Observations and Modelling of Joule heating in the Sub-Auroral Ionosphere

Day, Elliott and Grocott, Adrian and Wild, Jim and Walach, Maria (2024) Observations and Modelling of Joule heating in the Sub-Auroral Ionosphere. PhD thesis, Lancaster University.

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Abstract

Collisional interactions between plasmas and neutrals in Earth’s upper atmosphere results in one of the largest sinks of magnetosphere-ionosphere-thermosphere energy: Joule heating. At mid, and specifically sub-auroral latitudes, a combination of electrodynamical and neutral wind drivers contribute to the produced Joule heating. The individual drivers are less well understood than at high-latitudes. The Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM) is one of the most used within the scientific community to study Joule heating. Due to limited validation and the uncertainties in the mid-latitude drivers, little is known about its performance at the mid-latitudes. This thesis investigates the mid-latitude ion and neutral interactions and resulting Joule heating, while comparing our findings to outputs from TIEGCM. In Chapter 3 we identify an interval of co-located ion and neutral observations by the Blackstone (BKS) Super Dual Auroral Radar Network (SuperDARN) radar and the Ann Arbor (ANN) North American Thermosphere Ionosphere Observing Network (NATION) Fabry-Perot interferometer (FPI) respectively, and compare our outputs to the TIEGCM model. Despite geomagnetically quiet conditions, we observe strong sub-auroral ion and neutral flows, which TIEGCM does not model due to a lack of dynamic sub-auroral drivers in the model. In Chapter 4, we estimate the local Joule heating rates from the observations in Chapter 3. We find that the excited ion motion drives Joule heating enhancements and that the neutrals account for between 24% and 42% of the total Joule heating, while the Joule heating magnitudes produced by TIEGCM are smaller and driven by the neutrals instead. Finally in Chapter 5, we statistically analyse observed sub-auroral ion velocities and find that while low velocity events are modelled well, extreme Joule heating events cannot be represented in TIEGCM. Furthermore the direction of the neutral wind effectively modulates the total Joule heating, by up to 4 orders of magnitude.