Jet stream= - where is it?

narrow, fast-moving, easterly air flow - may cause unusual weather by steering air masses - at middle lats just below the top of troposphere

17. Hurricanes Flashcards by Kathryn Ayroud

Storms=

disturbances with strong winds and precipitation

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Air Masses=

large volumes of air with distinct properties

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Land air masses are ___(dry/ moist) and marine air masses are ___

land= dry
marine= moist

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Front=

a boundary between air masses

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Warm front=

contact where warm air mass moves to colder area

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Cold front=

contact where cold air mass moves to warmer area

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Where do storms typically develop?

at fronts

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Jet stream=

where is it?

narrow, fast-moving, easterly air flow
- may cause unusual weather by steering air masses

at middle lats just below the top of troposphere

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Hurricane=

How are they classified?

A large rotating mass of low pressure, bringing strong winds and torrential rain. Defined by having sustained winds of 120km/hr or more

classified by max sustained wind speed

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Hurricanes require 3 things:

ocean water warmer than 26C
warm, moist air
The Coriolis Effect

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Hurricane winds need water vapor. What provides the energy?

latent heat of condensation

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Explain the difference between a hurricane, typhoon, and cyclone

Hurricane= extreme tropical storm over Atlantic & Eastern Pacific Oceans
Typhoon= over western pacific ocean
Cyclone= over Indian ocean & Australasia

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Why are hurricanes inhibited near the equator?

Because they need the impact of the Coriolis effect, which is not at the equator

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Hurricanes depend on the availability of ___ water as an energy source

warm

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T/F
Tropical cyclones are rare in the south atlantic

true

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There are __ categories of hurricanes. What do larger numbers indicate?

larger numbers= lower central pressure, greater winds, and stronger storm surges

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What is the typical central pressure of a hurricane system?

950hPa

As low as 870hPa

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T/F
The energy release by a single hurricane can exceed the annual electricity consumption of the US and Canada

true

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What’s the approx diameter of a hurricane?
How does this compare to the size of a mid-latitude cyclone?

100-400+km

1/3 of the size of a mid lat cyclone

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Hurricanes occur where a ____(deep/shallow) layer of warm eater exists and during times of ____(highest/ lowest) SSTs

deep
highest

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What’s the hurricane season in NH vs SH?

NH: august and sept

SH: Jan-March

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Tropical disturbance=

clusters of small thunderstorms

Can lead to a hurricane

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Tropical depression=

when at least 1 closed isobar is present

Can lead to a hurricane

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Tropical storm=

further intensification of a tropical depression: winds speeds must reach 60km/hr

At this point, the system is named. Becomes classified as a hurricane once wind speeds of 120km/hr are reached

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Most tropical disturbances develop from ______ waves . Some also form from ____-related convection or in association with mid-latitude ____

easterly ITZC troughs (migrating toward lower lats)

Easterly waves=

undulations in the trade wind pattern - spawn hurricanes in the Atlantic

~__% of tropical disturbances intensify into more organized rotating storms

10%

Between which latitudes do hurricanes typically form? Why?

Between 5 and 20 degrees Optimal formation coniditions here - Between 0 and 5 degrees, can't form because no coriolis - higher than 20 degrees= the water is not warm enough

Hurricane formation requires an atmosphere which cools fast enough w/ height so that it's potentially unstable to: Where is this available

moist convection Available in the western tropical oceans but not in the eastern parts of the ocean

Hurricane formation requires relatively moist air near which part of the atmosphere? Why?

Mid-level of the troposphere (4900m) For latent heat release

What kind of vertical wind shear b/w the sfc and upper troposphere is required for hurricane formation?

