ISOM 1.0: A fully mesoscale-resolving idealized Southern Ocean model and the diversity of multiscale eddy interactions

Abstract. We describe an idealized Southern Ocean model (ISOM 1.0) that contains simplified iconic topographic features in the Southern Ocean and conduct a fully mesoscale-resolving (2 km) simulation based on the Massachusetts Institute of Technology general circulation model (MITgcm). The model obtains a fully developed and vigorous mesoscale eddying field with a k^-3 eddy kinetic energy (EKE) spectrum and captures the topographic effect on stratification and large-scale flow. To make a more naturally conceptual introduction of large eddy simulation (LES) methods into ocean mesoscale parameterization, we propose the concept of mesoscale ocean direct numerical simulation (MODNS). A qualified MODNS dataset should resolve the first baroclinic deformation radius and ensure that the affected scales by the dissipation schemes are sufficiently smaller than the radius. Such datasets can serve as the benchmark for a priori and a posteriori tests of LES schemes or mesoscale ocean large eddy simulation (MOLES) methods into ocean general circulation models (OGCMs). The 2 km idealized simulation meets the requirement of MODNS and also captures part of the submesoscale processes. Therefore, its output can be a type of MODNS and provide reliable data support for relevant a priori and a posteriori tests. We also illustrate the diversity and high complexity of multiscale eddy interactions related to mesoscale processes. We emphasize the importance of submesoscale phenomena on the evolution of mesoscale processes when mesoscale activities are vigorous and of high eddy number density. In addition, we use the model to conduct multipassive tracer experiments and reveal guidelines for the initial settings of passive tracers to delay the homogenization process and ensure the mutual independence of tracers over a long period.