What Controls the Duration of El Niño and La Niña Events?

Xian Wu, Yuko Okumura and Pedro DiNezio

University of Texas Institute for Geophysics (UTIG)

Impact of Multi-year La Nina Events

Contours: SLP (1 hPa)

SST (°C) Precip. (mm/day)

Nov(0)-Apr(1) Nov(1)-Apr(2)

Okumura, DiNezio and Deser (2017, GRL)

Composite Anomalies (HadISST/GPCC/20CR, 1901-2012)

Diverse Evolution of ENSO EventsNiño-3.4 SST Index

(HadISST, 1900-2016)

El Niño

La Niña

| Niño-3.4 | > 0.75σin Oct(0)-Feb(1)

Dec(0)Dec(-1) Dec(+1)

Dec(0)Dec(-1) Dec(+1)

What controls the duration of El Niño and La Niña?

1-yr vs. 2-yr Events: Observations (1900-2016)El

Niñ

oLa

Niñ

a

1-yr Events 2-yr Events

|Niño3.4| < 0.5σin Oct(1)-Feb(2)

|Niño3.4| > 0.5σin Oct(1)-Feb(2)

Composite (p=0.2)

Dec(0)Dec(-1) Dec(+1)

Dec(0)Dec(-1) Dec(+1)

Precedingevent amp.

Onsettiming

Peak amp.

Precedingevent amp.

Peak amp.

1-yr vs. 2-yr Events: CESM1 PI Control Run (1800 yrs)El

Niñ

oLa

Niñ

a

1-yr Events 2-yr Events

|Niño3.4| < 0.5σin Oct(1)-Feb(2)

|Niño3.4| > 0.5σin Oct(1)-Feb(2)

Composite (p=0.01)

Dec(0)Dec(-1) Dec(+1)

Dec(0)Dec(-1) Dec(+1)

Precedingevent amp.

Onsettiming

Peak amp.

Precedingevent amp.

Peak amp.?

Relative Importance of These Factors (CESM1)

Precedingevent amp.

Peak amp.

Precedingevent amp.

El Niño

La Niña

Preceding Event Amp. Onset Timing Peak Amp.

Onsettiming

Peak amp.

DiNezio et al. (2017, Clim. Dyn.)

CESM1

Leading Factors for El Niño and La Niña Duration (CESM1)

OnsetTiming

#%

#%

El Niño La Niña

Niño3.4in Dec(-1)

How do these factors affect the duration ofEl Niño and La Niña in CESM1?

Dec(0)

Dec(-1)

Dec(1)

Dec(0)

Dec(-1)

Dec(1)

Dec(0)

Dec(-1)

Dec(1)

Role of Oceanic Adjustments (CESM1)

1-yr Event

Earlier Onset

1-yr minus 2-yr

Apr(1) ZTC

Thermocline Depth (ZTC) and SST Composite Anomalies (3S-3N)

Dec(1) N34r=0.79

Earliernegativefeedback

Apr(1) ZTC

2-yr Event

El N

iño

LaN

iña

Weaker El Nino

Smaller discharge

Dec(-1) N34

r=-0.52

Wind inFeb/Mar(1)

WindFeb/Mar(1)

Dec(1) N34r=0.66

1-yr

2-yr

Diff(1-2)

SST and Surface Wind Composite Anomalies in Feb/Mar(1) El Niño La Niña

SST (°C)

Role of Atmospheric Adjustments (CESM1)

CAM5 forced with tropical SST anomalies from CESM1 (15 members)

Diff(1-2)

1-yr Event 1-yr minus 2-yr2-yr EventSST Composite Anomalies (3S-3N)

Interbasin SST AdjustmentsEl

Niñ

oLa

Niñ

a

Indian Pacific Atlantic

SST (°C)

Dec(0)

Dec(-1)

Dec(1)

Earlier onset

Earlierinterbasin

adjustments

Negative SST gradienttoward the Pacific

Dec(0)

Dec(-1)

Dec(1)

WeakerEl Nino

Weakerinterbasin

adjustments

Apr(1)

Apr(1)WeakerLa Nina Positive SST gradient

toward the Pacific

SummarySummary of Diagnostic Analysis

El Niño

La Niña

Timing of Onset

Timing of1) Thermocline adjustments E Pacific thermocline Duration

2) Indian/Atlantic SST adjustments W Pacific winds

Amplitude of Preceding El Nino

Amplitude of1) Eq. heat content discharge E Pacific thermocline Duration

2) Indian/Atlantic SST adjustments & La Nina W Pacific winds

Can we predict the duration of El Niño and La Niñaevents based on these factors?

CESM1 Perfect Model Forecast ExperimentsLa

Niñ

a

Strong El Nino (Jan 1455)Weak El Nino (Jan 1225)30-member ensemble

forecasts initializedwith oceanic conditions

from the CESM1 PIcontrol run

DiNezio et al. (2017, Clim. Dyn.)

Early Onset (Apr 1729) Late Onset (Sep 1236)

El N

iño

20-member ensembleforecasts

What is the predictabilityin the real world?

Analysis of the CESM1decadal prediction

large ensemble(DiNezio et al. 2017, GRL)