Spatial and temporal variability of solar penetration depths in the Bay of Bengal and its impact on SST during the summer monsoon
Spatial and temporal variability of solar penetration depths in the Bay of Bengal and its impact on SST during the summer monsoon
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DOI：
10.5194/os-2020-125
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发表时间：
2021-01
期刊：
影响因子：
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通讯作者：
J. Giddings;K. Heywood;A. Matthews;M. Joshi;B. Webber;A. Sanchez‐Franks;B. King;P. Vinayachandran
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文献类型：
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作者：
J. Giddings;K. Heywood;A. Matthews;M. Joshi;B. Webber;A. Sanchez‐Franks;B. King;P. Vinayachandran
摘要。叶绿素通过影响太阳辐射吸收从而影响海表温度来影响区域气候。在孟加拉湾，叶绿素对海温的影响已被证明对印度夏季（西南）季风有显著影响。然而，人们对西南季风期间孟加拉湾叶绿素变化的驱动因素和影响知之甚少。本文利用海洋滑翔机和三个剖面浮标测量的下流辐照度观测数据，确定了2016年夏季季风期间孟加拉湾南部太阳吸收的时空变化。采用双波段指数太阳吸收方案拟合光合有效辐射的垂直剖面，以确定蓝光的有效尺度深度。研究发现，当混合层叶绿素浓度最高时（0.3-0.5 mg m−3），蓝光的尺度深度为12 m，当混合层叶绿素浓度低于0.1 mg m−3时，蓝光的尺度深度超过25 m。与孟加拉湾南部其他地区相比，西南季风流和孟加拉湾沿海地区的混合层叶绿素浓度较高，太阳穿透深度较浅。观测到太阳辐射吸收的大量亚日变化，这突出了近地表海洋过程在调节混合层叶绿素中的重要性。基于2016年7月观测到的地表强迫的一维k廓线参数化海洋混合层模式模拟表明，叶绿素浓度每增加0.3 mg m−3，一个月内海面温度就会升高0.35°C，在平静和晴朗条件下，海温差异迅速扩大。这有可能影响孟加拉湾周围的季风降雨及其季节内变化。
Abstract. Chlorophyll influences regional climate through its effect on solar radiation absorption and thus sea surface temperature (SST). In the Bay of Bengal, the effect of chlorophyll on SST has been demonstrated to have a significant impact on the Indian summer (southwest) monsoon. However, little is known about the drivers and impacts of chlorophyll variability in the Bay of Bengal during the southwest monsoon. Here we use observations of downwelling irradiance measured by an ocean glider and three profiling floats to determine the spatial and temporal variability of solar absorption across the southern Bay of Bengal during the 2016 summer monsoon. A two-band exponential solar absorption scheme is fitted to vertical profiles of photosynthetically active radiation to determine the effective scale depth of blue light. Scale depths of blue light are found to vary from 12 m during the highest (0.3–0.5 mg m−3) mixed layer chlorophyll concentrations, to over 25 m when the mixed layer chlorophyll concentrations are below 0.1 mg m−3. The Southwest Monsoon Current and coastal regions of the Bay of Bengal are observed to have higher mixed layer chlorophyll concentrations and shallower solar penetration depths than other regions of the southern Bay of Bengal. Substantial sub-daily variability in solar radiadion absorption is observed, which highlights the importance of near-surface ocean processes in modulating mixed layer chlorophyll. Simulations using a one-dimensional K-profile parameterisation ocean mixed layer model with observed surface forcing from July 2016 show that a 0.3 mg m−3 increase in chlorophyll concentration increases sea surface temperature by 0.35 °C in one month with SST differences growing rapidly during calm and sunny conditions. This has the potential to influence monsoon rainfall around the Bay of Bengal and its intraseasonal variability.