Radar and Lightning Observations of Deep Moist Convection across Northern Alabama during DC3: 21 May 2012

Abstract

The Deep Convective Clouds and Chemistry (DC3) experiment seeks to understand the kinematic and microphysical controls on the lightning behavior of deep moist convection. This study utilized multiple dual-polarization Doppler radars across northern Alabama to quantify microphysical and kinematic properties and processes that often serve as precursors to lightning, such as the graupel echo volume, graupel mass, and convective updraft volume. The focus here was on one multicellular complex that occurred on 21 May 2012 in northern Alabama during DC3. The graupel echo volume and the graupel mass in the charging region correlated well with the total lightning flash rate (FR), and even better than the updraft volumes and maximum updraft velocities. The flash length scales (LS) and flash areas were generally anticorrelated to the FR, while it was correlated to the nonprecipitation ice volume. More specifically, the presence of smaller flashes was associated with a stronger lower positive charge region caused by larger graupel volumes, stronger updraft volumes, and stronger maximum updraft velocities while larger flashes occurred during lower FRs and were associated with a weakened lower positive charge region in combination with a stronger upper positive charge region, weaker updraft velocities, a smaller graupel volume and mass, and an increase in nonprecipitation ice volume.

Lightning channel length and flash energy determined from moments of the flash area distribution

“…Mean flash size and, to a lesser extent, the standard deviation of flash size tended to peak when flash rates were small, and vice versa, as predicted by Bruning and MacGorman [] and recently confirmed in Alabama storms by Mecikalski et al [] and for other DC3 storms by Barth et al []. Flash sizes increased from the time of first flash until 2124 UTC (at the local minimum in flash rate), when the mean flash size was 10km.…”

“…Flash area was determined from the convex hull A h of the plan projection area of the VHF sources that comprised the flash. These ideas have begun to be used more widely in the DC3 analyses [ Barth et al , ; Mecikalski et al , ] and have even been applied to lightning from volcanoes [ Behnke and Bruning , ]. This study is concerned with the optimal use of the lightning measurements in such contexts and in particular the use of the distribution of lightning flash sizes (defined by a length scale determined from their area), the length of channels associated with those flashes, and their relationship to the electrical potential energy available to each flash.…”

Evaluation of deep convective transport in storms from different convective regimes during the DC3 field campaign using WRF‐Chem with lightning data assimilation

“…On 21 May, several deep moist convective storms developed in south central Tennessee and northern central Alabama well ahead of a weak cold front [ Mecikalski et al , ]. Our storm of interest (updraft A in Figure a) started around 1930 UTC in south central Tennessee.…”

Kinematic and Microphysical Significance of Lightning Jumps versus Nonjump Increases in Total Flash Rate

“…The variational technique is chosen for this analysis for continuity between the methods used in this study and other studies using the ARMOR-KHTX baseline (e.g., , Johnson 2009, Mecikalski et al 2015, Carey et al 2016. The advantage of the variational integration technique is that it redistributes errors from both boundary conditions to produce profiles of vertical air motion and divergence that converge to a solution (O'Brien 1970, Matejka andBartels 1998).…”

“…However, the trend in the updraft can still be characterized, especially with horizontal resolution ≤ 1.5 km in the domain used in this study. This longer baseline approach is used in similar lightning/updraft studies like , Mecikalski et al (2015) and Carey et al (2016).…”