Sem#2 Chap 4 Flashcards
Tropical Cyclones Always originate in ________
in the tropics, over warm oceans
* Can move into mid-latitudes and over land
Strong topical cyclones are called _________ over Atlantic and eastern Pacific Oceans
hurricanes over Atlantic and eastern Pacific Oceans
Strong topical cyclones are called ________ over western Pacific Ocean
typhoons over western Pacific Ocean
Strong topical cyclones are called _________over Indian Ocean
cyclones over Indian Ocean (or in the
southern hemisphere)
Tropical cyclones are, Any storm originating between ____ and ____ latitude
5° and 30° latitude
Hurricanes
- Large spiral storms in tropical latitudes
- Sustained winds >119 km/h
Tropical disturbance
A cluster of thunderstorms lasting >1 day
Tropical depression
- A disturbance circulating around low-pressure center
- Maximum sustained winds of 37–61 km/h
Tropical storm: (wind speeds classification)
- Maximum sustained winds of 63–118 km/h
Hurricane (wind speeds classification)
- Maximum sustained winds >119 km/h
Category: 1
Dangerous winds produce some damage:
Well-constructed frame homes could have damage to roof shingles, vinyl siding, and
gutters. Large branches of trees snap, and shallowly rooted trees
may topple. Some power outages occur.
Category: 2
Extremely dangerous winds cause extensive damage:
Well constructed frame homes sustain major roof and siding damage.
Many shallowly rooted trees are snapped or uprooted, blocking
roads. Near-total power outages occur.
Category: 3
Devastating damage occurs:
Well-built frame homes may incur major damage or removal of roof decking. Large trees snap or are uprooted. Numerous roads become blocked. Electricity and water
are unavailable for days to weeks.
Category: 4
Catastrophic damage occurs:
Well-built homes sustain severe damage. Most trees snap or are uprooted, and most power lines are downed. Debris isolates residential areas, and power outages
last weeks to months. The area becomes temporarily
uninhabitable.
Category: 5
Total catastrophic damage occurs:
Most homes are destroyed. Only strongly reinforced buildings remain standing. Debris isolates large areas, and power outages last for weeks to months. Most of
the area remains uninhabitable for weeks or months.
Class Question #1
What variable does the Saffir-Simpson scale use to classify hurricane
intensity?
a) atmospheric pressure at center
b) amount of rainfall
c) diameter of entire storm
d) sustained wind speed
d) sustained wind speed
A Hurricane’s Eye
- A nearly cloud-free, circular area in the storm’s center
- Top of eye is at tropopause, base is ~1 km from sea level
- Eye base diameter can reach ~65 km
- Eye diameter tapers down, top is ~2 times diameter of base
A Hurricane’s Eye Wall
- Swirling clouds around eye
- Fastest winds are in eye wall
- Air spirals up but slows at higher elevations.
Spiral Rainbands
Arc-shaped banks of aligned thunderstorms
Air flows along rainbands to the hurricane’s eye.
Heavy downpours occur from the bases of rainbands.
Gaps between rainbands have less/no rain.
Eye typically has no rain.
Hurricanes typically have several distinct rainbands.
Hurricane’s Inner core:
- Extends from eye, through rainbands surrounding eye
- Wind circulates completely around eye.
- Principle rainband defines inner core boundary.
Hurricane’s Outer zone:
- Location of outer rainbands
- Rainbands do not completely surround eye.
Hurricane’s Forward motion:
- Average speed ~20–35 km/h
- Stalling is common.
- Winds shift direction as a hurricane passes overhead.
Hurricane Season
Hurricanes need 26°C water at a depth of 60m to develop.
Warm tropical water develops by late summer and early fall.
Atlantic and eastern Pacific season: June 1–November 30
Western pacific season: July 1–October 30
Hurricanes may develop later if water retains warmth.
Latent Heat Fuels Hurricanes
Heat from ocean moves into air via evaporation and condensation.
Ocean water initially evaporates, then rises as vapor.
Rising vapor molecules condense into clouds, releasing latent heat.
Released latent heat warms surrounding air, fueling the storm.
Warmed, unstable air continues rising.
Hurricanes strengthen when moving over warmer ocean water.
Positive Feedback Mechanisms
Storms create conditions that provide them with more energy
Positive feedback #1:
- Sea spray from wind increases evaporation by 100–1,000 times.
- Increased evaporation creates more rising vapor molecules.
Positive feedback #2:
- Updrafts carry vapor molecules into dry, upper troposphere.
- Evaporation, and latent heat release, occurs in upper troposphere.
Converging air …
is a lifting mechanism for hurricanes
Converging scenarios
- A fast-moving air stream merges with slow moving air.
- Air streams moving in different directions merge.
Merging air is forced upward. What happens?
- Cooling occurs as air rises.
- Cooled air condenses into liquid (cloud droplets).
- Condensed vapor releases latent heat.