El Nino Teleconnections Philip Kreycik EPS 131 4/30/04

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 the Australian 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 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 phase  constructive interference –cold central Pacific, warm East Pacific –Strong effect on N. Am. monsoon NPO low, El Nino phase  destructive 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