Transcript Jet Streams

It all starts with the SUN!
The Sun’s energy is efficiently stored on Earth in such things as
oil, coal, and wood (plant materials) .
Each of these was produced by some biological means when the sun
acted upon living organisms.
Our existence depends on the Sun because without the Sun, there
would be virtually no warmth on Earth, no food for plant life, and no
plants to feed animal life, as the sun drives the hydrologic cycle.
Although the Sun radiates its energy
in all directions, only a small portion
reaches our atmosphere.
This relatively small portion of the
Sun’s total energy represents a large
portion of the heat energy for our
Earth. This thermal energy is of vast
importance to our meteorology.
Thermal energy transfer on
Earth occurs in several
different ways.
Convection is the movement of molecules
within fluids (liquids and gases). It cannot
take place in solids, since diffusion cannot
move among molecules of a fixed nature.
Convection is one of the major modes of
heat transfer on Earth. Convective heat
takes place through diffusion – the random
Brownian motion of individual particles in
the fluid.
It is through radiation that the sun’s energy
reaches us here on Earth, and convection
that it moves through our atmosphere and
hydrosphere (both of which are fluid in
nature)
The solid Earth conducts thermal energy.[1]
How is energy transferred through Earth’s
solid surface?
What is the major mode of thermal energy
transfer on Earth?
Why is Earth so efficient at convection?
What is the ultimate source of most of the
energy on Earth?
Give an example of radiant energy transfer
on Earth.
Atmospheric or air pressure is the force exerted on the
Earth’s surface by the weight of the air above the surface.
• created by the molecules’
 Sizes
 Motion
 Density (number present)
Air pressure is not uniform
across the Earth, however.
These pressure differences are the
result of low and high air pressure
systems which are caused by unequal
heating across the Earth's surface.
Atmospheric circulation patterns are one of the factors responsible for
the distribution of thermal energy on the surface of the Earth. Once
the sun’s energy reaches us, it doesn’t just stay in one place.
The distribution of thermal energy, of
course, is what drives weather at the
surface of our planet.
For the most part, air moves along
pressure gradients from conditions of
high pressure to lower pressure; warm
air rises, cold air sinks.
If the high pressure area is very close to the low
pressure area, or if the pressure difference is very
great, the wind can blow very fast.
Movements of air are influenced by several factors,
including the motion of the Earth itself, as well as gravity.
What other
forces? Notice
that the equator
spins with a
greater velocity
than the pole.
The differential
velocities
associated with
the Earth’s
rotation give rise
Things
to on
notice:
Observe how all wind directions are
to an effect
deflected
in the northern
the air
knownare
as named
• Winds
for the direction
from whichand
theysouthern
COME
the Coriolis Force hemisphere, due to the Coriolis Force.
• Certain latitudes are important in global circulation patterns
Describe why there is wind on Earth.
What causes pressure difference in the
atmosphere of Earth?
The higher in altitude you go on Earth, the _____
the air pressure.
What is the origin of Coriolis force?
What direction does Coriolis force deflect air in
the northern and southern hemispheres?
• At the equator warm air rises and diverges aloft toward
each hemisphere's poles
• Around 30° N & S
latitudes, the air has cooled
sufficiently to begin sinking.
This colder sinking air forms
a high at the surface (the
Subtropical High).
• This is known as the Hadley
Cell and as it reaches the
surface, it spreads out such
that the flow returns to the
equatorial zone to complete the
cell movement.
Jeopardy Reflection :
I will give you the answer, and you will write the question. Phrase it as they do
on Jeopardy! (Such as “What is…or Who is…”)
This force is a result of
differential rotational
velocities experienced at the
poles, and the equator of
Earth.
• Between 30 and 60° latitudes the Ferrel Cell experiences a reversed
flow pattern of the Hadley Cell.
• Warm (but not hot, as in the equatorial zone), moist air around 60°
latitude rises and draws in the cooler 30° latitude air to replace it. This
causes an area of very low wind conditions, known as the horse
latitudes.
•The warm air reaching altitude
moves towards the equator,
cooling as it goes, and then sinks
where it encounters air from the
Hadley Cell.
• Surface air in the Ferrel
Cell flows poleward and
again is deflected to the
right (north) and left
(south).
The smallest global circulation cell is the Polar Cell.
With the circulation patterns established in both the
Hadley and Ferrel Cells, you could probably deduce the air
flow within the Polar Cell without a diagram.
As you can see, they
indeed flow equatorially
at the surface, and
poleward aloft.
Ferrel Cell
Hadley Cell
Starting at the equator, the term ITCZ refers to the InterTropical
Convergence Zone, which indicates that surface air (windflow) is
converging from both hemispheres.
The direction of
prevailing winds
between the
Subtropical Lows
and the ITCZ is
westward in both
hemispheres, and
are called
“Easterlies”, or
Tradewinds.
Given this, can
you deduce the
direction of the
polar winds?
Generally, prevailing surface winds between the Subtropical high, and the
Subpolar low flow in an eastward direction, making them “Westerlies”.
Remember, winds are named for the direction they flow FROM.
Describe how and where a Hadley Cell
forms.
Describe how and where a Ferrel Cell forms.
What is the smallest global circulation
pattern?
What is the ITCZ, and where does it form?
What is another name given to the Easterly
winds at the equator?
Any discussion of global
circulation patterns cannot be
complete without talking about
the Jet Streams you hear about
on the Weather News.
•These function as steering
currents for surface air masses
and as zonal boundaries for sharp
differences in temperature.
•Jets are something like "rivers of
air" found at high altitudes and
noted for their high speeds.
Not to be outdone…the
•They develop just below the
southern hemisphere also
Tropopause.
