FY 2021

Niño 4 West (Niño-4W) sea surface temperature variability

Feng, M., Y. Zhang, H. Hendon, M.J. McPhaden, and A.G. Marshall

Geophys. Res. Lett., 126(9), e2021JC017591, doi: 10.1029/2021JC017591, View online (2021)

Sea surface temperature (SST) variability in the western half of the Niño 4 region (Niño-4W), bounded by 160°E−175°W and 5°S–5°N, has a significant impact on weather and the marine environment of the Indo-Pacific. It exhibits significant negative skewness, with the strong penetration of the cold tongue into the western Pacific during strong La Niñas but a more muted response during El Niños. Zonal advection plays a dominant role in driving Niño-4W SST cooling during the strong La Niña events; vertical processes also contribute, with air-sea heat fluxes providing weak negative feedback. Advection also plays a key role in driving the Niño-4W SST warming, which is not always in sync with El Niño events. Among the advection terms, the advection of mean temperature by zonal velocity anomalies, or zonal advective feedback, plays a key role during the development phase of the warm and cold events. Strong negative air-sea heat flux anomalies during the development of warm events are linked to the negative SST skewness in the Niño-4W region.

Plain Language Summary. Sea surface temperature variability in the western-central equatorial Pacific (the Niño-4W region) affects marine heatwaves and rainfall variability in Australia and other areas of the Indo-Pacific. In contrast with the central-eastern equatorial Pacific, negative temperature anomalies in the region tend to be stronger than positive temperature anomalies. This study used an upper ocean temperature budget analysis to reveal that zonal temperature advection plays a key role in driving surface temperature variability in the Niño-4W region. The high surface temperature in the warm pool may damp any further increase in ocean temperature in the region through air-sea heat flux adjustment.