Investigating the relative contribution of charge deposition in organizing charge within a thunderstorm

Date

2017-08

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Abstract

Many processes contribute to the hydrometeor charge budget within a thunderstorm. These include advection, hydrometeor differential sedimentation, turbulent mixing and diffusion, microphysical separation, and the attachment of ion charge deposited by the lightning channel. Previous observational studies used balloon soundings of thunderstorm electric fields to quantify charge deposited by the lightning channel and concluded that charge deposition complicates the charge structure of a thunderstorm. The Kinematic Texture and Lightning (KTaL) campaign at Texas Tech University is designed to study aspects of the charge redistribution budget, with a particular focus on quantifying turbulence, but as with all observation campaigns quantification of the complete budget is challenging. Therefore, it is helpful to use numerical modeling for quantifying the relative contributions of charge deposition and hydrometeor motions to the overall budget.

The NSSL version of the Collaborative Model for Multiscale Atmospheric Simulation (COMMAS) contains microphysical charging and branched lightning parameterizations. The model produces fairly realistic representations of intra-cloud (IC) and cloud-to-ground (CG) flashes that concur with previous observational analyses. Two simulations were run using soundings from the KTaL field campaign in addition to the classic Weisman and Klemp sounding to assess the charge budget contributors throughout the storms. The lightning deposition, sedimentation, and non-inductive charging tendencies contributed the most overall charge while the charge advection tendency provided the most ``texture'' at small scales to the net charge field near the updraft region of the storm, especially for more robust storm simulations. Lightning deposition and sedimentation operated at a somewhat larger and smoother scale which resembled the distribution of the electric potential. The clear scale separation between the advection and other net charge tendency fields suggests the charge advection is most capable of providing net charge texture, however a clear cut causality was not obtained from this study. Future work discussed provides a roadmap for studies to further strengthen the argument for the coupled kinematic and electrical characteristics of a storm.

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Keywords

Lightning, Charge budget, Thunderstorm

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