Atmospheric & Ocean Circulation- Overview: Atmosphere & Climate

• Atmospheric layers • Heating at different latitudes • Atmospheric cells (Hadley, Ferrel, Polar) • Coriolis Force • Generation of winds • Low pressure, wet, convergence • High pressure, dry, divergence • Climate zones Recall: Atmospheric temp. vs. height

Heated from top: ozone absorbs energy

Heated at the bottom: where the land is warm Atmospheric layers have different stability

STRATOSPHERE: Stable because cool dense air is beneath warm dense air: STRATIFIED CONDITIONS ~19.9% of mass of atm TROPOSPHERE: Unstable because atmosphere is heated from below: CONVECTING CONDITIONS ~80% of mass of atm overall: TROPOSPHERE =the Weather Zone Also in TROPOSPHERE: CONVECTION due to heating from below

STRATOSPHERE: STABLE because cool dense air is beneath warm dense air: STRATIFIED CONDITIONS STEPPING BACK:

Fundamentally, Why does the Atmosphere circulate at all?

What is energy source that sets it in motion? Oceanic motion ultimately derives from the ’s rays

http://www.solarviews.com/raw/misc/ss.gif © Calvin J. Hamilton

NASA http://starchild.gsfc.nasa.gov/docs/StarChild/questions/question31.html Lights Please! Uneven solar heating with latitude

• Solar energy in high latitudes: – Has a larger “footprint” – Is reflected to a greater extent – Passes through more atmosphere • Therefore, less solar energy per square meter is absorbed at high latitudes than at low latitudes Uneven solar heating with latitude another way to visualize: how “high” is sun in sky? Recall: basic radiation budget

Reflected solar

• Energy arrives as visible (shortwave) sunlight

• About 30% is reflected “albedo” Earth • Higher reflection “albedo” at higher latitudes Incoming visible

• The remainder leaves as outgoing infrared (longwave) radiation Outgoing infrared

*+ GREENHOUSE GASSES : In atm. trap that outgoing long-wave radiation This basic model does a good job of predicting AVG global temp..

BUT: Do you think it does a good job of predicting the temp at Equator vs. Santa Cruz?

Reflected solar

Earth

Incoming visible

Outgoing infrared In a word: “NO”

Reflected solar

Earth

Incoming visible

Outgoing infrared Recall Solar heating imbalance with latitude: 1. Curvature of the Earth’s surface (flashlight effect..) 2. Albedo increases with latitude (more snow in N..) Predicts WAY too much heat at Equator (ie, predicts mid-latitudes warmer than they are..)

WAY too little heat at poles (ie, predicts them to be colder than they are) Actual- much more EVEN

• Means: a net heat gain is experienced in low latitudes

• A net heat loss is experienced in high latitudes

•? How do we explain the global Heat transfer that must be happening? Recall.. Convection: the soup analogy.! As with earth’s crust: its still all about Density If air mass WARMS

•molecules move more quickly Up inatmosphere •air mass expands •DENSITY DECREASES •AIR MASS RISES

If air mass COOLS •molecules move less quickly •air mass contracts •DENSITY INCREASES •AIR MASS SINKS Implications of differential warming: Convection in Troposphere*!

• Warm, low density air rises

• Cool, high density air sinks

• Creates circular- moving loop of air (convection cell) Figure 6-5

* remember, this is lower layer that is heated from BELOW One more thing: High vs. Low air Pressures

•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

Figure 6-6 A big result of Different “Pressure” zones: moisture.

WIND Cold sinking air As air rises, it cools, As air sinks, water it warms, condenses, lots of lots of rain evaporation

Warm rising air LOW PressureWIND HIGH Pressure Equator 30˚ N What does water this transport have to do with heat? Water phase changes require enormous energy (in part due to H-bonding)

Figure shows “” of each water phase change Evaporation (liq.=> ) removes heat from atm. Rain (gas => ) releases heat to atm. So: Basic Global wind patterns RESULT differential heating/cooling.

They then redistribute heat due

So, thinking about a circulation cell,

WHAT WOULD YOU EXPECT THEM TO BE LIKE? To review: Basic Convection Cell “Ideal” Circulation for a non-rotating Earth • Warm air would rise at the equator • Cold air would sink at the poles • Single circulation cell with equator-ward flow

Fig. 6-7 But, of course , it doesn’t work in the “ideal” way.

