Transcript Cyclone - Atmospheric and Oceanic Sciences

Cyclones
AOS 101 Discussion Sections 302 and 303
Cyclones
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A cyclone is: An area of low pressure around which the
winds flow counter-clockwise in the northern
hemisphere, and clockwise in the southern hemisphere
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Hurricane (tropical cyclone)
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Mid-latitude cyclone
Ridge
Trough
Ridge
Cyclones
L
Fronts and Advection
Locate a Cyclone
L
Norwegian Cyclone Model (NCM)
Polar Front
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The wave cyclone (often called
a frontal wave) develops along
the polar front
When a large temperature
gradient exists across the polar
front - the atmosphere contains
a large amount of Available
Potential Energy
Incipient Stage
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Northward moving warm air
and southward moving cold
air are forced around each
other, forming a bend in the
temperature gradient (b).
This forms the warm front
and the cold front. Now with
a counter-clockwise spin,
winds converge at the newly
formed low pressure
minimum at the center of
rotation.
Mature Stage
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A fully-developed cyclone is
seen 12-24 hours It consists
of:
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a warm front moving to the
northeast
a cold front moving to the
southeast
region between warm and cold
fronts is the "warm sector"
central low
wide-spread precip. ahead of the
warm front
narrow band of precip. along the
cold front
Wind speeds continue to get
stronger as the low deepens
Occluded Stage
As the cold front moves swiftly
eastward, the systems starts
to occlude.
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Storm is most intense at this
stage
have an occluded front trailing
out from the surface low
triple point/occlusion - is
where the cold, warm, and
occluded fronts all intersect
Occluded Fronts
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A region where a faster
moving cold front has caught
up to a slower moving warm
front.
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Generally occurs near the
end of the life of a cyclone
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Drawn with a purple line
with alternating semicircles
and triangles
Cold and Warm Occlusion
Diminishing Cyclone
The warm sector
diminishes in size as
the systems further
occludes.
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The storm has used most
all of its energy and
dissipates
cloud/precip production
has diminished
The warm sector air has
been lifted upward
The cold air is at the
surface - stable situation.
Cyclone on Radar
Tropical Storms
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Low pressure cyclones over tropical waters
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Between 30° N and 30° S
Develop in areas with no horizontal temperature gradient
Season (Atlantic)
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June 30 – November 30
Conditions for a Tropical Storm
3
4
2
1
Tropical Depressions
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Cyclonic rotation
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Not very organized
Low pressure system
No eye
Winds up to 38 mph
Not named yet
Tropical Storm
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Now named
More organized
Usually no eye
Winds up to 73 mph
Tropical Cyclones
Hurricane
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Names
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Western Pacific: Typhoon
Indian Ocean: Tropical Cyclone
Atlantic/Eastern Pacific Oceans: Hurricanes
Tropical Cyclone
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Names
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NOAA
Rotate six lists
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Alternate male and female names
Retire certain names after particularly damaging hurricanes
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Ex. Andrew (1992), Katrina (2005), Rita (2005), Ike, (2008), Igor (2010)
Greek names
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Used for when there are more than 21 cyclones in a year
Cyclone Structure
Eye
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Center of the cyclone
Calmest part of the
storm
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Due to downdraft at
the very middle
Often clear skies, but
sometimes have haze
instead
Center of extremely
low pressure
Eyewall
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Ring of thunderstorms
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Produce heavy rains
Usually produce the strongest
winds
Clouds also are the highest in the
storm here
Eyewall replacement
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When inner wall weakens, outer
wall replaces it
A new outer wall can be made
RAINBAND
EYEWALL
EYE
HURRICANE KATRINA