Influence of tropical wind on global temperature from months to decades

Changes in surface wind stress can have a strong influence on the ocean circulation and, hence, on climate. Our focus here is on variations of tropical winds and their impact on the global mean surface temperature (GMST) on time scales from months to decades. The smallness of Coriolis parameter near the equator implies that even small changes in the local winds can translate into large changes in the equatorial upwelling, affecting the depth of thermocline and tropical sea surface temperature (SST). The time scale of the tropical thermocline response to variations in the winds is relatively short, ranging from months to less than a year, being set by tropical ocean wave dynamics (McCreary 1978; Philander and Pacanowski 1981; Gill 1982). It is therefore expected that, to the first order, GMST would respond to a change in tropical winds in less than a year, through the associated change in the depth of thermocline. However, reproducing the observed GMST response to tropical winds in climate models presents a challenge (Douville et al. 2015). To better understand the link between tropical winds and GMST, and to identify the main components in this link in climate models, it is instructive to partition the propagation of the wind-induced signals into several stages—an approach adopted here. This includes the generation and eastward propagation of Kelvin waves along the equator and the associated changes in equatorial thermocline depth, followed by the generation of off-equatorial Rossby waves that carry the associated changes in the thermocline and SST westward, filling a wider tropical region with the wind-induced SST signals that are then expressed as changes in GMST. On longer time scales, from years to decades, changes in the tropical Pacific winds can lead to periods of prolonged Abstract Using an Earth System Model and observations we analyze the sequence of events connecting episodes of trade wind strengthening (or weakening) to global mean surface temperature (GMST) cooling (or warming), with tropical ocean wave dynamics partially setting the time scale. In this sequence tropical west Pacific wind stress signals lead equatorial east Pacific thermocline depth signals which lead tropical east Pacific sea surface temperature (SST) signals which lead GMST signals. Using the anthropogenic, natural and tropical wind signals extracted from our simulations in a multivariate linear regression with observed GMST makes clear the balance that exists between anthropogenic warming and tropical wind-induced cooling during the recent warming slowdown, and between volcanic cooling and tropical wind-induced warming during the El Chichón and Pinatubo eruptions. Finally, we find an anticorrelation between global-mean temperatures in the near-surface (upper ∼100 m) and subsurface (∼100–300 m) ocean layers, linked to wind-driven interannual to decadal variations in the strength of the subtropical cell overturning in the upper Pacific Ocean.