Evaluation of Lightning Flash Rate Parameterizations in a Cloud‐Resolved WRF‐Chem Simulation of the 29–30 May 2012 Oklahoma Severe Supercell System Observed During DC3

Abstract

Eighteen lightning flash rate parameterization schemes (FRPSs) were investigated in a Weather Research and Forecasting model coupled with chemistry cloud‐resolved simulation of the 29–30 May 2012 supercell storm system observed during the Deep Convective Clouds and Chemistry (DC3) field campaign. Most of the observed storm's meteorological conditions were well represented when the model simulation included both convective damping and lightning data assimilation techniques. Newly‐developed FRPSs based on DC3 radar observations and Lightning Mapping Array data are implemented in the model, along with previously developed schemes from the literature. The schemes are based on relationships between lightning and various kinematic, structural, and microphysical thunderstorm characteristics (e.g., cloud top height, hydrometeors, reflectivity, and vertical velocity) available in the model. The results suggest the model‐simulated graupel and snow/ice hydrometeors require scaling factors to more closely represent proxy observations. The model‐simulated lightning flash trends and total flashes generated by each scheme over the simulation period are compared with observations from the central Oklahoma Lightning Mapping Array. For this supercell system, 13 of the 18 schemes overpredicted flashes by >100% with the group of FRPSs based on storm kinematics and structure (particularly updraft volume) performing slightly better than the hydrometeor‐based schemes. During the storm's first 4 hr, the upward cloud ice flux FRPS, which is based on the combination of vertical velocity and hydrometeors, well represents the observed total flashes and flash rate trend; while, the updraft volume scheme well represents the observed flash rate peak and subsequent sharp decline in flash rate.

Lightning NOx in the 29–30 May 2012 Deep Convective Clouds and Chemistry (DC3) Severe Storm and Its Downwind Chemical Consequences

“…The ICEFLUX scheme is based on the upward flux of cloud ice at 440 hPa. However, Cummings et al (2024) found that for this storm evaluating the flux at 390 hPa produced a better comparison with observed flash rates. Figure 1 shows the time series of flash rates produced by the modified ICEFLUX scheme over this time period.…”

“…These peaks of roughly 100, 300, 800, and 2,200 total flashes 10-min 1 occurred at 22:00, 22:50, 23:50, and 01:00 UTC. Following the primary peak, the observed flash rate decreased at a faster rate than it increased (see Cummings et al, 2024). The 29-30 May 2012 convection contained high flash rate supercells with small flash extents (Barth et al, 2015).…”

“…The scaled hydrometeors were used only in the FRPS calculations. Cummings et al (2024) determined that the ICEFLUX FRPS of Finney et al (2014) yielded the best comparison with the LMA flash rate data for the 29-30 May storm for the period from storm initiation through the end time of the aircraft sampling (∼0100 UT) in terms of total predicted flashes, centered root mean squared error per 10-min, and mean bias per 10-min. The ICEFLUX scheme is based on the upward flux of cloud ice at 440 hPa.…”

“…The soluble species most relevant to LNO x calculations is HNO 3 , and Bela et al (2016) found that HNO 3 was not sensitive to values tested for ice retention fractions. Using the same WRF-Chem configuration, Cummings et al (2024) tested 18 FRPSs, finding that FRPSs based on upward cloud ice flux (Finney et al, 2014) and updraft volume (Deierling & Petersen, 2008) provided the best representation of lightning activity in the early and later stages of storm simulation, respectively. Li et al (2017) examined convective transport of trace gases in cloud-resolved simulations of this severe storm, as well as two additional DC3 storms (an air mass thunderstorm and an mesoscale convective system (MCS)).…”

“…The availability of this large, cohesive data set provides the necessary surface and upper air measurements required for model simulations of electrical and chemical relationships within thunderstorms. Cummings et al (2024) tested numerous flash rate parameterization schemes (FRPSs) in Weather Research and Forecasting model simulations of the 29-30 May 2012 DC3 severe storm that occurred in Oklahoma. The FRPS that yielded the best prediction of total flashes over the period from storm initiation through the end of aircraft sampling of the storm system was the upward cloud ice flux scheme of Finney et al (2014).…”