Terrestrial Water Storage Anomalies Emphasize Interannual Variations in Global Mean Sea Level During 1997–1998 and 2015–2016 El Niño Events

Interannual variations in global mean sea level (GMSL) closely correlate with the evolution of El Niño‐Southern Oscillation. However, GMSL differences occur in extreme El Niños; for example, in the 2015–2016 and 1997–1998 El Niños, the peak GMSL during the mature stage of the former (9.00 mm) is almost 2.5 times higher than the latter (3.72 mm). Analyses from satellite and reanalysis data sets show that the disparity in GMSL is primarily due to barystatic (ocean mass) changes. We find that the 2015–2016 event developed not purely as an Eastern Pacific El Niño event but with Central Pacific (CP) El Niño forcing. CP El Niños contribute to a stronger negative anomaly of global terrestrial water storage and subsequent higher barystatic heights. Our results suggest that the mechanism of hydrology‐related interannual variations of GMSL should be further emphasized, as more CP El Niño events are projected to occur. Plain Language Summary The global mean sea level (GMSL) varies at year‐to‐year timescale because of El Niño‐Southern Oscillation, and GMSL is usually higher than normal during El Niños. The top two strongest El Niños in the past 30 years were the 1997–1998 and 2015–2016 events, whose strengths were similar, but the peak of GMSL in 2015–2016 was 2.5 times higher than that in 1997–1998. We analyze satellite and observation‐based data sets with global coverage to show that the difference of GMSL mainly came from the increasing ocean water mass associated with decreasing land water storage. The higher sea level in the 2015–2016 El Niño was because the event was forced from the midlatitude atmosphere, established by the Central Pacific El Niño, instead of a pure tropical forced Eastern Pacific El Niño. The different El Niño types make different teleconnections affect land water storage, which is critical for global sea level variation. Key Points Variations of global mean sea level (GMSL) in two extreme El Niño events during the altimetry era are mainly due to barystatic differences Higher terrestrial water storage (TWS) anomalies during typical Eastern Pacific (EP) El Niño cause lower barystatic variations in the 1997–1998 event 2015–2016 and 1997–1998 El Niños were different in partitioning of their Central Pacific/EP forcings, leading to different TWS and corresponding GMSL