eureka lightning climatology

Eureka Lightning Climatology

Matthew Bloemer Daniel Waller Eureka WFO5/6/10

What to CoverOutline

Background & Motivations What is the Need for this Research Data Constraints, Caveats to Research

Details about the NLDN Research Contributions

Lightning Density and Frequency. By Region By Month of the Year, Time of the Day

Contributing Environmental Factors Storm Relative Flow Thermodynamic Considerations

Previous Topic Research

Need for the Research

- Previous research examined lightning frequency on a national basis (Orville & Huffiness 2002)

-Scales of lightning density have lacked quality of definition for the western region.-Lightning remains as a primary cause of wildfires in the west. (Rorig and Ferguson 2002)

-Several previous studies have shown traditional convective indices to be insufficient for the west. i.e. HLTT Research (Milne 2004)

NCDC Data Characteristics (Current Network Precision Values)

Data comes from the National Lightning Detection Network (NLDN)

Archive recently made available to NWS employees for research purposes

(previously only real time data) Records each individual Cloud-to-Ground Flash Data available back to 1986 Data for each flash includes:

Time of Occurrence (1 Millisecond Temporal Resolution)

Latitude/Longitude (500 meter Spatial Resolution)

Flash Current (signed as positive or negative)

Multiplicity (# of return strokes per flash)

Number of detectors observing a strike.

Flash

Stroke

Stroke

Timeline Improvements Detection Efficiency1984 – 1989 - Continual sensor improvements

- 3 Separate regional lightning detection networks.

N/ASignificant Gaps in data

1989 - Reliable nationwide data available 60%-80%

1994-1995 - First major system-wide upgrade 80%-90%2002-2003 - Second major system wide upgrade

- Flash and stroke detection > 90% Flash Detection60% - 80% Stroke Detection

History of the NLDN…

Since the early 1980’s the NLDN under constant development and refinement

Inconsistencies in data from year to year make pure quantitative comparison troublesome

Largest benefit is in identifying high impact, large outbreaks

Southwest Lightning Density

• Encompasses 1994 - 2008

• Shows Monsoonal Dominated Patterns to the South

• Terrain Driven Events in North and Central California

• Minima ~ 1 lightning strike in 100 yrs / sq km. (Monterey, Marin, and Humboldt Counties)

Key Features

• Local Maxima Areas

• South Fork Mountain ridge / Yolla Bolla • Trinity Tip / Siskiyou • Mount Shasta• Lassen/Modoc• Central Sierra Crest

• Shasta County Relative Maxima (Wintertime Dominated)

Northern California

Winter Months

• Transition Season has two regimes of lightning patterns

• 1 Coastal lightning from cold core systems over the ocean

• December Maxima

• 2 Central Valley…• Storms initiate over terrain• Intensify over warmer surfaces

• Northern Central Valley has some lightning throughout the winter (Shasta Co. Maxima)

• Convergence of low level Southerly winds at as they are funneled by terrain

Summer Months

• April has the lowest Warm Season Lightning Frequency

•May/September have Similar Frequencies

• May – Dynamic• Sept- Thermodynamic

• July is the peak in activity

• June and August have similar overall frequencies

• June - Coastal• August – Inland

• Tip of Trinity County… Same frequency June to July

Summer Months Only

•To further compare lightning occurrences over coastal regimes and inland regimes.

• KMFR Sample Zone• KREV Sample Zone

•Temporal Occurrences of Lightning

• Time of day• Month of year

Geographic Comparison

Temporal Comparison

• Nocturnal lightning more prevalent in coastal areas

• Peak in afternoon lightning occurs 2 hours later at in the KMFR zone than in the KREV zone

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 240%

2%

4%

6%

8%

10%

12%

14%

16%

1 2 3 4 5 6 7 8 9 10 11 1213

14

15

1617

18

19

20

21

2223 24

Lightning Frequency by Time of Day

KREVKMFR

Hour of the day (Pst)

Freq

uenc

y of

ligh

tnin

g

As a

per

cent

age

of t

otal


JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC0.00%

5.00%

10.00%

15.00%

20.00%

25.00%

30.00%

35.00%Lightning frequency by Month of the

Year

KREVKMFR

Month of the Year

Freq

uenc

y of

ligh

tnin

g As

a p

erce

ntag

eof

tot

al


• Nocturnal lightning more prevalent in coastal areas

• Peak in afternoon lightning occurs 2 hours later at in the KMFR zone than in the KREV zone

• Peak in monthly lightning activity occurs in July in both regimes…• KMFR Ramps up

very quickly

• KREV’s season is prolonged in to August

Temporal Comparison

Summer Months Only

•Evaluation of summer daytime lightning

•May - September•11 am - 8pm PST

•. Correlated all lightning that occurred on a given day to the prevailing storm motion at the nearest sounding location

•Assumes the storm motion is valid over the entire zone•Winds < 5 kts considered Calm

• Calculated the density of all lightning that occurred for a given wind direction

•Divided by the number of lightning days to normalize a density for a given wind direction

•Units are Strikes Per 100 Square km per event

Wind Direction Comparison

WEST WINDS

Number of cases130

Average Wind Speed (kts)

11.9Max Wind Speed (kts)

5.0Min Wind Speed (kts)

31.6

SOUTHWEST WINDS

Number of cases185




5.1

SOUTH WINDS

Number of cases95




5.3

SOUTHEAST WINDS

Number of cases31




5.4

EAST WINDS

Number of cases11




5.2

NORTH WINDS(NE to NW)

Number of cases128




5.1

CALM WINDS

Number of cases76


3.4 Max Wind Speed (kts)


0.3

WEST WINDS

Number of cases93




5.0

SOUTHWEST WINDS

Number of cases186




5.0

SOUTH WINDS

Number of cases60




5.5

SOUTHEAST WINDS

Number of cases23




5.0

EAST WINDS

Number of cases10




1.0

NORTH WINDS(NE to NW)

Number of cases47



38Min Wind Speed (kts)

6.5

CALM WINDS

Number of cases54




0.63

HLTT Evaluation

Thermodynamic Considerations

1 10 100 1000 100000

5

10

15

20

25

30

35

40

45

f(x) = 0.966084937617253 ln(x) + 24.6097573138006R² = 0.190968047808722

HLTT vs Strike Count -- KREV

Strike Count

HLTT (00 Z)

HLTT Evaluation

Thermodynamic Considerations

1 10 100 1000 1000025

26

27

28

29

30

31

32

33

34

35

36

37

f(x) = 0.966084937617253 ln(x) + 24.6097573138006R² = 0.190968047808722

HLTT vs Strike Count -- KREV

Strike Count

Numerous

Scattered

Isolated

Possible

Thank You!

Questions??

Suggestions?

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