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.

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30º

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60º

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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.

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30º

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60º

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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

Heat transport: redistribution

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

RELEVANCEStorm behaviour

Seasonal climate patterns

Air travel

Monsoon rains

An Earth with continents:

Northern hemisphere Southern hemisphere

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)…

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•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

Cloud patterns in hurricanes: What’s the air doing in this picture?

Hurricane Kate, 2003, NASA

The weather: A surface analysis map

 

En

viro

nmen

t Ca

nad

a

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

X

HL

HPGF

Coriolis

Geostrophic Flow: Coriolis = HPGF

High Pressure: Circulation

 

H1008

10041000

L

L

L

L

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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

Northernhemispherejet streams

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

Natl. Weather Service

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