Transcript Meteorology Part II - myersparkenvironmental

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What type of weather is associated with a
low pressure system?
How does pressure change as you go
towards the center of a high pressure
system?
What direction do the winds blow in a high
pressure system in the Northern
hemisphere? Why does the direction
change in the Southern hemisphere
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Why does it take a plane longer to travel
from NC to Russia than from Russia to NC?
How are air masses named?
What type of air is associated with a mT air
mass?
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Most common features on any weather map
& weather generalizations can be made using
them
- Winds are influenced by pressure (pressure
gradients) centers and the Coriolis effect
CYCLONE
TYPE
LOW
(Cyclones)
CHARACTERISTICS
(Northern hemisphere)
* Winds blow counterclockwise
EXPECTED
WEATHER
* Cloudy
conditions
* Net flow of air inward
* Precipitation
* Produces
* Rising air
violent storms if
* Move roughly west to east direction
the Low pressure
across the often requiring a few days to system is strong
more than a week to move from the west enough
to the east
* Unpredictable – making
accurate estimation of movement
difficult
HIGH
* Winds blow clockwise
(Anticyclone
s)
* Net flow of air outward (due to
friction)
* Sinking air
* Fair weather
* Clear skies
AIR PRESSURE
Pressure decreases
from the outside
towards the center
Pressure increases
as you move from
the outside toward
the center
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Horizontal Convergence- inward movement
of air causes the area occupied by the air
mass to shrink
 - must increase in height to allow for the
decreased area it occupies.
 - produces a taller and heavier air column
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a surface low can exist only as long as the
column of air above it exerts less pressure
than the air that surrounds it
low-pressure center causes a net
accumulation of air increasing its pressure.
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When there is a converging air mass at the
surface, it must be balanced by outflow
 a surface convergence can be maintained if a
divergence occurs above the low at the same rate
as the inflow below and vise versa
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Air spreads out
(diverges) above
surface cyclones and
comes together
(converges) above
surface anticyclones
Recall:
 Warm Air RISES, and Cool Air SINKS.
(ADIABATIC temp. changes)
 At low altitudes, air pressure is HIGH. At high
altitudes, air pressure is LOW.
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So….. in a giant convection
cell…
1. At the equator, air becomes
WARMER and RISES to an
area of LOWER pressure.
2. The LOW pressure causes
the air to EXPAND, moving
it toward the POLES.
3. Next, the air COOLS and
SINKS back to the earth.
4. Finally, the air will move
toward the EQUATOR, where
the cycle begins again.
THE EARTH ROTATES TOWARD THE EAST.
 The resulting wind movement is called the
CORIOLIS EFFECT.
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link
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NOTE: ---Wind systems are measured using
an ANEMOMETER (see p. 545)
---Wind systems are named for THE
DIRECTION THEY COME FROM
 Ex: a
wind would specifically be called a
SOUTHWESTERLY wind.
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TRADE WINDS
Occurs at 30° north and south latitudes.
Air SINKS, WARMS, and moves toward the
equator in an EASTERLY wind.
At the equator, it RISES again and moves
back toward 30°, continuing the cycle.
Called a HADLEY CELL for George Hadley
(who described it in 1735)
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High pressure of sinking air at 30° latitude
forms very CALM winds.
 Called HORSE LATITUDES because SAILORS
WERE STUCK HERE, COULDN’T FEED THE
HORSES, & HAD TO THROW THEM OVERBOARD.
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Low pressure of converging air at the equator
also forms calm winds.
 Called DOLDRUMS because SAILORS WERE
STUCK HERE, ALSO.
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PREVAILING WESTERLIES
Between 30° and 60° north and south
latitude
Circulates OPPOSITE of the Trade Winds.
Air moves AWAY FROM the equator
in an easterly.
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POLAR EASTERLIES
Between 60° and the POLES
Air moves similar to the TRADE WINDS
Characterized by COLD AIR
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Wind caused by TEMPERATURE and
PRESSURE differences
Jet Stream: narrow bands of FAST, highALTITUDE, WESTERLY winds.
