Quantitative Analysis of the Turbulent Structure of Convection and Its Relation to Thunderstorm Electrical Properties

Previous work has suggested a tie between the turbulent characteristics of thunderstorms and the organization of electrical charge within convective systems. Bruning and MacGorman (2013) calculated the energy spectra for an ensemble of lightning flashes and noted the similarities to the expected spectra of turbulent kinetic energy. Lightning energy spectra demonstrate both a 5/3 slope in the inertial subrange and a peak at 10 km, which is similar to what is expected from TKE spectra. Well-characterized turbulence measurements are necessary to ensure that future comparisons of TKE and lightning energy spectra provide a valid test of the links between the two phenomena.

Doppler radar provides a useful means to examine the turbulent structure of convection. The resolved mean radial velocities and the Doppler spectrum width provide information about the variance of velocities of hydrometeors embedded within the thunderstorm flow, from which turbulent energy characteristics can be calculated and inferred.

This study utilizes high-resolution radar data to create turbulent kinetic energy spectra and to calculate eddy dissipation rates for selected areas within an RHI scan, collected with the TTU Ka-band mobile Doppler radars. Data were collected during the spring of 2014, 2015, and 2016 for the Kinematic Texture and Lightning (KTaL) field experiment. The objective of taking these measurements is to examine and further understand the distribution of energy within diverse regions of turbulent and more uniform flow in convection, and to examine potential correlations to the lightning energy characteristics in those same regions. Fourier analysis of the variance of mean Doppler velocities is used to create the TKE spectra. Both Doppler spectrum width and variance of mean Doppler velocities are used to calculate eddy dissipation rates for the turbulence within the convection. A comparison between the eddy dissipation rates found using variance of radial velocities and those found using spectrum width serves to further validate results, as well as provide an assessment of the accuracy of the different techniques.