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Lightning in Colorado Forest Fire Smoke Plumes During Summer 2012

Lightning in Colorado Forest Fire Smoke Plumes During Summer 2012. Timothy Lang, Paul Krehbiel, Brenda Dolan, Dan Lindsey, Steve Rutledge, Bill Rison. Hewlett Gulch Fire. Started 14 May 2012 Contained 22 May 2012 Burned 7,685 acres Human caused (accident) No burned structures or fatalities.

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Lightning in Colorado Forest Fire Smoke Plumes During Summer 2012

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  1. Lightning in Colorado Forest Fire Smoke Plumes During Summer 2012 Timothy Lang, Paul Krehbiel, Brenda Dolan, Dan Lindsey, Steve Rutledge, Bill Rison

  2. Hewlett Gulch Fire Started 14 May 2012 Contained 22 May 2012 Burned 7,685 acres Human caused (accident) No burned structures or fatalities

  3. CSU-CHILL Polarimetric Radar • Unique Dataset – Combined polarimetric, dual-Doppler, LMA coverage of electrified pyrocumulus atop smoke plume (16 May 2012) • Plume/pyrocumulus is easily distinguished from surrounding cloud: • Low reflectivity • High ZDR • Low correlation • Little diff. phase shift • Indicates irregularly shaped smoke and ash particles are contributing the most to reflectivity • Note diffluence near echo top, also decrease in ZDR and increase in correlation Correlation Coefficient Reflectivity Differential Reflectivity Radial Velocity

  4. Hewlett Gulch Plume CSU-CHILL Polarimetric Radar CSU Pawnee Doppler Radar CO LMA Black Dots = LMA sources

  5. CSU-CHILL Polarimetric Radar CSU Pawnee Doppler Radar CO LMA Hewlett Gulch Plume • Updraft growth leads eventual lightning by 10-15 min • Updraft growth coincides with growth of plume above 10 km MSL • Lightning occurs after that (lower break-even fields at altitude?) • Note: Due to significant heat, updraft processes may not be hydrostatic, leading to significant underestimate of updrafts from dual-Doppler syntheses

  6. GOES Shortwave IR (3.9 µm) True Color from NPP/VIIRS – 1928 Z GOES Longwave IR (10.7 µm) Fort Collins GOES and NPP Satellite Gridlines = 0.2° Black Dots = LMA sources

  7. Lightning 16 May 1945-2010 (density) Intracloud, high altitude (~10 km MSL) Substantial precursor activity Single flash near 1950 UTC (points) Positive charge above 10 km, negative charge below

  8. High Park Fire Started 9 June 2012 Contained 1 July 2012 87,284 acres burned Lightning-caused (storms occurred evening of 6 June) 259 structures burned, 1 fatality $31.5 million firefighting costs

  9. NEXRAD Composite Radar Mosaic Gridlines = 0.2° Black Dots = LMA sources High Park Plume Lightning: ~2330-0030 13-14 June Fort Collins

  10. High Park Plume Lightning: ~2330-0030 13-14 June NEXRAD Composite Radar Mosaic Vertical cross-section Black Dots = LMA sources

  11. Shortwave IR Visible Longwave IR Fort Collins GOES Satellite Gridlines = 0.2° Black Dots = LMA sources

  12. Correlation Coefficient Reflectivity CSU-CHILL did not operate day of electrification. However, plume characteristics (besides height and width) did not exhibit significant day-to-day variability. 22 June 2012 observations (right) similar to many other days plume was scanned, with low Z, high ZDR, and low ρHV Radial Velocity Differential Reflectivity

  13. Early lightning (2328-2336 UTC) High-altitude intracloud (10-11 km MSL) Later lightning (0008-0033 UTC) High-altitude intracloud w/ one exception

  14. Waldo Canyon Fire Started 23 June 2012 Contained 10 July 2012 Burned 18,247 acres Human-caused (reason unknown) 346 structures burned, 2 fatalities 32,000 evacuated (incl. USAFA) $16.7 million to fight $352.6 million insurance costs

  15. NEXRAD Composite Radar Mosaic Gridlines = 0.2° Black Dots = LMA sources Waldo Plume Lightning: ~2340-0040 26-27 June Colorado Springs

  16. Normal Convection Waldo Plume Lightning: ~2340-0040 26-27 June NEXRAD Composite Radar Mosaic Vertical cross-section Black Dots = LMA sources

  17. Shortwave IR Visible – 2300 Z Longwave IR Colorado Springs GOES Satellite Gridlines = 0.2° Black Dots = LMA sources

  18. Early Lightning (density; 2340-2359)Intracloud w/ positive charge near 11 km MSL Later Lightning (points; 0000-0040)Interaction w/ electrified convection to north?

  19. Conclusions • Smoke plumes exhibiting pyrocumuli atop forest fires occasionally electrified when conditions of deep dry adiabatic layers and explosive fire growth were met. • Compact IC flashes with significant precursor activity • Significant updrafts and growth above 10 km MSL (-40 °C) preceded the electrification. • Coincident hot spots observed in shortwave IR in two cases, one case featured colder clouds • Polarimetric observations indicated mainly smoke and ash particles, and not the traditional graupel and ice crystals in the mixed-phase region, however. • Weak electrification due to ice crystals/rimed ash? • Radon/other ionization? • Reduced breakeven field at high altitude important?

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