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.
Convergence Lifting in Easterly Waves
An easterly wave is a curve in the flow path of trade winds.
Air on eastern side of wave slows as it turns north.
Faster-flowing air merges with slowed air, creating lift.
Air becomes unstable, and thunderstorms develop.
Satellite imagery illustrates successive easterly wave storms.
Class Question #2
Why does hurricane season occur in late summer?
a) Late summer is when tropical water is warmest.
b) The Intertropical Convergence Zone (ITCZ) is south of the equator
during late summer.
c) Condensation, and thus latent heat absorption, is most likely during
late summer.
d) Late summer creates atmospheric conditions that are especially
likely to create high-pressure cells.
(NO GIVEN ANSWER)
Stages in the Formation of an Atlantic Hurricane
Atlantic hurricanes begin with winds blowing off the Indian Ocean.
Easterly waves spawn thunderstorms as air blows across Ethiopia.
Ocean water feeds energy to thunderstorms when over the Atlantic
Thunderstorms begin rotating around a low-pressure center.
Thunderstorms organize into spiral bands, and an eye develops.
Storm’s centrifugal force intensifies low-pressure center.
A hurricane’s track depends on regional winds.
High-Altitude Divergence and Thunderstorm Intensification
Warm Atlantic provides ample water vapor for thunderstorms.
Latent heat causes air to expand laterally at high elevations.
High-altitude divergence intensifies low pressure center.
Air pressure at sea level drops.
A distinct low-pressure center develops.
Eye Wall and Rainbands Evolve with Cyclonic Flow
Thunderstorms cluster around low-pressure center.
A spiral-shaped storm begins forming.
Coriolis force creates cyclonic flow around low-pressure.
Wind and waves create positive feedback for thunderstorms.
Thunderstorms intensify due to increasing release of latent heat.
Tropical depression develops when winds blow >37 km/h.
Eye wall and spiral rainbands begin to form.
Centrifugal Force and Low-Altitude Divergence
Centrifugal force causes air to move outward at storm’s base.
Air pressure at storm’s base decreases.
Centrifuging intensifies air column’s already low pressure.
Centrifuging provides a positive feedback for storm growth.
Tropical storm develops when winds blow 63-119 km/hr.
Hurricane develops when winds blow >119 km/h.
Hurricanes grow due to:
- Condensing water vapor releasing latent heat
- Weak high-altitude winds limiting wind shear
Hurricanes weaken due to:
- Cool ocean water at high latitudes
- Land surfaces limiting latent heat supply
- Strong high-altitude winds shearing away storm clouds
Hurricane Air Flow and Eye Development
Angular momentum increases air speed as air spirals inward.
Eye wall air rises to tropopause, then spirals outward.
A low, vertical air pressure gradient evolves.
Steepest air pressure gradient exists across eye wall.
Steep eye wall gradient creates fastest winds across eye wall.
Air also rises in the updrafts of spiral rainbands.
Air sinks between rainbands.
The Importance of Gravity in Hurricane Eye Development
Gravitational force first equals vertical air pressure gradient force.
Gravity eventually exceeds vertical air pressure gradient force.
Air sinks into storm’s center due to gravity’s stronger force.
Descending air compresses, warms, dries, and becomes cloudless.
Warmed, sinking air expands at low altitudes.
Low-altitude divergence creates positive feedback for storm
Hurricanes cannot form on, or cross, ____________
the equator
Coriolis force is too weak near the equator to initiate rotation
Hurricane Tracks often shift towards _______
poles
Coriolis force is stronger on pole side of hurricane
Tropical disturbances strengthen into ________
depressions.
Tropical depressions strengthen into _____
into storms.
Tropical storms strengthen into _______
hurricanes.
Hurricane intensity changes _______
over time.
Hurricanes are downgraded as _______
winds weaken.
Hurricane Dimensions Criteria (not numbers but the things measured)
- Eye wall diameter
- Extent of hurricane-force winds
- Diameter of clouds seen from space
Class Question #3
Identify a variable that strengthens hurricane intensity.
a) strong, high-altitude winds creating wind shear
b) the release of latent heat after ocean water first evaporates and then
condenses
c) land surfaces supplying storms with plenty of water vapor
d) cool ocean water at low latitudes supplying storms with energy in
the form of calories
(No answer given)
Wind damage depends on ________
intensity and duration.
Wind applies __________ to objects
dynamic pressure (push)
Wind flows create pressure differences __________
around buildings
- Low-pressure zones pull on built structures.