What is the tropopause? has its version of polar and
The tropopause is the boundary of
subtropical jets, as seen in
atmosphere that forms between the
the image above.
troposphere and stratosphere.
In the Northern Hemisphere, there are two such streams: the MidLatitude Jet - which is the one usually affecting weather in the U.S.,
Europe and Asia, and the Subtropical Jet. Typical positions of the two
are shown in this diagram
The Jet Streams affecting the U.S. move up and down
across the continent, being directly over the area where
temperature differential between surface and aloft is
greatest.
When it is farther north, the weather to its south tends to
be mild or at least less cold.
When the stream swings south, very cold, often harsh
weather prevails at the surface on the northern side.
This diagram shows
two typical positions
at the height of
Summer and of
Winter.
With wind speeds between 50 and 250
mph, it is easy to see how the economics
of air travel may be influenced.
What is the difference between typical westerlies,
like we already learned about, and the jet stream?
In which direction do jet streams flow in the
hemispheres?
During which season in North America, does the
midlatitude jet usually migrate southward?
What are jet streams in the southern hemisphere
called?
Why are jet streams economically important?
What do jet streams do, besides slow down
westward moving aircraft?
Atlantic hurricanes usually begin off the African coast in
subtropical waters that are very warm in summer - often in
excess of 28° C.
Ocean water is vaporized by the Sun's rays, producing warm air that
rises. Its moisture then condenses with upward cooling, releasing great
amounts of heat that drive the disturbance until, if conditions persist,
it graduates into a hurricane.
Hurricanes in the
Atlantic tend to
average from about
5 to 15 events per
year.
Worldwide,
between 80 and 100
normally occur.
Most are
Categories 1 to 3.
Driven by westward flowing upper level trade winds, and
powered by their extreme internal energy derived from hot
air condensation, hurricanes move across the Atlantic
toward North and South America.
Depending on
interactions with
air masses on the
continents or the
open ocean,
(westerlies)
hurricanes will
frequently be
blocked or
deflected
northward and
may or may not
make landfall.
Hurricanes which do manage to impact land, do so in
an unforgettable way!
It is helpful to look at the map below which plots
the worldwide distribution of the paths of major
cyclones (hurricanes) during the last 150 years.
By far, the
South Pacific
and the west
coast of
Central
America are
more often
targeted by
hurricanes
than the
Atlantic
Basin.
Relatively few
form in the
Southern
Hemisphere.
What is the origin of HURRICANES?
Where would TYPHOONS form and impact?
In what area of the world would CYCLONES form
and impact?
What prevailing winds might influence an Atlantic
Hurricane from making landfall?
By far, which hemisphere is most targeted by
hurricanes?
El Nino Southern Oscillation
El Niño is a warm water surface
current appearing annually around
Christmas time along the coast of
Ecuador and Peru and lasting a few
weeks to a month or more.
El Nino Neutral
El Niño is observed when the easterly trade winds, which usually drive
the warm waters westward, weaken, allowing warmer waters of the
western Pacific to migrate eastward and eventually reach the South
American Coast. The cool nutrient-rich sea water normally found along
the coast of Peru is replaced by warmer water depleted of nutrients,
resulting in a dramatic reduction in marine fish and plant life.
La Niña is characterized by unusually cold ocean
temperatures in the Equatorial Pacific, compared
to El Niño, which is characterized by unusually
warm ocean temperatures in the Equatorial
El Niños were
Pacific.
present 31% of the time
La Niñas
23% of the
In a La Nina year, the easterly tradeand
winds
are unusually
time
from
1950 towater
1997,
stronger than average, blowing all the
warm
surface
leaving
about
46%
of the
to the south pacific, drawing up even
colder
water
from
in a neutral state.
Antarctica off the coast of South period
America.
The frequency of El
Niños has increased in
recent decades, a shift
being studied for its
possible relationship to
global climate change.
How does El Nino form?
In an ENSO neutral year, describe the water off
the west coast of South America, near Peru and
Ecuador.
What are the ramifications of an El Nino event on
the biodiversity and overall health of the
ecosystem in the region described above?
How does a La Nina differ from an El Nino event?
Which event is most common?
El Niño’s negative impacts have included damaging winter storms in
California and increased storminess across the southern United States.
Some past El Niños have also produced severe flooding and mudslides in
Central and South America, and drought in Indonesia.
On the positive side, El Niño can help to suppress Atlantic hurricane
activity. In the United States, it typically brings beneficial winter
precipitation to the arid Southwest, less wintry weather across the
North, and a reduced risk of Florida wildfires.
The
consequences
of an El Nino
year
GLOBAL
Weather
Patterns
The
consequences
of a La Nina
year
Neutral conditions persist with a slight hint of a coming La
Nina as seen here, with the tiny expanse of below-average
sea surface temperatures (SSTs) across the eastern
What type of Winter
equatorial Pacific Ocean
can we expect this
year, as a result?
Slightly warmer and wetter…
However, this is due to a
stronger than normal jet.
We could see a few severe
outbreaks…more chance
of snow, and especially
ice. (Greatest chance of
precipitation in Jan and
Feb)
This data represents
departures from normal.
Climate prediction center says that the neutral conditions will continue
through the summer of 2014.
Just like the opening…this is Jeopardy! I will give you the
answer, and you must write the question, phrased as they
do in Jeopardy. “What is…?” You have 20 seconds for each
question, and you MAY use your notes.
1. The scale by which hurricane intensity is measured
2. Typical cyclonic storm originating off of the western
coast of Africa.
3. The high speed, high altitude air current which most
influences North America
4. Air circulation cell which forms between ITCZ and 30°
North and South Latitude
5. Region in our atmosphere where Jet streams form