Emulating the Thermosphere-Ionosphere Electrodynamics General Circulation Model (TIE-GCM)

We analyse the response of the TIE-GCM computer model of the upper atmosphere to atmospheric tides at its lower boundary and to variations of night-time ionization rates. TIE-GCM is an expensive code, and we choose to use our thirty evaluations of the model to construct an emulator, and then use the emulator for the analysis. TIE-GCM has some non-standard features, namely a periodic input, and modeloutput which is a periodic function of time, and our emulator must account for these. With only a limited number of evaluations our prior choices are important: we model the interaction between two of the inputs explicitly, as well as making informed choices for the emulator’s prior R2 and predictive variance. We validate our choices with detailed predictive diagnostics. Using the updated emulator we are able to quantify TIE-GCM’s response to atmospheric tides and night-time ionization rates.