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 homepage OR “Assessments” on the left panel. Opens Sept 16 th at 1 pm, and will remain open until October 21 st ALSO, the extra credit survey closes Sept 18 th ! (link in VISTA)

Rotating Earth. No continents. 0º0º 30º 60º 90º FROM what direction do the surface winds blow for the sailboat? FROM the… One more clicker question: A. north B. south C. northeast D. southwest E. southeast

Rotating Earth. No continents. 0º0º 30º 60º 90º Northeast Trades Southeast Trades Westerlies 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

Heat transport: redistribution

Summary: General Atmospheric Circulation Different latitudes receive and emit different amounts of energy due to Earth’s curvature & heat transfer processes Hot, wet air rises. Cold, dry air sinks. Objects in motion on this rotating planet tend to follow curved paths (Coriolis effect: to the RIGHT in the N. Hem. & to the LEFT in the S. Hem.) Differential heating, air rising and sinking, the Earth rotating, all lead to the general atmospheric circulation (which you can develop) Relevance: weather, climate, energy

Goals for Today 1.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

RELEVANCE Storm behaviour Seasonal climate patterns Air travel Monsoon rains

An Earth with continents: Northern hemisphere Southern hemisphere

How easy is it to heat/cool land versus ocean water? Effect of HEAT CAPACITY Heat capacity of fresh water = 4.18 J/gK Heat capacity of seawater = 3.93 J/gK Heat capacity of granite = 0.79 J/gK Takes more energy to heat/cool Takes less energy to heat/cool

How easy is it to heat/cool land versus ocean water? Effects of CONVECTION, CONDUCTION & MIXING Energy (heat) RAPIDLY transferred downward by mixing Energy (heat) transferred down- ward SLOWLY by conduction

Our situation today: Northern hemisphere MORE LAND HEATS/COOLS more QUICKLY Southern hemisphere LESS LAND HEATS/COOLS more SLOWLY

For our water-covered earth (last class)… 0º0º 30º 60º 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 equator

Earth’s Thermal Equator, a.k.a., the INTERTROPICAL CONVERGENCE ZONE (ITCZ) Image: GFDL Geographic equator 0 ⁰ …on today’s Earth, with continents

ITCZ average location Tracer: ascent/descent of air Image: W.M. Connolley Blue = rising Red/pink = sinking Equator

NOAA, GOES satellite image Clicker question: Within the box, where is the ITCZ? A B C D E (this is a satellite image showing clouds)

Incoming/Outgoing energy distribution Top of Atmosphere Absorbed at Surface Energy Latitude 90°N0°90°S (after Gill, Figure 1.1) ITCZ

Cloud patterns in hurricanes: What’s the air doing in this picture? Hurricane Kate, 2003, NASA

The weather: A surface analysis map Environment Canada

High Pressure: Atmospheric Circulation H L L L L L L Direction of PRESSURE GRADIENT FORCE (NOT the wind!)

Horizontal Pressure Gradient: temperature WARM COLD HPGForce Warm vs. cold air column Same number of air molecules (in this case, no pressure gradient at the surface. Pressure gradient aloft.) Notes

High Pressure: HPGF H L L P L Horizontal Pressure Gradient Force Horizontal Pressure Gradient Force

High Pressure: Circulation X H L HPGF Coriolis Geostrophic Flow: Coriolis = HPGF

Geostrophic Wind Development PGFGeostrophic WindCoriolis force Notes

Effect of Friction Notes

High Pressure: Circulation H L L L L L L Flow clockwise around a high (N. Hemisphere) Coriolis = HPGF HPGF = Coriolis

Low Pressure: Circulation L H H H H H H Flow counterclockwise around a low (N. Hem.) HPGF = Coriolis Notes

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

Northern hemisphere jet streams

Clicker question: What about the southern hemisphere? What direction do the jet streams flow there? Marshak, Figure 20.14a South Pole A. West to east B. East to west C. North to south D. South to north

Natl. Weather Service

Surface Winds and Sea-level pressure January JANUARY Notes

JULY Surface Winds and Sea-level pressure Notes

Rotating Earth WITH continents.

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

Extra slides below this one

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

Clicker question: Where is the ITCZ?

NOAA, Natl. Weather Service 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 G 2-3