An article submitted to Geophysical Research Letters (GRL) titled "ULF wave power features in the topside ionosphere revealed by Swarm observations" and authored by Dr. George Balasis has been accepted for publication. Visit our Publications page for a complete list.
In this letter, we address the issue of the characteristics of ULF wave activity in the topside ionosphere. First, we demonstrate, for the first time, how a ULF wave event is recorded by the Swarm satellites. Moreover, we are capable to make an interesting observation, where the ULF wave signal of the lower pair of satellites is stronger than the signal observed by the higher satellite. If this effect was to be associated with the decay of the Pc3 wave amplitude with altitude in the topside ionosphere then we would be able to confirm a theoretical prediction of compressional ULF wave propagation. Then, we proceed with the analysis of one year of Swarm mission ULF wave observations to generate wave power maps at the satellites' orbiting altitudes. We compare these maps against the wave power map derived from more than 9 years of CHAMP data. Prior to this we have used Langmuir Probe data onboard Swarm and CHAMP to correct the ULF wave power maps for contamination by postsunset Equatorial Spead-F events. In this way, we have obtained the pure compressional Pc3 wave signal.
From these maps, we are able to confirm earlier work (based on CHAMP observations) and provide new observations based on the three-satellite measurements. Swarm maps present features of the ULF wave power in the topside ionosphere with unprecedented detail showing subtle differences in the wave power observed between the upper satellite and the lower pair of satellites and between Swarm and CHAMP missions. By shifting the Swarm B Pc3 power map one hour in magnetic local time we find excellent agreement between the ULF wave power characteristics observed by Swarm A and C and those seen by the upper satellite, which indicates that the satellites probe the same wave events.
Moreover, a puzzling enhancement, not predicted by current ULF wave theories, of compressional Pc3 wave energy was revealed by Swarm in the region of South Atlantic Anomaly.