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Ultimately the effect of energy input into the ionosphere is Joule heating of ions and consequently of neutrals. The subject has been studied for many years, both from a theoretical approach (Cole, 1962; Vasyliunas & Song, 2005) and on the basis of empirical and physics‐based modeling (e.g., Ahn et al., 1983a; Lu et al., 2016, and many others). In general, the models show significant Joule heat in the auroral zone but little heating outside these latitudes.

As might be expected from the model assessment described in section 1.5 above, when model predictions are compared with observations for specific locations during specific events, there are significant discrepancies between models and data. Examples have been shown by Huang et al. (2016) where measured ion temperatures at DMSP show the largest increases at polar, and not auroral, latitudes. Anomalously high ion temperatures have also been reported from ISR studies at auroral and polar latitudes (Akbari et al., 2017), suggestive of non‐Maxwellian plasma distributions.

Discrepancies also appear when comparisons of neutral density and model predictions are carried out (Shim et al., 2012). Storm‐related neutral density perturbations have been observed poleward of the auroral zone in several event and statistical studies (Lühr et al., 2004; Liu et al., 2010; Huang et al., 2014, 2016).