Huang Rui Xin

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Huang

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Rui Xin

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0000-0002-0944-9993

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Mass-induced sea level change in the northwestern North Pacific and its contribution to total sea level change

(John Wiley & Sons, 2013-08-02) Cheng, Xuhua ; Li, Lijuan ; Du, Yan ; Wang, Jing ; Huang, Rui Xin

Over the period 2003–2011, the Gravity Recovery and Climate Experiment (GRACE) satellite pair revealed a remarkable variability in mass-induced sea surface height (MSSH) in the northwestern North Pacific. A significant correlation is found between MSSH and observed total sea surface height (SSH), indicative of the importance of barotropic variability in this region. For the period 2003–2011, MSSH rose at a rate of 6.1 ± 0.7 mm/yr, which has a significant contribution to the SSH rise (8.3 ± 0.7 mm/yr). Analysis of the barotropic vorticity equation based on National Centers for Environmental Prediction/National Center for Atmospheric Research reanalysis product, GRACE, and altimetry data suggests that the MSSH signal is primarily caused by negative wind stress curl associated with an anomalous anticyclonic atmospheric circulation. Regression analysis indicates that trends in MSSH and surface wind are related to the Pacific Decadal Oscillation, whose index had a decreasing trend in the last decade.
Episodic subduction patches in the western North Pacific identified from BGC-Argo float data

(European Geosciences Union, 2021-10-13) Chen, Shuangling ; Wells, Mark L. ; Huang, Rui Xin ; Xue, Huijie ; Xi, Jingyuan ; Chai, Fei

Subduction associated with mesoscale eddies is an important but difficult-to-observe process that can efficiently export carbon and oxygen to the mesopelagic zone (100–1000 dbar). Using a novel BGC-Argo dataset covering the western North Pacific (20–50∘ N, 120–180∘ E), we identified imprints of episodic subduction using anomalies in dissolved oxygen and spicity, a water mass marker. These subduction patches were present in 4.0 % (288) of the total profiles (7120) between 2008 and 2019, situated mainly in the Kuroshio Extension region between March and August (70.6 %). Roughly 31 % and 42 % of the subduction patches were identified below the annual permanent pycnocline depth (300 m vs. 450 m) in the subpolar and subtropical regions, respectively. Around half (52 %) of these episodic events injected oxygen-enriched waters below the maximum annual permanent thermocline depth (450 dbar), with >20 % occurring deeper than 600 dbar. Subduction patches were detected during winter and spring when mixed layers are deep. The oxygen inventory within these subductions is estimated to be on the order of 64 to 152 g O2/m2. These mesoscale events would markedly increase oxygen ventilation as well as carbon removal in the region, both processes helping to support the nutritional and metabolic demands of mesopelagic organisms. Climate-driven patterns of increasing eddy kinetic energies in this region imply that the magnitude of these processes will grow in the future, meaning that these unexpectedly effective small-scale subduction processes need to be better constrained in global climate and biogeochemical models.
Retrieving density and velocity fields of the ocean's interior from surface data

(John Wiley & Sons, 2014-12-12) Liu, Lei ; Peng, Shiqiu ; Wang, Jinbo ; Huang, Rui Xin

Using the “interior + surface quasigeostrophic” (isQG) method, the density and horizontal velocity fields of the ocean's interior can be retrieved from surface data. This method was applied to the Simple Ocean Data Assimilation (SODA) and the Hybrid Coordinate Ocean Model (HYCOM)/Navy Coupled Ocean Data Assimilation (NCODA) reanalysis data sets. The input surface data include sea surface height (SSH), sea surface temperature (SST), sea surface salinity (SSS), and a region-averaged stratification. The retrieved subsurface fields are compared with reanalysis data for three tested regions, and the results indicate that the isQG method is robust. The isQG method is particularly successful in the energetic regions like the Gulf Stream region with weak stratification, and the Kuroshio region with strong correlation between sea surface density (SSD) and SSH. It also works, though less satisfactorily, in the Agulhas leakage region. The performance of the isQG method in retrieving subsurface fields varies with season, and peaks in winter when the mixed layer is deeper and stratification is weaker. In addition, higher-resolution data may facilitate the isQG method to achieve a more successful reconstruction for the velocity retrieval. Our results suggested that the isQG method can be used to reconstruct the ocean interior from the satellite-derived SSH, SST, and SSS data in the near future.
On the seasonal variations of ocean bottom pressure in the world oceans

(Asia Oceania Geosciences Society (AOGS), 2021-10-12) Cheng, Xuhua ; Ou, Niansen ; Chen, Jiajia ; Huang, Rui Xin

