Predicting the upper atmospheric response to extremes of space weather forcing

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 Currently, the most state-of-the-art whole atmosphere models include limited and outdated parameterisations of the ionospheric electric field, based on decades old datasets and assumptions, which do not allow for realistic time-variability or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.

This project will have wider impact beyond academic impact regarding a number of areas:

(1) Climate and weather prediction agencies, such as the U.K. Meteorological Office and European Centre for Medium Range Weather Forecasting, have recognised the importance of raising the upper altitude of weather and climate forecasting models to improve prediction accuracy and capabilities. As a result, the electrodynamics of the thermosphere need to be better understood. The development of improved atmospheric modelling capabilities will result in the largest impact outside of academia. Understanding the time-variability of the thermospheric response to space weather that feeds into the global atmospheric dynamics will have a particular impact in this area. The MetOffice in particular are currently working towards expand the height of their Whole Atmosphere Modelling capabilities and they will be interested in learning how they can build their model to encompass the ionosphere and thermosphere in a physically representative way. Our scientific findings will inform their work as the project progresses and it will have a lasting effect by informing future generations of models, which means our work will have a short-term impact (months) ranging to very long-term (decades).

(2) Agencies such as the Ministry of Defence, commercial airlines, and electricity supply companies will benefit from a better understanding of the geospace environment. Feedback from the lower atmosphere to the ionosphere and thermosphere can produce significant effects that are not well reproduced in existing models. In particular, when high solar activity causes an increase in the level of geomagnetic activity, astronauts and commercial spacecraft can be endangered and power systems on the Earth can be damaged by induced electrical current surges. Our studies of geomagnetic storms and other space weather events will provide valuable new insights into the physics of these highly energetic phenomena. This impact will primarily be long term, as future decisions and models for space weather may be based on our findings.

(3) Schools, amateur associations and the general public have an established interest in space research evidenced by television programmes such as the BBC's Stargazing Live, that have focussed on near-Earth space and space weather, increasing readership of websites such as AuroraWatchUK, and engagement with university knowledge exchange programmes. Space weather science is central to this project and many aspects of our work will be used to continue our established public engagement activities and outreach projects. The impact in this area will be over the course of the project.