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STEPS 2000 Research Highlights from Colorado State University

STEPS 2000 Research Highlights from Colorado State University. Sarah Tessendorf*, Kyle Wiens**, Timothy Lang and Steven Rutledge Radar Meteorology Group * Univ. of Colorado/CIRES Department of Atmospheric Science ** Los Alamos National Lab Colorado State University

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STEPS 2000 Research Highlights from Colorado State University

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  1. STEPS 2000 Research Highlights from Colorado State University Sarah Tessendorf*, Kyle Wiens**, Timothy Lang and Steven Rutledge Radar Meteorology Group * Univ. of Colorado/CIRES Department of Atmospheric Science ** Los Alamos National Lab Colorado State University Supported by NSF, Div. of Atmospheric Sciences, Physical Meteorology Program

  2. Background/Motivation:Anomalous electrification and +CGs • Particular focus on +CG storms • Previous studies of +CG storms include only ground strike data with little or no information about parent charge structure and origins of lightning • Previous studies largely lack detailed kinematic/microphysical context for the lightning activity. Urgently needed are observations that constrain the location of the positive charge region participating in the anomalous ground flashes. --Williams (2001)

  3. Background: Positive CG hypotheses Williams (2001)

  4. Background:Previous results • Lang and Rutledge (2002) argued that increased kinematic intensity (updraft volume) was a distinguishing factor of predominantly +CG (PPCG) storms. More detailed analyses of STEPS storms provided additional insights based on charge structure information…. = +CG From Lang and Rutledge (2002)

  5. Radar Network Dual-Doppler and Triple Doppler configurations

  6. Instrumentation:New Mexico Tech Lightning Mapping Array (LMA) • Time and 3-D location of VHF (60-66 MHz) lightning radiation sources (100s-1000s of sources per flash) • Maps total (IC and CG) lightning activity • Allows for computation of total flash rates • Allows inference of charge structure • Allows for determination of flash origin locations where the +CGs are coming from

  7. STEPS Fixed Instrumentation: Triple-Doppler Network and LMA (VHF TOA) • At KGLD: • NWS • T-28 • NSSL • Electric field balloon • Mobile mesonet • MGLASS

  8. LMA charge structure methods • 1) Initiation in max E-field between charge regions of opposite polarity • 2) Bi-directional breakdown • 3) Negative breakdown is noisier at VHF • 4) No charge structure w/o lightning Most LMA sources are negative breakdown through region of positive charge! Courtesy K. Wiens

  9. B A 19 June 2000 overviewNegative CGs • Max reflectivity ~ 65 dBZ, Max updraft ~ 15 m/s Moderately intense multicell storm

  10. Total FR: Order of 10/min UV10: Order of 10 km3 Graupel, updraft, flash rate (FR) evolution 19 June 2000 (-CG multicell) A B

  11. 3 June 2000 overviewNo CGs • Max reflectivity ~ 60 dBZ, Max updraft ~ 25 m/s Low precipitation supercell, no CG’s detected by NLDN

  12. Total FR: Order of 10/min UV10: Order of 100 km3 Graupel, updraft, flash rate (FR) evolution 3 June 2000 (no CG supercell)

  13. AB A C B 22 June 2000 overviewPositive CGs • Max reflectivity ~ 67 dBZ, Max updraft ~ 50 m/s Intense, multicell storm, CG’s predominately positive after cell merger

  14. Total FR: Order of 100/min UV10: Order of 1000 km3 +CG FR: 10/min after merger Graupel, updraft, flash rate (FR) evolution 22 June 2000 (+CG multicell)

  15. 29 June 2000 overviewPositive CGs • Max reflectivity ~ 70 dBZ, Max updraft ~ 50 m/s Classic supercell, CG lightning predominately positive

  16. Total FR: Order of 100/min UV10: Order of 1000 km3 +CG FR: 2-4/min after right turn Graupel, updraft, flash rate (FR) evolution 29 June 2000 (+CG supercell)

  17. 19 June charge structure (-CG multicell) • Main negative with positive charge above = “Normal” • Lower positive charge layer • In precip core • With -CG flashes (not shown) • More low-level ICs during peak storm intensity when no -CGs Radar data time: 0019 UTC LMA data time: 00:19:14-00:19:17 UTC Tessendorf and Rutledge, 2007

  18. 3 June charge structure (No CG supercell) • Negative above main positive charge in updraft and precip core = “Inverted” • NO LOWER NEGATIVE CHARGE!? • Upper level positive seen in some flashes above upper negative layer Radar data time: 2325 UTC LMA data time: 23:26:28-23:26:48 UTC Tessendorf et al, 2007

  19. 22 June charge structure—CG dominated supercell Radar data time: 0022 UTC NLDN data time: 0022-0027 UTC LMA data time: 00:25:13-00:25:14 UTC • +CG flashes in northern Cell 22AB, in precipitation core • Mid-level positive with lower negative in region for +CGs = “Inverted” tripole Tessendorf and Rutledge, 2007

  20. 29 June charge structure (+CG supercell) • “Inverted” tripole in precipitation; dipole in updraft • Lower negative charge present in region of +CGs Radar data time: 2325 UTC NLDN data time: 2320-2330 UTC LMA data time: 23:24:42-23:24:57 UTC Wiens et al. 2006

  21. Summary • We observed inverted charge structures in 3 June, 22 June and 29 June • Main positive charge around 8 km, where a normal charge structure would have negative charge • The +CG storms had inverted (tripole) charge structures with a lower negative charge layer in the presence of the +CG lightning • The no CG storm was also inverted, but we did not detect a lower negative charge layer • Lower negative charge layer may be impetus for +CG flashes • The +CG storms in STEPS had stronger kinematic intensity’s (UV10, max updraft)

  22. Conclusions • Strong kinematic intensity a distinguishing factor for +CG storms, however it is not likely a sufficient condition Add lower negative to hypothesized charge structure for +CG storms making Inverted Tripole - - Adapted from Williams (2001)

  23. Thoughts….. • What causes the charge structure to become inverted? • (Regional) environmental variables, increased kinematic intensity… • More case studies, statistical analysis, and modeling work are needed

  24. 11 June 2000 2340-2350 Z -2350Z Strat Conv Southern MCS All Stratiform Lightning Strat Conv Dark - Negative Light - Positive Northern MCS Stratiform-Initiated Stratiform IC Flash 12 June, 0010Z w/ S-Pol FHC Green - Negative Red - Positive Lang and Rutledge

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