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Lecture 16: Wind 2Introduction to Oceanography

Wind speed and direction about 1.5 km above sea levelBy Trent Schindler (NASA) using satellite data. Public Domain

https://svs.gsfc.nasa.gov/4571

Coriolis Effect Movies

Movie: University of Illinois (not sure if that’s the original source) http://ww2010.atmos.uiuc.edu/%28Gh%29/guides/mtr/fw/crls.rxml

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The Coriolis Effect on Earth

National Snow and Ice Data Center, free for educational use, http://nsidc.org/arcticmet/factors/winds.html

• Surface velocity increases from pole to

equator• Points on the equator

must move faster than points near the poles to go around once a day• Latitude velocity

differences lead to curving paths

– Example: Merry-go round

The Coriolis Effect• To an Earthbound observer (i.e., us): • Northern Hemisphere: Earth’s

rotation causes moving things to curve to their right

Moving things: Air masses, oceanic flows, missiles, anything with mass

• Southern Hemisphere: Earth’s rotation causes moving things to curve to their left

National Snow and Ice Data Center, free for educational use, http://nsidc.org/arcticmet/factors/winds.html

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Questions ?

Southern Hemisphere: Cyclone Drena (1997) NASA, Public Domain, http://www.ngdc.noaa.gov/dmsp/hurricanes/1997/drena.vis.gif (now moved)

Northern Hemisphere: Hurricane Isabel (2003) NASA, Public Domain, http://visibleearth.nasa.gov/view_rec.php?id=5862

But wait – why do storms(including hurricanes and cyclones) go

backwards?

Atmospheric Circulation including Coriolis

Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html

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Actual forecast of

surface winds

Pacific surface wind forecast-hindcast, National

Weather Service Environmental Modeling

Center/NOAA, Public Domain, GIF by E. Schauble

using EZGif

Atmospheric Circulation including Coriolis

• 3 convection cells in each hemisphere– Each cell: ~ 30o latitudinal width

• Vertical Motions– Rising Air: 0o and 60o Latitude– Sinking Air: 30o and 90o Latitude

• Horizontal Motions– Zonal winds flow nearly along latitude lines– Zonal winds within each cell band

• DUE TO DEFLECTIONS BY CORIOLIS!

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Atmospheric Circulation including Coriolis

3 Cells per hemisphere:Polar

Active (updraft on hot side, downdraft on cold side)

FerrelPassive (downdraft on

hot side!)

HadleyActive

UCLA figure – background image unknown.

Atmospheric Circulation including Coriolis

• Latitudinal winds:– 0-30o:

Trade Winds

– 30-60o: Westerlies

– 60-90o: Polar Easterlies

Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic, http://en.wikipedia.org/wiki/File:AtmosphCirc2.png

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Atmospheric Circulation including CoriolisCell Boundaries:

60o: Polar Front

30o: Horse Latitudes

0o: Doldrums

Vertical air movement(up at Polar Front and Doldrums, down at Horse Latitudes)

Doldrums

Horse Latitudes

Polar Front

Figure by Hastings, Wikimedia Commons, Creative Commons A S-A 1.0 Generic, http://en.wikipedia.org/wiki/File:AtmosphCirc2.png

Questions

Figure from NASA, Public Domain, http://sealevel.jpl.nasa.gov/overview/climate-climatic.html

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Local Meteorology of Southern CaliforniaMarine layer against the Southern California mountainsPhoto by Dr. Jonathan Alan Nourse, CalPoly Pomona, http://geology.csupomona.edu/janourse/Storms,%20Floods,%20Landslides.htm

Mediterranean Climate• LA: Subtropical latitude, abutting ocean• Subsiding flow: sinking air

– Clear most of the year• Effects of coast:

– Higher humidity--- thermal buffer• Winter Storms

– Pole-equator temp difference larger in winter– Speeds up jet stream, big storms get pushed our

way

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Sea Breeze

Jesús Gómez Fernández, Wikimedia Commons, Creative Commons A S-A 3.0, http://commons.wikimedia.org/wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.png

Land warms fastest during the day. Air expands and rises

Ocean surface temperature changes

slowly. Air displaces less dense rising air on land.

