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GOPH375 > Ch 11 > Flashcards

Ch 11 Flashcards

1
Q

What are hurricanes?

A

Large tropical cyclones that generate winds over 240kph and push massive amounts of water onshore as surges, up to 6m over sea lvl
- Heat engines that convert heat of tropical ocean into winds and waves
- Tornadoes can form from their clouds
- Transporters for excess tropical heat to mid-lats

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2
Q

Tropical storm vs hurricane

A

Storm: >63kph
Hurricane: >118kph and centrifugal acceleration causes clear, central eye
Strength: depends on the efficiency of energy transfer, winds flowing to core then upward (no wind shear aloft)

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3
Q

Requirements for development of hurricane:

A
  • Upper 60m of seawater >27C
  • Warm, humid, unstable air
  • High enough latitude for Coriolis effect to spin it -> 5º+
  • Weak upper lvl winds, good if blowing in same direction as developing storm is moving
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4
Q

Begins with tropical disturbance:

A

Low pressure zone draws in cluster of thunderstorms
- Weak surface winds
Coriolis effect creates tropical depression
- Cyclonic rotation
- Receives identifying #
Core sends warm, moist air into stratosphere
Rising moist air cools to dewpoint temp, then condenses and releases latent heat
- Stronger updrafts

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5
Q

How a hurricane works

A
  • Beyond the hurricane air mass, descending air warms adiabatically (density decreases) and clears area outside of the hurricane boundary
  • Large latent heat release from rising winds in core = warms eye
  • Low pressure core relative to surroundings
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6
Q

Eyewall and Eye

A
  • Inward-flowing air rotates faster closer to core
  • when speed can’t increase further, converging winds rise sharply
  • Eyewall = cylinder-shaped area of spiraling upward thunderstorms around eye with heaviest rainfall and high winds in storm
  • Cool air sinks into eye and warms/absorbs moisture -> clear core forming eye into atmosphere
  • Eyes can be 8-200km in diameter
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7
Q

Tornadoes within hurricanes

A

Form predominately from outer rain bands in hurricanes that are:
- Large, intense, strongly curving
- Moving as system at 12-30kph
- Interacting with old, weakened fronts
- Over land
Friction from movement on land = slows surface wind, higher winds keep up momentum (provides vertical shear for tornado rotation)

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8
Q

Energy flow in hurricane

A
  • Warm, moist surface winds pick up heat from ocean as converge on eyewall
  • Rising eyewall winds release latent heat and cool = increased buoyancy and velocity
  • Flow outward and lose long-wave energy
  • Turbulent waves from surface winds
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9
Q

Hurricane energy release

A

Transfers heat: tropical seas to hurricane core
Huge amounts of latent heat released as air rises
Generates energy 200x than worldwide electricity generating capacity
Cloud formation and rain

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10
Q

Differences from high-lat storms:

A
  • Latent heat from condensation = main energy source
  • Moves onto land and weakens rapidly
  • Not associated with fronts
  • Weaker high-alt winds = stronger hurricane
  • Hurricane winds weaken with height
  • Air in center of eye sinks
  • Hurricane centers are warmer than surroundings
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11
Q

Different names in different parts of the world:

A

Cyclones = Indian Ocean
Typhoons = Western Pacific Ocean
Hurricanes = Atlantic Ocean

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12
Q

Hurricane Origins

A

Form on west sides of oceans where warm water is concentrated or off Pacific coast of Mexico (Not off coast of Brazil, Atlantic too narrow, not enough warm water)
Form b/w 5-20º lat (not along equator due to zero Coriolis effect, cannot cross equator once formed -> would lose rotation)

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13
Q

Saffir-Simpson scale for damage, categories:

A

1) Some wind damage
2) Some trees, roofs, mobile homes blown down
3) Larger trees down, destroy mobile homes
4) Signs, windows, roof, damaged, inland flooding
5) Severe building damages

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14
Q

North Atlantic Ocean Hurricanes

A
  • Large, mobile, and long-lasting hurricanes, 4-28/yr
  • Most form in late summer when sea surface temps are warmest
  • Most hit US from Aug-Oct
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15
Q

Cade Verde-type Hurricanes

A
  • Begin as easterly waves moving W from Africa
  • May gain typical cyclone status in warm waters near Cape Verde Islands
  • Blow W with trade winds, gaining energy over great distances of warm seawater
  • Movement curves N due to Coriolis effect when reach western Atlantic
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16
Q

Hurricane paths are difficult to track because:

