Shaojun Zheng

Oceanic circulation along the Antarctic shelf break regulates heat and material exchanges between the continental shelf and the open ocean, playing a crucial role in ice shelf melting and global overturning circulation. However, the circulation remains poorly understood due to limited observations. By combining the Surface Water and Ocean Topography (SWOT) mission with traditional AVISO altimetry, this study identifies an eddy train along the shelf break of the Ross Sea, which consists of alternating cyclonic and anticyclonic circulations with spatial scales of ∼100 km. A notable phase reversal of the eddy train occurred around 2014, coinciding with a broader climate variability of the Southern Ocean. SWOT reveals sea surface height amplitudes of the eddy train roughly twice those from AVISO, while current reanalysis products fail to reproduce this feature, highlighting the need for improved observations and modeling to better resolve Antarctic shelf‐region dynamics. Plain Language The ocean circulations around the Antarctic shelf break, where the shallow continental shelf meets the deep open ocean, regulate heat and material exchange between the shelf and open ocean. This exchange is critical for the formation of dense shelf water and ice shelf melt, thereby impacting the global overturning circulation and sea level rise. However, this region remains poorly understood due to limited observations. Using data from new‐generation SWOT and traditional AVISO satellites, we investigated ocean circulations at the Ross Sea shelf break. We discovered a chain of ∼100 km circulations along the shelf break with alternating clockwise and counterclockwise rotations. Around 2014, their pattern shifted dramatically, aligning with broader climate changes in the Southern Ocean. Existing ocean reanalysis products fail to reproduce these features, highlighting the need for improved observations such as SWOT to enhance our understanding of Antarctic currents and their climatic impacts.

Marine heat waves (MHWs) are significant extreme climate events within the oceanic system that profoundly impact ecosystems and socioeconomic conditions. The south Indian Ocean (SIO) plays a critical role in both global and regional climate regulation, influencing climate variability in regions such as Africa and East Asia. This study systematically investigates the interannual variability and dynamic mechanisms of MHWs in the SIO based on satellite sea surface temperature data and reanalysis datasets from 1982 to 2021. The MHWs in the SIO exhibit significant interannual variability associated with El Niño–Southern Oscillation (ENSO). The mean intensity anomaly of MHWs in the SIO region of 60°–90°E, 15°–25°S is significantly correlated with the Niño-3.4 index with a correlation coefficient of 0.57, lagging the Niño-3.4 index by 3 months. The mixed-layer heat budget analysis indicates that the energy source for MHWs in the SIO is mainly from the atmospheric net surface heat flux, particularly influenced by latent heat and longwave radiation. During the decaying phases of El Niño events, abnormal northwesterly winds suppress the background southeasterly winds, reducing evaporation and suppressing latent heat release from the ocean. The increase in total clouds in the SIO weakens the shortwave radiation reaching the ocean surface, but the increase in high clouds strengthens the longwave radiation as a greenhouse effect. Meanwhile, the relatively shallow mixed-layer depth could promote the formation of MHWs. This study contributes to a deeper understanding of MHWs in the SIO and their relation to large-scale ocean–atmosphere processes.

The Wyrtki Jet (WJ), a pivotal surface circulation system in the equatorial Indian Ocean, exerts significant regulatory control over regional climate dynamics through its intense eastward transport characteristics, which modulate water mass exchange, thermohaline balance, and cross-basin energy transfer. To address the scarcity of in situ observational data, this study developed a satellite remote sensing-driven multi-parameter coupled model and reconstructed the WJ’s seasonal variations using the XGBoost machine learning algorithm. The results revealed that wind stress components, sea surface temperature, and wind stress curl serve as the primary drivers of its seasonal dynamics. The XGBoost model demonstrated superior performance in reconstructing WJ’s seasonal variations, achieving coefficients of determination (R²) exceeding 0.97 across all seasons and maintaining root mean square errors (RMSE) below 0.2 m/s across all seasons. The reconstructed currents exhibited strong consistency with the Ocean Surface Current Analysis Real-time (OSCAR) dataset, showing errors below 0.05 m/s in spring and autumn and under 0.1 m/s in summer and winter. The proposed multi-feature integrated modeling framework delivers a high spatiotemporal resolution analytical tool for tropical Indian Ocean circulation dynamics research, while simultaneously establishing critical data infrastructure to decode monsoon current coupling mechanisms, advancing early warning systems for extreme climatic events, and optimizing regional marine resource governance.

