Xiao-Yi Yang

Material transport and air‐sea coupling dynamics associated with monsoon‐related mesoscale and submesoscale processes in the Indian Ocean significantly modulate biogeochemical cycles, the large‐scale energy balance, and both regional and global climate change. A thorough understanding of mesoscale and submesoscale variability in the Indian Ocean is therefore crucial for elucidating the physical mechanisms governing complex interactions among the ocean, ecosystems, and climate. However, substantial challenges remain in accurate observations, diagnoses, and simulations of such variability in the Indian Ocean, which hinders our ability to quantify their impacts on large‐scale processes. This synthetic paper presents an interdisciplinary review on key characteristics of the unique mesoscale and submesoscale processes in the Indian Ocean. We first synthesize current understanding of the generation of bidirectional energy cascades, feedback mechanisms between mesoscale/submesoscale dynamics and the atmosphere, and physical‐biogeochemical interactions mediated by horizontal and vertical transport induced by mesoscale/submesoscale motions. We then highlight outstanding knowledge gaps and uncertainties related to small‐scale physical properties, and provide recommendations for observational, modeling, and theoretical strategies to advance future research on air‐sea interactions and climate change. This review aims to complement existing global ocean process syntheses. Future directions are outlined with an emphasis on short‐term (e.g., dedicated observational campaigns), long‐term (e.g., improved modeling, climate integration) goals, and the emerging applications of machine learning and artificial intelligence in small‐scale parameterization and data assimilation.

Dust activity is controlled by multiple environmental factors and exhibits substantial spatiotemporal and interannual variability. In spring 2025, China experienced unusually frequent dust storms. Surface meteorological observations and PM₁₀ levels show that dust events in 2025 were the most frequent and intense of the last decade. The dust event analysis indicates a pronounced change in transport pathways, with affected regions extending to Central, Southwest, and South China. This differs markedly from the 2021 and 2023 events, which impacted northern China more broadly. Source attribution indicates that the Gobi Desert was the dominant contributor to downstream dust, accounting for 80.0%, 83.1%, and 78.6% of dust concentrations in North, Southwest, and South China, respectively. In addition, enhanced surface winds over the Gobi Desert were identified as the primary drivers of intensified dust emissions, while concurrent changes in precipitation, soil moisture, and vegetation cover played secondary roles. An anomalous low-pressure system over the Bohai–Yellow Sea facilitated northerly wind anomalies, enabling long-range southward dust transport from the Gobi Desert all the way to southern China. These findings improve our understanding of extreme dust events and emphasize the need to consider both emission strength and transport efficiency in regional air quality assessments.

In the spring of 2023, dust outbreaks were unusually active in East Asia, posing substantial risks to air quality. Accurately simulating dust storms is essential for improving regional dust prediction and impact assessment. In this study, we evaluated dust simulations over East Asia using different dust emission schemes in the FLEXDUST/FLEXPART model and quantified the regional dust budget. Overall, the GOCART (Goddard Chemistry Aerosol Radiation and Transport) scheme shows the highest skill among the evaluated schemes. Under mild dust conditions (300–1000 μg m⁻³), it yielded a mean PM₁₀ bias of −89.2 μg m⁻³, markedly smaller than those from other schemes/models (−450.2 to −265.6 μg m⁻³). It also better reproduced the dominant spatial patterns of dust optical depth over Xinjiang and Inner Mongolia, with lower errors and higher correlations. Budget diagnostics show that the Taklamakan and Gobi Deserts are net dust exporters (7.4 and 11.6 Tg, respectively), whereas East Asia exhibits a negative net external flux (−12.1 Tg). The comparable magnitudes of these terms underscore the role of inter-regional transport in shaping the East Asian dust budget. These results offer insights for improving dust emission schemes in the FLEXDUST/FLEXPART model, thereby enhancing dust simulations over East Asia.

The shelfbreak jet of the Beaufort Sea is the main conduit of Pacific water progressing eastward from the Chukchi shelf, delivering heat, freshwater, and nutrients that impact the hydrographic state and ecosystem of the western Arctic Ocean. A mooring has been maintained in the center of the jet since 2002 (with a few gaps). Here we use this long timeseries to quantify the seasonal signal in water mass properties and transport of the jet and explore the interannual variability. The annual mean transport is 0.064 ± 0.018 Sv over the 20‐year period. It is largest during summer and decreases to near zero during the remainder of the year. Early in the record there was a single transport peak in July, but in recent years a second peak has occurred in October. Warm water first appears at the mooring site in July and lasts until December, after which winter water is the prevalent water mass advected by the jet. Using timeseries of ice thickness from the mooring, satellite ice concentration, and weather station wind data, we demonstrate that the transport of the shelfbreak jet is significantly reduced due to the combination of wind and ice cover. The reduction is greatest in the spring and fall when the pack‐ice is more mobile. The strength of the jet, and the fluxes of the individual water masses it advects, display pronounced interannual variability. The dominant year‐to‐year changes in transport are due to changes in the undisturbed transport; that is, in the absence of local winds.