 Speed: up to 185 km/hr
 Altitude: 10.7 km to 12.2 km
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Resemble JETS of WATER
2 types:
* POLAR = stronger of the two
SUBRTOPICAL = controls much of the
weather in the US
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an immense body of air that is characterized
by similar temperature and amounts of
moisture at any given altitude
can be 1,600 km or more across… take
several days to move over an area
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When an air mass moves out of the region
over which it formed, it carries its temp &
moisture
- The characteristics of an air mass change as
it moves and so does the weather in that area
- Air masses are classified according to the
surface over which they form (ex: continental
form over the continent)
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Air masses collide forming _fronts_.
Front: narrow region separating 2 air masses
of different densities____
Can cause dramatic __changes__ in weather.
4 Types: _cold , __warm__, ___stationary__,
and __occluded___
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Cold, dense air displaces ___warm___ air,
forcing the warm air _up__ along a steep
front.
Warm air _rises _, cools, and _condenses_
Forms __clouds__, __showers__, and
sometimes __thunderstorms_____
Twice as __steep _ as a warm front and
advance more ___rapidly___ than a warm
front
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Advancing _warm___ air displaces __cold___
air, and the warm air rises above the cold air.
The warm air moves easily, forming a rather
__gradual___ frontal slope
Extensive _cloudiness__ and
___precipitation____
Gradual _warming__ in temp occurs in the
area
Wind shift from the _E___ to the _SW__ is
associated with a warm front
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Warm and Cold air meet, but neither moves
into the other’s territory, which __stalls__ the
front.
Wind moves __parallel _ to the lines of the
front
They stall because the ___temperature__ and
__pressure___ gradients are small.
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A cold air mass moves so rapidly that it
__overtakes a warm front____.
The cold air masses collide, pushing the warm
air ___upward____.
Causes precipitation on both sides of the
front_______.
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Main weather producers in the United States
Large centers of low pressure that generally
travel from west to east causing storms
Air moves in a counter clockwise direction
towards the center of the low.
Most middle latitude cyclones have a cold
front and a warm front extending from a
central area
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Thunderstorms: Form when warm humid
air rises in an unstable environment
generates lightning and thunder and
frequently produces gusty winds, heavy rain
& hail
•Strong updrafts
•Supply moist air
•Cloud grows vertically
•Amount of precipitation
is too great for updrafts to
support
•Heavy precipitation
•Gust winds, lightning
•Downdrafts dominate
through the cloud
•Cooling effect of falling
rain and the flowing of
colder air from high above
calms the storm
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Violent windstorms that take the form of a
rotating column of air called a vortex that
extends downward from a cumulonimbus
cloud.
Violent windstorms that take the form of a rotating column of air called a vortex that
extends downward from a cumulonimbus cloud.
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mesocyclone- vertical
cylinder of rotating air
that develops in the
updraft of a
thunderstorm
strong winds high in the
atmosphere
 cause winds lower in the
atmosphere to roll
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updrafts cause the
rolling air to tilt and
become well
established
3. not all mesocyclones
produce tornadoes
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Low pressures within a tornado cause air near
the ground to rush into a tornado from all
directions
As the air streams inward, it spirals upward
around the core
Rating of a tornado is determined by the
worst damage left behind
 Fujita tornado intensity scale (F0- F5) Maximum
winds can reach 480 km/hr
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Whirling tropical cyclones that produce winds
of at least 119 Km/hr
Cause high winds, huge waves, and extensive
flooding hundreds of miles away
Growing threat- >50% of the US population
lives within 75 km of the coast.
The north pacific has the greatest number of
storms (~20 per year)
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Late summer when temps are warm enough
to provide heat and moisture the air
Begins as a tropical disturbance- disorganized
clouds & thunderstorms w/ low pressure
Inward rush of warm moist air moves towards
the center
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Air turns upwards and rises in a
cumulonimbus cloud (eye wall)
 eye wall has the greatest wind speeds & heaviest
rain
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Rising air is carried away from the storm
center- provides room for more inward flow
At the very center of storm is the eye
 zone where precipitation ceases and winds
subside.
 air gradually descends in the eye and compressedwarmest part of the storm
Storm Surge: dome of water 65- 80 km
 wide that sweeps across the coastwhere the eye moves onto land
 Hurricanes weaken when they move over
cool ocean waters- can’t supply heat and
moisture necessary to maintain its strength
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friction with rough land surfaces causewinds
to subside
Eventually, the hurricane reaches a location
where the air aloft is unfavorable and it will
die out.