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EESA09H3 (200)
Lecture 5

EESA09H3 Lecture Notes - Lecture 5: Tornado Climatology, Natural Disaster, Canadian Prairies


Department
Environmental Science
Course Code
EESA09H3
Professor
Tanzina Mohsin
Lecture
5

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Wind lecture week 5: thunderstorms and tornadoes
What is a thunderstorm?
Convective storm: caused primarily by surface heating, also topography, surface wind
convergence
Most thunderstorms occur in the summer.
Common in southern Ontario
Only type of storm with thunder and lightning
Condition for thunderstorm: vertical unstable air mass
Formed mostly in tropical and ITCZ areas.
Four categories:
Ordinary
Multi-cell
Supercell
Mesoscale convective
complexes
develop within
large air masses
Gust front of one
initiates another
storm
upper level
winds from
the north;
can form
tornadoes,
microbursts
multiple thunderstorms
when one is about to
die the other one
starts.
circulation fashion.
Little vertical
wind shear
required.
moderate wind
shear
strong wind
shear
Weak vertical wind
shear
Relatively
shorter; < 1
hour; diameter,
1 km or less.
lasts longer than
ordinary
storm can
last for
several
hours
Over 12 hours
Dynamics:
Rising air cools down due to expansion; condensation releases latent heat
Condensation creates cumulonimbus clouds.
Heat forces air upwards into a strong updraft, rising air.
three stages (common for all types):
o cumulus: surface heat forms this cloud
o mature: updraft (hot air rises) and down draft(precipitation) formation of cell
called convective cell. Gust front forces more air into the updraft.
o Dissipating: downdraft cuts off updraft and storm loses energy source and
dissipates
Microbursts: localized downdrafts; radial burst of surface wind.
Squall line
String of thunderstorms along a cold front
Lightning
Thunderstorm clouds have hydrometeors:
find more resources at oneclass.com
find more resources at oneclass.com
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