Air-sea interactions at small-scales (from O(10−) to O(100km)). Why does it matter ? Implications for regional atmospheric dynamics and associatedrainfall.

– Fabien Desbiolles, Université de Milan –

Résumé :

The climate modeling community faces numerous challenges in representing crucial regionalto-mesoscale circulation processes, notably resulting in an inadequate representation of key features, including regional cloud cover and rainfall. Indeed, complex and nonlinear regional atmospheric dynamics are notably driven by a large number of processes acting from large to local scales, and conversely. Particularly, a key role in shaping oceanic and atmospheric dynamics is attributed to the local thermodynamic imbalance between the two fluids and the highly variable exchange of heat and momentum at the interface. Ubiquitous in the ocean, mesoscale eddies and fronts (O(10 − 100km)) impact air column stability, dynamic adjustment, convective processes, low-level cloud formations, and secondary marine atmospheric boundary layer (MABL) circulations, driving air-sea flux variability which can fluctuate over several orders of magnitude.

This presentation aims to address a non-exhaustive overview of thermodynamical processes between the low-level atmosphere and the upper ocean. As an example, the so-called Downward Momentum Mixing (DMM) and Pressure Adjustment (PA) are the two main thermal feedback mechanism which affect MABL thermodynamics. The DMM-mediated response of the atmosphere implies turbulence and large eddies in the lower troposphere. They are affected by atmospheric stability, modified by local SST, resulting in enhanced vertical mixing and larger surface winds over warmer waters. For the PA-mediated response, the thermodynamic adjustment of air density to the underlying SST structures and the subsequent changes in atmospheric pressure drive secondary circulations. We aim here to disentangle the effects of these processes, explore the environmental conditions that favor them and study their effects on larger-scale variability and associated rainfall. From local to remote responses, from small to regional/global scales, form sub-daily to seasonal, the mesoscale air-sea interactions and their associated thermal and dynamical feedbacks represent an essential component of the climate variability.

Lien Zoom :

https://ird-fr.zoom.us/j/82431569672?pwd=VlFtakxHdTlOV3UvM1ZRMFJSZEU3UT09