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 conditionsEl 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 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, 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 and

El Nino or La Nina?