Recent studies have reported that global upper ocean stratification has intensified under the influence of global warming. Nevertheless, using both observations and long‐term reanalysis data, we find that concurrent with the significant ocean warming, the increasing trend of upper ocean stratification attenuated in the western tropical Pacific after 2000. This study highlights the effects of subsurface high spiciness (warm and salty) anomalies on the attenuation of the increasing stratification trend, which mirrors distinct vertical structures in the long‐term changes in temperature and salinity. Subsurface warming, rather than sea surface warming, is the primary driver of the increase in the ocean heat content and the weakening of ocean stratification as it substantially reduces the magnitude of the trend in the vertical thermal density gradient after 2000. These phenomena are closely associated with processes on isopycnals and reflect ocean dynamics driven by large‐scale atmospheric circulation. Intensified tropical trade winds and accelerated undercurrents facilitate the convergence of heat and salt in the western tropical Pacific. In addition, changes in the depth of the isopycnal layers induced by anomalous wind stress curl contribute to the subsurface spiciness variability through heaving. Notably, the consistent increase in the salinity from the surface to the subsurface also contributes to the post‐2000 weakening trend of the vertical haline density gradient. Analysis within the isopycnal framework demonstrates that the emergence of subsurface salty water effectively offsets the negative contribution of the thermal component to the weakening of density stratification in relatively deeper layers.

Interannual variability of the South Equatorial Current (SEC) in the southeast Indian Ocean is investigated using Archiving, Validation, and Interpretation of Satellite Oceanographic Data (AVISO) and Global Ocean Reanalysis and Simulations (GLORYS) data from January 1993 to December 2022 and a 1.5-layer reduced-gravity model. Interannual variability of the SEC averaged over the upper 200 m in the southeast Indian Ocean is influenced by El Niño–Southern Oscillation (ENSO). The SEC has a significant positive correlation with the Niño-3.4 index and lags the Niño-3.4 index by 12–15 months, with the SEC weakening significantly during the decaying years of El Niño events and vice versa for La Niña events. Mechanistic studies suggest that during the developing years of El Niño events, the northward sea level anomaly (SLA) pressure gradient between the negative SLA off Sumatra–Java coast and the positive SLA of SEC region (90°–115°E, 9°–13°S) strengthens the SEC under geostrophic equilibrium. During the decaying years of El Niño events, the negative SLA in the tropical western Pacific Ocean propagates through the Maritime Continent to the SEC region. The SLA pressure gradient between the Sumatra–Java coast and the SEC region reverses to southward. This induces an eastward geostrophic current anomaly under geostrophic equilibrium, significantly weakening the SEC. The converse holds for La Niña events. Local wind in the southeast Indian Ocean has a suppressive effect on the SLA propagated to this area. The results of the 1.5-layer reduced-gravity model verify these phenomena, and the westward-propagating SLA from the Maritime Continent induced by the Pacific wind plays a dominant role in the SLA variation in the SEC region from model experiment. This study can improve the understanding of the effects of ENSO processes on ocean circulation in the southeast Indian Ocean.

Interannual variability of the South Equatorial Current (SEC) in the southeast Indian Ocean is investigated using Archiving, Validation, and Interpretation of Satellite Oceanographic Data (AVISO) and Global Ocean Reanalysis and Simulations (GLORYS) data from January 1993 to December 2022 and a 1.5-layer reduced-gravity model. Interannual variability of the SEC averaged over the upper 200 m in the southeast Indian Ocean is influenced by El Niño–Southern Oscillation (ENSO). The SEC has a significant positive correlation with the Niño-3.4 index and lags the Niño-3.4 index by 12–15 months, with the SEC weakening significantly during the decaying years of El Niño events and vice versa for La Niña events. Mechanistic studies suggest that during the developing years of El Niño events, the northward sea level anomaly (SLA) pressure gradient between the negative SLA off Sumatra–Java coast and the positive SLA of SEC region (90°–115°E, 9°–13°S) strengthens the SEC under geostrophic equilibrium. During the decaying years of El Niño events, the negative SLA in the tropical western Pacific Ocean propagates through the Maritime Continent to the SEC region. The SLA pressure gradient between the Sumatra–Java coast and the SEC region reverses to southward. This induces an eastward geostrophic current anomaly under geostrophic equilibrium, significantly weakening the SEC. The converse holds for La Niña events. Local wind in the southeast Indian Ocean has a suppressive effect on the SLA propagated to this area. The results of the 1.5-layer reduced-gravity model verify these phenomena, and the westward-propagating SLA from the Maritime Continent induced by the Pacific wind plays a dominant role in the SLA variation in the SEC region from model experiment. This study can improve the understanding of the effects of ENSO processes on ocean circulation in the southeast Indian Ocean.

