Xuhua Cheng

Hubei University

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Yan Du

South China Sea Institute Of Oceanology

Yiquan Qi

Hohai University

Jianhuang Qin

Ministry of Natural Resources

Chengcheng Yang

Shanghai Jiao Tong University

Niansen Ou

Guangdong Ocean University

Jiajia Chen

Hohai University

Guidi Zhou

Hohai University

Shaojun Zheng

Ministry of Natural Resources

Yuhong Zhang

Chinese Academy of Sciences

Shang‐Ping Xie

University of California, San Diego

Cooperative Institutions

Chinese Academy of Sciences

Institute of Oceanology

Ministry of Natural Resources

South China Sea Institute Of Oceanology

Hohai University

Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou)

University of Chinese Academy of Sciences

Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai)

Hubei University

Ocean University of China

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Abnormal upwelling and chlorophyll‐a concentration off South Vietnam in summer 2007

Journal of Geophysical Research Atmospheres (2012)

Xin Liu Jing Wang Xuhua Cheng Yan Du

The present study investigates a strong upwelling and concurrent phytoplankton bloom off the South Vietnam coast in August 2007. Analysis of the alongshore wind, offshore Ekman transport, wind stress curl and other parameters indicates the southwesterly summer monsoon plays an important role in this peculiar case. The change of monsoonal wind involves variations of atmospheric circulation on multiple time scales. On the interannual time scale, a positive Indian Ocean Dipole (IOD) in 2007 accompanying with a La Niña event acts to enhance the southwesterly monsoon over the South China Sea (SCS). The enhanced southwesterly wind is regarded as a major factor in promoting the upwelling and the phytoplankton bloom off the South Vietnam coast. On the intraseasonal time scale, variations of the sea surface temperature (SST) and sea surface wind at 30–60 day periods reveal that the SST cooling develops with the evolution of the southwesterly wind anomalies with nearly one week delay, implying the great significance of the Madden‐Julian Oscillation (MJO). Moreover, a tropical storm formed in the western SCS in early August reinforces the westerly wind and SST cooling. Among multiple factors on different time scales, the MJO event is considered as the major cause, since it induces the maximum velocity (4 m/s) of the southwesterly wind anomalies. As a result, the high chlorophyll‐ a concentration (>0.56 mg/m 3 ) and low SST center (<27°C) develops in the region off the South Vietnam coast and advects to the central SCS, riding on the northern rim of the southern anticyclonic gyre.

Wind Stress

Ekman transport

Madden–Julian oscillation

Downwelling

10.1029/2012jc008052

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Citations (48)

Mechanism of seasonal eddy kinetic energy variability in the eastern equatorial Pacific Ocean

Journal of Geophysical Research Oceans (2017)

Minyang Wang Yan Du Bo Qiu Xuhua Cheng Yiyong Luo

Abstract Enhanced mesoscale eddy activities or tropical instability waves (TIWs) exist along the northern front of the cold tongue in the eastern equatorial Pacific Ocean. In this study, we investigate seasonal variability of eddy kinetic energy (EKE) over this region and its associated dynamic mechanism using a global, eddy‐resolving ocean general circulation model (OGCM) simulation, the equatorial mooring data, and satellite altimeter observations. The seasonal‐varying enhanced EKE signals are found to expand westward from 100°W in June to 180°W in December between 0°N and 6°N. This westward expansion in EKE is closely connected to the barotropically‐baroclinically unstable zonal flows that are in thermal‐wind balance with the seasonal‐varying thermocline trough along 4°N. By adopting an 1½‐layer reduced‐gravity model, we confirm that the seasonal perturbation of the thermocline trough is dominated by the anticyclonic wind stress curl forcing, which develops due to southerly winds along 4°N from June to December.

Ekman transport

Anticyclone

Mooring

Trough (economics)

10.1002/2017jc012711

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Citations (16)

Weakened Seasonality of the Ocean Surface Mixed Layer Depth in the Southern Indian Ocean During 1980–2019

Geophysical Research Letters (2024)

Shang‐Min Long Shichang Zhao Zhen Gao Shantong Sun Jia‐Rui Shi

Abstract Temporal 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.

