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)