The East African Coastal Current (EACC) is an important western boundary current of the tropical south Indian Ocean and plays an important role in the ocean circulation and biogeochemical cycles in the Indian Ocean. This study investigates the interannual variability of the EACC and its dynamical mechanisms. The result shows that the EACC has interannual variability associated with El Niño–Southern Oscillation (ENSO) during 1993–2017. The EACC shows a significantly positive correlation with the Niño-3.4 index with a correlation coefficient of 0.65, lagging the Niño-3.4 index by 18 months. During the decaying phases of El Niño (La Niña) events, the negative (positive) sea level anomaly (SLA) propagates westward as upwelling (downwelling) Rossby waves from the southeast Indian Ocean to the southwest Indian Ocean and then strengthens (weakens) the EACC due to zonal SLA gradient off the East African coast under geostrophic equilibrium. The SLA gradually weakens in the southeast Indian Ocean during its westward propagation but strengthens in the southwest Indian Ocean promoted by local wind stress curl anomaly. This study can improve our understanding of the relationship between the western boundary current of the tropical south Indian Ocean and large-scale ENSO air–sea processes and is important for managing marine fisheries and ecosystems on the East African coast.

Using multiple observational and reanalysis data, this paper investigates the impact of the interdecadal shift in summer Arctic Oscillation (AO) on precipitation in East Asia, by removing ENSO influences. The results indicate that the lower-layer activity center of summer AO in Atlantic shifted eastward after the mid-1980s. This regime shift of summer AO has a significant impact on precipitation in East Asia. Before the mid-1980s, the key regions in which precipitation was affected by AO in East Asia were northern East Asia and Northeastern China and adjacent regions. After the mid-1980s, the key regions in which precipitation was affected by AO in East Asia were central Inner Mongolia and Southern China. The mechanism of precipitation changes can be attributed to changes in atmospheric circulation and water vapor transport related to AO changes. After the mid-1980s, the influence of AO on geopotential height over northern East Asia weakened; meanwhile, the impact of AO on geopotential height over China increased. Consistent with the changes in atmospheric circulation, water vapor transport in East Asia also underwent interdecadal changes before and after the mid-1980s. The differences in atmospheric circulation and water vapor transport in East Asia can be traced back to the North Atlantic. Before the mid-1980s, wave activity flux related to summer AO tended to propagate in high latitudes and subtropics; after the mid-1980s, the wave activity flux changed in its subtropical path and propagated eastward from the North Atlantic through the Middle East to China, significantly affecting the summer precipitation in China.

In 1998 and 2016, boreal summer intraseasonal oscillation (BSISO) could reach the middle-lower reaches of the Yangtze River basin (YRB), leading to extreme precipitation. Based on multiple daily data, this study reveals the differences in BSISO events and mechanisms between 1998 and 2016. In June–July of 1998 (2016), YRB precipitation was impacted by 30–60-day oscillation, i.e., BSISO1 (10–30-day oscillation, i.e., BSISO2), with two strong (three) precipitation events occurring. In 1998, when BSISO1 was in phases 1–4 (phases 5–8), the YRB experienced a wet (dry) episode. In 2016, when BSISO2 was in phases 1–2 and 7–8 (phases 3–6), the YRB experienced a wet (dry) episode. In 1998, in event 1, the active convection of the YRB first originated in the South China Sea–western Pacific (SCS–WP) and then in the tropical Indian Ocean (IO). In 1998, in event 2, the active convection of the YRB originated in the SCS–WP. In 2016, in events 1 and 3, the active convection of the YRB originated from the SCS–WP. In 2016, in event 2, the active convection of the YRB originated from the tropical IO and the extratropical WP. Different SST and atmospheric circulations explain different BSISO modes that dominate in the YRB. In 1998 (2016), in summer, (no) strong easterly wind anomalies occurred in the SCS–WP, which are favorable (unfavorable) for the enhancement of BSISO1. Accompanying the suppressed BSISO1, BSISO2 was enhanced in 2016.