Transcript Thunderstorms 13-1

THUNDERSTORMS
Section 13-1, p.344
4/8/2016
How do they form?
 3 conditions
 Source of Moisture
 Lifting of air mass
 Unstable atmosphere
Moisture
 Must be abundant moisture in lower levels of
atmosphere
 Moist air rises, water vapor condenses into clouds
 Latent heat is released, warms air, continues to
rise
Lifting
 Warm air keeps getting lifted
 Cold front can push warmer air upward
Unstable atmosphere
 Surrounding air remains cooler than rising air
mass
 Air mass keeps rising
Thunderstorm Development
 3 stages – based on direction of air movement
 Cumulus stage
 Mature stage
 Dissipation stage
Cumulus stage
 Air starts to rise
vertically
 Water vapor
condenses
 Droplets coalesce
 Precipitation falls
Mature stage
 Updrafts and
downdrafts occur in
cumulonimbus cloud
 Precipitation cools the
air as it falls
 Cool, dense air begins
to sink rapidly
Dissipation Stage
 Warm, moist air runs out
 Updrafts stop
 Ends when previously formed precip. has fallen
OUCH!
 Have you ever been shocked by a
metal object?
 This is similar to what occurs with
lightning
 Differences in charge
 You picked up electrons through
friction
 Discharge of electrons occurred
when you touched metal
 Attraction to protons in metal
LIGHTNING
 Transfer of electricity generated by the rapid
rushes of air in the cumulonimbus cloud
 Clouds become charged when friction between
updrafts/downdrafts removes electrons from some
atoms in cloud
 Some regions of air become (+) & some (-)
Stepped leader
 Differences in charge
causes channel of
partially charged air
 Moves from center of
cloud toward ground
Return Stroke
 Channel of positively-charged particles rush up
to meet stepped leader
 Surges from the ground to the cloud
 Brightest part of lightning
 100 million volts of electricity
What is thunder????
Thunder
 SOUND OF LIGHTNING
 Superheated air rapidly expands and contracts
 Why don’t we hear the thunder at the same
time we see the lightning?
 Sound waves travel more slowly than light waves
 The lightning makes it to us first
Thunderstorm Safety
 300 injuries in US per year
 93 deaths
 TIPS
 If outdoors and feeling hair stand on end,
squat low and duck your head
 Avoid using electrical appliances and landline
telephones
 Stay away from water!