A Conjunction of Pc5 ULF Waves From Spaceborne and Ground‐Based Observations

Abstract

Large scale (low wavenumber m) ultra‐low frequency (ULF) waves observed in the inner magnetosphere can propagate into the ionosphere and to the ground, which are recognized as magnetic pulsations by ground‐based magnetometers. We present the conjunctive observations of Pc5 ULF waves from Van Allen Probes (at ∼6MLT, earlier), GOES13 (at ∼1MLT, later), SuperDARN radar (at ∼6MLT), and ground magnetometers. The phase shifts of the waves observed by satellites at different MLTs indicate westward propagation from the noon sector. The traveling Alfven waves are thought to propagate along the field line and reflect mostly at the ionosphere, while a few wave energy leak from the ionosphere to the ground. Thus, we suppose that standing waves are observed by the spacecraft while traveling signals are observed by the ground‐based magnetometers in the form of electromagnetic waves. By mapping the ground magnetic pulsations to the magnetic equatorial plane (which depends on the total ionosphere conductivity from IRI and MSIS model), the expected ULF waves match well with the satellite observations. Besides, it suggests that the ionosphere conductivity can be estimated from the conjunctive ULF waves observed on the ground and in the magnetosphere. The calculated total conductivity is 15–30% higher than the model.