Time-dependent modeling of Alfvénic precipitation observed in the ionosphere

Abstract. Small scale dynamic auroras are generally related with dispersive Alfvén waves. Due to the short spatial and time scales involved, investigating the effects of this type of auroral precipitation on the ionosphere is challenging. In this study, we address this challenge by introducing a recently developed and improved time-dependent electron transport code entitled AURORA. We use high-resolution data from the Visualizing Ion Outflow via Neutral Atom Sensing-2 (VISIONS-2) sounding rocket campaign as input for the modeling. The rocket flew through the active dayside auroral region and the onboard instrumentation measured signatures of Alfvénic precipitation varying on sub-second timescales. With the code, we model the propagation of the electron flux in the ionosphere and we provide a first-order validation for the case studied here. We then present two examples illustrating the modeling capabilities by showing ionization and optical emission rates for Alfvénic and mono-energetic precipitation with similar downward energy flux. The model results show variations in the height of maximum ionization from about 120 km to 180 km in less than 0.3 s for the Alfvén case, while it remains stable at about 160 km for the mono-energetic case. Additionally, For Alfvénic precipitation, the modeled intensities exhibit a short lived peak at 6730 Å and 4278 Å, while for the latter case, the intensities are constant and dominated by 6730 Å and 8446 Å emissions. The modeling introduced here opens for possibilities to further advance our understanding of small scale dynamic aurora.