El Nino Teleconnections

Philip KreycikEPS 1314/30/04

El Niño - What it is

• Periodic anomaly in climate conditions– Irregular period– Centered in Tropical Pacific

• Local SST changes, surface pressure change• Local and Global consequences

– South American floods– African droughts– North American rains

’97-’98 El Niño Beginning to Peak

Fig. From JPL

Walker Circulation

Fig. From theAustralian Bureau of Meteorology

El Niño- what causes it

• We’re still uncertain– Atmosphere is a chaotic system– Difficult to sort out causes and effects

• Pressure seems to be the driving force– Slackening of trade winds impacts temp. profile

in ocean– But what causes changes in the trans-Pacific

pressure gradient?

Attempts to Predict and Prepare

Fig. From Natl. Geographic online

Southern Oscillation Index (SOI)

• Oscillation in pressure difference across tropical Pacific– Normalized to the average difference

• + means La Nina

• - means El Niño

Recent SOI Values

Teleconnections- Floods

• Deep Convection- the mechanism

• NW Peruvian Coast– Sechura Desert

• Southern Brazil • Europe• Implications for human health

– Food resources– Disease

                              

Teleconnections- Drought

• Shifting Walker Circulation shifting wet and dry areas

• Africa, India, Polynesia, Australia, New Zealand

                              

Photo from the Royal Society of New Zealand

North American Teleconnections

“Hurricane Linda, spawned during an El Niño, churns northeastward in September 1997. Linda’s 185-mile-an-hour [298-kilometer-an-hour] winds made it one of the strongest eastern Pacific storms ever recorded”

Photo and caption from Natl. Geographic

Teleconnections- N. American Storms and Rain

Fig. from the NOAA

North American Monsoon

• Christopher Castro et al. “The Relationship of the N. Am. Monsoon to Tropical and N. Pacific SST as Revealed by Observational Analyses”

• Highly variable period of wet weather

• Short bursts of intense precipitation

Western US Sensitivity to ENSO

• Not as simple as the NOAA diagram makes it seem!

• Dependence on several oscillating systems– ENSO– NPO– Others

• Relative phases

ENSO and the N. Pacific Oscillation

• NPO high, El Nino phaseconstructive interference– cold central Pacific, warm East Pacific– Strong effect on N. Am. monsoon

• NPO low, El Nino phasedestructive interference

Some Results

Final conclusion of the study

• Moisture drawn in from Gulf of Mexico– Low pressure displaced

to lower lat. in El Nino

– Circulation around pressure system

• Predictive power still leaves something to be desired