1. Today – 2/28 Weather report More climate Earthquakes

2. Last Time Transform plate boundaries – plates slide by each other Convergent plate boundaries – plates collide

3. This Year LA has already received 5 more inches of rain since January 1 st than it usually gets all year! Seattle is 3.5 inches behind for the year. Is this because of El Niño?

4. Seattle and US West Coast – Mediterranean Climate One rainy season – winter Mild – ocean moderates temperature West coast of continents between 30° and 50° Seasonality controlled by Aluetian Low and California (Hawaii) High (these are sea level pressures)

5. Unusual Properties of Water Already know that expands upon freezing Very high heat capacity – four times more thermal energy required to raise the temperature of water than air or soil Oceans cool nearby land in summer, warm them in winter

6. Air Must Rise for Precipitation Orographic uplift – winds hit mountains, get pushed up: west coast, Tucson in winter. Rainshadow on the other side of mountains Frontal uplift – warm moist air collides with cold air, gets forced up and over the cold air: tornado alley Convective uplift: monsoon season

7. What’s Going On This Year? LA normal YTD – 6.75”, actual – 20.34” Seattle normal YTD – 8.89”, actual – 5.40” Tucson normal YTD – 1.81”, actual – 2.62” Is El Niño responsible?

8. El Niño Basic Idea Hadley cells + spinning Earth (Coriolis Force) create low level wind patterns Low level winds blow ocean surface driving surface currents called gyres Tradewinds (equatorial easterlies) blow warm water into western Pacific When trades weaken, warm water rushes east, causing El Niño

9. El Niño Southern Oscillation El Niño: warm water in the eastern equatorial Pacific Southern oscillation: associated changes in pattern of atmospheric pressure in South Pacific Easterly tradewinds weaken, allowing warm water to move east, NA jetstream often split La Niña: cold water in eastern Pacific; La Nada: normal water in eastern Pacific

10. Walker Circulation NOT a Hadley cell – Hadley is a N-S circulation, this is an E-W circulation Named for Sir Gilbert Walker, who realized the importance of ENSO about the time of WWI, but the rest of the world remained skeptical

11. 1997 - 1998 El Nino SST Anomaly www.cdc.noaa.gov

12. The Current El Niño Sea surface temperatures Weak to moderate and fading Very similar to the 2002 – 2003 mild El Niño

13. Peru and El Niño World’s most productive fishery crashes. Fishery results from tradewinds blowing warm surface water west, pulling cool, nutrient rich water up along coast (upwelling). 85% drop after 1998 El Niño All of country, including arid coast, gets incredible rain falls causing floods and mudslides