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Understanding Low Frequency Cloud Lightning Data from the National Lightning Detection Network

This publication explores the significance and characteristics of Low Frequency (LF) cloud lightning data from the National Lightning Detection Network (NLDN). LF cloud lightning is often found near cloud-to-ground (CG) lightning and typically occurs before CG events in approximately 70% of thunderstorms. The paper includes a comprehensive overview, discusses spatial representation of lightning activity, and presents validation data on LF cloud performance. The study highlights detection challenges and the differential capability of the NLDN to identify LF cloud flashes.

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Understanding Low Frequency Cloud Lightning Data from the National Lightning Detection Network

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  1. Cloud Lightningfrom the NationalLightningDetection Network(NLDN) • Ronald L. Holle, Nicholas Demetriades, and Martin Murphy • Vaisala, Inc. • Tucson, Arizona

  2. Outline -- Value of LF cloud data-- Overview of LF cloud data-- Spatial representation of lightning activity-- Validation of LF cloud performance

  3. 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

  4. Outline -- Value of LF cloud data -- Overview of LF cloud data-- Spatial representation of lightning activity-- Validation of LF cloud performance

  5. 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

  6. The main challenge for LF cloud lightning detection:Source signal strengths All cloud Large cloud CG The median LF large cloud pulse amplitude is 5% as strong as for CGs A network configured for optimal detection of CGs on a national level will not detect most LF cloud flashes

  7. 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

  8. Outline -- Value of LF cloud data -- Overview of LF cloud data-- Spatial representation of lightning activity-- Validation of LF cloud performance

  9. LF cloud lightning detection data - Flash level Dallas- Fort Worth region Blue: Total VHF lightning mapping (1190 sources) Red: LF cloud lightning (5 sources)

  10. 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

  11. VHF total lightning mappingAreal coverage of flashes at the storm level Dallas- Fort Worth region 18-minute period

  12. Outline -- Value of LF cloud data -- Overview of LF cloud data-- Spatial representation of lightning activity-- Validation of LF cloud performance

  13. The main challenge for LF cloud lightning detection:Source signal strengths All cloud Large cloud CG The median LF large cloud pulse amplitude is 5% as strong as for CGs A network configured for optimal detection of CGs on a national level will not detect most LF cloud flashes

  14. LF cloud validation with LDAR II VHF mapping networkIsolated storms,Dallas/Fort Worth, close NLDN spacing 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 DE = detection efficiency

  15. The end Photo by James Gluba, Bloomington, IL

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