Anomalous Enhancement of Thermospheric Hydrogen Density Prior to the Severe Storm of September 7-8, 2017

Abstract:

Atomic hydrogen is an important aspect of Space Weather manifestations in the near-Earth space environment. It plays a key role for the plasmasphere, exosphere, and the nighttime ionosphere. It directly impacts the rate of plasmasphere refilling after strong magnetic storms as it is the primary source of hydrogen ions. It is the source of the geocorona, which significantly affects ring current decay during the recovery phase of magnetic storms.

Our previous measurements with the Kharkiv incoherent scatter radar (49.6° N, 36.3° E) and observational based simulations with field line interhemispheric plasma (FLIP) model conducted during magnetically quiet periods of 2016–2018 showed that the hydrogen density was generally a factor of 2 higher than from the NRLMSISE-00 model (Kotov et al., 2018).

Significant enhancement of the thermospheric hydrogen density occurred prior to the severe storm of September 7-8, 2017. We found that during the nights of September 5 to 6 and September 6 to 7, the thermospheric hydrogen density had to be at least a factor of 4 higher than the values from NRLMSISE-00 model i.e. ~100% higher than expected from our previous studies. This result is very surprising, nothing similar was observed before. Such high hydrogen densities may have implications for Space Weather by significantly affecting the development of the further severe storms. We discuss the possible mechanisms that could lead to the enhancement of hydrogen density.

References:

Kotov, D. V. et al. (2018). Geophys. Res. Letters, 45, 8062–8071. https://doi.org/10.1029/2018GL079206.