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Introduction to Lecture 16: Wind 2

Wind speed and direction about 1.5 km above By 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

1 The Coriolis Effect on Earth

• 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

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

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.ht ml

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

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

Southern Hemisphere: Cyclone Drena (1997) NASA, Public Domain, http://www.ngdc.noaa.gov/dmsp/hurricanes/199 7/drena.vis.gif (now moved)

Questions ?

Atmospheric Circulation including Coriolis

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

3 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!

4 Atmospheric Circulation including Coriolis 3 Cells per hemisphere: Polar Active (updraft on hot side, downdraft on cold side) Ferrel Passive (downdraft on hot side!) Hadley Active

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

5 Atmospheric Circulation including Coriolis

Cell Boundaries: Polar Front 60o: Polar Front Horse Latitudes 30o: Horse Latitudes

Doldrums 0o: Doldrums

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

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

6 Local Meteorology of Southern California Marine layer against the Southern California mountains Photo 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

7 Sea Breeze

Land warms fastest during the day. Air expands and rises

Ocean surface changes slowly. Air displaces less dense rising air on land.

Result – wind from sea towards land

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 Breeze 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

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

8 Marine Layer • Cold waters, warm air: thin cloud layer on ocean surface – Subtropics: H , regional subsidence • Cloud layer flows onto land at night • Evaporates over land by day

LAND OCEAN UCLA figure

UCLA Marine Layer

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

9 Santa Ana Winds

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

Santa Ana Winds

Winter: Canadian cold air pushes down into Southwestern US High pressure pushes dry desert air downslope, to sea Compression of sinking air causes heating Heating lowers humidity Piotr Flatau, Wikimedia Commons, Public Domain, http://en.wikipedia.org/wiki/File:Santa_ana_wind1.jpg Wind Speeds: up to ~ 70mph ≈115 km/hr San Gabriel/Bernardino Mtns. Funneling effect through canyons Feeds dangerous brush fires Weaker in summer Los High Plateau Angeles Mojave Desert Adapted from N. Short Remote Sensing Tutorial/NASA, Public Domain, http://rst.gsfc.nasa.gov/Sect14/katabati c.jpg

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

~ 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

11 Santa Ana Winds

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

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

Questions?

12 Currents

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

Portrait of Ben Franklin, Currents in the Ocean 1785, by Duplessis What is a current? Ocean currents transport water A current is a flow of material Wind is a current of air MASS IS TRANSPORTED Map by Ben Franklin, 1787

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

13 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 Currents Caused 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

14 Wind-Driven Currents

• Wind accelerates ocean currents – Frictional Drag

Atmosphere Wind

Drag Wind

Current Current

Ocean Map View SIDEVIEW TOPVIEW 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 L Wind Drag H Wind H Current Current Ocean L SIDEVIEW TOPVIEW Figures, UCLA

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