Lightning Outbreaks in the Eyewall MET 614 Seminar Antti Pessi.
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Transcript of Lightning Outbreaks in the Eyewall MET 614 Seminar Antti Pessi.
Lightning Outbreaks in the Eyewall
MET 614 Seminar
Antti Pessi
Introduction - Lightning Outbreaks Introduction - Lightning Outbreaks
Updrafts and flash rates in the eyewall usually Updrafts and flash rates in the eyewall usually modest. Core neutral to slantwise convection modest. Core neutral to slantwise convection (Emanuel, 1989)(Emanuel, 1989)
Lightning outbreaks in the eyewall may indicate Lightning outbreaks in the eyewall may indicate rapid intensity changerapid intensity change
Often associated with eyewall cyclesOften associated with eyewall cycles Usually hidden on VIS and IR by central dense Usually hidden on VIS and IR by central dense
overcastovercast Potential of lightning observations in forecasting Potential of lightning observations in forecasting
intensity changes?intensity changes?
Radial Distribution of Radial Distribution of Lightning in HurricaneLightning in Hurricane
Lyons and Keen (1994), Lyons and Keen (1994), Molinari et al., (1994, Molinari et al., (1994, 1999), Black and Hallett 1999), Black and Hallett (1999), Cecil et al., (2002)(1999), Cecil et al., (2002)
Weak maximum near Weak maximum near eyewall (<40 km)eyewall (<40 km)
Clear minimum 80-160 Clear minimum 80-160 kmkm
Strong maximum in outer Strong maximum in outer rainbands (210-290 km)rainbands (210-290 km)
9 Hurricanes composite(Molinari et al., 1999)
Andrew ‘92(Molinari et al., 1994)
Eyewall Electrification
Effective electrification requires ice, graupel and supercooled liquid cloud droplets extending below -20ºC
Steady-state eyewall often lacks supercooled water above -5ºC and updrafts (<5m/s) are too weak to bring up larger supercooled drops and graupel
Instead, new ‘fresh’ eyewall and contracting eyewall have been observed to have updrafts >10m/s and be electrically active
Black and Hallett, 1999
Charge Distribution in the EyewallCharge Distribution in the Eyewall
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Negative strokes usually originate close to max echoes (a few km outward of sfc eyewall, near -10…-15˚C)
Positive strokes originate from stratiform area (outward blown ice crystals)
Coldest cloud tops outward of max echoes
Andrew ‘92(Molinari et al., 1994)
Jorgensen (1984)
Eyewall CyclesEyewall Cycles
Storm weakens when: Outer eyewall forms, act as a
barrier to high theta-e inflow Convection in the outer eyewall
leads to secondary circulation: latent heat release, updrafts in the eyewall, descent and adiabatic warming over the inner eyewallIntensifies:
This secondary circulation also causes isobaric height falls in the area it encloses.
Height fall is concentrated at the inner edge of wind maximum causing the gradient wind to increase there and the maximum to contract
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Jorgensen (1984)
Willoughby (1995)
Flight Through Double EyewallFlight Through Double Eyewall
Electric field
W
CLW (sensor problem!
TemperatureWind
Black and Hallett, 1999
Hurricane Charley 13 Aug. 2004 Landfall in Florida, Cat. 4, 130kt,
941mb 10 direct deaths, damage $14 Billion Rapid intensification prior to landfall:
964->941mb in 4.5h (5mb/h) Lightning outbreak in the eyewall
coincided with intensification
Lightning data from Lightning data from International Long-Range International Long-Range Network (practically from Network (practically from NLDN)NLDN)
Flash positions overlaid Flash positions overlaid on GOES-12 IRon GOES-12 IR
Data Sources - Hurricane Charley Case
Detection efficiency and sensor locations
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
12Z
20Z
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Last 6 hours before landfall:
Eyewall radius shrunk from 20 to 7 km
Storm intensified from 965 to 941 mb
Lightning Rate vs. IntensityLightning Rate vs. Intensity
Hurricane Charley Lightning and Intensity
0
20
40
60
80
100
120
140
160
12 13 14 15 16 17 18 19
Time (UTC) on 13 August 2004
Lightning Rate
940
945
950
955
960
965
970
Central Pressure (hPa)StrokesPressure (hPa)
660 eyewall flashes during last 8h
Lightning Rate vs. Intensity
Andrew ‘92(Molinari et al., 1994)
Elena, Hugo, Bob(Molinari et al., 1999)
Summary Convective updrafts and lightning are physically related
manifestations of eyewall Updrafts in a steady hurricane are too weak to electrify
the eyewall Lightning outbreaks in the eyewall are often associated
with eyewall cycles or contracting eyewall and storm intensity changes
Eyewall lightning in hurricane Charley coincided with rapid deepening
Lightning observations are continuous, near real-time and have sometimes potential to show changes in intensity
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
Charley 13 Aug. 2004 12-20Z
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Hurricane Charley Lightning and Intensity
0
20
40
60
80
100
120
140
160
12 13 14 15 16 17 18 19 20
Time (UTC) on 13 August 2004
Number of Strokes
940
945
950
955
960
965
970
Strokes
Pressure (hPa)