The Role of Clouds in Shaping Tropical Pacific Response Pattern to Extratropical Thermal Forcing

Hsiao, Wei‐Ting; Hwang, Yean Ren; Chen, Yong‐Jhih; Kang, Sarah M.

doi:10.1029/2022gl098023

Cited by 13 publications

(12 citation statements)

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“…The PMM then acts as a surface conduit by which extratropical cooling can then reach the tropics. We also note the strong similarity between subtropical BF cooling of SST from this low cloud‐WES pathway with subtropical responses of motionless slab ocean models to similar forcing schemes (Hsiao et al., 2022; Hwang et al., 2017; Kang et al., 2014, 2020; Luongo et al., 2022).…”

Section: Extratropical‐tropical Pathwaysupporting

confidence: 59%

“…In the Pacific basin, a strong zonal SST gradient develops such that the eastern half of the basin is significantly cooler than the western half; SST perturbations are most highly negative below the marine stratiform cloud deck off the west coast of North America. In the marine stratocumulus regime, the positive low cloud feedback (Clement et al., 2009; Hsiao et al., 2022; Norris & Leovy, 1994; Norris et al., 1998; Wood, 2012; Yang et al., 2022) can amplify negative SST perturbations by increasing cloud cover, reducing solar insolation, and cooling local SSTs further. Figure S9 of Luongo et al.…”

Section: Extratropical‐tropical Pathwaymentioning

confidence: 99%

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A Pathway for Northern Hemisphere Extratropical Cooling to Elicit a Tropical Response

Luongo

Xie

Eisenman

et al. 2023

Geophysical Research Letters

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Previous studies have found that Northern Hemisphere aerosol-like cooling induces a La Niñalike response in the tropical Indo-Pacific. Here, we explore how a coupled ocean-atmosphere feedback pathway communicates and sustains this response. We override ocean surface wind stress in a comprehensive climate model to decompose the total ocean-atmosphere response to forced extratropical cooling into the response of surface buoyancy forcing alone and surface momentum forcing alone. In the subtropics, the buoyancy-forced response dominates: the positive low cloud feedback amplifies sea surface temperature (SST) anomalies which wind-driven evaporative cooling communicates to the tropics. In the equatorial Indo-Pacific, buoyancy-forced ocean dynamics cool the surface while the Bjerknes feedback creates zonally asymmetric SST patterns. Although subtropical cloud feedbacks are model-dependent, our results suggest this feedback pathway is robust across a suite of models such that models with a stronger subtropical low cloud response exhibit a stronger La Niña response.Plain Language Summary Anthropogenic aerosols are an important radiative forcing on the climate system contributing to observed climate variability. In prior modeling studies, idealized aerosol-like forcing applied to Northern Hemisphere high latitude regions has resulted in a tropical La Niña-like response in the Eastern Equatorial Pacific. In this study, we investigate the pathway by which high latitude aerosollike cooling is communicated to the tropics via a sequence of ocean-atmosphere positive feedback processes. We explore this pathway further by parsing out the total climate response into surface forcing which alters the buoyancy of seawater via heat or freshwater and surface wind stress forcing which alters the momentum of seawater. We find that subtropical patterns, arising from low clouds and wind-induced evaporative cooling, are primarily buoyancy-forced, while tropical asymmetries arise from momentum forcing. The results show that this pathway is robust across seven climate models such that stronger subtropical cloud responses elicit stronger sea surface temperature responses in the equatorial Pacific. The results highlight the important link between extratropical aerosol-like forcing and La Niña-like patterns via these coupled ocean-atmosphere feedbacks. The equatorial Pacific can drive major climate variability, suggesting global implications for these results.

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Section: Extratropical‐tropical Pathwaysupporting

confidence: 59%

Section: Extratropical‐tropical Pathwaymentioning

confidence: 99%

A Pathway for Northern Hemisphere Extratropical Cooling to Elicit a Tropical Response

Luongo

Xie

Eisenman

et al. 2023

Geophysical Research Letters

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“…2, A and F ), high-latitude warming effects from sea ice loss propagate equatorward via wind-evaporation-SST (WES) feedback, which are further amplified by positive shortwave cloud radiative feedback ( Fig. 3, A and B ) ( 34 , 35 ). Thus, our experimental setting allows us to gain insight into the central role of sea ice loss in the El Niño–like warming pattern, more so than the direct CO 2 forcing itself.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast to the strong north-south gradient, the tropical Pacific SST response shows little east-west gradient ( Figs. 1J and 2H ) ( 35 , 40 ). The Walker circulation change, hence, is negligible in SOM_NA ( Figs.…”

Section: Resultsmentioning

confidence: 99%

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Disentangling the mechanisms of equatorial Pacific climate change

et al. 2023

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Most state-of-art models project a reduced equatorial Pacific east-west temperature gradient and a weakened Walker circulation under global warming. However, the causes of this robust projection remain elusive. Here, we devise a series of slab ocean model experiments to diagnostically decompose the global warming response into the contributions from the direct carbon dioxide (CO 2 ) forcing, sea ice changes, and regional ocean heat uptake. The CO 2 forcing dominates the Walker circulation slowdown through enhancing the tropical tropospheric stability. Antarctic sea ice changes and local ocean heat release are the dominant drivers for reduced zonal temperature gradient over the equatorial Pacific, while the Southern Ocean heat uptake opposes this change. Corroborating our model experiments, multimodel analysis shows that the models with greater Southern Ocean heat uptake exhibit less reduction in the temperature gradient and less weakening of the Walker circulation. Therefore, constraining the tropical Pacific projection requires a better insight into Southern Ocean processes.

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The Longwave Cloud‐Radiative Feedback in Tropical Waves Derived by Different Precipitation Data Sets

Hsiao,

Maloney

2024

Geophysical Research Letters

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Anomalous tropical longwave cloud‐radiative heating of the atmosphere is generated when convective precipitation occurs, which plays an important role in the dynamics of tropical disturbances. Defining the observed cloud‐radiative feedback as the reduction of top‐of‐atmosphere longwave radiative cooling per unit precipitation, the feedback magnitudes are sensitive to the observed precipitation data set used when comparing two versions of Global Precipitation Climatology Project, version 1.3 (GPCPv1.3) and the newer version 3.2 (GPCPv3.2). GPCPv3.2 contains larger magnitudes and variance of daily precipitation, which yields a weaker cloud‐radiative feedback in tropical disturbances at all frequencies and zonal wavenumbers. Weaker cloud‐radiative feedbacks occur in GPCPv3.2 at shorter zonal lengths on intraseasonal timescales, which implies a preferential growth at planetary scales for the Madden‐Julian oscillation. Phase relationships between precipitation, radiative heating, and other thermodynamic variables in eastward‐propagating gravity waves also change with the updated GPCPv3.2.

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The Role of Clouds in Shaping Tropical Pacific Response Pattern to Extratropical Thermal Forcing

Cited by 13 publications

References 50 publications

A Pathway for Northern Hemisphere Extratropical Cooling to Elicit a Tropical Response

A Pathway for Northern Hemisphere Extratropical Cooling to Elicit a Tropical Response

Disentangling the mechanisms of equatorial Pacific climate change

The Longwave Cloud‐Radiative Feedback in Tropical Waves Derived by Different Precipitation Data Sets

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