MICHELLE WILSON LIGHTNING. BACKGROUND- LIGHTNING Separation of charges within the thunderstorm Ice particles tend to be positively charged Mix of water.
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Slide 1
MICHELLE WILSON LIGHTNING
Slide 2
BACKGROUND- LIGHTNING Separation of charges within the
thunderstorm Ice particles tend to be positively charged Mix of
water and ice (graupel) tends to be negatively charged Updrafts
separate the two Bringing light ice particles to top of
thunderstorm Keeping graupel near the base For best chance of
lightning Cumulonimbus cloud bases- 5-6 km up Extend to 15 km
Slide 3
BACKGROUND- LIGHTNING The surface will become positively
charged underneath the negatively charged cloud base Creation of an
electric field Downward (negatively) charged leaders extend down to
Earth Can be met with positively charged leader Taller objects at
the surface gain positive charge and connect easier to the cloud
base
Slide 4
BACKGROUND- DISCHARGE The positive charge is neutralized first
and causes a return stroke from the ground to the cloud Try to
balance out the charges Discharge stroke can reach temperatures
greater than 50,000 K Air expands due to rapid temperature change
creating thunder
Slide 5
BACKGROUND- TYPES Intra- Cloud Cloud to Cloud Cloud to Ground
(CG) Most dangerous Least common- 25% of worlds lightning
Slide 6
BACKGROUND- CLOUD TO GROUND Positive Less than 5% of lightning
Comes from the top of the positively charged anvil and extends
directly to the ground Due to farther distance to travel to the
ground experiences a stronger current and is hotter than Negative
Negative Extremely common cloud to ground Negative leader extends
from cloud base to surface to meet positively charged leader
Slide 7
BACKGROUND- CLOUD TO GROUND The discharge for positive CG
lightning occurs over a longer time period then negative This is
the most dangerous type of lightning
Slide 8
VAISALA NLDN The National Lightning Detection Network operated
by Vaisala Inc. Instruments used to detect CG lightning strikes in
the United States 100 remote ground based sensors spread out over
the United States Sensors able to pick up electromagnetic signals
that lightning produce when it hits the Earth
Slide 9
VAISALA NLDN
Slide 10
FLORIDA CLIMATOLOGY- COOL SEASON
Slide 11
FLORIDA CLIMATOLOGY- SPRING TRANSITIONAL
Slide 12
FLORIDA CLIMATOLOGY- AUTUMN TRANSITIONAL
Slide 13
FLORIDA CLIMATOLOGY- WARM SEASON
Slide 14
FLASH DENSITIES Paper: Warm Season Lightning Distributions over
the Florida Peninsula as Related to Synoptic Patterns (Lericos et
al.) Looked at CG lightning during the warm season from 1989-98
from May 1- Sept. 30 th
Slide 15
FLOW REGIMES Calm Flow < 2 m/s Number of flashes- 2,183,375
Ridge North of Florida Number of flashes- 1,435,873 Ridge South of
Florida Number of flashes- 2,859,765 Ridge between Tampa Bay and
Jacksonville, Florida Number of flashes- 1,838,043 Ridge between
Tampa Bay and Miami, Florida Number of flashes- 1,719,069 Northwest
Flow Number of flashes- 1,013,704
Slide 16
CALM DAYS Does not depend on the direction of the mean vector
wind- just the wind speed Subtropical ridge was present in various
locations throughout days categorized as calm Led to an average of
southeasterly flow due to the average 1000 mb height Most prominent
during June and July Least prominent in May Flash Max: Tampa Bay,
Ft. Meyers, Cape Canaveral, West Palm Beach Convection did not move
much through the day More flashes on west coast Tampa Bay Breeze
Warmer Sea Surface Temperatures over the Gulf Enhanced convergence
due to convex coastline
Slide 17
SUBTROPICAL RIDGE NORTH OF FLORIDA Southeast flow over Florida
Spring transition months and autumn transition months Least
prominent in June and July Less moisture into the state Strong
subsidence Due to location of the ridge 2 nd to last in number of
flashes of the six regimes
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SUBTROPICAL RIDGE NORTH OF FLORIDA West coast lightning greater
than East Maximums located over Tampa Bay and Ft. Meyers West Coast
Sea Breeze (WCSB) does not propagate ECSB is weak and short lived-
no max of flashes on east coast Minimum NW of Lake Southeasterly
flow pushes the lake breeze further west which enhances the chance
of interaction with WCSB Maximum in Ft. Meyers occurs earlier than
in Tampa
Slide 19
SUBTROPICAL RIDGE SOUTH OF FLORIDA Most common of the flow
regimes Southwesterly flow over the state 1000 mb height field low
pressure to the north of Florida Development of convection- from
ascent Most prominent in May and June
Slide 20
SUBTROPICAL RIDGE SOUTH OF FLORIDA Flashes dominate the east
coast Max. near Cape, and West Palm Beach ECSB stationary over east
coast Line of increased flashes located from Tampa Bay to the Cape
Convex coastline near Tampa Convection begins due to weak WCSB
Outflow from west coast convection creates line all the way to east
coast
Slide 21
SUBTROPICAL RIDGE BETWEEN TAMPA AND JACKSONVILLE Different wind
directions across the state Jacksonville- Southwesterly Tampa,
Miami- Southeasterly Most prominent during July Fairly weak high
pressure
Slide 22
SUBTROPICAL RIDGE BETWEEN TAMPA AND JACKSONVILLE Similar to
ridge north of Florida Little activity along east coast WCSB
dominates North Florida maximum Both WCSB and ECSB Light winds
(similar to calm regime)
Slide 23
SUBTROPICAL RIDGE BETWEEN MIAMI AND TAMPA Trough located North
of state Most prominent in July and August Jacksonville and Tampa-
Southwesterly flow Miami- Southeasterly flow
Slide 24
SUBTROPICAL RIDGE BETWEEN MIAMI AND TAMPA Maximums located:
Tampa, Cape, West Palm, Ft. Meyers Convex coastlines Cape dominates
with greatest maximum West coast and east coast About same number
of strikes
Slide 25
NORTHWESTERLY FLOW All areas experience NW flow Common in May
only Frontal systems High pressure over Gulf Dry air over the state
Least common flow regime
Slide 26
NORTHWESTERLY FLOW ECSB more dominant Line of storms from Tampa
to east coast More southeasterly though
Slide 27
CONCLUSIONS In Florida the mean low level wind pattern affects
the location and amount of lightning produced as well as WCSB and
ECSB Areas of Maximum lightning occurred along the leeward coast
Lake breeze enhances/restricts lightning Collides with sea breezes
on either coasts Convex coastlines enhance lightning Cape
Canaveral, August, 2009- Space Shuttle Discovery