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Holle | NWA Annual Meeting | October 06 Cloud Lightning from the National Lightning Detection Network (NLDN) Ronald L. Holle, Nicholas Demetriades, and Martin Murphy Vaisala, Inc. Tucson, Arizona

Cloud Lightning from the National Lightning Detection Network (NLDN)

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Cloud Lightning from the National Lightning Detection Network (NLDN). Ronald L. Holle, Nicholas Demetriades, and Martin Murphy Vaisala, Inc. Tucson, Arizona. Outline. - PowerPoint PPT Presentation

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Page 1: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

Cloud Lightningfrom the NationalLightningDetection Network(NLDN)

Ronald L. Holle, Nicholas Demetriades, and Martin Murphy

Vaisala, Inc.

Tucson, Arizona

Page 2: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

-- Value of LF cloud data

-- Overview of LF cloud data

-- Spatial representation of lightning activity

-- Validation of LF cloud performance

Outline

Page 3: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

Low frequency (LF) cloud data in the NLDN

• Low frequency (LF) cloud lightning is typically located near cloud-to-ground (CG) lightning

• Cloud lightning precedes CGs in ~70% of all thunderstorms

• Cloud lightning typically precedes CGs by several minutes, but can precede CGs by > 60 minutes in some severe thunderstorms

• Cloud flash rates are typically 3 times larger than CG flash rates, but may be >10 times larger in some severe thunderstorms

Page 4: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

-- Value of LF cloud data

-- Overview of LF cloud data

-- Spatial representation of lightning activity

-- Validation of LF cloud performance

Outline

Page 5: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

Low frequency (LF) cloud lightning data in theNational Lightning Detection Network (NLDN)

• Activated April 2006 to all users

• Detection methods are based on independent validation studies

• Weak positive cloud-to-ground (CG) flashes less than +15kA are now identified as cloud flashes, not as CGs

• 1/3 of the NLDN datastream is now LF cloud

• A network configured for optimal detection of CGs on a national level will not detect most LF cloud flashes

Page 6: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

The main challenge for LF cloud lightning detection:Source signal strengths

The median LF large cloud pulse The median LF large cloud pulse amplitude is 5% as strong as for amplitude is 5% as strong as for CGsCGs

A network configured for optimal A network configured for optimal detection of CGs on a national detection of CGs on a national level will not detect most LF level will not detect most LF cloud flashescloud flashes

CGCG LargeLarge

cloudcloud

All cloudAll cloud

• •

Page 7: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

LF cloud data - NLDN

• The vertical component of the cloud flash is located with a median accuracy of 500 meters

• Cloud data are available in both the CG flash and CG stroke datastreams

• A fraction of all cloud flashes that occur can be detected by the NLDN - the detection efficiency (DE) is typically 5-15% with the standard sensor spacing of the NLDN

• LF cloud does not provide mapping of cloud lightning

Page 8: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

-- Value of LF cloud data

-- Overview of LF cloud data

-- Spatial representation of lightning activity

-- Validation of LF cloud performance

Outline

Page 9: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

LF cloud lightning detection data - Flash level

Blue: Total VHF lightning mapping (1190 sources)

Red: LF cloud lightning (5 sources)

Dallas-

Fort Worth

region

Page 10: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

Green: NLDN CG flashes - Sources at storm levelRed: NLDN-based test network LF cloud sources

LF cloud flashes are typically located near the flash initiation point

Dallas-

Fort Worth

region

18-minute period

Page 11: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

VHF total lightning mappingAreal coverage of flashes at the storm level

Dallas-

Fort Worth

region

18-minute period

Page 12: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

-- Value of LF cloud data

-- Overview of LF cloud data

-- Spatial representation of lightning activity

-- Validation of LF cloud performance

Outline

Page 13: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

The main challenge for LF cloud lightning detection:Source signal strengths

The median LF large cloud pulse The median LF large cloud pulse amplitude is 5% as strong as for amplitude is 5% as strong as for CGsCGs

A network configured for optimal A network configured for optimal detection of CGs on a national detection of CGs on a national level will not detect most LF level will not detect most LF cloud flashescloud flashes

CGCG LargeLarge

cloudcloud

All cloudAll cloud

• •

Page 14: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

LF cloud validation with LDAR II VHF mapping networkIsolated storms, Dallas/Fort Worth, close NLDN spacing

DE = detection efficiency

Date Storm LDAR NLDN LF Relative Modeled

flashes cloud DE (%) DE (%)

01 May 04 A 431 72 17% 15-25%

01 May 04 B 91 35 38 25-30

01 May 04 C 275 101 37 25-30

13 May 04 39 9 23 25-30

Page 15: Cloud Lightning from the National Lightning Detection Network (NLDN)

Holle | NWA Annual Meeting | October 06

The end

Photo by James Gluba, Bloomington, IL