El Nio El Nio: A significant increase in sea surface temperature over the eastern and central equatorial Pacific that occurs at irregular intervals, generally ranging between two and seven years (glossary.ametsoc.org). Off the west coasts of continents, the Sea Surface Temperature is chilly. Fish love the cold water, especially anchovies. During El Nio, SST changes dramatically near Peru The SST changes have really big consequences for the atmosphere. This is the development of the most intense El Nio ever recorded in Sea Surface Anomalies during 2015 So, what happens during El Nio? The normal mean pressure features are these: 1. The Subtrop High moves south or weakens 2. Trade winds get weaker or reverse 3. The Aleutian Low strengthens H H L L For January, 1998, this was the 1000 mb (surface) Mean values Departures from the 30- year mean (Anomalies) At 250 mb, there were changes caused by the surface pressure and temperature anomalies Mean values Departures from the 30-year mean (Anomalies) Look at the effect on the 250 mb wind (the Jet Stream!) Mean values Departures from the 30- year mean (Anomalies) The much stronger subtropical Jet Stream explains all the U.S. anomalies La Nia This is the La Nia event of This is the latest drought map. The ENSO cycles vary in length and intensity ~ 6-18 months. There have been several big events in the last 20 years. From Other circulation patterns and their effects NAO: North Atlantic Oscillation AO: Arctic Oscillation PNA: Pacific/North American (oscillation) PDO: Pacific Decadel Oscillation The figures shown are from NAO (North Atlantic Oscillation) As the name tells us, this is a pattern located in the North Atlantic Ocean. From: https://crudata.uea.ac.uk/~timo/datapages/nao_ts.gif AO (Arctic Oscillation) Here we are just interested in the Arctic. From From: PNA (Pacific North American Oscillation PDO (Pacific Decadel Oscillation) Warm Phase Cold Phase From: Next: Climate Change