Research Progress made by QNLM on Ocean and Climate Change
Src:QNLM     00:00:00 09/24/2021

A research team in Laboratory for Ocean and Climate Dynamics, QNLM, has made major progress in the impact of North Pacific on tropical El Niño/Southern Oscillation (ENSO) recently.

North Pacific Meridional Mode (NPMM) is a dominant mode of coupled ocean-atmosphere variability that links the subtropical atmospheric fluctuations to the tropical ocean. The NPMM exerts significant impact on the occurrence, development and diversity of ENSO via wind-evaporation-SST feedback, summer deep convection response and trade wind charging mechanism, acting as an important precursor of ENSO. Moreover, a decadal strengthening of the NPMM around 1999/2000 may increase the ENSO complexity and partly explain an ENSO property shift from more eastern Pacific type to more central Pacific type. Since 1950, more than 50% of the El Niño/La Niña events were preceded by positive/negative NPMM events, including three extreme El Niño events (1982-83, 1997-98 and 2015-16 El Niño) and one extreme La Niña event (1998-99 La Niña) (Fig.1a-d). Nevertheless, how the precursory NPMM forcing on ENSO responds to greenhouse warming remains unknown.

Using outputs from CMIP5+CMIP6 and climate model experiments, the QNLM scientists find an enhanced future impact on ENSO by the NPMM (Fig.1e). This is manifested by increased sensitivity of boreal-winter equatorial Pacific winds and sea surface temperature (SST) anomalies to the NPMM three seasons before. The enhanced NPMM impact translates into an increased frequency of NPMM that leads to an extreme El Niño or La Niña. Under greenhouse warming, higher background SSTs cause a nonlinear evaporation-SST relationship to more effectively induce surface wind anomalies in the equatorial western Pacific, conducive to ENSO development. Thus, NPMM contributes to an increased frequency of future extreme ENSO events and becomes a more influential precursor for their predictability.

This research progress is another important discovery made by the QNLM in the climate change and predictability research area, highlighting the international leading role of QNLM in ocean-atmosphere interactions and climate change research. It has been published online in the high-impact journal Nature Climate Change entitled “Enhanced North Pacific impact on El Niño/Southern Oscillation under greenhouse warming”. The first author of the article is Fan JIA, an associate professor of Laboratory for Ocean and Climate Dynamics, QNLM. The article is co-authored by scientists from China, Australia and USA.

Fig.1 Composite SST anomaly of a three positive NPMM events (1982, 1997 and 2015), b three negative NPMM events (1975, 1998 and 1999), c three El Niño events following the positive NPMM events in a, and d three La Niña events following the negative NPMM events in b. e Enhanced impact of NPMM on ENSO under future climate in CMIP5+CMIP6 models.

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