Seasonality

Mixed layer

Surface layer

Ocean dynamics

10.1029/2023gl107644

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Interannual-to-decadal variability of sea level in the South China Sea

American Geophysical Union eBooks (2016)

Yan Du Xuhua Cheng Surui Xie J. Wang

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Seasonality of Submesoscale processes in the Bay of Bengal

Lanman Li Xuhua Cheng

<p>Mesoscale eddies that known as a dominant reservoir of kinetic energy has been studied extensively for its dynamics and variation.In order to maintain energy budget equilibrium,the energy stored in mesoscale eddies is dissipated by small scale processes around centimeters.Submesoscale processes that lie between mesoscale and microscale motions effectively extract energy from mesoscale motions and transfer to smaller scales.The Bay of Bengal(the&#160;BOB)&#160;receives large fresh water from precipitation and river runoff resulting in strong salinity fronts that conducive to the generation of submesoscale processes.Using the Regional Ocean Modeling System(ROMS) data&#160;with two horizontal resolutions:a high-resolution(~1.6km) that is partially resolve submesoscale,and a low-resolution(~7km) that not resolves submesoscale,we focus on the&#160;seasonality of&#160;submesoscale processes in the Bay&#160;of Bengal.To ensure that only the submesoscale motions is considered,we choose 40km as the length to separate submesoscale from the flow field.Results show that submesocale processes is ubiquitous in the BOB,mainly&#160;trapped in the mixed layer.As resolution increasing,submesoscale motions become much stronger.Seasonality of submesoscale&#160;in the BOB&#160;is apparent and is different from the Gulf stream region &#160;which is strongest in winter and weakest in summer.Submesoscale features in this region mostly present in fall,which the most important mechanisms is frontogenesis due to strong horizontal buoyancy flux associated with large strain.Submesoscale motions is also vigorous in winter.The proposed mechanism is that the depth of mixed layer is deep enough which contributes to the occurrence of mixed layer instability.During the whole year,mesoscale strain field is weakest in summer,which makes submesoscale weakest.</p>

Seasonality

Eddy

BENGAL

10.5194/egusphere-egu2020-12390

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SST Front Anchored Mesoscale Feature of Surface Wind in the Southern Indian Ocean

AGU Fall Meeting Abstracts (2018)

Xia Huang Xuhua Cheng Yiquan Qi

Using 28-year satellite-borne Special Sensor Microwave Imager observations, features of high-wind frequency (HWF) over the southern Indian Ocean are investigated. Climatology maps show that high winds occur frequently during austral winter, located in the open ocean south of Polar Front in subpolar region, warm flank of the Subantarctic Front between 55°E–78°E, and south of Cape Agulhas, where westerly wind prevails. The strong instability of marine atmospheric boundary layer accompanied by increased sensible and latent heat fluxes on the warmer flank acts to enhance the vertical momentum mixing, thus accelerate the surface winds. Effects of sea surface temperature (SST) front can even reach the entire troposphere by deep convection. HWF also shows distinct interannual variability, which is associated with the Southern Annual Mode (SAM). During positive phase of the SAM, HWF has positive anomalies over the open ocean south of Polar Front, while has negative anomalies north of the SST front. A phase shift of HWF happened around 2001, which is likely related to the reduction of storm tracks and poleward shift of westerly winds in the Southern Hemisphere.

Polar front

Westerlies

Cold front

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Three-dimensional thermohaline anomaly structures of mesoscale eddies in the South China Sea

