Date of Award

1-1-2016

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Content Description

1 online resource (ii, 228 pages) : illustrations (some color), maps (some color)

Dissertation/Thesis Chair

Christopher D. Thorncroft

Committee Members

Lance F. Bosart, John Molinari, Ryan D. Torn, Frank D. Marks, Christopher S. Velden

Keywords

diurnal cycle, numerical modeling, satellite, tropical cyclone, Cyclones, Meteorology, Atmospheric pressure

Subject Categories

Atmospheric Sciences

Abstract

The research presented in this thesis explores a phenomenon referred to as the tropical cyclone (TC) diurnal cycle (TCDC) and presents satellite, numerical modeling, and observational perspectives pertaining to how it can be monitored, its evolution in time and space, its relevance to TC structure and intensity, and how it manifests in numerical simulations of TCs. Infrared satellite imagery was developed and used to investigate diurnal oscillations in TCs and finds a diurnal pulsing pattern that occurs with notable regularity through a relatively deep layer from the inner core to the surrounding environment. A combination of satellite, numerical model simulations, and aircraft observations found diurnal signals in operationally analyzed radii of 50 kt winds in TCs and in satellite intensity estimates from the Advanced Dvorak Technique and spawned the development of a 24-hr conceptual clock that approximates the temporal and spatial evolution of the TCDC each day. TC diurnal pulses are revealed to significantly impact the thermodynamics and winds in the TC environment and appear as narrow, convectively active rings of high radar reflectivity in NOAA aircraft radar data and are hundreds of kilometers in length. Enhanced nighttime radiational cooling that is particularly favored in the TC outflow layer acts to pre-condition the TC environment in a way that favors triggering of the TCDC and TC diurnal pulses, while in the daytime, the stabilizing effects of shortwave warming begins to suppress TCDC processes in the storm, leading to the culmination of the TCDC each day. Schematics are presented that summarize many of the main findings in this work, including descriptions of the basic state of the TC environment as the TCDC evolves during its early and later stages each day and a TCDC-centric daytime evolution of a TC diurnal pulse, associated squall lines and gust fronts, and radial and vertical winds in the lower and upper levels of the storm. The TCDC represents a largely unexplored, yet possibly fundamental TC process.

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