el nino, la nina, and their affects in oklahoma. el nino conditions warming of central and eastern...
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El Nino, La Nina, and their Affects in Oklahoma
El Nino Conditions
• Warming of central and eastern equatorial Pacific waters
• Trade wind differences– Anomalous westerlies along the equator (weaker
easterly trade winds)• Thermocline deepens– Warm water upwelling off coast of Peru
• Walker Cell weakens and shifts eastward– Rainfall shifts east
Thermocline• Boundary between warm near surface water
and cold deep ocean water.
Cold water upwelling from below thermocline
Weaker upwelling from above the thermocline (warm water)
Neutral (normal) conditions
Walker Cell• A vertical circulation in the tropics.– Rising branch associated with convection and
sinking branch associated with dry conditions.
Normal conditions El Nino
Impacts in Oklahoma• Cooler and wetter• Cloudy/dreary days are more likely • No strong correlations with nationwide
tornado numbers• Of the 17 high impact winter weather events
in OK since 2000, 9 of them (53%) have occurred during positive ENSO phase years (El Nino conditions).– 35% during negative phase and 12% during
neutral conditions
Jan. 2010 in SW Oklahoma (El Nino Year)
La Nina• Essentially the opposite of El Nino– Cooling of central and eastern equatorial Pacific
waters.– Stronger easterly trade winds– Stronger Walker Cell that is shifted west• Enhanced precip over Indonesia
– Shallower thermocline• Cold water upwelling off Peru
La Nina
Shallow thermocline
Walker Cell shifted west
El Nino for comparison
Impacts in Oklahoma• Jet stream and therefore storm track shifted
northwards.– Warmer and drier in Oklahoma
• Major winter storms less likely – Only 35% occurred during negative ENSO phase
(La Nina conditions) since 2000• Potential drought conditions
January 1, 2012. Relatively classic La Nina pattern.
• Historical El Nino and La Nina events using the Multivariate ENSO Index• Red is positive phase and corresponds to El Nino events• Blue is negative phase and corresponds to La Nina events• Note strong El Nino events in 1982-1983 and 1997-1998
El Nino or La Nina?
