Impacts of Atlantic Multidecadal Variability on the Tropical Pacific: a multi-model study

Abstract

<p>The Atlantic Multidecadal Variability (AMV) has been linked to the observed slowdown of global warming over 1998-2012 through its impact on the tropical Pacific. Given the global importance of tropical Pacific variability, better understanding this Atlantic-Pacific teleconnection is key for improving climate predictions, but the robustness and strength of this link is uncertain. Analysing a multi-model set of sensitivity experiments, we find that models differ by a factor 10 in simulating the amplitude of the Equatorial Pacific cooling response to observed AMV warming. The inter-model spread is mainly driven by different amounts of moist static energy injection from the tropical Atlantic surface into the upper troposphere. We reduce this inter-model uncertainty by analytically correcting models for their mean precipitation biases and we quantify that, following an observed 0.26ºC AMV warming, the equatorial Pacific cools by 0.16ºC with an inter-model standard deviation of 0.03ºC.</p>

Mechanisms of Tropical Pacific Decadal Variability

“…Idealised numerical model experiments with prescribed surface warming in either the tropical Indian or Atlantic basins confirm the Gill-type induced global Walker circulation changes, including a Pacific trade wind acceleration (Fig. 5c,d), which leads to a central/eastern Pacific sea surface cooling in coupled model settings 27,134,135,[150][151][152] and is further amplified by the Pacific Bjerknes feedback 133,135,138 . These Pacific changes on decadal timescales can also modulate ENSO characteristics 151,153 .…”

“…However, observations suggest that this recent dominance of the Atlantic may have been different in the past 130 . The magnitude of the Pacific response to idealised Indian Ocean SST forcing appears to become more prominent further back in time (i.e., 1980-2010 or 1958-2010) 140,149 , while the response to Atlantic Ocean SST forcing appears relatively consistent 130,144,152 .…”

“…TPDV appears to have responded to Atlantic and Indian Ocean forcing over the historical period. Using partially coupled experiments, where SSTs are constrained by idealised observed SST in one basin, Atlantic warming was shown to play a prominent role 134,137,138,152 in the transition from TPDV+ in the 1990s to TPDV-in the early 2000s 11 . The Indian Ocean was reported as either playing a minor role 135,137 or amplifying the Pacific response to the Atlantic forcing 134 .…”

“…Internally-generated wind anomalies in the subtropical/tropical regions can create equatorial SST anomalies 102 , which can then reinforce the subtropical wind anomalies through atmospheric teleconnections, increasing their persistence to enhance lower-frequency variability 116 . Decadal timescale SST anomalies in the Atlantic and Indian Oceans can also induce wind anomalies in the tropical Pacific conducive to the development of SST anomalies of the opposite sign 134,137,150,152 . However, the extent to which wind forcing from the extra-tropics or from other ocean basins may itself be the result of forcing from the tropical Pacific is not clearly understood.…”