Global mean sea level variations and the land water cycle at the inter-annual scale during the 2014–2016 El Niño episode

Abstract

Since 1993, the global mean sea level (GMSL) has been rising at a rate of about 3 mm/a detected by multi-satellite radar altimetry. The spaceborne gravimetry satellite, Gravity Recovery and Climate Experiment (GRACE), has been monitoring Earth’s surface water mass variations since 2002. La Nina and El Nino events induces inter-annual variations of the GMSL manifest in ocean mass and steric sea level changes, linked with corresponding changes in land water cycle. Here we study the GMSL inter-annual variations and global land water mass changes integrating satellite altimetry, GRACE and Argo data, 2010–2016, during which strong La Nina and El Nino events occurred. First, we quantify the evolutions of GMSL during the study time period. The results show that during the 2010–2011 La Nina episode, the GMSL dropped rapidly to 7.6 mm, with the ocean mass and the steric sea level decreased to 5.1 mm and to 1.8 mm, respectively. GMSL then increased to 19.2 mm, with ocean mass increased to 12.3 mm during 2011–2013. From 2013 to 2014, the steric GMSL increased by 2.1 mm, and the ocean mass variations dropped by 2.3 mm, thus the total GMSL remains nearly unchanged. During the strong 2014–2016 El Nino, ocean mass variations increased by 13.1 mm and contributed over 90% of GMSL change, which rises up by 15.1 mm. Next, we analyze land water mass changes in four regions, namely Australia and Southeast Asia, South America, North America, Antartica and Greenland, and investigate their linkage to the GMSL inter-annual variations. Here, we used the Forward Modelling (FM) method for GRACE data post-processing to reduce signal leakage problem to estimate land water storage mass changes. The results show that during the 2014–2016 El Nino episode, the global ocean mass increasing is mainly due to the total land water storage decreasing in Australia and Southeast Asia, South America, and Antartica and Greenland. The inter-annual variations of global ocean mass variation during 2003–2016 is closely linked with the land water storage changes from Australia and Southeast Asia and the South America regions, which are strongly affected by La Nina and El Nino events. During 2003–2016, the ice ablations from the Antartica and Greenland ice sheets directly contributed to GMSL rising, as opposed to the land water mass increase in the North America region, which has a negative effect on GMSL trend. Finally, we estimated the GMSL, ocean mass and steric sea level trends at 3.4±0.4, 2.1±0.3, and 1.1±0.2 mm/a, respectively during 2003–2016, and 6.5±1.2, 4.1±1.0, and 1.9±0.4 mm/a, respectively during 2010–2016. We concluded that the ocean mass variation contributed to the GMSL trend two times larger than that of the steric sea level contribution during these two time periods. However the ocean mass variation is roughly equivalent to the steric sea level variation during 2003–2010.