Result – wind from sea towards land

Land Breeze

Adapted from Jesús Gómez Fernández, Wikimedia Commons, Creative Commons A S-A 3.0, http://commons.wikimedia.org/wiki/File:Diagrama_de_formacion_de_la_brisa-breeze.png

Land cools fastest at night. Air

contracts and sinks

Ocean surface temperature changes slowly. Air is pushed

away and up by cooler denser land air.

Result – wind from land towards sea

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Marine Layer• Cold waters, warm air: thin cloud layer

on ocean surface– Subtropics: H pressure, regional

subsidence• Cloud layer flows onto land at night• Evaporates over land by day

LAND OCEANUCLA figure

UCLA Marine Layer

Time lapse -- Sept. 23, 2003(?), J. Aurnou, UCLA

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Santa Ana Winds

• Canada: Chinook• Colorado: Downslope Winds• Germany: Foehn Winds• France: The Mistral• Southern CA: Santa Ana Winds

Santa Ana WindsWinter: Canadian cold air

pushes down into Southwestern USHigh pressure pushes dry desert air

downslope, to seaCompression of sinking air causes

heatingHeating lowers humidityWind Speeds: up to ~ 70mph ≈115

km/hrFunneling effect through canyonsFeeds dangerous brush firesWeaker in summer

Piotr Flatau, Wikimedia Commons, Public Domain, http://en.wikipedia.org/wiki/File:Santa_ana_wind1.jpg

Mojave Desert

San Gabriel/Bernardino Mtns.

Los AngelesHigh Plateau

Adapted from N. Short Remote Sensing Tutorial/NASA, Public Domain,

http://rst.gsfc.nasa.gov/Sect14/katabatic.jpg

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Santa Ana WindsNASA image, Public Domain, http://photojournal.jpl.nasa.gov/catalog/PIA03892

~ 30 mph

Santa Ana Winds

Santa Ana Winds: dry & warm,

Encourage destructive fires

Fertilize ocean?Porter Ranch Fire, Oct. 14 2008, NASA image, Public Domain,

http://www.nasa.gov/mission_pages/fires/main/usa/califires_20081014.html

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Santa Ana Winds

• Canada: Chinook• Colorado: Downslope Winds• Germany: Foehn Winds• France: The Mistral• Southern CA: Santa Ana Winds

Questions?

UCSD GOES-10/NASA, Public Domain, http://meteora.ucsd.edu/cap/images/junegloom_16jun2004.gif

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Currents

The Gulf Stream, Winslow Homer (1899), Metropolitan Museum of Art (NY). Public Domain, https://commons.wikimedia.org/wiki/File:Winslow_Homer_004.jpg

Currents in the OceanWhat is a current?A current is a flow of material

MASS IS TRANSPORTED

Ben Franklin, 1769, Map of the Gulf Stream, Public domain.

Ocean currents transport water

Wind is a current of airMap by Ben Franklin, 1787

Portrait of Ben Franklin, 1785, by Duplessis

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Currents in the Ocean• Two Types: Surface and Deep• Driving Forces

– Surface Currents: Wind-driven– Deep Currents: Density-driven

American Meteorological Society, http://oceanmotion.org/images/oc

ean-vertical-structure_clip_image002.jpg

Surface CurrentsCaused by: Wind Stress Pressure Gradients

Coriolis Effects Friction

Gene Paull, UT Brownsville, Public Domain(?),http://upload.wikimedia.org/wikipedia/commons/0/06/Corrientes-oceanicas.gif

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Wind-Driven Currents

• Wind accelerates ocean currents– Frictional Drag

Atmosphere

OceanSIDEVIEW

Drag

TOPVIEW

Wind

Wind

Current Current

Map View

Figures, UCLA

Pressure-Driven Currents

• Wind drives ocean currents• Currents run into continents and can’t continue

– UNLIKE ATMOSPHERIC FLOWS• Water piles up ---Pressure Gradients form

Atmosphere

OceanSIDEVIEW TOPVIEW

Wind

Wind

Current Current

Drag H H

L

L

Figures, UCLA