赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化
马天(1994—), 男, 海南省海口市人, 硕士研究生, 研究方向是物理海洋学和海洋热力与动力过程。E-mail: 412847469@qq.com |
Copy editor: 殷波
收稿日期: 2018-11-29
要求修回日期: 2019-03-03
网络出版日期: 2019-10-09
基金资助
国家重点研发计划课题(2018YFA0605702)
国家自然科学基金(41522601)
国家自然科学基金(41876002)
国家自然科学基金(41876224)
中央高校基本科研业务费项目)(2017B04714)
中央高校基本科研业务费项目(2017B04114)
版权
Intraseasonal-to-semiannual variability of barrier layer thickness in the eastern equatorial lndian Ocean and Bay of Bengal
Copy editor: YIN Bo
Received date: 2018-11-29
Request revised date: 2019-03-03
Online published: 2019-10-09
Supported by
National Key Research Development Program of China(2018YFA0605702)
Natural Science Foundation of China(41522601)
Natural Science Foundation of China(41876002)
Natural Science Foundation of China(41876224)
Fundamental Research Funds for the Central Universities(2017B04714)
Fundamental Research Funds for the Central Universities(2017B04114)
Copyright
利用2002—2015年ARGO网格化的温度、盐度数据, 结合卫星资料揭示了赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化特征, 探讨了其变化机制。结果表明, 障碍层厚度变化的两个高值区域出现在赤道东印度洋和孟加拉湾北部。在赤道区域, 障碍层同时受到等温层和混合层变化的影响, 5—7月和11—1月受西风驱动, Wyrtki急流携带阿拉伯海的高盐水与表层的淡水形成盐度层结, 同时西风驱动的下沉Kelvin波加深了等温层, 混合层与等温层分离, 障碍层形成。在湾内, 充沛的降雨和径流带来的大量淡水产生很强的盐度层结, 混合层全年都非常浅, 障碍层季节内变化和准半年变化主要受等温层深度变化的影响。上述两个区域障碍层变化存在关联, 季节内和准半年周期的赤道纬向风驱动的波动过程是它们存在联系的根本原因。赤道东印度洋地区的西风(东风)强迫出向东传的下沉(上升)的Kelvin波, 在苏门答腊岛西岸转变为沿岸Kelvin波向北传到孟加拉湾的东边界和北边界, 并且在缅甸的伊洛瓦底江三角洲顶部(95°E, 16°N)激发出向西的Rossby波, 造成湾内等温层深度的正(负)异常, 波动传播的速度决定了湾内的变化过程滞后于赤道区域1~2个月。
马天 , 齐义泉 , 程旭华 . 赤道东印度洋和孟加拉湾障碍层厚度的季节内和准半年变化[J]. 热带海洋学报, 2019 , 38(5) : 18 -31 . DOI: 10.11978/2018132
Based on the gridded temperature and salinity data of ARGO and satellite observations from 2002 to 2015, the intraseasonal-to-semiannual variability of barrier layer (BL) in the eastern equatorial Indian Ocean (EEIO) and Bay of Bengal (BOB) is revealed, and its variation mechanism is discussed. The results show that strong variation of barrier layer thickness (BLT) is located in the EEIO and northern BOB. In the equatorial region, the variability in BLT is affected by both isothermal layer depth (ILD) and mixing layer depth (MLD). From May to July and from November to January, driven by westerly winds, the Wyrtki jet carries high-salinity water from the Arabian Sea to the eastern equatorial region, forming salinity stratification with fresh water on the surface. The downwelling Kelvin wave, which is also driven by westerly winds, deepens the isothermal layer. Then, the isothermal layer separates from the mixed layer. The barrier layer is formed. In the northern BOB, a large amount of fresh water brought by abundant rainfall and runoff produces strong salinity stratification near the surface, which causes the mixed layer to be very shallow all year round. The intraseasonal-to-semiannual variability in BLT is mainly controlled by ILD. A dynamic correlation exists between the two high value regions. The equatorial westerly (easterly) winds force the downwelling (upwelling) Kelvin wave to spread eastward, and it turns into a coastal Kelvin wave when arriving at Sumatra Island; then, the waves propagate northward to the eastern and northern boundaries of the BOB. In addition, at the top of Burma's Irrawaddy Delta, the coastal Kelvin wave radiates Rossby waves that cause positive (negative) anomalies of ILD in the bay. The wave speed determines the change in the bay, which lags the equatorial region by 1~2 months.
