Physical and dynamical control of lightning jumps and use for assessing severe thunderstorm potential
Date of Award
Doctor of Philosophy (PhD)
Lawrence D. Carey
Kevin R. Knupp
Hugh J. Christian
Phillip M. Bitzer
Walt A. Petersen
Lightning., Severe storms., Thunderstorms.
The hypothesis tested in this dissertation is that a lightning jump provides unique identification of intensification of the mixed phase updraft and increases in mixed phase mass of a storm. Case study and large sample analyses were performed using multiple-Doppler, polarimetric and total lightning observations of 39 thunderstorms. For the first time kinematic and microphysical analyses were completed near the time of lightning jump occurrence to understand the unique control in which these properties are theorized to have on lightning jump development. The primary result of this study is that changes in intense updraft volume (> 10 m/s) and peak updraft speed were found to be the primary controls of lightning jumps. Ten m/s updraft volume and speed changes during a 15~minute period prior to lightning jump occurrence were statistically larger to the one tailed P=0.05 level versus increases in 10 m/s updraft volume and speed observed with general increases in total flash rate. Because the thunderstorm updraft plays a key role in severe weather production, the unique control of the updraft on lightning jumps provides evidence that lightning jump occurrence indicates an increase in severe weather potential. Outside of graupel mass jumps that occurred during thunderstorm growth, mixed phase graupel mass change exhibited little unique control on lightning jump occurrence, as general (i.e., non-jump) increases in total flash rate were supported by similar increases in mixed phase graupel mass as lightning jumps. Timing of updraft volume, speed and graupel mass these increases were found to be 4 to 12~minutes in advance of lightning jump occurrence. Furthermore, the robustness, reproducibility and reliability of the 2-sigma lightning jump algorithm were empirically demonstrated using a sample of 1500~thunderstorms. Results of this empirical analysis show that the 2-sigma lightning jump algorithm reliably indicates storm intensification prior to the observance of severe weather, with POD values between 73-79%, FAR values between 36-49% and an average lead time to severe weather occurrence of 15-21 minutes (+/-12-15 minutes). Therefore, the analysis in this dissertation demonstrates that the lightning jump is a unique indicator of thunderstorm intensification that can be used to assess severe thunderstorm potential.
Schultz, Christopher J., "Physical and dynamical control of lightning jumps and use for assessing severe thunderstorm potential" (2015). Dissertations. 61.