El Nino and La Nina
• An important atmospheric variation that has
an average period of three to seven years.
• Goes between El Nino, Neutral, and La
Nina (ENSO cycle, El Nino Southern
Oscillation)
• Has large influence both in the tropics and
midlatitudes.
• Main source of forecast skill beyond a few
weeks.
An Important Measure is the Temperature
in the Tropical Pacific
Niño Region SST Departures (oC)
Recent Evolution
The latest weekly SST departures are:
Niño 4
-0.6ºC
Niño 3.4
-1.1ºC
Niño 3
-1.2ºC
Niño 1+2
-1.3ºC
Why do we care?
• The circulations in the midlatitudes are
substantially different in El Nino, Neutral,
and La Nina years.
• Since the temperature of the tropical
Pacific changes relatively slowly, this gives
some meteorologist some insights into the
weather over the next several months.
El Nino – weak Aleutian High
La Nina – strong Aleutian High
Great Web Site on ENSO:
Climate Prediction Center
http://www.cpc.ncep.noaa.gov/p
roducts/precip/CWlink/MJO/ens
o.shtml