Seasonal variability of the ocean bottom pressure (OBP) in the world oceans is investigated using 15 years of GRACE observations and a Pressure Coordinate Ocean Model (PCOM). In boreal winter, negative OBP anomalies appear in the northern North Pacific, subtropical South Pacific and north of 40 °S in the Indian Ocean, while OBP anomaly in the Southern Ocean is positive. The summer pattern is opposite to that in winter. The centers of positive (negative) OBP signals have a good coherence with the mass convergence/divergence due to Ekman transport, indicating the importance of wind forcing. The PCOM model reproduces the observed OBP quite well. Sensitivity experiments indicate that wind forcing dominates the regional OBP seasonal variations, while the contributions due to heat flux and freshwater flux are unimportant. Experiments with daily sea level pressure (SLP) forcing suggest that at high frequencies the non-static effect of SLP is not negligible.
Role of gyration in the oceanic general circulation : Atlantic Ocean

(American Geophysical Union, 2008-03-14) Jiang, Hua ; Huang, Rui Xin ; Wang, Hui

Wind-driven gyres transport volume and heat in the meridional direction, which is an important component of the climate system. The contribution of wind-driven gyres to both poleward volume and heat fluxes can be clearly identified from numerical models by a simple diagnostic tool; thus the central location, strength, and dynamical roles of wind-driven circulation in the climatological mean state and decadal variability of the oceanic circulation can be examined in detail. This diagnostic tool was applied to the Simple Ocean Data Assimilation data generated from a numerical model, with data assimilation. Our analysis indicates the important contribution due to wind-driven gyres and the strong decadal variability in the volume flux, heat flux, and central location of the wind-driven gyres in the Atlantic Ocean.
Interplay between the Indonesian Throughflow and the Luzon Strait Throughflow

( 2006) Liu, Qinyan ; Huang, Rui Xin ; Wang, Dong Xiao ; Xie, Qiang ; Huang, Qizhou

Analysis based on the “Island Rule” and ocean assimilation dataset shows that the interannual variability of the Indonesian Throughflow and the Luzon Strait (South China Sea) Throughflow is out of phase. Wind anomaly in the equatorial Pacific plays an important role in setting up this phase relation. During El Niño events, the westerly wind bursts intensify the Northern Equator Current and induce a northward shift of its bifurcation point. As a result, the partition of volume transport between the Kuroshio and the Mindanao Current is changed, with the Kuroshio transport decreased and the Mindanao Current increased. The undershooting/overshooting phenomena occur at the Luzon Strait and the Sulawesi-Mindanao passage, caused by variability of these two currents. Water transport from the Pacific to the South China Sea increases with the Kuroshio transport decreased, and transport from the Pacific to the Indian Ocean decreases with the Mindanao Current transport increased. Therefore, the interannual variability of the Indonesian Throughflow and the Luzon Strait Throughflow is out of phase.
Decadal variability of pycnocline flows from the subtropical to the equatorial Pacific

(American Meteorological Society, 2005-10) Wang, Qi ; Huang, Rui Xin

A method based on isopycnal trajectory analysis is proposed to quantify the pathways from the subtropics to the Tropics. For a continuous stratified ocean a virtual streamfunction is defined, which can be used to characterize these pathways. This method is applied to the climatological dataset produced from a data-assimilated model. Analysis indicates that in each layer contours of the virtual streamfunction are a good approximation for streamlines, even if there is a cross-isopycnal mass flux. The zonal-integrated meridional transport per unit layer thickness through each pathway varies in proportion to 1/sinθ, where θ is latitude. The vertical-integrated total transport through pathways behaves similarly. Transport through pathways has a prominent decadal variability. Results suggest that in decadal time scales the interior pathway transport (IPT) anomaly may be mainly caused by the wind stress anomaly at low latitude. The western boundary pathway transport (WBPT) anomaly often has a sign opposite to the IPT anomaly, reflecting compensation between the IPT and the WBPT. However, more often than not the wind stress anomaly within tropical latitudes can also be used to explain the WBPT anomaly.
Universal structure of mesoscale eddies in the ocean

(John Wiley & Sons, 2013-07-30) Zhang, Zhengguang ; Zhang, Yu ; Wang, Wei ; Huang, Rui Xin

