Asian summer monsoon has a planetary‐scale, westward propagating “quasi‐biweekly” mode of variability with a 10–25 day period. Six years of moored observations at 18°N, 89.5°E in the north Bay of Bengal (BoB) reveal distinct quasi‐biweekly variability in sea surface salinity (SSS) during summer and autumn, with peak‐to‐peak amplitude of 3–8 psu. This large‐amplitude SSS variability is not due to variations of surface freshwater flux or river runoff. We show from the moored data, satellite SSS, and reanalyses that surface winds associated with the quasi‐biweekly monsoon mode and embedded weather‐scale systems, drive SSS and coastal sea level variability in 2015 summer monsoon. When winds are calm, geostrophic currents associated with mesoscale ocean eddies transport Ganga‐Brahmaputra‐Meghna river water southward to the mooring, salinity falls, and the ocean mixed layer shallows to 1–10 m. During active (cloudy, windy) spells of quasi‐biweekly monsoon mode, directly wind‐forced surface currents carry river water away to the east and north, leading to increased salinity at the moorings, and rise of sea level by 0.1–0.5 m along the eastern and northern boundary of the bay. During July–August 2015, a shallow pool of low‐salinity river water lies in the northeastern bay. The amplitude of a 20‐day oscillation of sea surface temperature (SST) is two times larger within the fresh pool than in the saltier ocean to the west, although surface heat flux is nearly identical in the two regions. This is direct evidence that spatial‐temporal variations of BoB salinity influences sub‐seasonal SST variations, and possibly SST‐mediated monsoon air‐sea interaction.

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孟加拉湾地表观测资料揭示了亚洲夏季风的准双周模式

亚洲夏季风具有行星尺度，向西传播的“准双周”变率模式，为10-25天。N在18 ^o N，89.5 ^o处停泊了6年孟加拉北部海湾的E在夏季和秋季显示出明显的准双周变化，海平面盐度（SSS）的峰峰值为3-8 psu。SSS的大幅度变化不是由于地表淡水通量或河流径流的变化引起的。我们从停泊的数据，卫星SSS和重新分析中显示，与准双周季风模式和嵌入式天气尺度系统相关的地表风驱动了2015年夏季风的SSS和沿海海平面变化。当风平和时，与中尺度海洋涡旋相关的地转流将恒河-布拉马普特拉-梅格纳河的水向南输送至系泊，盐度下降，海洋混合层变浅至1-10 m。在准双周季风模式的活跃（多云，大风）期间，直接由风力产生的地表水将河水带到东部和北部，导致系泊处的盐度增加，沿海湾的东部和北部边界海平面上升0.1-0.5 m。2015年7月至8月，东北海湾位于浅水区，盐度低。尽管两个地区的表面热通量几乎相同，但新鲜池中20天海面温度（SST）的波动幅度是西部咸海中的两倍。这直接证明孟加拉湾盐度的时空变化会影响亚季节的海表温度变化，并可能影响海表温度介导的季风空海相互作用。2015年7月至8月，东北海湾位于浅水区，盐度低。尽管两个地区的表面热通量几乎相同，但新鲜池中20天海面温度（SST）的波动幅度是西部咸海中的两倍。这直接证明孟加拉湾盐度的时空变化会影响亚季节的海表温度变化，并可能影响海表温度介导的季风空海相互作用。2015年7月至8月，东北海湾位于浅水区，盐度低。尽管两个地区的表面热通量几乎相同，但新鲜池中20天海面温度（SST）的波动幅度是西部咸海中的两倍。这直接证明孟加拉湾盐度的时空变化会影响亚季节的海表温度变化，并可能影响海表温度介导的季风空海相互作用。