3D multifluid simulations of the 29 October 2003 Halloween storm show the event to be a good example of conditions which lead to prompt penetration of solar wind electric field into the magnetosphere and prompt acceleration of heavy ionospheric ions. Causal relationships are established that tie solar wind conditions to ionospheric/magnetospheric responses, and the results are correlated with features in both IMAGE/HENA data and AMIE cross‐polar cap potential. The simulations are able to capture the AMIE potentials. Difference between model results and AMIE data can be attributed to the ability of the model to capture fast enhancements in the convective electric field that can be tied with the IMF variations. The total auroral currents show a smoother profile, with the magnetosphere acting like an inductor. A period of southward IMF with simultaneous rapid By rotation leads to the largest currents and ionospheric outflows. These outflows produce an initial ionospheric mass loading of the magnetosphere and originate from the dayside cusp/cleft region. During this period the energization of O+ lags that of H+, consistent with that seen in the HENA data. Once the ionospheric outflows mass load the magnetosphere, prompt acceleration of O+ is seen simultaneous with H+ acceleration. This prompt response is due to the acceleration of O+ ions that have previously flowed into the magnetosphere. The enhanced convective electric field, also leads to enhanced ionospheric outflows that resupply ionospheric ions into the magnetosphere. During this period of resupply, the nightside auroral zone becomes an important contributor to the outflows.