Mesoscale eddies dominate oceanic kinetic energy at sub-inertial frequencies. Their three-dimensional structure has, however, remained obscure, hindering better understanding of eddy dynamics. Here by applying the composite analysis of satellite altimetry and Argo float data to the globe, we show that despite remarkable regional differences in amplitude, extent and polarity, etc., mesoscale eddies have a universal structure in normalized stretched coordinates. Horizontally, the associated pressure anomaly is well described by a function of the normalized radial distance from the eddy center R(rn)=(1−rn2/2)• exp(−rn2/2), whereas vertically it is sinusoidal in a stretched coordinate zs = ƒ z0 (N/f )dz, where N and f are the buoyancy frequency and the Coriolis parameter.
A time-dependent Sverdrup relation and its application to the Indian Ocean

(American Meteorological Society, 2022-05-27) Chen, Gengxin ; Huang, Rui Xin ; Peng, Qihua ; Chu, Xiaoqing

The Sverdrup relation is the backbone of wind-driven circulation theory; it is a simple relation between the meridional transport of the wind-driven circulation in the upper ocean and the wind stress curl. However, the relation is valid for steady circulation only. In this study, a time-dependent Sverdrup relation is postulated, in which the meridional transport in a time-dependent circulation is the sum of the local wind stress curl term and a time-delayed term representing the effect of the eastern boundary condition. As an example, this time-dependent Sverdrup relation is evaluated through its application to the equatorial circulation in the Indian Ocean, using reanalysis data and a reduced gravity model. Close examination reveals that the southward Somali Current occurring during boreal winter is due to the combination of the local wind stress curl in the Arabian Sea and delayed signals representing the time change of layer thickness at the eastern boundary.
The mechanical energy input to the ocean induced by tropical cyclones

(American Meteorological Society, 2008-06) Liu, Ling Ling ; Wang, Wei ; Huang, Rui Xin

Wind stress and tidal dissipation are the most important sources of mechanical energy for maintaining the oceanic general circulation. The contribution of mechanical energy due to tropical cyclones can be a vitally important factor in regulating the oceanic general circulation and its variability. However, previous estimates of wind stress energy input were based on low-resolution wind stress data in which strong nonlinear events, such as tropical cyclones, were smoothed out. Using a hurricane–ocean coupled model constructed from an axisymmetric hurricane model and a three-layer ocean model, the rate of energy input to the world’s oceans induced by tropical cyclones over the period from 1984 to 2003 was estimated. The energy input is estimated as follows: 1.62 TW to the surface waves and 0.10 TW to the surface currents (including 0.03 TW to the near-inertial motions). The rate of gravitational potential energy increase due to tropical cyclones is 0.05 TW. Both the energy input from tropical cyclones and the increase of gravitational potential energy of the ocean show strong interannual and decadal variability with an increasing rate of 16% over the past 20 years. The annual mean diapycnal upwelling induced by tropical cyclones over the past 20 years is estimated as 39 Sv (Sv ≡ 106 m3 s−1). Owing to tropical cyclones, diapycnal mixing in the upper ocean (below the mixed layer) is greatly enhanced. Within the regimes of strong activity of tropical cyclones, the increase of diapycnal diffusivity is on the order of (1 − 6) × 10−4 m2 s−1. The tropical cyclone–related energy input and diapycnal mixing may play an important role in climate variability, ecology, fishery, and environments.
Horizontal eddy energy flux in the world oceans diagnosed from altimetry data

(Nature Publishing Group, 2014-06-17) Xu, Chi ; Shang, Xiao-Dong ; Huang, Rui Xin

During the propagation of coherent mesoscale eddies, they directly or indirectly induce many effects and interactions at different scales, implying eddies are actually serving as a kind of energy carrier or energy source for these eddy-related dynamic processes. To quantify this dynamically significant energy flow, the multi-year averaged horizontal eddy energy fluxes (EEFs) were estimated by using satellite altimetry data and a two-layer model based on hydrographic climatology. There is a strong net westward transport of eddy energy estimated at the mean value of ~13.3 GW north of 5°N and ~14.6 GW at the band 5°S ~ 44°S in the Southern Hemisphere. However, poleward of 44°S east-propagating eddies carry their energy eastward with an averaged net flux of ~3.2 GW. If confirmed, it would signify that geostrophic eddies not only contain the most of oceanic kinetic energy (KE), but also carry and spread a significant amount of energy with them.
Using the sigma-pi diagram to analyze water masses in the northern South China Sea in spring

(American Geophysical Union, 2020-06-20) Gao, Yang ; Huang, Rui Xin ; Zhu, Jia ; Huang, Yongxiang ; Hu, Jianyu

