Polar tongue of ionization (TOI) and associated Joule heating intensification investigated during the magnetically disturbed period of 1–2 October 2001

We investigate storm‐enhanced density (SED) and polar tongue of ionization (TOI) over North America under southward Interplanetary Magnetic Field conditions. We focus on the 30 September to 1 October 2001 medium magnetic storm's recovery phase (Period 1) and on the last substorm (Period 2) of the following 2 October substorm series. We aim to study the SED‐TOI structure in the time frame of solar wind energy input to the magnetosphere‐ionosphere system and in terms of Joule heating. We utilize GPS total electron content maps tracking SED plume and polar TOI, and spectrogram images detecting polar rain and precipitation void and thus evidencing dayside merging. The variations of merging electric (E) field (EM) and its mapped‐down polar equivalent (EP), energy input efficiency (EIeff), and modeled Joule heating rate (QJoule) are monitored. Results show multiple Joule heating intensification points implying multiple energy deposition points at high latitudes where the magnetic pole was one of the preferred locations. During the higher EIeff (~1.5%) Period 2, the polar TOI was associated with a well‐defined strong QJoule intensification and with polar rain (or void) on the dayside (or nightside). During the lower EIeff (~0.5%) Period 1, only weak QJoule intensification occurred in the absence of both polar TOI and polar rain. We highlight the polar TOI's potential impact on the thermosphere. We conclude that (i) strong (EM ≈ 5 mV/m during Period 2) or weak (EM ≈ 0.5–2 mV/m during Period 1) EM facilitated energy deposition close to the magnetic pole and (ii) EIeff could be used as a diagnostic of the polar TOI's intensity.