I propose to develop an innovative interdisciplinary model framework to refine the estimate of aerosol indirect effect (i.e. influence of atmospheric aerosol particles on cloud properties), which remains the single largest uncertainty in the current drivers of climate change. A major reason for this uncertainty is that current climate models are unable to resolve the spatial scales for aerosol-cloud interactions. We will resolve this scale problem by using statistical emulation to build computationally fast surrogate models (i.e. emulators) that can reproduce the effective output of a detailed high-resolution cloud-resolving model. By incorporating these emulators into a state-of-the-science climate model, we will for the first time achieve the accuracy of a limited-area high-resolution model on a global scale with negligible computational cost. The main scientific outcome of the project will be a highly refined and physically sound estimate of the aerosol indirect effect that enables more accurate projections of future climate change, and thus has high societal relevance. In addition, the developed emulators will help to quantify how the remaining uncertainties in aerosol properties propagate to predictions of aerosol indirect effect. This information will be used, together with an extensive set of remote sensing, in-situ and laboratory data from our collaborators, to improve the process-level understanding of aerosol-cloud interactions. The comprehensive uncertainty analyses performed during this project will be highly valuable for future research efforts as they point to processes and interactions that most urgently need to be experimentally constrained. Furthermore, our pioneering model framework that incorporates emulators to represent subgrid- scale processes will open up completely new research opportunities also in other fields that deal with heterogeneous spatial scales.

This project will address a major unsolved question in geosciences: how strongly is our planet's atmosphere subjected to forcing from space? The mesosphere–lower-thermosphere–ionosphere (MLTI) is the boundary of the Earth environment, and as such it undergoes forcing from above, in particular at high latitudes. The forcing includes charged particle precipitation from near-Earth space, associated with electric currents producing Joule heating in the upper atmosphere. It also involves trace gas production in the mesosphere which catalytically destroy ozone – including down to the stratosphere when long-lived species descend to lower altitudes – as well as neutral wind changes and atmospheric wave generation. However, these effects in terms of MLTI energetics, chemistry, and dynamics are largely unquantified, leading to unknown uncertainties in lower atmosphere and climate model results. The LOUARN project will bridge this gap by adopting a multidisciplinary approach, combining knowledge and methods from space physics and atmosphere sciences. With LOUARN, I aim at unravelling the MLTI forcing from space by using cutting-edge ground-based instruments measuring both the ionised medium and the neutral gas properties, together with numerical simulations of the upper atmosphere and novel citizen science methods. My objectives are to (1) quantify the energy deposited into the MLTI during geomagnetic disturbances, (2) provide accurate upper-boundary conditions on the ozone balance for atmosphere and climate models, and (3) characterise the wind and atmospheric wave response to this driving from space. My expertise in ionospheric physics and its driving from near-Earth space processes, along with my leadership in auroral citizen science, puts me in an ideal position to address this ambitious challenge. I aim at a breakthrough in atmosphere–ionosphere–space couplings with impacts on atmosphere and climate sciences and on solar–terrestrial physics.