Low values (less than 37km/hr) of vertical wind shear

vertical wind shear=

the change in wind speed with height

Fully developed hurricanes move ____

poleward

tropical disturbances and depressions are largely regulated by: Which direction do they therefore move?

trade wind flow simply move westward

T/F Upper level winds and ocean temperatures are more important for tropical disturbances/ depressions than for tropical storms/ hurricanes

false for tropical storms/ hurricanes, upper-level winds and ocean temp gain importance (not just trade wind flow)

The low pressure center of a hurricane is called:

the eye of the hurricane

Hurricane diameter is typically less than ___km Up to:

200km 800km

In a hurricane, does the horizontal pressure gradient increase or decrease with altitude?

decreases (slowly)

At what hPa are pressures within the hurricane approx = to pressure outside the storm

400hPa

Where in a hurricane is there cyclonic circulation? Anticyclonic?

From the surface up to 400hPa= cyclonic From the 400hPa level to the tropopause= anticyclonic

The upper portions of a hurricane storm are blanketed by what? Why?

a cirrus cloud cap due to overall low temps

Describe the eye of a hurricane: - what is the air/ weather doing? - Diameter of the eye? - What is indicated by a shrinking eye? - How fast does the eye move?

- an area of descending air, relatively clear sky & light winds - 25km ish - shrinking eye= storm intensifying - 20km/hr

Hurricane Eye wall=

The area just outside the eye, where the air ascends from the sfc to the tropopause - the winds are strongest here - Largest clouds & highest precipitation (100 inches/day!)

T/F The sinking air in a hurricane eye warms adiabatically, making the eye much warmer than the rest of the hurricane

true

How quickly does air in the hurricane eye sink?

Most of it descends very slowly, taking days to traverse the eye's depth

Where in a hurricane is the pressure gradient strongest?

near the eye wall, where the most violent winds are produced

Where do the strongest storm surges occur in relation to the hurricane?

to the right of the hurricane

There are 4 main causes of hurricane dissipation:

- Passing over land or cold water: this removed warm water source, which is the basic fuel driving the storm - The storm meets vertical wind shear - Dry, cool air is pulled into the storm system: this reduces the deep convection that keeps the storm going - Low pressure develops above the storm in the higher part of the atmosphere

Describe what happens when there's an area of high pressure above a hurricane vs an area of low pressure

High: helps move out the buildup of air above the storm, so the storm can keep drawing in new air at the surface (keeps the storm alive) Low: causes inward flow above the storm. The rising air within the storm then has no escape --> storm collapses in on itself!

T/F Even as a hurricane weakens, it can still bring huge amount of rainfall 100s of km inland

true

storm surge=

abnormal increase in shoreline sea level generated by a storm - greatest threat to life & property from a hurricane

Give 4 main ways hurricanes are destructive

high winds intense rainfall storm surges tornadoes

Where are winds and surge typically most intense? Why?

In the right front quadrant of the storm - b/c this is where wind speeds combine with the speed of the storm's movement to create the area of highest potential impact

There are 2 processes that can cause storm surges:

1. hurricane winds drag surface waters forward and pileup the waters near coasts 2. lower atmospheric pressure raises sea level (1mb decrease= 1cm increase of sea level)

Storm surges raise coastal sea level by __-__m typically, but can be as much as __m

1-2 7

most hurricanes contain clusters of tornados. - where do they occur? - How do they form?

The right front quarter of the hurricane's movement The slowing of the wind by friction at landfall= tornado formation

The Fujita intensity scale for tornados goes from ___ to____

F0 (light) F6 (inconceivable damage)

Give up to 5 historical tropical storms/ hurricanes that were very destructive

Andrew, 1992 Mitch, 1998 Katrina, 2005 Irene, 2011 Sandy, 2012

A hurricane watch is issued if:

an approaching hurricane is predicted to reach land in more than 24hrs

A hurricane warning is issued if:

an approaching hurricane is predicted to reach land in less than 24hrs

Hurricane ____ is the largest Atlantic hurricane on record. What category? What did it cause? Why did it cause so much damage?

Sandy, cat 1 - severe coastal erosion, extreme flooding - 233 deaths & $68 billion in damages - a storm surge coincided with peak high tides in heavily populated New York & New Jersey

Which hurricane was the costliest & deadliest US hurricane? Where did it flood?

Katrina, Cat 3 New Orleans