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Seasonal variability and its influencing factors of ocean bottom pressure in the Arabian Sea
ZHANG Kun, ZHANG Tao, WU Binjie, ZHANG Deng, ZHENG Hua, DING Ruibin
Journal of Marine Sciences ›› 2026, Vol. 44 ›› Issue (1) : 83-92.
PDF(4461 KB)
PDF(4461 KB)
Seasonal variability and its influencing factors of ocean bottom pressure in the Arabian Sea
The study of ocean bottom pressure (OBP) is great significance for understanding the mechanisms of sea level budget changes and deep ocean circulation. Based on 23 years of OBP data observed by the Gravity Recovery and Climate Experiment (GRACE) satellites, this study systematically reveals the spatiotemporal characteristics and mechanism of OBP variations in the Arabian Sea. There is a strong OBP oscillation center in the central area of the Arabian Sea. The OBP changes throughout the region are unified in space and time. It has significant seasonal variation features, showing a double-peak structure of negative anomalies in winter (January to March) and positive anomalies in summer (July to September). Combining the reanalysis data of ERA5, it is found that there is a dynamic divergence mechanism of OBP oscillation between the northern and southern areas of the Arabian Sea. The southern area is dominated by wind stress curl, with a negative correlation response leading OBP by 30° (about 1 month). The northern area is regulated by the wind-driven Ekman process, with Ekman pumping/suction leading by 1 month to trigger a positive correlation. This divergence mechanism is attributed to the boundary constraint effect of the meridional mean atmospheric pressure standard deviation. The impact of the Indian Ocean Dipole (IOD) on OBP shows seasonal asymmetry: in summer, OBP is significantly correlated with the dipole mode index (DMI) leading by 6 months, while in winter, the correlation between the mean OBP and the DMI in each mounth is not significance.
ocean bottom pressure / GRACE / wind stress curl / Ekman pumping/suction / Arabian Sea
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The study of ocean bottom pressure (OBP) helps to understand the changes in the sea level budget and ocean deep circulation. In this study, the characteristics and mechanisms of interannual OBP variability in the Southern Indian Ocean are examined using Gravity Recovery and Climate Experiment (GRACE) satellite data from 2003 to 2016. Results show that there are two energetic OBP centers in the Southern Indian Ocean (50°–60°S, 40°–60°E and 45°–60°S, 80°–120°E). The OBP magnitudes at two centers have strong variability on interannual time scales, and their values are larger during austral summer (NDJF) and winter (JJAS). Atmospheric forcing plays an important role in local OBP variability. The high (low) sea level pressure (SLP) over the Southern Indian Ocean benefits positive (negative) OBP anomalies via the convergence (divergence) of Ekman transport driven by local wind. Such SLP anomalies are related to the Southern Annular Mode (SAM), Southern Oscillation (SO) and Indian Ocean dipole (IOD). SAM can influence the OBP changes in both austral summer and winter, while SO and IOD have positive correlations with OBP variability during austral summer and austral winter, respectively. These results are validated by a mass-conservation ocean model, which further confirms the importance of atmospheric forcing on the interannual OBP variations.
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利用2003—2015年的重力恢复和气候实验(Gravity Recovery and Climate Experiment, GRACE)卫星观测数据, 揭示了印度洋海底压强的变化特征, 并探讨了其变化机制。结果表明, 印度洋海底压强具有显著的季节变化特征, 北半球冬季在40°S以北(南), 海底压强呈负(正)异常, 夏季分布与冬季相反。印度洋区域的海底压强空间分布与Ekman输送空间分布有较好的对应关系。正压涡度方程诊断结果表明, 利用风场重构的海底压强能够较好地解释印度洋海底压强的季节和长期变化。此外, 海平面变化收支分析表明, 海底压强的变化在高纬度区域主导了海平面变化。
Using the GRACE satellite observation during 2003-2015, we reveal characteristics of the ocean bottom pressure (OBP) variability in the Indian Ocean, and explore their potential dynamics. The results show that the OBP in the Indian Ocean has significant seasonal variability. In the boreal winter, the OBP shows negative (positive) anomaly north (south) of 40 oS; and the pattern in summer is opposite to that in winter. The spatial pattern of the Ekman transport has a good correspondence with the OBP pattern in the Indian Ocean. The diagnosis results derived from the barotropic vorticity equation show that the OBP reconstructed by sea surface wind can better explain both the seasonal and long-term variations of the OBP in the Indian Ocean. In addition, analysis of sea level budget suggests that variation of OBP dominates sea level changes at high latitudes. |
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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.
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