The temperature‐salinity (T‐S) diagram is widely used in water mass analysis, but the boundaries between water masses are vaguely distinguished by conventional T‐S‐based methods. Herein, we propose a new method based on the potential density‐potential spicity (sigma‐pi) diagram. The new method has been applied to the conductivity‐temperature‐depth data collected in the northern South China Sea during a spring cruise in 2011. The water masses in the study region are classified into 13 types according to both the standard deviation of potential spicity in each potential density layer and the water volumetric distribution in the sigma‐pi space. The results suggest that this new method is reasonable and robust for classifying water masses in the sigma‐pi space as compared to previous methods based on the traditional T‐S space. In addition, the westward intrusion of the West Pacific Ocean water to the northern South China Sea can be clearly detected by the tongue‐like potential spicity structure and relatively high potential spicity patches on potential density layers, further verifying the robustness and efficiency of our method in the water mass analysis.
Topographic beta spiral and onshore intrusion of the Kuroshio Current

(John Wiley & Sons, 2018-01-15) Yang, De-Zhou ; Huang, Rui Xin ; Yin, Bao-shu ; Feng, Xing-Ru ; Chen, Hai-ying ; Qi, Ji-Feng ; Xu, Ling-jing ; Shi, Yun-long ; Cui, Xuan ; Gao, Guan-Dong ; Benthuysen, Jessica A.

The Kuroshio intrusion plays a vitally important role in carrying nutrients to marginal seas. However, the key mechanism leading to the Kuroshio intrusion remains unclear. In this study we postulate a mechanism: when the Kuroshio runs onto steep topography northeast of Taiwan, the strong inertia gives rise to upwelling over topography, leading to a left-hand spiral in the stratified ocean. This is called the topographic beta spiral, which is a major player regulating the Kuroshio intrusion; this spiral can be inferred from hydrographic surveys. In the world oceans, the topographic beta spirals can be induced by upwelling generated by strong currents running onto steep topography. This is a vital mechanism regulating onshore intruding flow and the cross-shelf transport of energy and nutrients from the Kuroshio Current to the East China Sea. This topographic beta spiral reveals a long-term missing link between the oceanic general circulation theory and shelf dynamic theory.
Estimate of eddy energy generation/dissipation rate in the world ocean from altimetry data

( 2011-02) Xu, Chi ; Shang, Xiao-Dong ; Huang, Rui Xin

Assuming eddy kinetic energy is equally partitioned between the barotropic mode and the first baroclinic mode and using the weekly TOPEX/ERS merged data for the period of 1993~2007, the mean eddy kinetic energy and eddy available gravitational potential energy in the world oceans are estimated at 0.157 EJ and 0.224 EJ; the annual mean generation/dissipation rate of eddy kinetic energy and available gravitational potential energy in the world oceans is estimated at 0.203 TW. Scaling and data analysis indicate that eddy available gravitational potential energy and its generation/dissipation rate are larger than those of eddy kinetic energy. High rate of eddy energy generation/dissipation is primarily concentrated in eddy rich regions, such as the Antarctic Circumpolar Current and the western boundary current extensions. Outside of these regimes of intense current, the energy generation/dissipation rate is 2 to 4 orders of magnitude lower than the peak values; however, along the eastern boundaries and in the region where complicated topography and current interact the eddy energy generation/dissipation rate is several times larger than those in background.
Deep South China Sea circulation

(American Geophysical Union, 2011-03-01) Wang, Guihua ; Xie, Shang-Ping ; Qu, Tangdong ; Huang, Rui Xin

The analysis of an updated monthly climatology of observed temperature and salinity from the U.S. Navy Generalized Digital Environment Model reveals a basin-scale cyclonic circulation over the deep South China Sea (SCS). The cyclonic circulation lies from about 2400 m to the bottom. The boundary current transport of the cyclonic circulation is around 3.0 Sv. Our results suggest that the cyclonic circulation is mainly forced by the Luzon overflow, with bottom topography playing an important role. The structures of potential temperature, salinity, and potential density in the deep SCS are consistent with the existence of the cyclonic circulation. Specifically, low salinity water is found in the interior region west of Luzon Island, and surrounded by saline Pacific water in boundary current regions to the north, west and southwest. Our results show the potential density distribution and the corresponding cyclonic circulation in deep SCS are primarily controlled by salinity variations in the deep basin.
Decadal changes of wind stress over the Southern Ocean associated with Antarctic ozone depletion

(American Meteorological Society, 2007-07-15) Yang, Xiao-Yi ; Huang, Rui Xin ; Wang, Dong Xiao

Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.
Decadal weakening of abyssal South China Sea circulation

(American Geophysical Union, 2022-10-10) Zhu, Yaohua ; Yao, Jingxin ; Li, Shujiang ; Xu, Tengfei ; Huang, Rui Xin ; Nie, Xunwei ; Pan, Haidong ; Wang, Yonggang ; Fang, Yue ; Wei, Zexun

