Cheng Xuhua

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  • Article
    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.
  • Article
    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.
  • Article
    Southern 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-Ping
    The 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.