The surface mixed layer plays a critical role in heat, carbon, and nutrient exchange within the atmosphere–ice–ocean system. Using the latest observations from the ice‐tethered profilers in the Canada Basin, we find the mixed layer became 9.6 m deeper and 0.7 psu saltier from 2006–2013 to 2014–2022. The mixed layer deepening coincides with the warming and freshening in the subsurface layer, thereby diminishing stratification beneath the mixed layer. The physical mechanisms of the mixed layer changes were investigated from two perspectives: the mixed layer local freshwater budget and remote control of Pacific inflow. Results indicate the saltier mixed layer maybe attributed to reduced freshwater inflow from the boundary driven by the southeastward contraction of the Beaufort Gyre. Lagrangian particle tracking experiments with GLORYS12 reanalysis reveal that subsurface layer salinity decreases, which can be explained by intensified entrainment of the fresh Pacific Summer Water (PSW) into the basin. It is driven by the local and remote effects: (a) Weakened northeasterly winds over Barrow Canyon facilitate PSW further approaching the southern edge of the basin, moving westward at deeper isobaths along the Chukchi slope and finally into the basin. (b) The southeastward contraction of the Beaufort Gyre drives more PSW from the Chukchi slope northeastward into the basin with the clockwise circulation. If the deepening of the mixed layer and the weakening of subsurface stratification persist, increased upward entrainment of heat and nutrients from the halocline may significantly accelerate ice melt and impact the local ecosystem.

This study investigates the mechanisms driving the acceleration and meandering of the Agulhas Current (AC), focusing on the role of eddy‐mean flow interactions. The analysis revealed that anticyclones originating from the Mozambique Channel and south of Madagascar played pivotal roles in accelerating the AC. Simultaneously, when anticyclones collide with the AC, they undergo processes of rotating and elongating into ellipses. In addition to the previously suggested barotropic instability induced by anticyclones, this study revealed that the merging of cyclones with the AC plays a role in the generation of meanders. Upstream cyclones reduce the horizontal potential vorticity gradient, facilitating eddies to traverse the current. The AC envelops these cyclones and flows in meandering patterns. The places where these meanders form are not exclusive to the Natal Bight. In addition, we further diagnose the kinetic energy conversion to reveal the interaction between eddy anisotropy (i.e., eddy deformation and orientation) and mean flow strain (i.e., stretching and shearing). The results suggest that the anisotropy of anticyclonic and cyclonic eddies prompts downscale KE transfer and the growth of meanders, establishing a positive feedback loop. Contrary to the findings of previous hypotheses, the acceleration of AC in turn leads to a decrease in the mean flow strain rate, exerting negative feedback on energy conversion and inhibiting the development of meanders. These two feedback mechanisms work together to determine the fate of AC meandering. The energetic anisotropy diagnosis holds potential applicability to other western boundary current systems.

The Agulhas Return Current (ARC), as a primary component of the Agulhas system, contributes to water exchange and mass transport between the southern portions of the Indian and Atlantic Ocean basins. In this study, satellite altimeter data and reanalysis datasets, and a new set of criteria for the piecewise definition of the jet axis are used to explore the long-term change of the ARC’s axis position in recent three decades. It is found that the ARC axis exhibits a significant slanting trend with its western part (35–48°E) migrating northward and the eastern part (48–70°E) migrating southward. The meridional movement of the ARC path could be attributed to large-scale wind forcing. The anomalous surface wind stress curl, by Ekman pumping mechanism, leads to positive–negative–positive sea surface height anomalies in the western section and negative–positive–negative anomalies in the eastern section, thus the ARC axis tilts accordingly, in a northwest–southeast direction. Further analysis suggests that this ARC slanting trend is more dependent on the southward shift of the downstream axis and less on the topographic steering upstream. The downstream axis is more likely to interact with the ACC fronts and its migration could dominate the local EKE pattern by changing the background circulation and energy cascade direction. For the headstream west of 35°E, the ARC axis is more subject to topography, thus the EKE change is more dominated by eddy activity processes, including shedding, propagation and merging. This study provides some new insights into the long-term change of ARC and its interaction with the local EKE variability.

In this study, we detect and track extratropical cyclones using 6-hourly mean sea level pressure data taken from the Twentieth Century Reanalysis version 3 (20CRv3) over the period 1951–2015 and compare them with those in the Interim and fifth generation of ECMWF reanalyses over the period 1979–2018. Three indices were employed to characterize cyclone activity, including cyclone count, cyclone intensity, and a cyclone activity index (CAI) that combines the count and intensity. The results show that the cyclone indices in the three datasets have comparable annual climatologies and seasonal evolution over the northern extratropical land and ocean in recent decades. Based on the cyclone indices over the period 1951–2010 in 80 ensemble members of 20CRv3, cyclone count and intensity are negatively correlated in winter and tend to be positively and weakly correlated in summer. The interannual CAI variability is dominated by the cyclone count variability. Regional mean cyclone activity can be well represented using the ensemble average cyclone index. We then examined the linkage of the cyclone activity in 20CRv3 and observed cold and warm extremes over Eurasia and North America over the period 1951–2010. In winter, the principal components of interannual cold and warm extreme anomalies are more correlated with the regional mean cyclone count index over Eurasia, while they are more correlated with the cyclone intensity index over North America. The temperature anomalies associated with the regional and ensemble mean cyclone count index explain about 10% (20%) of interannual cold (warm) extreme variances averaged over Eurasia. The temperature anomalies associated with the mean cyclone intensity explain about 10% of interannual cold and warm extreme variances over North America. Large-scale atmospheric circulation anomalies in association with cyclone activity and the induced temperature advection drive temperature anomalies over Eurasia and North America. In summer, circulation and thermal advection anomalies associated with cyclone activity are weak over the two continents. Hence, that season’s relationship between cyclone activity and extreme temperature variability is weak.