Download File - Down the Rabbit Hole

GLOBAL CLIMATE
UNDERSTANDING EARTH’S SYSTEMS
Global Circulation
• Although the loss and gain of radiation is balanced
over the entire climate system, no one part of the
planet’s surface is in equilibrium at a given time.
Global Circulation
• The solar radiation hitting the Earth is unequal…WHY?
– Earth is oblate (slightly flattened)
Spring (sun aims directly
at equator)
To
Polaris
The tilt (23½°
inclination) causes
the seasons
Winter (Northern
Hemisphere tilts away
from sun)
Fall (sun aims
directly at equator)
Summer (Northern
Hemisphere tilts toward
sun)
The Earth is tilted and rotating and revolving
Solar Heating of Earth Varies with Latitude
• The atmosphere reflects,
scatters and absorbs solar
radiation.
• At high latitudes solar radiation
travels a longer path through
atmosphere.
• Equal amounts of sunlight are
spread over a greater surface
area near the poles than in the
tropics.
• Ice near the poles reflects
much of the energy that
reaches the surface there.
Heat Redistributed
•
•
•
•
Heat gained at Equatorial latitudes
Heat lost at higher latitudes
Winds and ocean currents redistribute heat around the Earth
Oceans do not boil away near the equator or freeze solid near
the poles because heat is transferred by winds and ocean
currents from equatorial to polar regions.
Physical Properties of the Atmosphere:
Density
• Warm, low density air
rises
• Cool, high density air
sinks
• Creates circular- moving
loop of air (convection
cell)
Physical Properties of the Atmosphere:
Water Vapor
• Cool air cannot hold
much water vapor, so
is typically dry
• Warm air can hold
more water vapor, so
is typically moist
• Water vapor
decreases the density
of air
Physical Properties of the Atmosphere:
Pressure
• A column of cool, dense air causes high pressure at the
surface, which will lead to sinking air
• A column of warm, less dense air causes low pressure at the
surface, which will lead to rising air
Physical Properties of the Atmosphere:
Movement
• Air always
moves from
high-pressure
regions toward
low-pressure
regions
• Moving air is
called wind
Atmospheric Circulation (convection)
• Heated air rises at
equator
Maximum
Sun warming
• Cooler air
descends at poles
The Coriolis Effect
• As Earth rotates,
different latitudes
travel at different
speeds
• The change in
speed with latitude
causes the Coriolis
effect
The Coriolis Effect
• The rotation of the Earth deflects
the path of moving objects.
• As observed from space,
cannonball 1 (shot northward) and
cannonball 2 (shot southward)
move as we might expect; that is,
they travel straight away from the
cannons and fall to Earth.
• Observed from the ground,
however, cannonball 1 veers
slightly east and cannonball 2
veers slightly west of their
intended targets.
• The effect depends on the
observer’s frame of reference.
The Coriolis effect
• The Coriolis effect
– Is a result of Earth’s rotation
– Causes moving objects to follow
curved paths:
• In Northern Hemisphere, curvature is to right
• In Southern Hemisphere, curvature is to left
– Changes with latitude:
• No Coriolis effect at Equator
• Maximum Coriolis effect at poles
Add rotation Add land mass
Unequal heating and cooling of the Earth
Wind Belts of the World
The Total Atmosphere Effect
Global air circulation as described in the six-cell circulation model. Air rises
at the equator and falls at the poles, but instead of one great circuit in each
hemisphere from equator to pole, there are three in each hemisphere.
Cell Circulation
Centers on the
Meteorological
(Not
Geographical)
Equator
Ocean Currents
Why is Ocean Circulation Important?
• Transport ~ 20% of
latitudinal heat
– Equator to poles
• Transport nutrients and
organisms
• Influences weather and
climate
• Influences commerce
Ocean Currents
• Surface Currents
– The upper 400 meters of the
ocean (10%).
– Wind-driven currents occur in
the uppermost 100 m or less
• Deep Water Currents
– Thermal Currents (90%)
– Density differences causes by
salinity and temperature
produce very slow flows in
deeper waters.
Current Gyres
Gyres are large circular-moving loops of water
Five main gyres (one in each ocean basin):
•
• North Pacific
• South Pacific
• North Atlantic
• South Atlantic
• Indian
Generally 4 currents in
each gyre
• Centered about 30o
north or south
latitude
Lost at Sea
North Pacific Subtropical Gyre
• “Great Pacific Garbage Patch”
• Estimate: 46,000 pieces of floating garbage/mi2.
135° to 155°W and 35° to 42°N
Upwelling and Downwelling
Vertical movement of water
– Upwelling = movement of deep water to
surface
• Hoists cold, nutrient-rich water to surface
• Produces high productivities and abundant
marine life
– Downwelling = movement of surface water
down
• Moves warm, nutrient-depleted surface water
down
• Not associated with high productivities or
abundant marine life
El Niño-Southern Oscillation
(ENSO)
• El Niño = warm surface current in
equatorial eastern Pacific that occurs
periodically around Christmastime
• Southern Oscillation = change in
atmospheric pressure over Pacific
Ocean accompanying El Niño
• ENSO describes a combined oceanicatmospheric disturbance
Forecast
El Niño will likely peak during the Northern
Hemisphere winter 2015-16, with a transition
to ENSO-neutral anticipated during the late
spring or early summer 2016.
The expectation that this El Niño could rank
among the top three strongest episodes as
measured by the 3-month SST departures in
the Niño 3.4 region going back to 1950.
Forecast
Seasonal outlooks generally favor belowaverage temperatures and above-median
precipitation across the southern tier of the
United States, and above-average
temperatures and below-median
precipitation over the northern tier of the
United States.
Normal
•
•
Occurs during December
2 to 7 year cycle
El Niño
1997
El Niño events over the last 55 years
El Niño warmings (red) and La Niña coolings (blue) since 1950.
Source: NOAA Climate Diagnostics Center
http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html
Effects of severe El Niños
Effects of El Niño
• Hurricanes: Below normal number of tropical
storms/hurricanes in the Atlantic, although this does not
imply any limits on the strength or location of any given
tropical system.
• Monsoons: A drier-than-normal North American Monsoon,
especially for Mexico, Arizona and New Mexico.
• Drought: A drier-than-normal fall and winter in the U.S.
Pacific Northwest.
• Wintertime Storms: A wetter-than-normal winter in the Gulf
Coast states from Louisiana to Florida, and in central and
southern California if El Nino is strong.
• Warmer Temperatures: A warmer than normal late fall and
winter in the northern Great Plains and upper Midwest.