Rahman Raheema, Rahaman Hasibur
Indian National Centre for Ocean Information Services (INCOIS), Ministry of Earth Sciences (MoES), Government of India, Hyderabad, 500090, India.
KUFOS-INCOIS Joint Research Centre, Kerala University of Fisheries and Ocean Studies, Panangad, Ernakulam, Kerala, 682506, India.
Sci Rep. 2024 Apr 5;14(1):8008. doi: 10.1038/s41598-024-58464-2.
The Regional Indian Ocean model based on Modular Ocean Model (MOM4p1) was used to understand the importance of a realistic representation of bathymetry on Ocean General Circulation. The model has 1/4° uniform horizontal resolution and is forced with Coordinated Ocean-Ice Reference Experiments (CORE-II) inter-annual forcing with two simulations named BLND (realistic bathymetry) and OM3 (smoothed bathymetry), which only differ in the representation of bathymetry for the years 1992-2005. We also used recent reanalysis products from ORAS5 and SODA3 and ADCP observation to compare the subsurface currents. We show that by the inclusion of realistic bathymetry, there is a significant improvement in the upper ocean salinity, temperature, and currents, particularly near the coast. The salinity and temperature of the upper ocean are very close to the observed value near the coast. The bias in the salinity and temperature was reduced to half in BLND simulation compared to OM3, which led to a more realistic East India Coastal Current (EICC). We show the first evidence of a basin-wide cyclonic gyre over the Bay of Bengal at 1000 m depth during spring, which is just opposite to that of a basin-wide anti-cyclonic gyre at the surface. We found the presence of poleward EICC during spring at 1000 m and 2000 m depth, which is opposite to that of the surface. The presence of this deeper EICC structure is completely absent during fall. We show the presence of a boundary current along the coast of Andaman and Nicobar Island at a depth of 2000 m. The observed Wyrtki Jet (WJ) magnitude and spatial structure are most realistically reproduced in BLND simulation as compared to OM3 simulations. Both ORAS5 and SODA reanalysis products underestimate the WJ magnitude. The presence of the Maldives Islands is responsible for the westward extent of Equatorial Under Current (EUC). The presence of Maldives also creates wakes on the leeward side in the EUC zonal current. During fall, EUC is better defined in the eastern Equatorial Indian Ocean and lies at a depth of between 50 and 100 m, unlike its spring counterpart, in which its core is located slightly deeper, between 100 and 150 m depth. During peak summer months, June-July, a strong eastward zonal jet is present at 1000 m depth, similar to Wyrtki Jet (WJ). Inter-monsoon Jets, i.e., spring and fall jets, are also seen but are in the opposite direction, i.e., westward, unlike eastward in WJ.
基于模块化海洋模型（MOM4p1）的区域印度洋模型被用于了解真实地形表示对海洋环流的重要性。该模型具有1/4°的均匀水平分辨率，并采用协调海洋-冰参考实验（CORE-II）的年际强迫，有两个模拟，分别命名为BLND（真实地形）和OM3（平滑地形），它们在1992 - 2005年期间仅在地形表示上有所不同。我们还使用了来自ORAS5和SODA3的最新再分析产品以及声学多普勒流速剖面仪（ADCP）观测数据来比较次表层洋流。我们表明，通过纳入真实地形，上层海洋的盐度、温度和洋流有了显著改善，特别是在海岸附近。上层海洋的盐度和温度在海岸附近非常接近观测值。与OM3相比，BLND模拟中盐度和温度的偏差减少了一半，这导致了更真实的东印度沿岸流（EICC）。我们首次证明了春季在1000米深度的孟加拉湾存在一个全盆地范围的气旋式环流，这与表层的全盆地范围反气旋式环流正好相反。我们发现春季在1000米和2000米深度存在向极的EICC，这与表层情况相反。秋季完全不存在这种更深层的EICC结构。我们显示在2000米深度沿着安达曼和尼科巴群岛海岸存在一个边界流。与OM3模拟相比，在BLND模拟中观测到的维尔基急流（WJ）的强度和空间结构得到了最真实的再现。ORAS5和SODA再分析产品都低估了WJ的强度。马尔代夫群岛的存在导致了赤道潜流（EUC）的向西延伸。马尔代夫的存在也在EUC纬向流的背风侧产生了尾流。在秋季，EUC在赤道印度洋东部定义更清晰，位于50至100米深度之间，与其春季情况不同，春季其核心位置略深，在100至150米深度之间。在夏季高峰期的6月至7月，在1000米深度存在一股强烈的向东纬向急流，类似于维尔基急流（WJ）。也可以看到季风间急流，即春季和秋季急流，但方向相反，即向西，与WJ向东的方向不同。
