Recent studies highlight the importance of small-scale coherent structures associated with atmospheric convection and (sub-)mesoscale ocean dynamics on atmosphere-ocean feedbacks in key regions of the climate system. In state-of-the-art coupled climate models, such small-scale atmosphere-ocean feedbacks are either ignored or rely on parameterizations, which may lead to model biases and energetic inconsistencies. In this subproject, we investigate these small-scale coupling mechanisms using coupled simulations on a global scale, based on resolutions allowing us, for the first time, to directly simulate the underlying key processes. More specifically, we focus on the following topics:
(i) With the help of storm-resolving coupled simulations and data from a large-scale field experiment conducted in the tropical Atlantic, we investigate the interaction of shallow atmospheric convection and near-surface processes in the ocean. A special focus here is on the dynamics of thin (meter-scale) "diurnal warm layers" and "rain layers" at the ocean surface, their role in mediating air-sea fluxes, and their feedback with atmospheric convection (see figure 1).
(ii) We also study the effect of parameterized submesoscale dynamics like baroclinic instability and symmetric instability on atmosphere-ocean coupling (see figure 2). To this end, the role of submesoscale dynamics on atmosphere-ocean feedbacks in selected key regions of the climate system is investigated with the help of coupled global simulations at unprecedented resolution (see figure 3). These simulations are also used to develop and test parameterizations of these effects in more coarsely resolved global ocean-atmosphere models. Our final goal is to obtain an integral estimate of the role of submesoscale dynamics on the coupling between the atmosphere and the ocean.
(iii) Finally, we aim to clarify the effect of resolved mesoscale eddies on air-sea coupling (see figure 2), develop a new stochastic parameterization that represents such effects in surface fluxes of heat and momentum, and investigate the global and regional impact of the parameterization in coupled atmosphere-ocean simulations that cannot use high enough resolution to represent those processes explicitly.
Peng, J., Dräger-Dietel, J., North, R. P., & Umlauf, L. (2021). Diurnal Variability of Frontal Dynamics, Instability, and Turbulence in a Submesoscale Upwelling Filament, J. Phys.Oceanogr., 51(9), 2825-2843, doi: https://doi.org/10.1175/JPO-D-21-0033.1.
Li, Q., Bruggemann, J., Burchard, H., Klingbeil, K., Umlauf, L., & Bolding, K. (2021). Integrating CVMix into GOTM (v6.0): a consistent framework for testing, comparing, and applying ocean mixing schemes. Geosci. Model Dev., doi: https://doi.org/10.5194/gmd-14-4261-2021.
Carpenter, J. R. , Rodrigues, A., Schultze, L. K. P., Merckelbach, L. M., Suzuki, N., Baschek, B. & Umlauf, L. (2020). Shear Instability and Turbulence Within a Submesoscale Front Following a Storm. Geophys. Res. Lett., doi: https://doi.org/10.1029/2020GL090365.
Rackow, T., & Juricke, S (2019). Flow‐dependent stochastic coupling for climate models with high ocean‐to‐atmosphere resolution ratio. Q. J. Roy. Meteor. Soc., 1-17, https://doi.org/10.1002/qj.3674.