Holle | NWA Annual Meeting | October 06

Cloud Lightningfrom the NationalLightningDetection Network(NLDN)

Ronald L. Holle, Nicholas Demetriades, and Martin Murphy

Vaisala, Inc.

Tucson, Arizona

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

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

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

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

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

• •

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

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

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

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

Holle | NWA Annual Meeting | October 06

VHF total lightning mappingAreal coverage of flashes at the storm level

Dallas-

Fort Worth

region

18-minute period

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

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

• •

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

Holle | NWA Annual Meeting | October 06

The end

Photo by James Gluba, Bloomington, IL