The thermosphere is the uppermost layer of our atmosphere at the edge of space (85 to 1000 km altitude). Within this region orbit thousands of satellites worth billions of pounds that provide essential modern services including satnav, satcomms, and remote sensing. There are also many thousands more orbiting pieces of man-made space debris which present a significant risk to operational satellites because of the chance of collision. We have now passed a tipping point where the increase in debris from collisions exceeds losses, leading to a net growth of the space debris population and thus ever-increasing risk of collisions.
Short- and long-term predictions of satellite and debris trajectories are vital to avoid the destruction of satellites in low-Earth orbit. A major factor limiting factor is knowing the density of the thermosphere, which can vary by up to 800% during extreme times. The variability is due to effects in near-Earth space from disturbances on the Sun, collectively called space weather. In the polar regions, where there is the greatest concentration of satellites, the largest uncertainties in thermospheric density arise from “Joule” heating. This is caused by collisions between electrically-charged and neutral particles in the thermosphere, driven by space weather. Crucially, we have yet to properly understand when and where Joule heating will occur and how predictable it is.Accurate models and prediction of Joule heating are vital to safeguard the space assets on which modern society depends.
In this project we will develop a better understanding of Joule heating by analysing more than a decade of data from two major international polar instrument networks. We will use a statistical method developed in meteorology called Empirical Orthogonal Function (EOF) analysis, which is capable of uncovering the underlying patterns in a large, noisy data set. In this way we will both resolve the Joule heating in unprecedented detail and separate it into patterns which depend to greater or lesser degrees on the solar sources of space weather. Since these sources can be observed before they cause space weather at Earth, this will allow us to quantify the limits of predictability of the Joule heating. By then assessing the relationship between the Joule heating and satellite trajectories, this will allow us to describe which orbital paths are most at risk from space weather.