Stanford University

*** Ph.D. Thesis/ Oral Defense ***

The Role of Boundary Layer Dynamics in the Intensification of Tropical Cyclones

Ipshita Dey

Friday, September 27, 2024

Green Earth Science 365

Department of Earth System Science

Advisor: Dr. Morgan O’Neill

Tropical cyclones (TCs) are one of the world's most lethal geophysical hazards and their global impact has dramatically increased in the last few decades. The intense winds inside TCs cause significant damage to life and property along with other hazards such as storm surges and torrential rainfall. In this dissertation, we address one of the major challenges in the prediction of maximum winds inside TCs by investigating the complex tropical cyclone boundary layer (TCBL) processes. These processes control the development and intensification of TCs in a favorable environment. We attempt to delineate the multi-scale nature of the TCBL mechanisms, which range from large-scale processes such as surface heating to small-scale instabilities that result in the formation of coherent structures.

Chapter 1 begins with a novel characterization of the TCBL structure that unifies the large-scale thermodynamic and dynamic properties. Next, we study the effects of surface friction and heating on the TCBL structure, which reveals a strong interplay between heat and momentum transfers inside the TCBL, and controls TC behavior. In Chapter 2, we focus on the small-scale coherent structures (O(10 km)) in three-dimensional numerical simulations of the TCBL. A new method to identify the coherent structures in the boundary layer is proposed, which allows a systematic analysis of these features and their overall impacts on the boundary layer dynamics. This study highlights the challenges of capturing these small-scale processes in numerical simulations. Chapter 3 leverages recently available high-resolution surface wind observations from satellites to examine the small-scale coherent structures in TCBL. The observations confirm the findings of idealized simulations and offer new opportunities to study TCBL processes in near real-time.

Zoom link: 

https://stanford.zoom.us/j/5968981061?pwd=Yzg1MTZKS1JvUEsxbTdkLzFEM3BLQT09

Meeting ID: 596 898 1061

Passcode: 072868