Shi
Jia-Rui
Shi
Jia-Rui
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ArticleTwo distinct modes of climate responses to the anthropogenic aerosol forcing changes(American Meteorological Society, 2022-05-06) Shi, Jia-Rui ; Kwon, Young-Oh ; Wijffels, Susan E.Unlike greenhouse gases (GHGs), anthropogenic aerosol (AA) concentrations have increased and then decreased over the past century or so, with the timing of the peak concentration varying in different regions. To date, it has been challenging to separate the climate impact of AAs from that due to GHGs and background internal variability. We use a pattern recognition method, taking advantage of spatiotemporal covariance information, to isolate the forced patterns for the surface ocean and associated atmospheric variables from the all-but-one forcing Community Earth System Model ensembles. We find that the aerosol-forced responses are dominated by two leading modes, with one associated with the historical increase and future decrease of global mean aerosol concentrations (dominated by the Northern Hemisphere sources) and the other due to the transition of the primary sources of AA from the west to the east and also from Northern Hemisphere extratropical regions to tropical regions. In particular, the aerosol transition effect, to some extent compensating the global mean effect, exhibits a zonal asymmetry in the surface temperature and salinity responses. We also show that this transition effect dominates the total AA effect during recent decades, e.g., 1967–2007.
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ArticleSurface warming-induced global acceleration of upper ocean currents(American Association for the Advancement of Science, 2022-04-20) Peng, Qihua ; Xie, Shang-Ping ; Wang, Dongxiao ; Huang, Rui Xin ; Chen, Gengxin ; Shu, Yeqiang ; Shi, Jia-Rui ; Liu, WeiHow the ocean circulation changes in a warming climate is an important but poorly understood problem. Using a global ocean model, we decompose the problem into distinct responses to changes in sea surface temperature, salinity, and wind. Our results show that the surface warming effect, a robust feature of anthropogenic climate change, dominates and accelerates the upper ocean currents in 77% of the global ocean. Specifically, the increased vertical stratification intensifies the upper subtropical gyres and equatorial currents by shoaling these systems, while the differential warming between the Southern Ocean upwelling zone and the region to the north accelerates surface zonal currents in the Southern Ocean. In comparison, the wind stress and surface salinity changes affect regional current systems. Our study points a way forward for investigating ocean circulation change and evaluating the uncertainty.
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ArticleSubsurface ocean temperature responses to the anthropogenic aerosol forcing in the North Pacific(American Geophysical Union, 2023-01-09) Shi, Jia‐Rui ; Kwon, Young‐Oh ; Wijffels, Susan E.Separating the climate response to external forcing from internal climate variability is a key challenge. While most previous studies have focused on surface responses, here we examine zonal‐mean patterns of North Pacific subsurface temperature responses. In particular, the changes since 1950 driven by anthropogenic aerosol emissions are found by using a pattern recognition method. Based on the single‐forcing large‐ensemble simulations from two models, we show that aerosol forcing caused a nonmonotonic temporal response and a characteristic zonal‐mean pattern within North Pacific, which is distinct from the pattern associated with internal variability. The aerosol‐forced pattern with the nonmonotonic temporal feature shows a substantial temperature change in subpolar regions and a reversed change on the southern flank of the subtropical gyre. A similar characteristic pattern and nonmonotonic time evolution are extracted from the subsurface observations, which likely reflect the subsurface responses to the aerosol forcing, although differences exist with the simulated responses.
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ArticleSouthern Ocean warming and its climatic impacts(Elsevier, 2023-05-12) Cai, Wenju ; Gao, Libao ; Luo, Yiyong ; Li, Xichen ; Zheng, Xiaotong ; Zhang, Xuebin ; Cheng, Xuhua ; Jia, Fan ; Purich, Ariaan ; Santoso, Agus ; Du, Yan ; Holland, David M. ; Shi, Jia-Rui ; Xiang, Baoqiang ; Xie, Shang-PingThe Southern Ocean has warmed substantially, and up to early 21st century, Antarctic stratospheric ozone depletion and increasing atmospheric CO2 have conspired to intensify Southern Ocean warming. Despite a projected ozone recovery, fluxes to the Southern Ocean of radiative heat and freshwater from enhanced precipitation and melting sea ice, ice shelves, and ice sheets are expected to increase, as is a Southern Ocean westerly poleward intensification. The warming has far-reaching climatic implications for melt of Antarctic ice shelf and ice sheet, sea level rise, and remote circulations such as the intertropical convergence zone and tropical ocean-atmosphere circulations, which affect extreme weathers, agriculture, and ecosystems. The surface warm and freshwater anomalies are advected northward by the mean circulation and deposited into the ocean interior with a zonal-mean maximum at ∼45°S. The increased momentum and buoyancy fluxes enhance the Southern Ocean circulation and water mass transformation, further increasing the heat uptake. Complex processes that operate but poorly understood include interactive ice shelves and ice sheets, oceanic eddies, tropical-polar interactions, and impact of the Southern Ocean response on the climate change forcing itself; in particular, limited observations and low resolution of climate models hinder rapid progress. Thus, projection of Southern Ocean warming will likely remain uncertain, but recent community effort has laid a solid foundation for substantial progress.
