Today – 2/28Today – 2/28

• Weather report

• More climate

• Earthquakes

Last Time

Transform plate boundaries – plates slide by each other

Convergent plate boundaries – plates collide

This Year

LA has already received 5 more inches of rain since January 1st than it usually gets all year!

Seattle is 3.5 inches behind for the year.

Is this because of El Niño?

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)

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

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

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?

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

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

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

1997 - 1998 El Nino SST 1997 - 1998 El Nino SST AnomalyAnomaly

www.cdc.noaa.gov

The Current El Niño

Sea surface temperatures

Weak to moderate and fading

Very similar to the 2002 – 2003 mild El Niño

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