matthew bloemer daniel waller eureka wfo 5/6/10. outline background & motivations what is the...
TRANSCRIPT
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 12
13
14
15
16
17
18
19
20
21
2223 24
Lightning Frequency by Time of Day
KREVKMFR
Hour of the day (Pst)
Fre
quency o
f lightn
ing
As a
perc
enta
ge o
f to
tal
Geographic Comparison
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
Fre
quency o
f lightn
ing
As a
perc
enta
g e
of
tota
l
Geographic 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
• 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 cases
130
Average Wind Speed (kts)
11.9Max Wind Speed (kts)
5.0Min Wind Speed (kts)
31.6
SOUTHWEST WINDS
Number of cases
185
Average Wind Speed (kts)
14.7Max Wind Speed (kts)
33.9Min Wind Speed (kts)
5.1
SOUTH WINDS
Number of cases
95
Average Wind Speed (kts)
13.4Max Wind Speed (kts)
27.5Min Wind Speed (kts)
5.3
SOUTHEAST WINDS
Number of cases
31
Average Wind Speed (kts)
14.5Max Wind Speed (kts)
30.9Min Wind Speed (kts)
5.4
EAST WINDS
Number of cases
11
Average Wind Speed (kts)
10.8Max Wind Speed (kts)
22.8Min Wind Speed (kts)
5.2
NORTH WINDS(NE to NW)
Number of cases
128
Average Wind Speed (kts)
11.9Max Wind Speed (kts)
30.1Min Wind Speed (kts)
5.1
CALM WINDS
Number of cases
76
Average Wind Speed (kts)
3.4 Max Wind Speed (kts)
5.0Min Wind Speed (kts)
0.3
WEST WINDS
Number of cases
93
Average Wind Speed (kts)
14.2Max Wind Speed (kts)
41.6Min Wind Speed (kts)
5.0
SOUTHWEST WINDS
Number of cases
186
Average Wind Speed (kts)
15.5Max Wind Speed (kts)
50.8Min Wind Speed (kts)
5.0
SOUTH WINDS
Number of cases
60
Average Wind Speed (kts)
19.1Max Wind Speed (kts)
47.9Min Wind Speed (kts)
5.5
SOUTHEAST WINDS
Number of cases
23
Average Wind Speed (kts)
11.3Max Wind Speed (kts)
5.3Min Wind Speed (kts)
5.0
EAST WINDS
Number of cases
10
Average Wind Speed (kts)
10.0Max Wind Speed (kts)
15.3Min Wind Speed (kts)
1.0
NORTH WINDS(NE to NW)
Number of cases
47
Average Wind Speed (kts)
12.6Max Wind Speed (kts)
38Min Wind Speed (kts)
6.5
CALM WINDS
Number of cases
54
Average Wind Speed (kts)
3.3Max Wind Speed (kts)
4.9Min Wind Speed (kts)
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