researchers to investigate the disturbing phenomena that have affected spacecraft transiting in the F-region ionosphere over the last ten years, in addition to the mission's primary scientific goals. Indeed, plasma density irregularities in the ionospheric region traversed by Swarm satellites can affect both the phase and amplitude of electromagnetic waves propagating through it. As a result, the accuracy and reliability of the Global Navigation Satellite System's (GNSS) performance may be compromised. In the worst-case scenario, a GNSS signal interruption could occur while a Loss of Lock (LoL) event is taking place. This type of events appears to be important in the space weather framework, as it is favored by increased solar activity and disturbed geomagnetic conditions. The high-latitude ionospheric region is particularly impacted by these GNSS signal interruptions.

Here, we look into how the orientation of the interplanetary magnetic field affects the growth of the plasma irregularities that give rise to GPS LoL events. We use LoL events recorded between July 15, 2014, and December 31, 2021, onboard two of the three Swarm satellites, and examine how the orientations of the interplanetary magnetic fields affect the GPS LoL events distribution in magnetic local time and magnetic latitude, in both hemispheres. The results show that there is a clear dependence on the IMF orientation in the y-z plane. The effect of the IMF x component on the LoL distribution is found to be linked to the IMF y component, mainly due to the IMF spiral structure. The results are discussed considering the ionospheric convection patterns as reconstructed by SuperDARN radar observations. The capacity provided by Swarm to track these events and study their dependence on solar, interplanetary, and geophysical parameters may pave the way for a further development of LoL hazard maps at high-latitudes, and thus significantly contribute to space weather effect mitigation.