Geocoronal hydrogen emission variation over two solar cycles

Ground-based hydrogen Balmer-α observations from Northern midlatitudes span multiple solar cycles, facilitating investigation of decadal scale variations, including natural variability in the hydrogen response to solar geophysical changes. Here we present a reanalysis of ground-based hydrogen emission observations from the early 1990s and their comparison with observations obtained in 2000–2001 in the context of the extended Northern Hemisphere midlatitude geocoronal hydrogen emission data set.