A
  • Adjust to other high- and low- pressure systems
  • Trade winds blow them W
  • Coriolis effect add curve to right
  • Bermuda high (high-pressure zone) commonly sits above North Atlantic Ocean
17
Q

Bermuda High influences paths:

A

If small and E = hurricane curves around it
If strong and large = hurricane pushed along US E coast
If SW = hurricanes pushed into Caribbean Sea and Gulf of Mexico

18
Q

Caribbean sea and Gulf of Mexico-type hurricanes

A
  • Form at ITCZ, where trade winds meet
  • Daily thunderstorms, add more rotation to cyclone
  • Location of ITCZ moves with migration of Sun, avgs 5ºN
  • ITCZ S of equator in Northern hemi winter and N of equator in summer
  • Low-pressure area forms where air flows converge = thunderstorms = hurricanes
19
Q

How Hurricanes are Named

A
  • North Atlantic basin tropical storms and hurricanes given names, alternating male and female
  • Premade lists for next 6yrs
  • Begins with 21 letters (skip Q, U, X, Y, Z)
  • Names of especially destructive storms are retired
  • If >21 storms, start over with Greek alphabet
20
Q

Is the increase of hurricane due to human activity or natural variation?

A

Total energy release by hurricanes is higher, probably due to increasing sea-surface temps and increased H2O vapour in lower atmosphere, possibly due to global warming

21
Q

Atlantic Multidecadal Variability

A
  • Alternating pattern in North Atlantic Ocean surface temps
  • Involves ocean, atmosphere, natural, and human changes
  • Since 1870, each multidecadal stretch when sea-surface temps were higher = more hurricane activity
  • Since 1870, each multidecadal stretch when sea-surface temps were lower = less hurricane activity
22
Q

Atlantic Cyclone Energy

A
  • Index compiles energy expended in each tropical cyclone in each season, calculated every 6hrs and added cumulatively
23
Q

Hurricane Damages

A

Hurricane deaths are down in recent decades
- Better advanced warnings
Hurricane dmgs are up
- More ppl living on coastline
- Larger, more expensive homes on coastlines
- Damages calculated in constant dollars suggests the future will be even more costly

24
Q

Storm Surge Hazards

A

Most deaths associated with sea surges
Cubic yard of water is 1685 pounds, incompressible -> water hits with a lot of force
Rise in sea lvl under storm due to:
- Winds push water ashore to pile up above normal lvls, blow inalnd on right of eyewall, out from land on left of eye
- Low atmospheric pressure causes water to mound up under eye of hurricane
- 95% of surge is wind-driven
- Surge greatest on Eastern side of hurricane

25
Q

Inland Flooding

A
  • After moving on land, no more water vapour is absorbed into hurricane = loses strength
  • Precipitation of massive vol of water in dissipating hurricane can cause massive flooding
  • Even weak hurricanes can cause flooding
  • 59% of hurricane deaths is from flooding
26
Q

Can New Orleans be Protected?

A
  • Water and floods are part of New Orleans
  • City built on delta
  • 3 centuries of river and hurricane floods
  • Levees built to protect the city
  • Deltas naturally subside -? parts of New Orleans 6m below sea lvl and continues to subside
  • Levees also prevent deposition of new layers of sand and mud that would build up land lvl
  • Creates bowl, with lake and river water lvls higher than city land
27
Q

Problems w/ New Orleans:

A
  • Subsidence will continue
  • Mississippi River is increasingly elevated
  • High lake lvls
  • Much marshland in Gulf of Mexico destroyed
  • Globally rising sea lvls
28
Q

Reduction of hurricane damages

A

Manufactured homes
Roofs
- 1st step in destroying build is often to lift off roof
- Prevention: elimination or strengthened of eaves, strap roofs to walls, ban stapled asphalt roofing sheets on plywood

29
Q

Global rise in sea lvl

A
  • Global rise of ~1ft in 20th century
  • Likely to rise 2ft or more in 21 century
  • 1ft of sea lvl can move beaches inland by 1000ft in low-lying areas
30
Q

Cyclones and Bangladesh

A
  • 7/9 world’s most deadly weather events in 20th century were cyclones hitting densely pop Bangladesh -> low-lying sediments of deltas of Ganges and Brahmaputra Rivers, 1/3 below 6m elevation
  • In avg year, 20% of country is submerged in floods
  • 1970 cyclone during full moon high tides brought surge of 7m, winds of 255kph -> 300k ppl killed
  • 1991 cyclone with 6m surge, 235 winds killed 140k ppl, 10mil homeless
  • Pop of Bangladesh is expected to double in next 30yrs

GOPH375 (10 decks)

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