Effects of the Ionospheric Conductance on the Dynamics of the Magnetotail

We have carried out a series of numerical experiments designed to evaluate the sensitivity of global magnetohydrodynamic simulations to changes in ionospheric conductance. We multiplied the precipitating energy fluxes due to both strong pitch angle scattering and parallel currents by constant factors in the Robinson et al. (1987, https://doi.org/10.1029/JA092iA03p02565) model and used them as input to a simulated substorm interval on 14 March 2008. We also used the Kaeppler et al. (2015, https://doi. org/10.1002/2015JA021396) model. When we reduced the energy fluxes by a factor of about three (0.34), the agreement on substorm location was best. Larger conductances led to onset at later local times. For multiplication factors greater than one, the magnetotail became line tied and no flows entered the inner magnetotail region. Relatively small (<50%) differences in the conductances lead to major changes in the tail configuration. We calculated auroral indices from the simulations and compared them to observations. None of the models reproduced the DP1 system but, we obtained much better agreement with the observed DP2 system. The model with the basic Robinson formula gave the best agreement with the DP2 system. We also ran a generic simulation with constant solar wind and southward IMF using the basic Robinson et al. model. The results were very similar to those of the event simulation suggesting that the changes were due to the ionospheric boundary condition. In the simulation, the energy flux obtained by assuming strong pitch angle scattering makes a larger contribution to the conductance than the field-aligned current energy flux.