The global ocean mass has significantly changed during recent decades, which may induce changes in the abyssal ocean circulation. Due to the lack of in situ observations, the response of the abyssal South China Sea (SCS) circulation to ocean mass changes remains unclear. The ocean state estimate, Estimating the Circulation and Climate of the Ocean (ECCO), provides the long‐term ocean mass changes in terms of ocean bottom pressure (OBP). Here we use the ECCO OBP data to quantify decadal changes in the abyssal SCS circulation and reveal a weakening trend. The OBP gradient trend manifests in forms of an anomalous anticyclonic circulation that is intensified by topographic effects along the continental slopes to reduce the existing abyssal circulation. The weakening abyssal circulation corresponds to the weakening Luzon Strait overflow that yields a decreasing vorticity budget in the abyssal SCS.
An experimental study on thermal circulation driven by horizontal differential heating

(Cambridge University Press, 2005-09-27) Wang, Wei ; Huang, Rui Xin

Circulation driven by horizontal differential heating is studied, using a double-walled Plexiglas tank (20×15×2.5 cm3) filled with salt water. For instances of heating/cooling from above and below, results indicate that there is always quasi-equilibrium circulation. In contrast to most previous results from experimental/ numerical studies, circulation in our experiments appears in the form of a shallow cell adjacent to the boundary of thermal forcing. The non-dimensional stream-function maximum confirms the 1/5-power law of Rossby, Ψ ∼Ra1/5 L . Dissipation rate measured in the experiments appears to be consistent with theory. For cases of heating/cooling from a sloping bottom, circulation is similar to cases with a flat bottom; circulation is strong if heating is below cooling, but it is rather weak if heating is above cooling. Nevertheless, circulation in all cases is visible to the naked eye.
Regulation of South China Sea throughflow by pressure difference

(John Wiley & Sons, 2016-06-12) Qin, Huiling ; Huang, Rui Xin ; Wang, Weiqiang ; Xue, Huijie

Sea Surface Height (SSH) data from the European Centre for Medium-Range Weather Forecasts-Ocean Reanalysis System 4 (ECMWF-ORAS4) are used to determine the pressure difference in connection with variability of the South China Sea ThroughFlow (SCSTF) from 1958 to 2007. Two branches of SCSTF, the Karimata-Sunda Strait ThroughFlow (KSSTF) and the Mindoro Strait ThroughFlow (MSTF), are examined. Using the ensemble empirical mode decomposition method (EEMD), time series of pressure difference and volume transport are decomposed into intrinsic mode functions and trend functions, with the corresponding variability on different time scales. Pressure difference agrees with the KSSTF volume transport on decadal time scale; while for the MSTF, pressure difference varies similarly with volume transport on interannual time scale. Separating the dynamic height difference into the thermal and haline terms, for the KSSTF more than half of the dynamic height difference (32 cm) is due to the thermal contributions; while the remaining dynamic height difference (23 cm) is due to the haline contributions. For the MSTF, the dynamic height difference (29 cm) is primarily due to the thermal contribution (26 cm).
Tidal mixing in the South China Sea : an estimate based on the internal tide energetics

(American Meteorological Society, 2016-01) Wang, Xiaowei ; Peng, Shiqiu ; Liu, Zhiyu ; Huang, Rui Xin ; Qian, Yu-Kun ; Li, Yineng

By taking into account the contributions of both locally and remotely generated internal tides, the tidal mixing in the Luzon Strait (LS) and the South China Sea (SCS) is investigated through internal-tide simulation and energetics analysis. A three-dimensional nonhydrostatic high-resolution model driven by four primary tidal constituents (M2, S2, K1, and O1) is used for the internal-tide simulation. The baroclinic energy budget analysis reveals that the internal tides radiated from the LS are the dominant energy source for the tidal dissipation in the SCS. In the LS, the estimated depth-integrated turbulent kinetic energy dissipation exceeds O(1) W m−2 atop the two subsurface ridges, with a dissipation rate of >O(10−7) W kg−1 and diapycnal diffusivity of ~O(10−2) m2 s−1. In the SCS, the most intense turbulence occurs in the deep-water basin with a dissipation rate of O(10−8–10−6) W kg−1 and diapycnal diffusivity of O(10−3–10−1) m2 s−1 within the ~2000-m water column above the seafloor as well as in the shelfbreak region with a dissipation rate of O(10−7–10−6) W kg−1 and diapycnal diffusivity of O(10−4–10−3) m2 s−1. These estimated values are consistent with observations reported in previous studies and are at least one order of magnitude larger than those based solely on locally generated internal tides.

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