Pressure Centers and Winds

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Transcript Pressure Centers and Winds

Global Winds
 It’s all about the open system, our
atmosphere, trying to restore equilibrium,
balance!!
 Obi-wan, I feel a disturbance in the force!!
Climatic Variation & Seasons on Earth
I. Uneven heating of Earth’s surface causes predictable latitudinal variation
in climate. Why? - Angle of incidence… equator vs. poles
North Pole
Equator
Earth
South Pole
Thus, radiation is more intense near the equator compared to the poles.
For this reason, it’s warmer near the equator than at the poles.
Earth’s Seasons
I.
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts toward the
sun, it gets more radiation – more warmth
during the summer
When the north pole tilts toward the
sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
SUMMER (Northern Hemisphere)
WINTER (Southern Hemisphere)
Earth’s Seasons
I.
Tilt of the Earth’s axis towards or away from the sun creates the seasons
When the north pole tilts away
from the sun, it gets less radiation –
So it’s colder during the winter
When the north pole tilts away from the
sun, the south pole tilts toward it…
When it’s winter in the north,
it’s summer in the south
WINTER (Northern Hemisphere)
SUMMER (Southern Hemisphere)
Air cools as it
rises, moisture
condenses and
falls as rain
Intense radiation at the
equator warms the air
Warm air rises,
collecting moisture
Lots of rain in the tropics!
Rising air is now dry…
some of the rising
air flows north
some of the rising
air flows south
Dry air descends
at around 30º N
Deserts
…and at around
30º S
The descending air flows N and S
Deserts
What causes
global wind patterns?
Uneven heating of the earth causes
• less dense hot air to rise at equator = low
pressure
• More dense cold air to sink at poles =
high pressure
• Air moves from high P (poles) to low P
(equator)
Paper strips activity
Non-Rotating Earth Model
• On a hypothetical
non-rotating planet
with a smooth
surface of either all
land or all water,
two large
thermally produced
cells would form.
Circulation on a Non-Rotating Earth
Rotation of earth activity
• Pen and paper activity
Rotating Earth Model
• If other effects
were added to the
global circulation
model, the two-cell
convection system
would break down
into smaller cells.
Global Winds!
Circulation on a Rotating Earth
WIND BELTS
 Trade winds are two belts of winds
that blow almost constantly from
easterly directions and are located on
the north and south sides of the
subtropical highs.
 Westerlies are the dominant west-
to-east motion of the atmosphere that
characterizes the regions on the
poleward side of the subtropical highs.
WIND BELTS
 Polar easterlies are winds
that blow from the polar high toward
the subpolar low. These winds are not
constant like the trade winds.
 A polar front is a stormy frontal
zone separating cold air masses of
polar origin from warm air masses of
tropical origin.
Interesting stuff happens at the boundaries
between convection cells…..
A Closer Look
60o
• Make note of
the location
of borders
of the
convection
cells.
30o
There are 3 Main Climate Zones
Analyzing Evidence
• 60o N and S latitude mark the border
between the temperate regions and the
polar regions.
• It also marks the border between the
• 300 N and S latitude mark the border
between the temperate regions and the
tropical region.
• So…
Explanation
• So when the
warm air rises at
equator.
• As it approaches
30o N & S
latitude some of
the air must be
cooling down so
sinks.
Continued
• When its closer to
the surface, the
surface absorbs a
lot of the sun’s
energy so the air
must warm up
again and rises.
Continued
• Then when the
air approaches
60o N & S
latitude the some
air cools down
and so sinks
again.
6 Convection Cells
• So we end up with 3 convection cells in
each hemisphere.
What else is going on at the boundaries
between convection cells ?
• Air rises, low pressure at
– Equator
– 60 N and S
 RESULT
– can be cloudy, rainy weather
• Air sinks, high pressure at
– Poles
– 30 N and S
 RESULT
– fair, nice weather
At 30 N and S….
• up high – subtropical jetstream
• At surface – weak winds known as the
horse latitudes
• Weird?? Why ‘horse latitudes’?
At 60 N and S….
• Up high – POLAR JET STREAM !!!
At equator….
• At surface, weak winds - doldrums
Jet Stream
High velocity Polar and
subtropical jet stream winds are
located in the lower tropopause
Polar jet stream travels at 150350 mph, ~ 4-7 miles up, 1-3
miles thick and 100-400 mi wide
HUGE!!!
Two jets in each hemisphere
• Polar jet is stronger, lower
• Sub tropical jet is weaker, higher up
How does the jetstream affect our
weather patterns?
It controls how much polar air drops into the mid
latitudes and how much mid-latitude air moves
into the northern, polar areas.
It moves with the seasons, more south in the
winter and more north in the summer.
What are the other factors that
affect the global wind patterns?
• besides Coriolis effect?
Land vs sea worksheet
Global Winds Influenced
by Continents
• The only truly continuous pressure belt is the
subpolar low in the Southern Hemisphere. In the
Northern Hemisphere, where land masses break
up the ocean surface, large seasonal
temperature differences disrupt the pressure
pattern.
Global Winds Influenced
by Continents
•
Monsoons are the seasonal reversal of wind
direction associated with large continents,
especially Asia. In winter, the wind blows from land
to sea. In summer, the wind blows from sea to land.
We just learned this !!! 
The difference is that at the Jersey Shore
the land and sea breezes change
according to __________ and ________
• In Asia the land and sea breezes change
according to _____________ and
__________
Monsoon Photos
Click here to learn more about monsoons…
Who needs this information?
• What occupations, etc.?
• Why?
Thinking back to people who need
global wind info ….
• Why do meteorologists need the info?
• What is the difference between weather
and climate???
• Do global winds affect weather or climate?
There are 3 Main Climate Zones
“Air Pressure & Wind”
High
&
Low
Pressures
Pressure Centers and Winds
 Cyclones are centers
of low pressure.
(storms occur here)
 Anticyclones are
centers of high
pressure.
 In cyclones, the pressure decreases from the
outer isobars toward the center. In anticyclones,
just the opposite is the case—the values of the
isobars increase from the outside toward the
center.
How are weather maps made?
In cyclones, (L) the pressure decreases
from the outer isobars toward the
center.
In anticyclones, (H) just the opposite is
the case—the values of the isobars
increase from the outside toward the
center.
Pressure Differences
• Low Pressure system
air coming up either
cloud cover and
precipitation or no
clouds because no
moisture
• High pressure system
air coming down
generally fair skies
Wind and Pressure Relationships
950 mb.
970 mb.
H
960 mb.
930 mb.
L
•WINDS ALWAYS MOVE FROM HIGH
PRESSURE AREAS TO LOW PRESSURE
AREAS!!!!!!!
Cyclonic and Anticyclonic Winds
• When the pressure gradient and the
Coriolis effect are applied to pressure
centers in the Northern Hemisphere,
winds blow:
•Counterclockwise around a low
pressure area
•Clockwise around a high pressure
area
Cyclonic and Anticyclonic Winds
Pressure Centers and Winds
 Weather and Air Pressure
• Rising air is associated with cloud formation
and precipitation, whereas sinking air
produces clear skies.
 Weather Forecasting
• Weather reports emphasize the locations and
possible paths of cyclones and anticyclones.
• Low-pressure centers can produce bad
weather in any season.
Identify the Wind Belts
Click on the link below to see the wind belts in action and answer
some questions!
http://meted.ucar.edu/hurrican/strike/orig/htc5_1.htm