Predicting the upper atmospheric response to extremes of space weather forcing

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Space weather describes the effects of solar activity on our planet, its atmosphere and space environment. For example, energetic particles from the Sun can impact and damage Earth-orbiting spacecraft. Electric fields driven by solar winds can modify the upper atmosphere causing heating and changing the propagation characteristics of radio waves for communications systems. Rapid changes produced in the Earth's magnetic field can induce electrical currents in grounded technical infrastructure. Understanding space weather is thus an important scientific goal, and given the relatively sparse nature of observatories capable of measuring space weather effects directly, it is clear that a capability to model space weather is required.To model the atmospheric effects of space weather we need to consider the whole atmosphere. Although space weather effects are most apparent at high-altitudes, the dynamics of the upper atmosphere - the thermosphere and ionosphere - are driven both from space ('top-down' forcing) and from the atmospheric layers below ('bottom-up' forcing). Even during extreme space weather events such as geomagnetic storms, model studies have shown that the state of the lower atmosphere can influence the thermospheric response. Electric fields are included in ionosphere-thermosphere models to couple the dynamics of the magnetosphere (the region of near-Earth space controlled by the solar wind), and hence the drivers of space weather, to the neutral atmosphere. Currently, the most state-of-the-art whole atmosphere models include limited and outdated parameterisations of the ionospheric electric field, based on decades old datasets and assumptions, which do not allow for realistic time-variability or extreme events to be captured.We propose to utilise our expertise in exploring and modelling ionosphere-thermosphere electrodynamics to bring state-of-the-art ionospheric electric field inputs to the Whole Atmosphere Community Climate Model - Extended (WACCM-X). We will test the new model configurations by running simulations of pre-selected events for which we have observations and measurements of ionospheric and thermospheric flows, densities, and temperatures. The model configuration that is best able to reproduce the observations will then be used to specify global thermospheric parameters for a range of different space weather drivers during intervals of variable solar wind forcing and geomagnetic activity. Our results will enable us to solve a number of outstanding questions on the thermospheric response to space weather and inform the next generation of whole atmospheric modelling and space weather modelling.