The effects of ionospheric outflow on ICME and SIR driven sawtooth events

Abstract

Magnetosphere sawtooth oscillations have been observed during interplanetary coronal mass ejection (ICME) events, when the solar wind conditions are relatively steady, and during periods when the interplanetary magnetic field (IMF) fluctuates between northward and southward, as during interplanetary stream interaction regions (SIR). The impact of ionospheric outflow on the ICME‐driven 18 April 2002 and SIR‐driven 24 October 2002 sawtooth events is investigated using a multifluid adaptation of the Lyon‐Fedder‐Mobarry global simulation. The mechanisms that generate the sawtooth oscillations are investigated by comparing a baseline simulation without outflow and a simulation that includes an O+ outflow model. The ionospheric outflow is regulated by a statistical relationship between Alfvénic Poynting flux and O+ ion outflow flux. In the baseline simulation for the 18 April 2002 ICME‐driven event, one substorm is observed that is generated by the southward turning of the IMF, after which the magnetosphere‐ionosphere system settles into a quasi‐steady convection mode. When outflow is included, quasi‐periodic substorms are observed suggesting that the sawtooth oscillations are generated internally by the effects of the O+ ions. In contrast, during the 24 October 2002 SIR‐driven event, quasi‐periodic substorms are generated regardless of whether outflow is included or not. For this event, the generation and triggering of the substorms is controlled by the external driving of the solar wind. For both events, when outflow is included, the signatures of the substorms are more intense and are more noticeable across a wider range of local times than in the baseline simulations.