BoBBLE: Bay of Bengal Boundary Layer Experiment

南亚夏季季风（6月至9月）为超过10亿人提供了80%的年降雨量，其中许多人依靠季风降雨维持生计农业和淡水。准确预测季节性降雨量和夏季降雨量变化至关重要。亚季节性的“活跃”和“中断”阶段可能持续数周，导致南亚广大地区发生洪水和干旱。海气相互作用是理解和预测季风行为的关键。印度东部孟加拉湾的海洋表面温度在整个夏天都保持非常温暖（高于28摄氏度）。海湾的蒸发为海湾上空形成的季风低压提供了水分和能量，并为印度带来了大量降雨。目前还不清楚，尽管这些系统失去了能量，但海湾如何保持温暖。众所周知，海湾的海洋温度和盐度变化会导致海湾和周围土地的降雨量变化，但尚不清楚这些变化是如何产生的，也不清楚它们是如何维持的。这对于南部海湾的东西变化尤其如此，这是该项目的重点。虽然海气相互作用对季风很重要，但天气预报只使用大气模型。通过在模型中纳入有代表性的海气相互作用，有可能改进季风预报。孟加拉湾边界层实验（BoBBLE）提出了一个观测活动的南部海湾，在建立季风（6月中旬至7月中旬）。BoBBLE将部署两艘船、六架海洋滑翔机和八架浮标，以收集前所未有的海洋和海气通量观测数据。这些船将占据西南湾和东南湾的位置，并在这些位置之间追踪东西和南北路径，测量海洋温度，盐度和海流。每艘船将配备两个滑翔机（自动水下航行器），另外两个在船之间，每两小时潜水500米，测量温度，盐度和水流。海气通量和海洋温度的日变化可能影响天气系统的发展。一种新的滑翔机配置将允许计算热量和盐的水平传输。浮标（自动潜水器）将部署在海湾，每5天测量2000米的海洋。他们将在BoBBLE之后留在海湾，加强观测网络。船舶和滑翔机还将测量海洋叶绿素，叶绿素吸收阳光并改变近表面海洋温度，影响海气相互作用。BoBBLE的科学家将分析这些观测结果，沿着常规数据集，以了解海湾条件的演变以及它们如何影响大气。将特别强调通过对照现有观测数据验证现有海气通量数据集来估计其不确定性。性能最好的数据集将用于改进对海气交换及其在每日至十年时间尺度上的变化的估计，计算印度洋和海湾的热量和淡水通量的预算，并验证模型模拟。模型模拟的层次结构将揭示海湾的条件是如何维持的，以及海气相互作用如何影响季风。模拟与海洋模型，迫使和验证对BoBBLE观测，将隔离的作用，海气通量（包括昼夜循环），叶绿素和水平运输在维护和充电海洋结构后，每个天气系统通道。回顾性预测的BoBBLE期间的大气和大气-海洋耦合模式将展示如何海气相互作用影响季风降雨预测。多年代际模拟将评估海气相互作用和耦合模式系统误差如何影响每日到季节性季风变化。

The South Asian summer monsoon (June-September) provides 80% of the annual rainfall for over one billion people, many of whom depend on monsoon rains for subsistence agriculture and freshwater. It is critical to forecast accurately not only the seasonal rainfall, but also rainfall variations within the summer. Sub-seasonal "active" and "break" phases can last weeks, resulting in floods and droughts across broad areas of South Asia. Air-sea interactions are key to understanding and predicting monsoon behaviour. Ocean surface temperatures in the Bay of Bengal, east of India, remain very warm (above 28 Celsius) throughout the summer. Evaporation from the Bay provides moisture and energy to monsoon depressions that form over the Bay and bring substantial rain to India. It is not understood how the Bay remains warm despite losing energy to these systems. Ocean temperature and salinity variations across the Bay are known to drive changes in rainfall over the Bay and surrounding land, but it is not clear how these arise or how they are maintained. This is particularly true for east-west variations in the southern Bay, a focus of this project. Although air-sea interactions are important to the monsoon, weather predictions are made with models of only the atmosphere. There is potential to improve monsoon forecasts by including well-represented air-sea interactions in models. The Bay of Bengal Boundary Layer Experiment (BoBBLE) proposes an observational campaign for the southern Bay, during the established monsoon (mid-June to mid-July). BoBBLE will deploy two ships, six ocean gliders and eight floats to collect an unprecedented range of oceanic and air-sea flux observations. The ships will occupy locations in the southwest and southeast Bay, as well as tracing east-west and north-south paths between those locations, measuring ocean temperature, salinity and currents. Two gliders (automated underwater vehicles) will accompany each ship, with two others between the ships, diving to 500 metres every 2 hours to measure temperature, salinity and currents. Diurnal variations in air-sea fluxes and ocean temperatures may affect the development of weather systems. A novel configuration of the gliders will allow computations of horizontal transports of heat and salt. The floats (automated submersibles) will be deployed in the Bay to measure the ocean to 2000 metres every 5 days. They will remain in the Bay after BoBBLE, enhancing the observing network. Ships and gliders will also measure ocean chlorophyll, which absorb sunlight and alter near-surface ocean temperature, influencing air-sea interactions. BoBBLE scientists will analyse these observations, along with routine datasets, to understand the evolution of conditions in the Bay and how they influence the atmosphere. Particular emphasis will be placed on estimating the uncertainty in existing datasets of air-sea fluxes by validating them against available observations. The best-performing datasets will be used to improve estimates of air-sea exchanges and their variability on daily to decadal timescales, to calculate budgets of heat and freshwater fluxes in the Indian Ocean and the Bay, and to validate model simulations. A hierarchy of model simulations will reveal how conditions in the Bay are maintained and how air-sea interactions influence the monsoon. Simulations with an ocean model, forced by and validated against BoBBLE observations, will isolate the roles of air-sea fluxes (including the diurnal cycle), chlorophyll and horizontal transports in maintaining and recharging ocean structure after each weather system passage. Retrospective forecasts of the BoBBLE period with atmosphere-only and atmosphere-ocean coupled models will demonstrate how air-sea interactions influence monsoon rainfall predictions. Multi-decadal simulations will evaluate how air-sea interactions and coupled-model systematic errors influence daily-to-seasonal monsoon variability.