The Role of Ocean Dynamics in the Cross-equatorial Energy Transport under a Thermal Forcing in the Southern Ocean

Liu, Fukai; Luo, Yiyong; Lu, Jian; Wan, Xiuquan

doi:10.1007/s00376-021-1099-6

Cited by 9 publications

(8 citation statements)

References 45 publications

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“…In contrast to previous studies, however, they also found that the buoyancy-driven changes in the STCs are the primary driver of the cross-equatorial OHT changes in the Indo-Pacific basin. This finding corroborates the study by Liu et al (2021), who warmed the surface of the Southern Ocean and found that the generated cross-equatorial heat transport is not via the AMOC, but rather a buoyancy-driven anomalous overturning circulation beneath the STCs, which also dampens the ITCZ shift.…”

Section: Introductionsupporting

confidence: 92%

Asymmetric response of cross-equatorial ocean heat transport to latitudinal thermal forcing in CESM

Liu,

Luo

et al. 2024

Preprint

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The response of cross-equatorial ocean heat transport (OHT) to interhemispheric radiative imbalances is investigated using a set of fully coupled experiments with external radiative forcing imposed at different latitudinal bands at the top of the atmosphere. The modeling results reveal a first-order collaborative relationship between the ocean and the atmosphere, both working in tandem to facilitate the cross-equatorial heat transport to offset the imposed energy imbalance. Considerable asymmetry is also found between the responses to the radiative forcing placed at the same latitude, but in opposite hemispheres. This asymmetry is mainly attributed to the different changes in ocean circulation. When the radiative forcing is placed over the Southern Ocean, a buoyancy-driven clockwise cell is created that extends from the Southern Ocean into the tropics in both the Indo-Pacific and Atlantic basins, effectively transporting energy into the northern hemisphere. Conversely, when the radiative forcing is placed over the northern high latitudes, the Atlantic Meridional Overturning Circulation (AMOC) is weakened, leading to anomalous southward energy transport. In addition, our study reveals the reduced effectiveness of tropical forcing relative to higher latitude forcing in generating anomalous cross-equatorial OHT. This reduced effectiveness is due to the cancellation of the overturning cell-induced cross-equatorial OHT anomaly by the contribution of the horizontal gyre.

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Section: Introductionsupporting

confidence: 92%

Asymmetric response of cross-equatorial ocean heat transport to latitudinal thermal forcing in CESM

Liu,

Luo

et al. 2024

Preprint

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“…To investigate the impact of wind-driven ocean circulation changes, we analyze another set of large ensemble members, mechanically decoupled (MD) historical simulations with CESM2, in which ocean surface wind stress is fixed to its seasonally varying pre-industrial climatological state 33 (see Methods) using the wind stress overriding technique [36][37][38][39][40] . Through this approach, the Bjerknes feedback is cut off, and therefore the effects of ENSO variability and Walker Circulation adjustment on SST trends are both eliminated 41 .…”

Section: Mechanically Decoupled Simulationsmentioning

confidence: 99%

“…Wind stress overriding experiments have been demonstrated to be helpful in isolating the influence of wind-driven ocean circulation on the ocean-atmosphere coupled system [36][37][38][39][40] . The second CESM2 ensemble, MD for "Mechanically Decoupled Model", is created by branching 20 members from a pre-industrial MD model run 33 .…”

Section: Large Ensemble Historical Simulationsmentioning

confidence: 99%

Historical changes in wind-driven ocean circulation drive pattern of Pacific warming

Fu,

Hu,

Zheng

et al. 2024

Nat Commun

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The tropical Pacific warming pattern since the 1950s exhibits two warming centers in the western Pacific (WP) and eastern Pacific (EP), encompassing an equatorial central Pacific (CP) cooling and a hemispheric asymmetry in the subtropical EP. The underlying mechanisms of this warming pattern remain debated. Here, we conduct ocean heat decompositions of two coupled model large ensembles to unfold the role of wind-driven ocean circulation. When wind changes are suppressed, historical radiative forcing induces a subtropical northeastern Pacific warming, thus causing a hemispheric asymmetry that extends toward the tropical WP. The tropical EP warming is instead induced by the cross-equatorial winds associated with the hemispheric asymmetry, and its driving mechanism is southward warm Ekman advection due to the off-equatorial westerly wind anomalies around 5°N, not vertical thermocline adjustment. Climate models fail to capture the observed CP cooling, suggesting an urgent need to better simulate equatorial oceanic processes and thermal structures.

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“…Many previous wind stress overriding studies have used a configuration of CESM in their simulations (Luo et al, 2015;Larson et al, 2017;F. Liu et al, 2017;Larson et al, 2018Chakravorty et al, 2020Chakravorty et al, , 2021F. Liu et al, 2021;McMonigal & Larson, 2022;Luongo et al, 2022Luongo et al, , 2023.…”

Section: Wind Stress Overriding Simulationsmentioning

confidence: 99%

“…More recently, global climatological wind stress overriding has been used to study non-ENSO phenomena as well. These studies explore topics such as Pacific sea surface temperature (SST) variance (Larson et al, 2018), buoyancy-forced characteristics of the Atlantic Meridional Overturning Circulation (AMOC, , cross-equatorial energy transport (F. Liu et al, 2021), and extratropical atmospheric variability (Larson et al, 2022). Other studies have opted to override with climatological wind stress in only the Equatorial Pacific (with the wind freely evolving elsewhere) to study the Pacific Meridional Mode (PMM) in the absence of ENSO (Zhang et al, 2021) or Indian Ocean meridional heat transport (McMonigal & Larson, 2022).…”

Section: Introductionmentioning

confidence: 99%

Retaining Short-term Variability Reduces Mean State Biases in Wind Stress Overriding Simulations

Luongo

Brizuela

Eisenman

et al. 2023

Preprint

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Positive feedbacks in climate processes can obscure the initial drivers of climate phenomena. Some recent global climate model (GCM) studies partially circumvent this issue by controlling the wind stress felt by the surface ocean such that the atmosphere and ocean become mechanically decoupled. Most mechanical decoupling studies have chosen to override wind stress with an annual climatology. In this study we introduce an alternative method of interannually variable overriding which maintains higher frequency momentum forcing of the surface ocean. Using CESM1, we then compare the size of the residuals between these two methods of overriding with a freely evolving control integration. We find that the simple act of overriding with a climatology, as has been done in previous studies, creates sea surface temperature (SST) residuals throughout the global oceans on the order of $0.5-1^\circ$C. This is substantially larger than residuals from the interannually variable overriding case introduced here. We attribute the SST biases in the climatological overriding case to the lack of synoptic and subseasonal variability, which creates too shallow of a mixed layer throughout the global surface ocean. This shoaling of the mixed layer reduces the effective heat capacity of the surface ocean and prevents anomalous heat from mixing into the thermocline. These results have implications for the reevaluation of past studies which have used climatological wind stress overriding and for avoiding these biases in future wind stress overriding studies by using interannually varying wind stress fields.

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The Role of Ocean Dynamics in the Cross-equatorial Energy Transport under a Thermal Forcing in the Southern Ocean

Cited by 9 publications

References 45 publications

Asymmetric response of cross-equatorial ocean heat transport to latitudinal thermal forcing in CESM

Asymmetric response of cross-equatorial ocean heat transport to latitudinal thermal forcing in CESM

Historical changes in wind-driven ocean circulation drive pattern of Pacific warming

Retaining Short-term Variability Reduces Mean State Biases in Wind Stress Overriding Simulations

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