Short‐Term Variability of Equatorial Electrojet Modulation by Solar Tidal and Planetary Waves, as Derived From the Swarm Constellation

Abstract

AbstractESA’s constellation mission Swarm with its three identical spacecraft allows the separation of spatial and temporal variations of wave phenomena. Here we investigate the modulation of the equatorial electrojet (EEJ) amplitude by solar tides and planetary waves. This is the first study to exploit the short‐term variability of these signals in the EEJ. Based on 6‐day data sets of quasi‐simultaneous observations from the well separated Swarm A and Swarm B spacecraft we derive amplitudes and phases of solar tides and prominent planetary waves. Tidal amplitudes can vary by a factor of 2 from week to week. Conversely, the phases of the tides show steady changes, suggesting a stable tidal system. Simultaneous observations at different local times return quite different wave forms, suggesting local time dependent amplitude changes of the tidal signatures in EEJ. DE3 signatures get weak toward evening, while DE2 is strongest around 15:00 magnetic local time. Modulation of the EEJ by planetary waves up to 6 days is also analyzed. Clearly dominating is the westward propagating quasi‐6‐day wave. Derived amplitudes are largest around September and exhibit a secondary occurrence maximum at spring time. Generally, the influence of this planetary wave on the EEJ hardly reaches 30% of that caused by solar tides. For the first time we monitor the influence of eastward propagating ultra‐fast Kelvin waves at 2–3 days period on the EEJ. Related activity occurs sporadically at intervals of 1–4 months and the effects on the EEJ are even smaller than that from the 6‐day wave.