25.04.2022: Ocean Circulation and Climate Dynamics Colloquium

When?     Monday, 25. April 2022 at 11 am
Where?    ZOOM meeting room: https://geomar-de.zoom.us/j/88124064587?pwd=VFRNWlk2eEs5WnZsS3J0ckRySGZMdz09

Meeting-ID: 881 2406 4587
Kenncode: 362661

We would like to inform you that this seminar will be recorded. We will only record the presentation without the Q&A part.

Previous studies have arrived at a conclusion that the atmospheric forcing strongly affects the dynamics, stability, and turbulence of submesoscale structures in the surface boundary layer (SBL), focusing particularly on nighttime conditions. The impact of large diurnal variations in the surface heat flux on submesoscale processes remains unclear. Here, we investigated this issue using observational data sets collected from a submesoscale upwelling filament in the Benguela upwelling system. Our data show that during nighttime and early-morning conditions (i.e., the diurnal transition), when solar radiation is still weak, frontal turbulence is generated by a mix of symmetric and shear instability, providing an effective pathway for forward energy cascade. In this situation, turbulent diapycnal mixing is approximately balanced by frontal restratification associated with the cross-front secondary circulation. During daytime, when solar radiation is close to its peak value, the SBL quickly restratifies, the conditions for frontal instability are no longer fulfilled, and SBL turbulence collapses except for a thin wind-driven layer near the surface. When previous studies that focused on nighttime conditions are combined with the finding of this study, a general picture of diurnal variability of frontal dynamics, instability, and turbulence in a submesoscale upwelling filament is revealed.

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