图3 ARGO网格化数据(实线)与RAMA浮标数据(虚线)计算得到的障碍层(BLT)、等温层(ILD)、混合层(MLD)时间序列a、b、c位于(90°E, 0°N); d、e、f 位于(90°E, 15°N) Fig. 3 Barrier layer thickness (BLT), isothermal layer depth (ILD), and mixed layer depth (MLD) derived from gridded ARGO data (solid curves) and RAMA data (dashed curves) at (90°E, 0°) (a, b, c) and at (90°E, 15°N) (d, e, f) |
图6 区域A平均(a)和区域B平均(b)的障碍层厚度功率谱(7个月高通滤波)虚线表示95%信度水平 Fig. 6 Power spectra for barrier layer thickness after 7-month high-pass filtering in the regions A (a) and B (b). The dash curve indicates the 95% confidence levels |
图8 温度、盐度(填色)廓线和等温层深度(黑色实线)、混合层深度(黑色虚线)、障碍层厚度随时间变化a、b、c位于(90°E, 0°N); d、e、f位于(90°E, 15°N)。图c和图f中红线为障碍层厚度5~7个月带通滤波结果, 蓝线为障碍层厚度2.5~4.5个月带通滤波结果 Fig. 8 Depth-time sections of temperature, salinity (shaded), and time series of isothermal layer depth (black lines), mixed layer depth (black dashed lines), and barrier layer thickness. The red line indicates the barrier layer thickness in the 5~7 month band. The blue line indicates the barrier layer thickness in the 2.5~4.5 month band. Panels (a, b, c) are at (90°E, 0°); and (d, e, f) are at (90°E, 15°N) |
图9 海面高度异常(SLA)和等温层深度(ILD)时间序列a. 5~7个月带通滤波结果; b. 2.5~4.5个月带通滤波结果。图例中SLA表示区域A海面高度异常; ILD-A表示区域A等温层深度; ILD-B表示区域B等温层深度 Fig. 9 Time series of sea level anomaly (SLA) and isothermal layer depth (ILD). Blue line indicates SLA in Region A, and black line indicates ILD in Region A. Red line indicates ILD in Region B. Panels a and b show variability in the 5~7 month band, and 2.5~4.5 month band, respectively |
图11 断面纬向风应力和各站点海面高度异常随时间变化图a. 纬向风应力(170~190d带通滤波); b. 海面高度异常(170~190d带通滤波); c. 纬向风应力(75~135d带通滤波); d. 海面高度异常(75~135d带通滤波) Fig. 11 Time-longitude plots of zonal wind stress and time-station plots of sea level anomaly. (a) Zonal wind stress in the 170~190 day band; (b) Sea level anomaly in the 170~190 day band; (c) Zonal wind stress in the 75~135 day band; (d) Sea level anomaly in the 75~135 day band |
图13 区域A盐度收支与混合层深度变化a、b、c为5~7个月带通滤波结果; d、e、f为2.5~4.5个月带通滤波结果。图例中MLD表示混合层深度; ds/dt表示盐度月变化率; SUM表示盐度收支方程右侧各项之和; fwf表示淡水通量; adv表示水平平流和垂向夹卷之和; adv-x/y/z分别表示纬向输运、经向输运和垂向输运 Fig. 13 Salt budget and mixed layer depth variation in Region A, with MLD for mixed layer depth, ds/dt for salinity monthly tendency, SUM for sum of the right-hand side of salt budget, fwf for freshwater flux, adv for sum of horizontal (zonal & meridional) advections and entrainment, and adv-x/y/z for zonal/meridional/vertical transports, respectively. (a, b, c): 5~7 month band; (d, e, f): 2.5~4.5 month band |
图14 区域B盐度收支与混合层变化a、b、c为5~7个月带通滤波结果; d、e、f为2.5~4.5个月带通滤波结果。图例中MLD表示混合层深度; ds/dt表示盐度月变化率; SUM表示盐度收支方程右侧各项之和; fwf表示淡水通量; adv表示水平平流和垂向夹卷之和; adv-x/y/z分别表示纬向输运、经向输运和垂向输运 Fig. 14 Salt budget and mixed layer depth variation in Region B, with MLD for mixed layer depth, ds/dt for salinity monthly tendency, SUM for sum of the right-hand side of salt budget, fwf for freshwater flux, adv for sum of horizontal (zonal & meridional) advections and entrainment, and adv-x/y/z for zonal/meridional/vertical transports, respectively. (a, b, c): 5~7 month band; (d, e, f): 2.5~4.5 month band |
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