Storms 1 Flashcards
Thunderstorm hazards
lightning
tornado
hail
downpours of rain (flash flood)
downbursts of air (gustfronts)
Hurricane hazards
contain thunderstorms
storm surge / costal flooding
high waves
coastal erosion
in a lightning strike, what does the stepped leader do?
makes the first electrical connection between the cloud and the ground
what happens to the air when lightning strikes?
becomes super hot and explodes as a supersonic shockwave
- rapid expansion of air molecules create sound waves radiate out abt 1 mile/ 5 secs
What are the two most common lightning
intracloud (IC)
cloud to ground (CG)
1 to 10 more IC than CG
Is air a good conductor?
Nope, insulator
- can only flow thru if voltage very high
Where do CG negative strikes come from?
cloud base
- most initiate btwn mid-level -charge region & small positive charge region at base
What kind of CG strike is more common?
Negative strikes
What is a return stroke?
when there is a connection between the leaders from cloud (+) and ground (-), channel forms and electrons accel thru it causing heat and flash
How does a CG Negative strike happen?
- negatively charged step leaders -> ground
- positively charged leader from the ground reaches up
- the first connection completes the channel and electrons accel thru it = heat
Where do CG positive strikes come from?
the anvil
(higher in the thunderstorm)
Which is stronger and more dangerous, positive or negative CG strike?
Positive
-> travel greater distance, so they’re much hotter, brighter, longer in duration
CG Positive strikes strength and frequency
less frequent
can be 10x more strong (5x hotter than surface of sun)
are primary cause of wildfires
Where is lightning alley
Florida in North America
highest density (most frequent) of lightning worldwide
Central Africa
how many deaths does CG lightning strikes cause every year?
2.4 million CG strikes/year
6-12
- can be killed if directly struck
How do we detect lightning
ground based networks
space based satellites
Sound travels ____ than light
slower
How far away is lightning?
time (sec) between seeing lightning and hearing thunder
÷ 3
= number of km away
30/30 rule
if 30 seconds or less btwn the flash and bang,
move indoors and stay for 30 min after the last lightning/thunder
What are some safe areas to hide from lightning?
strong buildings
fully enclosed metal cars
What are some unsafe areas to hide from lightning?
small structures
metallic objects (pole, fence)
trees (can explode), water, open fields
What can we do if we are caught in the open during a lightning storm?
lightning safety crouch
- CPR can revive smb if striked
Explain the lightning safety crouch
feet together (if apart, it’ll make a circuit thru you)
hands on ears
bend down
Thunderstorm scientific term
Cumulonimbus (CB)
What are thunderstorms? Describe their appearance.
thick clouds w lightning & thunder, made of large cells that evolve in 15-30 min
Overshooting top or dome (if updraft too strong)
anvil/mushroom (can be 100 kms!)
mammatus clouds right below anvil
rain
main updraft (15km) & striations
flanking line / cloud base near ground (1km)
wall cloud
funnel cloud or tornado
What is the anvil?
thick cloud top near top of troposphere (10-15km, but can be 100km)
What causes /are the fuel for thunderstorms?
energy comes from temperature and humidity
Multicell thunderstorms
contain 2+ cells
Squall line
a line of thunderstorms
What are the three types of supercell thunderstorms
low precipitation
classical
high precipitation
supercell thunderstorm
very large, rotating single cell
can cause tornadoes, hail, lightning, heavy rain, strong winds
What are the three stages of thunderstorm devleopment?
- Cumulus stage
- updraft
- no rain
- no anvil - Mature Stage
- up & down drafts
- heavy rain
- crisp anvil - Dissipating stage
- downdraft
- light rain
- fuzzy anvil
Name the layers of atmosphere
Thermosphere
Mesopause (85km)
Mesosphere
Stratopause (45km)
Stratosphere
Tropopause (11km)
Troposphere
How does the warm ground affect the air?
Sensible heat
- warms air in troposphere
- increases TEMP
Latent heat
- evaporates water from lakes
- increases HUMIDITY
Together, they power storms!
What solar energy Is absorbed at the 3 heights?
- thermosphere -> absorb non visible light
- stratopause -> absorb UV by good ozone
- earth surface -> absorbs light & heats ground
Describe the charging cycle for Tstorms
Charge: solar heating input (day)
Discharge: Infrared radiation cooling (day & night)
When is the most likely time for Tstorm formation and why?
Late afternoon & early evening
End of charging cycle
- Greatest accumulation of heat near sunset everyday
most thunderstorms happen in which part of the atmosphere?
troposphere
How is lightning born
btwn two oppositely charged regions
-> thunderstorms have ability to separate charge = powerful electric fields
leaders
- electrically conductive channels
- tunnel path through air
- branch out in two directions in attempt to neutralize charge separation
lightning that occur inside the cloud are called?
cloud flashes
intercloud lightning
lightning that connects to the ground is called?
ground flash
cloud to ground lightning (CG)
what happens to the air when lightning strikes?
becomes super hot and explodes as a supersonic shockwave
- rapid expansion of air molecules create sound waves radiate out abt 1 mile/ 5 secs
the sound we hear is called
thunder
What are recoil leaders
positive
- scout path thru air with flickering segments following
- form on decayed segments of highly branched positive leaders
How are CG lightning characterized as positive or negative? Where do the electrons go?
depend on net charge of bolt shifts to the ground
-CG
negative leader w surplus of electrons connect to ground, ground gains net negative charge
+CG
positive leader w deficit of electrons connect to ground, ground gains net positive charge
Multistroke CG Flash
- after -CG return stroke, multiple other return strokes follow = causes main channel to flicker
Do return strokes of positive CG flicker?
rarely
Smooth channel lightning
positive CG
due to lack of branching and strong positive leaders
“Branchless lightning” -> leaders hidden in clouds
Bolt from the blue
bolt lead miles away from storm
startling zaps r prolly negative
lots of branching
How much volts is needed to make a spark in the air?
3 billion volts / km
What percent of Canadian CG lightning is positive?
10-25%
Percent of people who survive a lightning strike
90%
Favorable Tstorm locations in CANADA
praries cuz of advection
Favorable Tstorm locations in US
Florida, gulf states
Favorable Tstorm locations in general
close to equator
- warm ocean currents = warm humid air
Advection
warm humid air carried by wind