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ArticleThe competition between anthropogenic aerosol and greenhouse gas climate forcing is revealed by North Pacific water-mass changes(American Association for the Advancement of Science, 2023-09-20) Shi, Jia-Rui ; Wijffels, Susan E. ; Kwon, Young-Oh ; Talley, Lynne D. ; Gille, Sarah T.Modeled water-mass changes in the North Pacific thermocline, both in the subsurface and at the surface, reveal the impact of the competition between anthropogenic aerosols (AAs) and greenhouse gases (GHGs) over the past 6 decades. The AA effect overwhelms the GHG effect during 1950–1985 in driving salinity changes on density surfaces, while after 1985 the GHG effect dominates. These subsurface water-mass changes are traced back to changes at the surface, of which ~70% stems from the migration of density surface outcrops, equatorward due to regional cooling by AAs and subsequent poleward due to warming by GHGs. Ocean subduction connects these surface outcrop changes to the main thermocline. Both observations and models reveal this transition in climate forcing around 1985 and highlight the important role of AA climate forcing on our oceans’ water masses.
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ArticleInterhemispheric contrasts of ocean heat content change reveals distinct fingerprints of anthropogenic climate forcings(American Geophysical Union, 2023-08-12) Shi, Jia-Rui ; Wijffels, Susan E. ; Kwon, Young-Oh ; Xie, Shang-PingDuring recent decades, both greenhouse gases (GHGs) and anthropogenic aerosols (AAs) drove major changes in the Earth's energy imbalance. However, their respective fingerprints in changes to ocean heat content (OHC) have been difficult to isolate and detect when global or hemispheric averages are used. Based on a pattern recognition analysis, we show that AAs drive an interhemispheric asymmetry within the 20°-35° latitude band in historical OHC change due to the southward shift of the atmospheric and ocean circulation system. This forced pattern is distinct from the GHG-induced pattern, which dominates the asymmetry in higher latitudes. Moreover, it is found that this significant aerosol-forced OHC trend pattern can only be captured in analyzed periods of 20 years or longer and including 1975–1990. Using these distinct spatiotemporal characteristics, we show that the fingerprint of aerosol climate forcing in ocean observations can be distinguished from both the stronger GHG-induced signals and internal variability.
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ArticleThe emerging human influence on the seasonal cycle of sea surface temperature(Nature Research, 2024-03-15) Shi, Jia-Rui ; Santer, Benjamin D. ; Kwon, Young-Oh ; Wijffels, Susan E.Gaining insight into anthropogenic influence on seasonality is of scientific, economic and societal importance. Here we show that a human-caused signal in the seasonal cycle of sea surface temperature (SST) has emerged from the noise of natural variability. Geographical patterns of changes in SST seasonal cycle amplitude (SSTAC) reveal two distinctive features: an increase at Northern Hemisphere mid-latitudes related to mixed-layer depth changes and a robust dipole pattern between 40° S and 55° S that is mainly driven by surface wind changes. The model-predicted pattern of SSTAC change is identifiable with high statistical confidence in four observed SST products and in 51 individual model realizations of historical climate evolution. Simulations with individual forcings reveal that GHG increases are the primary driver of changes in SSTAC, with smaller but distinct contributions from anthropogenic aerosol and ozone forcing. The robust human ‘fingerprint’ identified here is likely to have wide-ranging impacts on marine ecosystems.
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ArticleWeakened seasonality of the ocean surface mixed layer depth in the Southern Indian Ocean during 1980-2019(American Geophysical Union, 2024-04-04) Long, Shang-Min ; Zhao, Shichang ; Gao, Zhen ; Sun, Shantong ; Shi, Jia-Rui ; Ying, Jun ; Li, Guancheng ; Cheng, Lijing ; Chen, Jiajia ; Cheng, Xuhua ; Lu, ShaoleiTemporal and spatial variations in the ocean surface mixed layer are important for the climate and ecological systems. During 1980–2019, the Southern Indian Ocean (SIO) mixed layer depth (MLD) displays a basin-wide shoaling trend that is absent in the other basins within 40°S–40°N. The SIO MLD shoaling is mostly prominent in austral winter with deep climatology MLD, substantially weakening the MLD seasonality. Moreover, the SIO MLD changes are primarily caused by a southward shift of the subtropical anticyclonic winds and hence ocean gyre, associated with a strengthening of the Southern Annular Mode, in recent decades for both winter and summer. However, the poleward-shifted subtropical ocean circulation preferentially shoals the SIO MLD in winter when the meridional MLD gradient is sharp but not in summer when the gradient is flat. This highlights the distinct subtropical MLD response to meridional mitigation in winds due to different background oceanic conditions across seasons.