Subtropical clouds key to Southern Ocean teleconnections to the tropical Pacific

Abstract

Excessive precipitation over the southeastern tropical Pacific is a major common bias that persists through generations of global climate models. While recent studies suggest an overly warm Southern Ocean as the cause, models disagree on the quantitative importance of this remote mechanism in light of ocean circulation feedback. Here, using a multimodel experiment in which the Southern Ocean is radiatively cooled, we show a teleconnection from the Southern Ocean to the tropical Pacific that is mediated by a shortwave subtropical cloud feedback. Cooling the Southern Ocean preferentially cools the southeastern tropical Pacific, thereby shifting the eastern tropical Pacific rainbelt northward with the reduced precipitation bias. Regional cloud locking experiments confirm that the teleconnection efficiency depends on subtropical stratocumulus cloud feedback. This subtropical cloud feedback is too weak in most climate models, suggesting that teleconnections from the Southern Ocean to the tropical Pacific are stronger than widely thought.

The Antarctic ozone hole and the pattern effect on climate sensitivity

“…In addition, we did the same analysis using a different wind and SST analysis, which produced similar patterns ( SI Appendix ). This SST response is similar in shape to the SST response found in the SO cooling experiments ( 23 , 27 ). These results are subject to uncertainty, and the mechanisms need to be investigated in a series of carefully controlled modeling experiments, but the weight of evidence from observations and model experiments suggests that some significant part of the cooling in the eastern tropical Pacific may be triggered by westerly wind accelerations associated with the Antarctic ozone hole.…”

“…These experiments on the effect of cloud reflection in the SO on climate resulted in a subprogram under the Climate Modeling Intercomparison Project in which a number of different climate models were subjected to the same reduction in absorbed solar radiation over the SO ( 26 ). Comparison among these models and with observations showed that models with a strong low-cloud feedback could transmit the cooling signal from the SO to the tropics, and that the models with a stronger low-cloud feedback were in better agreement with observed low-cloud behavior ( 27 ). The efficient movement of the cooling signal from the SO to the tropics involves interactions between SST, low clouds, atmospheric circulation, and ocean currents.…”

“…This northward current would carry cold water toward the north, feeding into the Peru Current. This northward advection of cold water would cause enhanced low-level clouds which extend the cooling poleward ( 23 , 27 ). The increased zonal winds at 60 ∘ S coupled with surface cooling extending farther into the subtropics lead to anomalous high pressure in the atmosphere off the coast of South America, which results in enhancement of the equatorward winds in the southeast Pacific, which advect the cooling equatorward and may also enhance the Peru Current upwelling as well as easterly winds closer to the equator.…”

“…The increased zonal winds at 60 ∘ S coupled with surface cooling extending farther into the subtropics lead to anomalous high pressure in the atmosphere off the coast of South America, which results in enhancement of the equatorward winds in the southeast Pacific, which advect the cooling equatorward and may also enhance the Peru Current upwelling as well as easterly winds closer to the equator. These changes lead to cooling in the eastern tropical Pacific Ocean ( 27 , 50 , 51 ).…”

Systematic Climate Model Biases in the Large‐Scale Patterns of Recent Sea‐Surface Temperature and Sea‐Level Pressure Change

“…(2019)). This remains plausible, though its relevance for lower latitude SST trends depends on an active body of work to quantify the teleconnections from Southern Ocean SST changes (Dong et al., 2022; Hwang et al., 2017; Kang et al., 2019; Kim et al., 2022; X. Zhang et al., 2021). Furthermore, there are several mechanisms for how recent Southern Ocean cooling and sea ice expansion could result from anthropogenic forcing, including wind shifts due to a combination of greenhouse gas and ozone forcing (Kostov et al., 2018; Thompson et al., 2011) and increased surface stratification resulting from precipitation changes and/or ice‐sheet melt (Bintanja et al., 2013; De Lavergne et al., 2014; Pauling et al., 2016; Purich et al., 2018), the latter of which is not included in CMIP models.…”