18 th annual glomw toronto, ontario y. helen yang / patrick king ontario storm prediction centre

© 2000 Roger Edwards

Investigating the Potential of Using Radar to Nowcast

Cloud-to-Ground Lightning Initiation over Southern Ontario

18th Annual GLOMW

Toronto, Ontario

Y. Helen Yang / Patrick King

Ontario Storm Prediction Centre

Environment Canada

23.03.2010

23.03.2010© 2000 Roger Edwards

Motivation

Lightning is a high-impact weather phenomenon!

timely & accurately forecast lightning

future lightning watch/warning products in Canada?

9-10 deaths & 92-164 injuries in Canada each year!(Mills et al. 2008)


Purpose

• To investigate the potential use of radar echoes in nowcasting cloud-to-ground (CG) lightning initiation– To determine a reflectivity threshold value that best

predicts the onset of CG lightning

– To find any correlation between radar echo tops and CG lightning initiation

– To study differences (if any) between negative and positive CG lightning initiation in terms of radar characteristics


Data

• Lightning data from CLDN– Detection efficiency ≥ 90%; location accuracy within 0.5 km

• Radar data from URP– Horizontal resolution ~ 1 km– Temporal resolution ~ 10 min– Data from the King City

Radar (WKR) only▪ Domain of study


Data

• ‘Airmass’ thunderstorms

CG lightning No CG lightning Total

negative 1st flash

positive 1st flash

both

1st flash

63 6 8 66 143

• 143 cases of airmass thunderstorms from Jun-Aug 2008

• A ‘case’ consists of one cell or a cluster of cells on a radar display that may or may not eventually produce lightning


Methods: the premise

• Graupel-ice mechanism for cloud electrification– larger riming graupel and smaller ice crystals collide,

and consequently electric charges are exchanged by these hydrometeors

– rebounding ice crystals tend to become positively charged, while graupel particles become negatively charged

– occur in the mixed-phase region in or near a storm updraft


Methods: the premise

• cloud electrification within a storm updraft

(MacGorman and Rust 1998)

ice crystals

graupel particles

• in mixed-phase layer

main negative charge region

• constant altitudes• • • where CG lightning is often initiated

-20°C

-10°C


Methods

• What reflectivity threshold value at which temperature level can best predict the onset of CG lightning?

• Recall one of the objectives from earlier…

Temp level

[ºC]

Radar reflectivity threshold value

[dBZ]

20 25 30 35 40 45

-20 X X X X X n/a

-15 X X X X X n/a

-10 n/a n/a X X X X

altitude?? temperatureupper air sounding data


Methods: x-section of a case

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 n/a

-15 X n/a

-10 n/a n/a

2120Z 18 Aug 2008

2130Z 18 Aug 2008

2140Z 18 Aug 2008

-10°C-15°C-20°C

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 X X n/a

-15 X X n/a

-10 n/a n/a X

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 X X X n/a

-15 X X X X n/a

-10 n/a n/a X X X

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 X X X X n/a

-15 X X X X n/a

-10 n/a n/a X X X

Hit (H)Miss (M)False (FA)AlarmLead time[min]

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 H H H H n/a

-15 H H H H n/a

-10 n/a n/a H H H

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 H H H H M n/a

-15 H H H H M n/a

-10 n/a n/a H H H M

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 H H H H M n/a

-15 H H H H M n/a

-10 n/a n/a H H H M

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 30 30 20 0 M n/a

-15 40 30 20 20 M n/a

-10 n/a n/a 30 20 20 M

2200Z 18 Aug 2008


Findings: reflectivity threshold

POD [%]

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 99 96 90 70 55 n/a

-15 100 100 96 91 73 n/a

-10 n/a n/a 100 100 88 64

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 36 31 27 10 7 n/a

-15 44 39 31 23 5 n/a

-10 n/a n/a 41 31 16 8

FAR [%]


Findings: reflectivity threshold

CSI [%]

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 64 67 68 65 52 n/a

-15 56 61 67 71 70 n/a

-10 n/a n/a 59 69 76 60

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 19 17 13 10 6 n/a

-15 23 22 19 14 10 n/a

-10 n/a n/a 23 19 17 13

Averageleadtime [min](±5 min)

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 64 67 68 65 52 n/a

-15 56 61 67 71 70 n/a

-10 n/a n/a 59 69 76 60

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 19 17 13 10 6 n/a

-15 23 22 19 14 10 n/a

-10 n/a n/a 23 19 17 13

FAR

ave.leadtime


Findings: echo top threshold

• Things to keep in mind:– Echo tops in relation to only warm season lightning– Echo tops of convections on warmer days higher

than those during cooler days

– Higher echo tops stronger updrafts

– Weak updrafts cannot produce intense electrification needed to generate lightning


