Turbulent boundary layers appear when a flow at sufficiently high Reynolds number interacts with a solid surface; this can be in engineering design (e.g. airplane wings), and in the Earth’s atmosphere. A better understanding of the processes in ​atmospheric boundary layers (ABL)and efficient simulations are required e.g. to improve climate predictions, and simulations of wind parks. We propose to develop, implement and optimise the next-level method for ABL, based on high-order accurate discretisation methods, proven stability, state-of-the-art solvers with efficient (accelerator) parallelisation, and advanced models for both the wall boundary conditions and the unresolved turbulent scales. We will produce a SeRC-branded next-generation ABL code to exploit exascale heterogeneous architectures, and apply it in a variety of applications, e.g. droplet dynamics and rain formation where shear and turbulent interfaces are crucial. The initial part of the project will identify whether existing modern codes can be adapted for our purpose, including a number of proven channel codes (e.g. UT Austin), modern cloud codes (e.g. PyCLES from Caltech), compressible climate codes (e.g. ESSENSE from LiU/SMHI). Also, an optimised port of Nek5000 for boundary-layer geometries is an interesting option. We will focus on robust numerical methods with proven stability (e.g. SBP-SAT methodology), together with latest developments in the prescription of boundary conditions. A number of people at various departments (MISU, FLOW, SMHI, NSC, PDC) have expressed clear interest in ExABL, and are willing to contribute both financially and in-kind. SESSI’s contribution will be focused on the performance of ExABL whereas the other partners will contribute their knowledge on numerics and fluids.