El Nino-Southern Oscillation signals in sea level, surface mass redistribution, and degree-two geoid coefficients

We use a coupled Earth system model to simulate and quantify the impact of the El Nino-Southern Oscillation (ENSO) on monthly to interannual variations of steric and eustatic global mean sea level (GMSL), surface mass loading, and on the corresponding degree-two geoid coefficients (C-21, S-21, and C-20). GMSL is dominated by eustatic variations on monthly to interannual timescales, but less than 10% of the eustatic variance is related to ENSO. In contrast, steric GMSL correlates linearly in phase with ENSO with an explained variance of nearly 46%. Together these results imply that total GMSL variations are only weakly correlated with ENSO. Despite this small correlation, we find a distinct ENSO pattern of sizable surface mass load anomalies. Over the continents, this pattern is similar to typical ENSO-related precipitation anomalies. Over the oceans, the pattern features a global, albeit weaker, response, with generally increased loading in the Arctic and Pacific oceans, and decreased loading in the Atlantic and Indian oceans. These surface loading anomalies lead to statistically significant ENSO-related variations in the S-21 and C-20 geoid coefficients, but not in C-21. In analyzing the individual subsystem contributions, we find that S-21 is influenced by both ocean mass redistribution and soil moisture loading, whereas C-20 is mainly influenced by soil moisture loading. Our results highlight the importance of high-amplitude regional loading anomalies that integrate to low-degree geoid anomalies.