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GOPH375 > Ch 10 > Flashcards

Ch 10 Flashcards

1
Q

Severe Weather

A
  • ~75% of yearly deaths and damages from natural disasters
  • More people are usually killed by severe weather than EQs, volcanoes, mass movements combined
  • Frequency of $1bil+ events is increasing
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2
Q

Winter Storms: Cold

A

Hypothermia: begins when body temp drops below 35C, deadly
- Most hypothermia deaths are associated with outdoor rec or disabled vehicles today
- Wind exacerbates cold temp by stealing heat from body

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3
Q

Winter Storms: Precipitation

A

Precipitation as snowflakes or ice particles/hail
- When snow or ice fall through warmer air, they may melt and continue as rain or enter below-freezing air where it:
~ refreezes into tiny ice particles = sleet
~ supercools to freezing rain and freezes upon impact with subfreezing surfaces
- Falling snow also accumulates on snow

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4
Q

Blizzards

A
  • Strong cold winds >56kph and blowing/falling snow reduce visibilities to <400m
  • Cyclone may travel slowly even though winds are fast
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5
Q

Ice Storms

A

Large volume of supercooled rain that freezes on impact (freezing rain)
- Adds mass to trees, power lines, roofs = collapse

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6
Q

Thunderstorms

A

Tall, buoyant clouds of rising moist air that generate lightning and thunder, often with rain, wind, and sometimes hail
- Air temp decreases with alt = unstable conditions
- Rising warm, moist air may begin condensing = cumulus clouds and releasing latent heat = energy needed for severe weather
- If warm air continues to rise, cumulonimbus clouds can build up to 20km high

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7
Q

Thunderstorms develop from airlifted by 3 different mechanisms:

A

1) Convectional lifting
2) Frontal lifting
3) Orographic lifting

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8
Q

Convectional lifting

A

Surface heated air rises buoyantly since it’s less dense, clouds form locally

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9
Q

Frontal lifting

A

Air masses collide at frontal boundaries, warmer air mass rises to form clouds

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10
Q

Orographic lifting

A

Air mass flows up a steep slope, expands and cools = increases relative humidity to form clouds and thunderstorms

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11
Q

Air-mass Thunderstorms

A
  • Common in afternoons/evenings
  • Year round in tropics, summer in midlats
  • Rising, moist warm mass cools, condenses into cumulus clouds, continued updraft yields cumulonimbus
  • Heavy rain produces downdraft
  • Warm updraft and cool downdraft side-by-side
  • Downdraft and rain evaporation (absorbs heat) at surface extinguishes updraft then storm ends
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12
Q

Severe Thunderstorms

A

Severe when: winds >93kph and hail diameter >25mm
- Commonly form at long (100-1000km) frontal collisions, allow up- and down- drafts @ same time
- Much smaller cyclonic thunderstorms with high wind speeds occur within larger systems

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13
Q

Thunderstorms in Canada

A
  • Distribution of lightening activity is non-uniform pattern, Southern Ontario has the most thunderstorms
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14
Q

Severe Thunderstorms: Supercells

A

Supercell thunderstorms: violent severe thunderstorms with huge updrafts
Really moist and warm air rises than hits troposphere where temp continues to increase = massive cloud
- 20-50km rotating mass or mesocyclone
- Vortex is rotating updraft about vertical axis
- Rain and hail fall at leading edge
- Potential powerful tornadoes spin of trailing edge

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15
Q

Thunderstorms in North America

A
  • Not geographically homogenous, most common in Florida, where Atlantic and Gulf of Mexico warm, moist air masses meet
  • Common in central and southern US states (warm moist air from Mexico hits cold air masses moving from north)
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16
Q

Heavy Rains and Flash Floods

A

Thunderstorms can be a major supplier of water to an area = flash floods

17
Q

Hail

A

Layered ice balls dropped from storms with:
- Buoyantly rising, hot, moist air -> keep moisture aloft in circular motion and accumulates water which freezers, then melts, then freezes again = layered
- Upper-lvl cold air creates large temp contrasts
- Strong updrafts keep hailstones aloft while adding layers
Most common in late spring and summer, along jetstream in colder midcontinent

18
Q

Tornadoes

A

Rapidly rotating column of air from large thunderstorm, spawn out of leading edge of supercells
- Highest wind speeds of any weather phenomenon
- 70% of Earth’s tornadoes occur in Tornado Alley in US, move from SW to NE
- Travel up to 100kph, wind speed can be >500kph
- Low pressure in core of vortex (<1km wide) and high velocity air = sucks up objects
- Commonly form high in atmosphere, many never touch ground or travel many km in irregular path along ground

19
Q

Tornadoes in 2011

A
  • 2nd deadliest tornado year with 553 deaths
  • 1706 confirmed tornadoes in US
  • Six EF5 (max cat) events with winds in access of 200mph
  • 24 tornado deaths everywhere else in world
20
Q