- Dynamic pressure pushes on built structures.
Wind speed at any site depends on 3 variables:
- Distance from eye
- Forward speed of storm
- The site’s position relative to storm’s forward motion
Greater wind speeds are on the side of the storm where:
- Rotation is in same direction as forward motion.
Lesser wind speeds are on the side of the storm where:
- Rotation is in opposite direction as forward motion.
(Storm Surge) Hurricanes create domes of ____________
water beneath their eyes:
* Rotating winds push water into a mound.
* Low pressure beneath eye pulls water into a mound.
More About Storm Surge
Waves exist on top of the storm surge.
Storm surge and waves are often several meters high.
Storm surges cause flooding in low-lying areas.
Storm surges and waves can wash away coastal communities.
Storm Surge Height variables include:
- Wind speed and direction
- Air pressure
- Site’s position relative to eye
- Tides
Storm Surge Higher storm surge:
- Wind blows towards shore
- Site is near the eye
- Surge occurs at high tide
- Surge enters a bay
Storm Surge Lower storm surge:
- Wind blows away from shore
- Site is far from eye
- Surge occurs at low tide
- Surge encounters a straight shoreline
Hurricane waves create extensive damage to:
- Coastal reefs
- Beaches and dunes
- Homes, buildings, and coastal structures
- Harbors
- Fishing fleets
- Sailing vessels and pleasure craft
Torrential rain and flash flooding often occur ____
inland
Mudslides and debris flows may occur ______
on saturated ground.
Stalled hurricanes may create _______
extensive flooding.
Hurricane threats to mountainous islands:
- Orographic uplift creates heavy rains.
- Flash floods and mudslides
Hurricane threats to low lying islands:
- Wind and salt spray
- Wave damage
- Storm surge inundation
Western Pacific Typhoons
Eastern Pacific hurricanes often drift west towards Asia.
China, Japan, Philippines, Taiwan, and Vietnam are at risk.
Western Pacific has Earth’s warmest surface seawater.
Some typhoons occur outside normal typhoon season.
Super typhoons are Category 4 and 5 hurricanes.
Typhoon impact is partially determined by topography.
Mountainous areas often have mudslides from heavy rainfall.
Hurricane Impacts and Predictions
Severe societal disruptions follow a hurricane’s landfall.
Hurricanes destroy buildings, roads, harbors, and utilities.
National Hurricane Center (NHC) collects storm data.
Aircraft release dropsondes that parachute into storms:
* Collect pressure, wind speed and direction, and GPS data
Data feeds computer models that predict hurricane tracks.
Multiple computer models increase prediction accuracy.
Ensemble Simulations and Cones of Uncertainty
Different computer models use slightly different data.
National Weather Service (NWS) averages all the predictions.
Maps are drawn showing a hurricane’s most likely path.
Cone of uncertainty represents the range of various models.
Locations inside cone have a higher probability of impact.
Simulations are fairly accurate 1–3 days into future.
Ensemble simulations are run 2–4 times a day.
Hurricane watch and/or tropical storm watch:
- 48 hours before landfall
- For areas within the cone of uncertainty
Hurricane and/or tropical storm warning:
- 36 hours before landfall
- For areas likely to experience hurricane force winds
- For areas likely to experience tropical-storm force winds
Storm-surge warnings follow ________ warnings.
hurricane warnings
Preparing for a Storm’s Arrival
Monitor the storm:
* Maintain batteries in cell phones and emergency radio
Secure your property:
* Secure valuables, vital documents, and medicine
* Close and reinforce windows and doors
Evacuate when ordered:
* Not doing so risks the lives of first responders.
Sheltering in Place
If unable to evacuate, prepare to shelter in place
Ensure adequate water supply
Stockpile non-perishable food
Stockpile prescription and overthe-counter medicines
Create a communication plan for family and friends
Avoid draining cell phone and emergency radio batteries
Stay in an interior room to avoid flying debris
Mitigating Hurricane Damage
Zoning laws establish building setbacks along risky coastlines.
Protective landscapes dampen wind and wave impacts:
* Wetlands and prairies absorb floodwaters.
* Forests help prevent mudslides.
Building codes ensure water- and wind-resistant construction.
* Build homes on reinforced concrete stilts
* Use reinforced concrete for walls, and steel cables to anchor roof
Poor communities often cannot afford mitigation strategies.
