Future changes in the seasonal evolution of the El Niño—Southern Oscillation (ENSO) during its onset and decay phases have received little attention by the research community. This work investigates the projected changes in the spatio-temporal evolution of El Niño events in the 21st Century (21 C), using a multi-model ensemble of coupled general circulation models subjected to anthropogenic forcing. Here we show that El Niño is projected to (1) grow at a faster rate, (2) persist longer over the eastern and far eastern Pacific, and (3) have stronger and distinct remote impacts via teleconnections. These changes are attributable to significant changes in the tropical Pacific mean state, dominant ENSO feedback processes, and an increase in stochastic westerly wind burst forcing in the western equatorial Pacific, and may lead to more significant and persistent global impacts of El Niño in the future.
In a warming climate, the Global Meridional Overturning Circulation (GMOC) is expected to change significantly with a risk of disrupting the global redistribution of ocean properties that sustains marine ecosystems, carbon cycle, and others. Here we make a novel attempt to utilize a diagnostic ocean & sea-ice model to estimate the GMOC and its interdecadal changes since the mid-1950s that are consistent with historical hydrographic observations. We find that significant changes in the GMOC have already occurred, most notably in the upper and lower overturning cells in the Southern Ocean. The former has expanded poleward and into denser water and strengthened by 3–4 Sv since the mid-1970s, while the latter has contracted and weakened by a similar rate during the same period. These changes are driven by the increasing Southern Hemisphere (SH) Ferrel cell and associated increases in the westerlies and the surface buoyancy loss over its sinking branch, and the increasing Antarctic meltwater discharge, in response to ozone depletion in the SH stratosphere and increasing atmospheric CO2. A large-scale readjustment of the GMOC seems to be underway in the South Atlantic and Indo-Pacific Oceans since the mid-2000s in response to the Southern Ocean changes.
At seasonal-to-interannual timescales, Atlantic hurricane activity is greatly modulated by El Niño - Southern Oscillation and Atlantic Meridional Mode. However, they develop predominantly in boreal winter or spring, and are relatively weaker during the Atlantic hurricane season. The leading mode of tropical Atlantic sea surface temperature (SST) variability during the Atlantic hurricane season is Atlantic Niño/Niña, which is characterized by warm/cold SST anomalies in the eastern equatorial Atlantic. However, the linkage between Atlantic Niño/Niña and hurricane activity has not been examined. Here, we use observations to show that Atlantic Niño, by strengthening the Atlantic inter-tropical convergence zone, enhances African easterly wave activity and low-level cyclonic vorticity across the deep tropical eastern North Atlantic. We show that such conditions increase the likelihood of powerful hurricanes developing in the deep tropics near the Cape Verde islands, elevating the risk of major hurricanes impacting the Caribbean islands and the U.S.
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