Assessing turbulence in different spots of lightning flash propagation

Date

2020-12

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Abstract

Studies show that high updraft speeds within a storm are correlated to a great amount of ice hydrometeors in the mixed phase region, high probabilities of ice hydrometeor collisions and consequent charge separation that can lead to lightning initiation. Fluid strain, including shear along updraft gradients, is responsible for the production of turbulence kinetic energy (TKE). Thus, turbulent regions are more likely to produce lightning once turbulence has the potential to locally concentrate charge and enhance the electric field. Within this context, the goal is to provide further evidence linking kinematic and electrical characteristics of a storm. This study utilizes the Doppler spectrum width from Ka-band radar to estimate the eddy dissipation rate (EDR) in range height indicator (RHI) scans of deep convection for nine storms during the Kinematic Texture and Lightning (KTaL) experiment. The radar-derived turbulence structure is overlapped with data from the West Texas Lightning Mapping Array (WTLMA) to identify where lightning flashes crossed the high resolution scans. We check for the association of EDR of analyzed regions with the distance between the location crossed by lightning in the RHI scan and its initiation. The majority of the storms during the radar sampling confirmed the hypothesis that high turbulent regions are involved in more lightning initiation and these regions experience more breakdown processes associated with smaller flashes. As the distance from flash initiation increases, there is a gradient to less turbulent regions favoring propagation of larger flashes. We identified other two contrasting behaviors. Small- and medium-sized flashes initiated at lower altitudes in regions of smaller EDR values that are consistent with the unmixed flow within the lower inner part of updrafts. A concentration of small flashes initiated in the upper portion of the cloud in high EDR values due to small scale variability associated with these regions. Sensitivity tests considering radar interpolation, LMA stations detection and assumptions on the EDR estimation algorithm validated the results as small sensitivity to the different choices of analysis methods were observed.

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Keywords

Turbulence, Lightning flashes, Radar

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