Prediction of total lightning in Colorado and Alabama thunderstorms based on storm dynamical and microphysical variables
Date
2015
Authors
Basarab, Brett Michael, author
Rutledge, Steven, advisor
Deierling, Wiebke, committee member
Kreidenweis, Sonia, committee member
Reising, Steven, committee member
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Abstract
Thunderstorms impact their environment in a variety of ways, including the production of nitrogen oxides (NOₓ) by lightning (LNOₓ). Accurate prediction of total lightning flash rate in thunderstorms is important to improve estimates of LNOₓ from the storm scale to the global scale. New flash rate parameterization schemes have been developed based on observed relationships between lightning flash rate and storm parameters for Colorado thunderstorms during the Deep Convective Clouds and Chemistry (DC3) experiment. Storm total flash rates are determined using an automated flash counting algorithm that clusters very high frequency (VHF) radiation sources emitted by electrical breakdown in clouds and detected by the northern Colorado lightning mapping array (LMA). Storm parameters such as hydrometeor echo volumes and ice masses are calculated from polarimetric radar retrievals. Measurements of updraft strength are obtained by synthesizing radial velocity retrievals from the CSU-CHILL and CSU-Pawnee radars to determine three-dimensional wind fields. Bulk storm parameters including the graupel echo volume, 30-dBZ echo volume, and precipitating ice mass are found to be robustly correlated to flash rate (R² ~ 0.8). It is shown that simple flash rate parameterization schemes based on these quantities predict gross flash rate behavior reasonably well. Updraft intensity-based flash rate schemes are also developed, but updraft parameters were not as strongly correlated to flash rate as storm volume quantities. The use of multiple storm parameters to predict flash rate is also investigated, since flash rate may be sensitive to multiple processes or characteristics within thunderstorms. A simple approach is found to be most effective: storm-total graupel and reflectivity echo volumes were split up into representative area and height dimensions and regressed against flash rate. The combined quantities predict flash rate variability somewhat better than simpler single-parameter flash rate schemes. All new flash rate schemes are tested against observations of Alabama thunderstorms documented during DC3 to examine their potential regional limitations. The flash rate schemes developed work best for strong Colorado storms with sustained high flash rates. Finally, relationships between total flash rate and flash size are discussed, with implications for the improved prediction of LNOₓ.
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Subject
dual-polarization radar
remote sensing
lightning
cloud physics