Special ClimaTea


Friday, November 8, 2019, 12:00pm


HUCE Seminar Room MCZ 440

Speaker: Professor Yuliya Troitskaya from Russian Academy of Sciences

Title: "Sea spray at strong winds: mechanisms of production and role in a hurricane mechanics and thermodynamics".

Abstract: Sea spray is a typical element of the marine atmospheric boundary layer (MABL) of large importance for marine meteorology, atmospheric chemistry and climate studies. They are considered as a crucial factor in the development of severe storms, since they can significantly enhance exchange of mass, heat and momentum between the ocean and the atmosphere. This exchange is directly provided by spume droplets with the sizes from 10 microns to a few millimeters mechanically torn off the crests of a breaking waves and fall down to the ocean due to gravity. However, the fluxes associated with the spray are strongly uncertain, since even the mechanism of spume droplets’ formation in extreme winds is unknown. Basing on high-speed video here we identify it as the bag-breakup mode of fragmentation of liquid in gaseous flows known in a different context. This regime is characterized by inflating and consequent bursting of the short-lived objects, bags, comprising sail-like water films surrounded by massive liquid rims then fragmented to giant droplets with sizes exceeding 500 micrometers. From first principles of statistical physics we develop statistical description of these phenomena and show that at extreme winds the bag-breakup is the dominant spray-production mechanism.

These findings provide a new basis for understanding and modeling of the air-sea exchange processes at extreme winds. Boosting the exchange processes by giant droplets can provide the pronounced increase in the air-sea thermal energy flux crucial for the observed fast intensification of hurricanes. We also discuss how the combined effect of spume droplets torn from the crest of waves by wind and foam on the water surface can explain the hitherto enigmatic reduction of the surface drag coefficient at extreme winds. (Related paper # 1, 2)