VIRTUAL - Thesis Defense: Sydney Sroka (MIT MechE)

Speaker: 
Sydney Sroka (MIT MechE)
Date: 
Monday, August 16, 2021 - 11:00am to 12:00pm
Location: 
Virtual via Zoom

Thesis Title: Sea Spray-Mediated Fluxes at Extreme Wind Speeds

Candidate: Sydney Sroka

Date: August 16, 2021

Time: 11:00 am - 12:00 pm ET

Password: Contact Megan Jordan (mkjordan@mit.edu)

 

Abstract

Tropical cyclones are complex systems that are challenging to forecast and model. Since tropical cyclones are powered by the warm ocean surface, the accuracy of intensity forecasts depends heavily on the air-sea interaction scheme. However, at extreme wind speeds the air-sea transition layer becomes replete with sea spray such that there is no longer a well-defined interface. This means that the microphysics of sea spray plays a critical role in mediating the fluxes which control tropical cyclone intensity. The first part of this thesis reviews and synthesizes results from the literature on parameterizations of air-sea enthalpy and momentum fluxes in tropical cyclones, with an emphasis on work that estimated the sea spray-mediated fluxes. The second part of this thesis analyzes the microphysical equations that describe how sea spray mediates enthalpy and momentum. The results from an ensemble of temperature, radius, and speed time histories of evaporating drops suggest that, for sufficiently high wind speeds, the formulation for air-sea exchange can be substantially simplified. The third part of this thesis describes the results from multiphase, direct numerical simulations of the sea surface subject to a strong forcing. The preliminary results showed that the vertical transport of liquid water was comparable to the expected volume flux, which is an encouraging outcome for the prospect of being able to supplement sparse observations of sea spray with numerical simulations.  Finally, the fourth part of this thesis presents and analyzes simple models of air-sea heat flux at the mesoscale using reanalysis data, with the goal of determining whether sea surface temperature perturbations in the form of persistent ocean eddies have a significant effect on the total time-averaged heat flux. The findings showed that the mesoscale ocean eddies have a small, but detectable influence on the total time-averaged heat flux in the reanalysis data. This thesis shows how air-sea interaction is a complex and fascinating subject in which many effects from small-scale processes project onto the large-scale dynamics. For tropical cyclones in particular, as model resolution improves, previously unresolved mechanisms will come into focus and help illuminate the workings of these complex natural phenomena.

 

Thesis Committee: 

Professor Gareth McKinley (Chair), Department of Mechanical Engineering

Professor Kerry Emanuel (Advisor), Department of Earth, Atmospheric, and Planetary Sciences

Professor Emilio Baglietto, Department of Nuclear Engineering

Professor Nicolas Hadjiconstantinou, Department of Mechanical Engineering