An Analysis of Small Changes in Environment Which Resulted in Diverse Charge Structures on 4 June 2012 in West Texas

As part of the Deep Convective Clouds and Chemistry field campaign, the disorganized cellular convection throughout West Texas on 4 June 2012 provided a unique opportunity to sample a full variety of charge structures in contemporaneous storms within tens of kilometers through the use of the West Texas Lightning Mapping Array. The surface moisture and related surface variables, while varying across the region, did not correlate to the observed charge structures, implying an above-surface influence dominated even what appeared to be a synoptically benign environment. Due to the close proximity of these storms to each other, a WRF ensemble was used to estimate the range of the mid-level environmental differences which may have resulted in the different charging within the storms. Most significantly, the representation of the elevated mixed layer, the base of which was near 700 mb (below cloud base), varied across the domain with the deepest and driest midlevel layers in the areas dominated by anomalous storms. This suggests that the above-surface dry modification of cloud parcels could be encouraging the positive charging of graupel within the cloud by limiting the warm cloud depth and increasing the availability of liquid in the mixed phase region. Besides the anomalous charge structures, these storms also contained fewer cloud-to-ground flashes and were slower to organize than those with a greater depth of moisture, although storms of both polarities were long-lasting. The case allows for a very unique examination of how small changes in environment can impact the storm-scale electrical and morphological properties. The ability of a set of idealized WRF models, using standard parameterizations, to capture any of these resulting differences in the overall charge structures given the very small changes in the environmental moisture across the region as resolved by the ensemble will be discussed.