Date of Award

January 2019

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Atmospheric Sciences

First Advisor

Gretchen Mullendore

Abstract

Out-of-cloud convectively induced turbulence (CIT) poses both a serious threat to aviation operations and a challenge to forecasting applications. This challenge is particularly large in the tropics, as CIT prediction and avoidance are limited due to sparse observations and lack of tropical turbulence research. This study uses high resolution numerical simulations to investigate out-of-cloud CIT properties including intensity, areal coverage, and location using popular turbulence diagnostics in both the tropics and midlatitudes. Convective types are varied in both regions to determine the influence of convective strength and stage (developing versus mature) on CIT characteristics. The Ellrod index, Richardson number, subgrid-scale eddy dissipation rate (EDR), and second-order structure functions are evaluated across various model resolutions and compared with observations of turbulence. Static stability and vertical wind shear are examined to characterize the environment and turbulence potential around simulated convection in the tropics and midlatitudes. This study found that model resolutions similar to operational forecasting systems underpredicted the probability of turbulence, while high resolutions had a probability of turbulence at aviation cruising altitudes that better agreed with observations. The biases in the probability of turbulence for various model resolutions were affected by storm type and synoptic features, and had more agreement for cases with strong dynamical forcing. Model resolution also influenced the locations that CIT was predicted. An investigation of variations in static stability and vertical wind shear in different locations around convective cores showed that these parameters subtly varied with model resolution and often did not correlate with the preferred direction of turbulence as would be expected from theory. A further study into convective stage found that developing convection poses the greatest threat to aviation as it is associated with the greatest turbulence intensity and probability of turbulence in both the tropics and midlatitudes. The environment near developing convection was altered more than near mature convection and likely increased turbulence production through shear-generation mechanisms and gravity wave propagation. This study motivates an increased effort to understand turbulence probability for convection globally in order to improve aviation thunderstorm avoidance guidelines.

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