Cloud-to-ground Lightning Characteristics of Derecho-producing Convective Systems in the Central and Southern Great Plains

The scientific literature is voluminous with respect to the cloud-to-ground (CG) lightning and electrical characteristics of mesoscale convective systems (MCSs). MacGorman and Morgenstern (1998) define an MCS as a long-lived storm system that amalgamates from a group of smaller storms through interactions with the local environment. One of the more common types of MCS is the squall line, which is composed of a narrow, linear region of strong convection with (oftentimes) a region of shallow, stratiform precipitation located downshear (relative to inflow) of the convective line. Rutledge and MacGorman (1988), among others, noted a distinct horizontal pattern of CG lightning in squall lines whereby most of the positive CG (+CG) lightning occurred in the stratiform precipitation while most of the negative CG (–CG) lightning occurred within the convective line (i.e. bipole). Observations of 25 MCSs across the Great Plains by MacGorman and Morgenstern (1998) revealed that the average +CG lightning fraction was <7% with only two storms exhibiting >20% +CG lightning. Further, 18 of the 25 storms exhibited total CG lightning densities >10,000. Later studies suggest that these figures are not consistent among all MCSs. For instance, Parker et al. (2001) noted that the fraction of +CG lightning and the total CG lightning density in linear MCSs may vary according to the extent and orientation of stratiform precipitation. One class of MCS that has received comparatively little attention in the published literature with respect to its CG lightning and electrical structure is the bow echo. In a bow echo one or multiple parts of the squall line segment accelerate, creating a bulge, or wave, in the convective line. Marshall and Rust (1993) reported that the electrical structure of bow echoes is composed of four main charge regions with the predominant polarity alternating with altitude. Murray and Orville (1999) studied a bow echo event across Kansas and Oklahoma and noted a total CG flash density of >50,000 and an average +CG lightning fraction of 42% during its 26-hr lifetime.