Use of Lightning and Radar Information To Understand Severe Thunderstorm Development and Tornadic Potential Daniel J. Cecil, NASA MSFC Lawrence D. Carey, UAH Chris Schultz, NASA MSFC Sarah Stough, UAH Phil Bitzer, UAH Themis Chronis, UAH Total lightning and supercell mesocyclone are physically linked by the updraft Non-inductive charging mechanism thought to be primary method of electrification (Takahashi 1978) Graupel-ice collisions in the presence of supercooled water and subsequent gravitational separation result in layered charge structure (Reynolds 1957; Takahashi 1978; Stolzenburg et al. 1998) Reversal Temperature (-10 C to -20C) - Background Electrification Stolzenburg et al. (1998), Fig. 3 Strengths and limits of using lightning data Total lightning (IC+CG, from GOES-R and LMA) has much greater information content for severe thunderstorms than CG lightning only Rapid increase in flash rate correlates to updraft surge, building a mesoscyclone, setting the stage for potential severe weather Knowledge of environment (instability, shear) greatly aids interpretation Processes in very low level wind / thermodynamic fields are critical to manifestation of severe weather (especially tornado) at the ground not directly related to lightning Rapid increase followed by rapid decrease in lightning may relate to downdraft development that does more directly influence tornadogenesis Lightning Jump Conceptual Model Jump Time A BC A to B Mixed phase updraft volume, updraft speed and graupel mass increase and a lightning jump occurs B to C As flash rates continue to increase, increases in intensity metrics (e.g., MESH, azimuthal shear) are observed resulting in enhanced severe weather potential. C tttt 5 Schultz et al. (2015) W = 10, 20, 30, 40, 50 m s -1 LMA flash initiation 6 km alt 2 km alt 1720 UTC 1728 UTC 1739 UTC Vertical Cross Sections 1720 UTC 1739 UTC 6 km alt Vertical Cross Sections 1739 UTC 1720 UTC 2 km alt Mesocyclogenesis Observations Mesocyclogenesis observed in 13 cases by: 1.Reflectivity features; 2.First MDA detection; and/or 3.MAS > 1.00x10 -2 s -1 50% of the time, the 1 st mesocyclone observation occurs minutes after the 1 st lightning jump Lightning Jump/Rotation Increase Observations Lightning Jumps occur prior to most increases, in Low Instability and High Instability cases More 6-9 km Max Az Shear increases followed the lightning jump than other layers (L) (MSm) (MDm) (H) Lightning Jump/Rotation Increases: Moderate Instability Cases Discrepancies between distribution of Shallow Meso and Deep Meso lightning/MaxAzShear increase associations Most Shallow Meso associations in lowest 3 km layer Deep Meso associations distributed further into the 3-6 km layer Tendency for more 0-3 km MaxAzShear increases to precede lightning jump and more 6-9 km MaxAzShear increases to follow lightning jump 6-9 km 3-6 km 0-3 km Lightning Jump/Rotation Increases: Moderate Instability Cases Most Mdt Inst / Shallow Meso associations in lowest 3 km layer Mdt Inst / Deep Meso associations distributed further into the 3-6 km layer Temporal differences may result from difference in time of updraft to act on lower regions, mid- regions, and lightning initiation regions Time scales observed agree with expected updraft parcel accelerations SFC 12 km 9 km 6 km 3 km Potential Downdraft Interactions Temporal distributions of lightning jump / 0-3 km layer MaxAzShear associations with respect to tornadic and tornadic storms Shift in tornadic associations after the time of the jump versus non- tornadic associations that occur prior to the time of the jump Potential Downdraft Interactions Believed that complex interactions between downdraft-generated vertical vorticity and cold pool alignment contribute to near- surface vorticity required for tornadogenesis (Markowski and Richardson 2014) Lightning jump signals updraft pulse that increases mixed-phase precipitation mass. Fallout of this precipitation results in downdraft and cold pool generation. Lightning jump, tied to updraft, may also signal onset of enhanced downdraft and potential for increased vorticity Potential Downdraft Interactions Further, several cases exhibited anti-correlated behavior between 0-3 km MaxAzShear and Flash Rate Ex: Case 4; October 26, 2010; Alabama Decrease in FR and increase in 0-3 km MAS follows jump by ~35 minutes and precedes brief tornado on the order of minutes Repeated pattern at the end of the storm precedes straight-line wind report Summary of Core Results From 19 diverse supercell cases: 1.The first lightning jump often coincides with or precedes mesocyclogenesis, and transition to supercell Pre-requisite is supercell-supporting environment Increased confidence in earlier warning decision 2.Subsequent lightning jumps shown to follow enhanced rotation in 0-3 km layer; exhibit diverse temporal spread in association with increases in the 3-6 km layer; and typically lead increases in the 6-9 km layer results vary based on environment and structure lightning jump gives indication of an enhanced updraft that is likely also stretching the column and enhancing rotation; particularly in moderate- to-high instability environments 3.Lightning jumps followed by decreasing flash rates may alert to enhanced low-level rotation and availability of conditions required for tornadogenesis Field Program thoughts Take Advantage of Lightning Mapping Arrays! 3-D mapping of lightning channels X z - Take advantage of relevant ground-based assets: fixed and deployable LMAs, fixed and deployable Doppler radars, etc. The satellite (GOES-R) will tell us a lot, but low level details from ground-based measurements are critical for the tornado problem. - Use over-storm aircraft and LMA as satellite simulators Tornado and SigTor Frequency Adapted from Coleman and Dixon 2014 WAF and their literature review (Smith et al. 2012; Ashley 2007; Carbin et al. 2012) SigTor Path Length SigTor Count SigTor Days All Tornadoes 5x5 array (777 nm passband) 5x1 array (alternate spectral features) Sample rate 100 kHz (sub-stroke resolution) Nominal footprint 10 x 10km (at cloud top) Spatial resolution 2 x 2 km Wide angle camera Electric-field change meter Flys Eye GLM Simulator for ER-2 10 km FEGS Footprint 5x5 array (777 nm passband) 5x1 array (alternate spectral features) Sample rate 100 kHz (sub-stroke resolution) Nominal footprint 10 x 10km (at cloud top) Spatial resolution 2 x 2 km Wide angle camera Electric-field change meter