New perspectives on equatorial electrojet tidal characteristics derived from the Swarm constellation

Abstract

AbstractUsing 2 years of magnetic field measurements from the Swarm constellation, we present a detailed study of the equatorial electrojet (EEJ) and its longitudinal gradient (ΔEEJ). This study represents for the first time the tidal characteristics derived from the longitudinal gradient of EEJ. Our analysis mainly focuses on the months around August (133 days centered on 15 August, day of year: 161–293) of 2014 and 2015 when the longitudinal wave number 4 (WN4) pattern is known to be most prominent. The EEJ intensity, derived from the average of the Swarm A and C current estimates, peaks around 11:30 LT and exhibits a clear WN4 pattern. These features are compatible with earlier CHAMP observations. The ΔEEJ, which can be considered as a high‐pass filtered result of EEJ, although having much smaller values than the EEJ, exhibits clearly the local time gradient of the EEJ diurnal variation. This kind of high‐pass filtering makes the tidal signatures in ΔEEJ more prominent. The crests of longitudinal WN4 patterns in ΔEEJ have locations different from those of EEJ. Prominent tidal components in ΔEEJ during August months are DE3, DW5, SW3, SW4, SW6, SPW1, SPW2, and SPW4. For a given wave number pattern the westward propagating components are more amplified in ΔEEJ than the eastward ones, which explains their numerous appearance. Using spectral analysis, we can confirm that the observed amplitude ratios of different tidal components between ΔEEJ and EEJ are as expected. Also, the phase differences between ΔEEJ and EEJ fit reasonably the theoretical values. The preferred amplification of westward propagating tides in ΔEEJ allows for a more detailed investigation of these components, which are assumed to be closer related to local electrodynamics processes.