Diffuse Auroral Precipitation Effects on Ionospheric Conductance During Magnetic Storms: Comparison of Simulated and Incoherent Radar Scatter-Inferred Conductance

We investigated the effects of storm-time diffuse auroral electron precipitation on ionospheric Pedersen and Hall conductivity and conductance during the CME-driven St. Patrick's Day storms of 2013 (min Dst = −131 nT) and 2015 (min Dst = −233 nT). These storms were simulated using the magnetically and electrically self-consistent RCM-E model with STET modifications, alongside the B3C auroral transport code to compute ionospheric conductivities and height-integrated conductance. The simulation results were validated against conductance inferred from Poker Flat Incoherent Scatter Radar (PFISR) and Millstone Hill Incoherent Scatter Radar (MHISR) measurements. Our simulations show that the magnetic latitude and local time distribution of Pedersen and Hall auroral conductance strongly correlate with diffuse electron precipitation flux, with the plasmapause marking the low-latitude boundary of conductance. Simulated Pedersen/Hall conductance agrees reasonably well with PFISR measurements at 65.9° MLAT during diffuse auroral precipitation. During the intense 2015 storm, diffuse aurora extended down to 52.5° MLAT, with simulated conductance agreeing within a factor of two with MHISR observations. Discrete auroral arcs observed during both storms enhanced PFISR conductance by tens of siemens, though these enhancements were not captured by the model. Additionally, the simulated electric intensity showed development of sub-auroral polarization streams (SAPS) and dawn SAPS features and followed the general trend of Poker Flat electric intensity at 65.9° MLAT during diffuse aurora, despite being updated every 5 min. The overall agreement between simulated ionospheric conductance and electric intensity with observations highlights the model's capability during diffuse auroral precipitation.