Findings: echo top threshold

• Maximum echo top prior to or at the start of CG lightning activity

altitude of 7 km ~ -13 to -29°C levels


Findings: vs

• Things to keep in mind:

– small sample size

Number of lightning-producing cases

‘-’ first lightning flash

‘+’ first lightning flash

Both

‘-’ & ‘+’

total

63 6 8 77

– Cases with both polarities were counted towards both ‘-’ and ‘+’ cases

776


Findings: vs

• Initial lightning flash location to storm location of maximum reflectivity on MAXR [km]

x


Findings: vs

• Initial lightning flash location to storm location of maximum reflectivity on MAXR [km]

mean 2.2 3.5

median 1.9 2.5

longest 7.5 11.2

shortest 0.0 0.0

storm location of max. reflectivity

highly-reflective graupel concentrated

main negative charge cloud region

(± 0.5)


Findings: vs

• Reflectivity threshold predictors

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 100 93 97 93 90 93 70 79 54 79 n/a

-15 100 100 100 100 97 93 92 93 72 93 n/a

-10 n/a n/a 100 100 100 100 87 100 68 64

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 37 76 33 72 28 66 11 35 7 21 n/a

-15 46 81 41 78 33 72 24 62 6 19 n/a

-10 n/a n/a 43 79 33 71 17 48 8 31

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 63 23 66 27 67 33 65 55 51 65 n/a

-15 54 19 59 22 66 27 71 37 69 76 n/a

-10 n/a n/a 57 21 67 29 74 52 64 50

P O D

F A R

C S I

?


Findings: vs

• Reflectivity threshold predictors– Average lead time [min] (±5 min)

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 19 15 18 14 14 8 11 5 7 3 n/a

-15 24 15 23 15 20 15 14 10 10 3 n/a

-10 n/a n/a 24 16 20 13 18 9 14 10

green = ‘-’ first lightning flashesred = ‘+’ first lightning flashes

Temp level

[ºC]


[dBZ]

20 25 30 35 40 45

-20 19 15 18 14 14 8 11 5 7 3 n/a

-15 24 15 23 15 20 15 14 10 10 3 n/a

-10 n/a n/a 24 16 20 13 18 9 14 10


Findings: summary

• -10ºC / 40 dBZ could best predict the onset of CG lightning

– POD=88% FAR=16% CSI=76%– Lead time ~ 17±5 minutes

• Trade-off between the lead time and FAR• Echo tops ≥ 7 km

– used in conjunction with reflectivity threshold to improve accuracy

• Above results are supported by other studies– e.g., Krehbiel 1986; Gremillion and Orville 1999;

Vincent et al. 2004; Wolf 2007


Findings: summary

• Negative vs. positive first lightning flashes– Negative flashes were located closer to the main

negative charge region in a storm cloud– No definitive difference in skills to forecast lightning

of different polarities– Positive-first-lightning-producing storm clouds

became strongly electrified faster than negative-lightning-producing storm clouds


Conclusions

• Potential to use radar echo reflectivity to nowcast CG lightning initiation

• Much more work is needed in developing a lightning nowcast algorithm in a future nowcasting software application tool


Thanks

• National Laboratory for Nowcasting & Remote Sensing Meteorology

• Ontario Storm Prediction Centre

• Ed Becker, Glenn Robinson, Paul Joe, Norman Donaldson, Dave Hudak, and Syd Peel


Outline

• Why…

• What purpose…

• How…

• What findings…

• What conclusions…• Thanks to…


What findings… vs

• Magnitude of electric current [kA]

mean 14.1 21.9

median 12.2 22.6

maximum 33.1 30.5

minimum 2.4 15.5


Methods

• Average altitudes corresponding to different temperature levels for the time periods examined in the study

A l t i t u d e s o f - 1 0 C , - 1 5 C , a n d - 2 0 C I s o t h e r m s

0 . 0

1 . 0

2 . 0

3 . 0

4 . 0

5 . 0

6 . 0

7 . 0

8 . 0

9 . 0

M a y 2 9 J u n 0 8 J u n 1 8 J u n 2 8 J u l 0 8 J u l 1 8 J u l 2 8 A u g 0 7 A u g 1 7 A u g 2 7

D a t e 2 0 0 8

Altitude MSL [km]

- 1 0 C - 1 5 C - 2 0 C

18 th annual glomw toronto, ontario y. helen yang / patrick king ontario storm prediction centre

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