•Why NOT?

•  Density and pressure differences create smaller “cells” of circulation!

Fig. 6-7 Sinking air •High pressure zone Atmospheric •Divergence •Dry - Arctic / Polar Cells Rising air •Low pressure zone •Convergence 90˚N P •Wet - Temperate / Sub-Polar olar Cell H F e r L r e l 60˚N C Sinking air e l •High pressure zone l •Divergence •Dry - Sub-tropical H Ha

30˚N d l e

y

C e Rising air l Equator l •Low pressure zone L •Convergence •Wet - Tropical Overview: Atmospheric Circulation

• 1) Think of density • 2) Think of pressure differences driving differences driving vertical movements horizontal • Warm air rises movements • Cool air sinks • Air moves from HIGH TO LOW pressure

• 3) Think of evaporation/ precipitation of water carried by winds as transporting heat. WIND Major circulation cells Cold sinking a  global moisture bands

Warm rising air WIND LOW Pressure HIGH Pres Equator 30˚ N Fig. 13.2 Rainy equator? ITCZ – Inter-tropical Convergence Zone ITCZ - Intertropical Convergence Zone

More evidence of “Hadley” cell” Cooling as the air rises causes the to condense as and rain - releasing its latent heat. The heat can then transported to higher latitudes by the Hadley cells (directly as warmer air, as well as indirectly as water vapor) BUT :

THERE IS YET ANOTHER COMPLICATION Big Complication #2: The Earth rotates  The “Coriolis” Effect

• Accounts for how things move relative to the earths surface (which is rotating underneath them!) • Causes objects in motion to curve (relative to the earth!) – To right in the North – To left in the south Coriolis effect

N. Hemisphere Deviate to Right (relative to direction of motion)

S. Hemisphere Deviate to Left (relative to direction of motion) Coriolis Effect Consequence of something moving over a turning object..

Figure 6-9 The Earth rotates  The Coriolis Effect

"Image/Text/Data from the University of Illinois WW2010 Project." Also explains direction that storm winds circulate

Flow around HIGH Flow around LOW Anti - Cyclonic flow Cyclonic flow Clockwise in NH Counter-clockwise in NH (Counter-clockwise in SH)` (Clockwise in SH) Resulting Polar Easterlies 90˚N Atmospheric Polar Cells & Winds Cell H F e r L r e 60˚N L l Prevailing Westerlies L L L C L e ll

H Ha 30˚N H H d H l H H H e Northeasterly

y Trade Winds C

e

l Equator l LLLLL L L

Southeasterly Trade Winds 30˚S H H H H H H H Major ”Circulation cells”- start with ideal Cells, then add the “twisting” of coriolis!

Polar Cell

Ferrel Cell

Resultant cells

Hadley Cell Note: BOUNDARIES BETWEEN WINDBELTS

Polar Front

Horse latitudes

Intertropical Convergence Zone Finally, the real world naturally deviates even more from this ideal “three cell” model Real world Complications:

Regional or local pressure gradients can be influenced by: • Seasons: Tilt of earth’s axis - latitude of max. heating changes through the year • Land: – Variations in land topography and albedo –Land -Sea contrasts Why does solar heating change seasonally?

Heat flux in January (W/m2)

Heat flux in July (W/m2) Seasonal Heating Differences Due to TILT

Aphelion Perihelion

Fig 6-1 Tilt = 23.5 ˚ , CAUSES SEASONS Land-driven Sea Breezes ( Very near to shore.)

• Heat capacity of rock is much less than that of water, so land heats up more quickly during the day than the water. • Air above land warms and rises.

• At nighttime, no solar influx, but outgoing radiation remains. So both land and sea cool.

• However, land cools more rapidly than water because of a lower heat capacity. Circulation reverses. Can experience this on our Coast: leads to afternoon onshore sea breezes (even better example is S. Cal coast) Real world: complicated and varies by region

• Seasonal heating changes • Variations in land topography and albedo

These factors produce: - some strong High and Low Pressure Zones - lots of change from one Season to another Next: Main wind bands lead to Ocean Circulation!