Regional Scale Formation of Tornadoes

A

3 air masses moving in different directions meet and give shear to thunderstorm
- Wind, humid, low Gulf of Mexico air + cold, dry, mid-alt Canadian or Rocky Mountain air + fast, high-alt jetstream winds
Rising Gulf air is spun 1 way by mid-alt cold air then spun other way by jetstream = corkscrew effect
- Warm air rising on leading side (rly fast)
- Cold air descending on trailing side

21
Q

Supercell Thunderstorm Scale Formation of Tornadoes

A

Tilt of supercell moves warm updraft to center of the storm = rotation that spins off
- Formed below main mass of mesocyclone where updraft is strongest, wall clouds are where powerful tornadoes can emerge
- Rotation develops in wide zone, core pulls into tighter spiral -> speed increases
- Wind speeds highest few hundred m above ground (slowed by friction @ ground)
- Hook echo: high reflectivity area in radar image shaped like a hook, indicator of tornado potential

22
Q

Vortex Scale Formation of Tornadoes

A
  • Air mass collisions low in atmosphere creates horizontal tube of air spinning parallel to ground
  • Warm rising air provides vertical wind shear that lifts spinning tube of air
  • As it rises, it stretches, diameter decreases, velocity increases (figure skater)
  • Can rise to mesocyclone status
23
Q

F scale

A

Wind damage scale (F0-F5) estimating wind speed from damage to structures, trees
- New EF scale is more precise
- Deaths and damages increase from F0-F5, most destruction from minority of large tornadoes

24
Q

Deaths from:

A
  • Wind blowing away buildings/trees
    -Wind-blown debris impacts
  • Winds remove roofs, lift out contents
25
Q

Most deaths in states between:

A

Gulf of Mexico and Canada
- Deaths on decline, due to better warnings
- Deaths primarily elderly, those in mobile homes, exterior rooms with windows, and those not receiving warning

26
Q

How Tornadoes Destroy a House

A

Given a wood frame house on a concrete slab:
- Flying debris shatters windows
- Wind under eaves and through windows raises pressure, lifting the roof
- Wind over root creates uplift
- Once roof is gone, the walls are less supported
- Exterior side walls go first, then front and back
- Inside walls progressively fall
- Safest place = inside room

27
Q

Tornadoes: Safe Rooms

A
  • Cellar was safest room traditionally
  • Safe rooms are an alternative for homes without cellar -> interior closet-like rooms with foot thick concrete walls and roof, like bank vaults
28
Q

Lightning

A
  • Generated from thunderstorms and cause thunder
  • Much less common over ocean than land
  • Influenced by topography, rainfall, and temp
  • top cause of naturally-lit forest fires
  • Major cause of weather-related death in US
  • Same geographic distribution as thunderstorms
29
Q

How Lightning Works

A
  • Flow of electric current: top of clouds have excess + charges seeking balance with bottom of clouds’ excess - charges
  • Charge imbalance from freezing and shattering of super-cooled water drops - charge separations distributed by updrafts and downdrafts during early cloud buildup
  • Neg charges in basal portion of cloud interact with ground, attracting + charges on ground surface
  • Lightning moves from cloud to gound, ground to cloud, or from cloud to cloud
  • Speeds up to 6k miles/sec, in several strokes within few seconds
30
Q

General Progression of lightning:

A
  • Static electricity builds in base of thundercloud inducing opp charge on ground
  • Discharge begins within cloud, initiates downward stream of e- -> stepped leader
  • Conductive stream moves earthward in 50m jumps as a stepped leader
  • As stepped leader near ground, ground electric field increases, sending streamer of + sparks upward, connecting with stepped leader ~50m above ground
  • Connection closes circuit and + charges rush to cloud as return stroke with flash
  • More strokes occur as charges flow
    All in 1-2 seconds
    Electrical discharge with temp up to 55k F
  • Heat explosively expands air surrounding the bolt yielding the thunder soundwaves
31
Q

Don’t get hit by lightning

A
  • Strikes up to 15km from thundercloud
  • Risk extends wherever thunder can be heard
    Avoid lightning:
  • get inside house, don’t touch anything with electrical cables or wires
  • get inside car, don’t touch anything!
  • if outside, move to low place, away from anything tall; assume lightning crouch (balls on feets w/ hands over ears)
  • remove electronic devices
32
Q

Heat Waves

A
  • invisible, silent killers
  • Biggest killer of all severe weather phenomena in US for past 30yrs
  • Hyperthermia (body temp over 40C) can be deadly
    Signs of heat exhaustion/stroke:
  • High body temp
  • Confusion, staggering, strange behavior
  • Fainting
  • dry skin with rapid slow of pulse
33
Q

Urban heat island

A

Cities are warmer than surrounding area, up to 10C at night
- Concrete, asphalt, and stone absorb heat during the day and release it at night
- Less evaporation than undeveloped areas

GOPH375 (10 decks)

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