Effects of Region 2 Field-Aligned Currents on Ionospheric Saturation and Resulting Impact on Auroral Radio Emission

We compare the effects of ionospheric saturation on auroral radio emission when driven by the differing sources of an increased ionospheric conductance and a decreased solar wind conductance through the use of the Multiscale Atmosphere Geospace Environment (MAGE) developed by the Center for Geospace Storms (CGS), which includes a coupled global magnetohydrodynamic (MHD) and inner magnetosphere model. This work is of particular interest to the detection of exoplanets, as the current method for estimating radio emission for magnetized Solar System planets, the empirically derived Radiometric Bodes Law (RBL), would predict exoplanets that produce radio emission capable of being detected with current observational methods. Because there have been no confirmed detections of exoplanetary radio emission yet, RBL is expected to be inaccurate for these extreme environments. Ionospheric saturation is a compelling explanation for the reduced radio emission of these exoplanets. While the mechanism by which ionospheric saturation occurs is still unresolved, the conditions for a saturated system are agreed to be met for a planetary system in which the ionospheric (Pedersen) conductance dominates the solar wind (Alfven) conductance. Current analytic models for estimating the effects of ionospheric saturation on auroral radio emission give a proportional relationship between the radio emission and the ratio of Alfven and Pedersen conductances. We explore the effect on radio emission via the two avenues of saturation: increasing Bz (the main mechanism of saturation during geomagnetic storms at Earth), and increasing the ionospheric conductance (the likely cause of saturation at exoplanets). We examine this relation using the MAGE model including the Magnetosphere-Ionosphere Coupler (ReMIX), which is used to compute radio emission from region 1 (high-latitude) field aligned currents (FACs) and the Rice Convection Model (RCM) which is used to compute the radio emission from region 2 (low-latitude) FACs. This work offers a unique insight into testing how region 2 currents scale with the degree of saturation. This work was supported by the Rice Space Institute and the Chancey and Evelyn Juday Endowment.