"Diurnal To Seasonal Hurricane Variability And Predictability" by Jeremiah Otero Piersante

Date of Award

5-1-2024

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

College/School/Department

Department of Atmospheric and Environmental Sciences

Dissertation/Thesis Chair

Kristen L Corbosiero

Committee Members

Ryan D Torn, Brian H Tang

Keywords

hurricane, tropical cyclone

Subject Categories

Atmospheric Sciences

Abstract

Prediction of tropical cyclone (TC) impact extends across a range of forecast lead times. At shorter timescales, radially outward-propagating, diurnal pulses in TCs are associated with TC intensity and structure changes. At weekly periods, synoptic-scale Rossby waves influence the direction of TC tracks. At seasonal timescales, climate modes affect the overall (in)favorability of TC activity. The research shown in this dissertation seeks to improve the understanding and predictability of TC variability across these scales using numerical weather prediction, reanalysis fields, and storm track observations.Diurnal pulses associated with cloud-top cooling, so-called cooling pulses (CPs), pose a risk for hazardous weather because they often assume characteristics of tropical squall lines. The first part of the dissertation evaluated the characteristics and origins of simulated CPs using various Weather Research and Forecasting (WRF) model and Model for Prediction Across Scales (MPAS) simulations of observed TCs that featured several pulses over the Atlantic Ocean. CP evolution was tested against choice of microphysics parameterization, whereby the Thompson and Morrison schemes presented distinct mechanisms for CP creation and propagation. Specifically, the Thompson CP was convectively coupled and propagated outward with a rainband. The Morrison CP was restricted to the cirrus canopy and propagated radially outward in the upper-level outflow layer, unassociated with any rainband. The Thompson simulation better represented the observations of the particular event, but it was speculated that CPs in nature can resemble characteristics from either scheme. It is therefore necessary to evaluate pulses beyond solely brightness temperature when possible (e.g., reflectivity, rain rate). Next, a series of sensitivity tests were conducted to identify how radiation affects the timing and structure of diurnal pulses. Interestingly, pulses still occurred after removing the diurnal cycle of shortwave radiation to produce “night-only” and “day-only” simulations. Shortwave cloud-radiative forcing (CRF) largely controlled the timing of pulses, whereas longwave CRF was required for pulses to propagate radially outward. Lastly, High Resolution Rapid Refresh (HRRR) model output was analyzed to determine the extent to which diurnal pulses within a real-time forecast model could be resolved. While CPs were accurately depicted within HRRR analyses (0-h forecasts), only unnatural, CP-like features that were consequences of model spin-up emerged within the forecasts. Thus, while other forecast models and leads times should be tested, the results suggest that diurnal pulse forecasts are poor. The second part of the dissertation investigated three ways in which estimations of TC activity and steering can be applied in real-time. First, TC activity and steering were quantified over 1950–2021 warm seasons using metrics introduced in recent literature. The Activity Index (Titus et al. 2021), corresponded well with the annual number of TCs and accumulated cyclone energy; however, the relationships varied in different phases of El Niño Southern Oscillation and the Atlantic Multidecadal Oscillation. Second, large-scale environments were compared for main development region (MDR)-originating TCs that either made landfall in the U.S. or recurved away from land. Landfall patterns featured an elongated mid-level anticyclone across the North Atlantic and enhanced easterly winds; in contrast, recurving storms were associated with a trough over North America. Landfall and recurve TCs on average had significantly different values of Steering Index (Titus et al. 2021). Third, it was shown that the environments of MDR-originating TCs that either made landfall along the U.S. Gulf Coast or East Coast largely contrasted over the Caribbean Islands. In particular, Gulf landfalls were associated with relatively higher heights and pressures over the region, steering TCs westward. To quantify the likelihood of TCs making landfall in either of the two regions, a new metric was introduced.

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