[A-OS11] Ocean Mixing Frontiers

[AOS11-P01] Sensitivity of the ocean state estimation to the vertical distribution of tidally induced far-field mixing

*Satoshi Osafune¹, Shinya Kouketsu¹, Toshimasa Doi¹, Nozomi Sugiura¹, Shuhei Masuda¹ (1.Japan Agency for Marine-Earth Science and Technology)

Keywords:tide, vertical mixing, thermohaline circulation

Vertical mixing plays an important role in determining the large-scale ocean circulation including the meridional overturning and the distribution of water properties. The breaking of internal tide is a major source of interior vertical mixing below the surface mixed layer. Recent numerical studies have shown the importance of incorporating tidally induced far-field mixing in addition to the near-field mixing. In our previous study under the OMIX project, we conducted a linear optimization experiment to reproduce the climatological distribution of water properties with an ocean general circulation model using tidally induced near- and far-field mixing schemes with an assumption that diffusivity is vertically constant for far-field mixing. The optimized model performed reasonably well in reproducing the deep-water properties of the Pacific Ocean. However, the reproducibility of water mass distribution is degraded in some places, especially in the sub-surface-intermediate layers, when compared with the optimized state in the earlier version of our model using semi-empirical interior mixing schemes. This shortcoming may be overcome by improving model interior mixing. Our new model uses the far-field mixing scheme only related to the wave-wave interactions, but the far-field mixing is caused through various mechanisms, on which the vertical structure of diffusivity depends. In this study, we conducted numerical experiments using our new model but with different vertical distribution function for the far-field mixing on the basis of a previous semi-empirical scheme. We show the incorporation of a vertical structure into the far-field mixing representation can possibly resolve the upper layer issues in our state estimation. It can be a clue to uncover nature of vertical mixing in the real ocean. We will discuss the effectiveness of the proposed implementation in our experiments, referring the recent vertical mixing schemes suggested in the theoretical studies.