PRACTICE QUIZ PARTS 1 & 2 Open Wednesday 16 Sept! Be sure to try BOTH PARTS of the practice quiz in...
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Transcript of PRACTICE QUIZ PARTS 1 & 2 Open Wednesday 16 Sept! Be sure to try BOTH PARTS of the practice quiz in...
PRACTICE QUIZ PARTS 1 & 2 Open Wednesday 16 Sept!
Be sure to try BOTH PARTS of the practice quiz in VISTA!
Go to either “Quizzes” from the homepageOR “Assessments” on the left panel.
Opens Sept 16th at 1 pm, and will remain open until October
21st ALSO, the extra credit survey closes
Sept 18th! (link in VISTA)
Rotating Earth. No continents.
0º
30º
30º
60º
60º
90º
90º
FROM what direction do the surface winds blow for the sailboat? FROM the…
One more clicker question:
A. northB. southC. northeastD. southwestE. southeast
Rotating Earth. No continents.
0º
30º
30º
60º
60º
90º
90º
Northeast Trades
Southeast Trades
Westerlies
Westerlies
Polar easterlies
Polar easterlies
Coriolis Effect: last point
ZERO at ZERO (the equator)
Not much difference in circumference between these latitudes
Large difference in circumference between these latitudes
MAXIMUM at poles
MAXIMUM at poles
Goals for Today1. PREDICT atmospheric circulation, location of
cloud formation and precipitation for today’s Earth with continents
2. EXPLAIN how a balance between atmospheric pressure differences and Coriolis results in geostrophic winds
3. APPLY geostrophic wind principles to storms and jet streams
Atmosphere II: Continents, pressure gradients, geostrophic winds
To achieve these goals, you’ll need to…
• Explain why the distribution of continents matters– At present, there is more land mass in the northern
hemisphere than in the southern hemisphere– Land heats up and cools off faster than oceans– Earth’s “thermal” equator is offset to the north, on average
• Use a logical sequence of events to deduce geostrophic flow– Air tends to move from high to low pressure, along any
horizontal pressure gradient– As an object in motion on a rotating planet, moving wind is
influenced by Coriolis– In cases where the horizontal pressure gradient force and
the Coriolis force are balanced geostrophic wind
How easy is it to heat/coolland versus ocean water?Effect of HEAT CAPACITY
Heat capacity of fresh water = 4.18 J/gKHeat capacity of seawater = 3.93 J/gKHeat capacity of granite = 0.79 J/gK
Takes more energy to heat/cool Takes less energyto heat/cool
How easy is it to heat/coolland versus ocean water?Effects of CONVECTION,CONDUCTION & MIXING
Energy (heat) RAPIDLY transferred downward by mixing
Energy (heat) transferred down-ward SLOWLY byconduction
Our situation today: Northern hemisphereMORE LANDHEATS/COOLS more QUICKLY
Southern hemisphereLESS LANDHEATS/COOLSmore SLOWLY
For our water-covered earth (last class)…
0º
30º
30º
60º
60º
90º
90º
•Warm, wet air rises at the equator. •Surface winds blow toward the equator to replace the rising air. •Surface winds CONVERGE at the equator
ITCZ @ equator
Earth’s Thermal Equator, a.k.a., the INTERTROPICAL CONVERGENCE ZONE
(ITCZ)
Image: GFDL
Geographic equator 0⁰
…on today’s Earth, with continents
ITCZ average location
Tracer: ascent/descent of airImage: W.M. Connolley
Blue = risingRed/pink = sinking
Equator
NOAA, GOES satellite image
Clicker question: Within the box, where is the ITCZ?
ABCDE
(this is a satellite image showing clouds)
Incoming/Outgoing energy distribution
Top of Atmosphere
Absorbed at Surface
Ene
rgy
Latitude
90°N 0° 90°S
(after Gill, Figure 1.1)
ITCZ
High Pressure: Atmospheric Circulation
H1008
10041000
L
L
L
L
L
LDirection of PRESSURE GRADIENT FORCE (NOT the wind!)
High Pressure: HPGF
H
LL
PL < PH > PL
HorizontalPressure
GradientForce
HorizontalPressure
GradientForce
High Pressure: Circulation
H1008
10041000
L
L
L
L
L
L
Flow clockwise around a high (N. Hemisphere)
Coriolis = HPGFHPGF = Coriolis
At a given altitude, air pressure over low latitude is greater than air pressure over high latitude.
L H
Upper atmosphere: Geostrophic flow and jet streams
Marshak, Figure 20.14a
Clicker question: What about the southern hemisphere?What direction do the jet streams flow there?
Marshak, Figure 20.14aSouth Pole
A. West to east B. East to westC. North to south D. South to north
• The presence and distribution of continents influences the average position of the ITCZ, locations of cloud formation, and precipitation. • Horizontal pressure gradients set air masses in motion. Once in motion, they are influenced by Coriolis. Geostrophic flow occurs when HPGF balances the Coriolis force.• You can use knowledge of the geostrophic balance to figure out wind directions in different scenarios, e.g. hurricanes, jet streams
Summary: Continents, pressure gradients, geostrophic winds
Relevance: storms, seasonal climate, air travel
OUTLINE• An Earth with continents
– The Intertropical Convergence Zone (ITCZ)– Differential heating of continents and oceans– Winds driven by atmospheric pressure gradients
• Monsoon circulation– Seasonal air movement– Seasonal precipitation patterns– The geologic record of monsoons