Xie Xudan Jing Wang Xiaoqing Chu Xuhua Cheng

Used the Sea Level Anomaly data during 1994 to 2015, based on the winding-angle eddy detection algorithm, total of 5 899 anticyclonic eddies (AE) and 3 792 cyclonic eddies (CE) in the SCS are identified. With the profiles from the WOD13 and the SCSIO, the 3-D thermohaline anomaly structures are constructed in the SCS and its different area with the objective interpolation approach based on the variational analysis. The results show that the proposed revised interpolation approach can simulate the boundary of eddies effectively, and ensure the correct eddies shape. Generally speaking, AE's intensity are obviously stronger than CE's. AE maintain its main structure till approximately 440 m depth while CE only remain stable above 320 m. Both of the maximum potential temperature anomalies appear in about 80m depth, 2.02℃ for AE and -1.60℃ for CE. The affecting depth of salinity anomaly of eddies reach to 150 m depth around and the maximum anomalies induced by AE and CE are -0.24 and 0.28, respectively, which occur near the depth of 50 m. Meanwhile, the structure of salinity anomaly of AE seems to be positive on the top and negative on the bottom, just opposite to CE,which attributed to the sea water sinking (rising) induced by AE(CE). The temperature anomalies in each area of the SCS are not quite consistent with the salinity anomalies, which may attributed to the background thermohaline fields and different formation mechanism of eddies.

Eddy

Anomaly (physics)

Anticyclone

Boundary current

Sea-surface height

Temperature salinity diagrams

10.3969/ji.ssn.0253-4193.2018.04.001

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Citations (1)

Annual and Interannual Variability of the Tropical Instability Vortices in the Equatorial Eastern Pacific Observed from Lagrangian Surface Drifters

Journal of Climate (2016)

Shaojun Zheng Ming Feng Yan Du Xuhua Cheng Jiaxun Li

Abstract This study documents the spatial distributions and temporal variations of anticyclonic eddies with identified radii ≥100 km in the equatorial eastern tropical Pacific Ocean [viz., tropical instability vortices (TIVs)] using Lagrangian surface drifters. The TIVs identified from Lagrangian surface drifters are distributed in a band along 5°N and are closely associated with latitudinal barotropically unstable shear between the westward South Equatorial Current (SEC) and the eastward North Equatorial Countercurrent (NECC). Fewer TIVs are identified from February to June when the shear between the SEC and NECC is weak, whereas more TIVs are found from July to January when the shear is enhanced. The number of identified TIVs also exhibits substantial interannual variability, with fewer TIVs identified during El Niño events and more TIVs found during La Niña events. This relationship is likely associated with the interannual variations of the zonal circulation in the equatorial Pacific modulated by El Niño–Southern Oscillation (ENSO).

Anticyclone

Tropical Atlantic

10.1175/jcli-d-16-0124.1

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Citations (10)

Mass-induced sea level change ihe northwestern Pacific and its contribution to sea level change

AGU Fall Meeting Abstracts (2012)

Xuhua Cheng

Sea-Level Change

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Impact of Indian Ocean Dipole on the salinity budget in the equatorial Indian Ocean

Journal of Geophysical Research Oceans (2013)

Yuhong Zhang Du Yan Shaojun Zheng Yali Yang Xuhua Cheng

[1] Based on observations and ocean reanalysis, this study analyzes the variability of salinity and its related ocean dynamics in the equatorial Indian Ocean (IO). The results show significant interannual variability of salinity associated with the Indian Ocean Dipole (IOD) mode in the boreal fall. During the positive phase of IOD (pIOD), when anomalous easterly winds prevail, westward advection along the equator strengthens in summer, while the eastward advection associated with the Yoshida-Wyrtki Jet weakens in fall. Analysis of salinity budget indicates that salinity anomalies are mainly due to advection, of which zonal component is dominant. As zonal current anomalies are symmetric with respect to the equator, the equatorward large northern IO zonal salinity gradient is more important than the current anomalies in determining the asymmetric distribution of low-salinity advection. During the mature phase of pIOD, low-salinity water is advected westward, which in turn shoals the surface mixed layer, thereby providing a favorable condition for warmer sea-surface temperature in the western equatorial IO. During the decay phase of pIOD, low-salinity water is advected across the equator to the southwestern IO. When pIOD concurs along with El Niño, the strengthened off-equatorial anticyclonic circulations, which is associated with El Niño, advect low-salinity water poleward after the decay phase.

Temperature salinity diagrams

10.1002/jgrc.20392

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Citations (52)