Surface Mixed Layer Salinity Budget in the Tropical Indian Ocean

麦登-朱利安涛动（MJO）是热带海洋上空的一种大气扰动，周期性在30至90天之间，由地面西风爆发、大气深层对流和强降水组成。MJO通常起源于赤道印度洋，沿着赤道以大约每秒5米的速度向东移动，直到到达太平洋中部，然后在绕地球飞行时加速，影响全球天气模式。MJO的预测是不令人满意的，特别是在它的起始阶段，海洋对大气的反馈可能是重要的。2011-2012年在热带印度洋中部进行的DYNAMO （Madden-Julian涛动动力学）实验成功地捕捉到了MJO的几个起始点。在这种情况下，DYNAMO的目标之一是了解盐度分层对热带印度洋湍流携流通量和海表温度的影响，其中盐度分层在海洋表面混合层的热量、动量和盐度收支中起着重要作用。DYNAMO实验的观测结果证实，地表混合层底部的湍流热通量是热量收支的主要组成部分。然而，在类似的地面风和浮力强迫下，在季节内（例如MJO）时间尺度上，湍流热通量的变化量大于每平方米100瓦，并且可能受到屏障层过程的调制。本研究将评估表层混合层盐度收支和阻隔层性质的细节及其时空变化。本研究的结果将量化并增加对盐度分层对湍流携带通量的影响的理解，从而改进热带印度洋中部和东部湍流通量的参数化。这个分析项目将完成一名博士生的培养。本项目主要研究热带印度洋中东部表层混合层盐度收支及其对海温的调制和Madden-Julian涛动的演变。作为DYNAMO实验的一部分，从热带印度洋中部和东部的海洋系泊处进行的综合现场观测，以及从宝瓶号卫星遥感的海面盐度将用于这一目的。系泊处收集了气象变量，以及上层海洋的温度、盐度和水平速度测量。所有DYNAMO系泊和一些RAMA系泊都配备了微结构传感器，可以直接测量湍流携流通量。这些观测结果提供了一个独特的机会来接近在DYNAMO实验期间不同MJO阶段在TIO中部和东部的地表混合层盐度收支。海气盐度通量将使用系泊气象测量来计算。平流盐度通量将通过系泊测量来计算，并辅以Aquarius测量。湍流盐度通量将使用直接微观结构测量来计算。确定了地表混合层盐度收支的主要通量。盐度通量和屏障层性质的时间（从日到季内）和空间（热带印度洋中部到东部）变率及其对剪切不稳定和湍流夹带通量的影响将在不同MJO阶段进行量化。这项研究将为建立一个基于物理的湍流参数化方案奠定基础，该方案包括阻挡层过程的影响，可以帮助改进MJO的开始和演变的模型预测。

The Madden-Julian Oscillations (MJO) is an atmospheric disturbance over the tropical oceans with a recurrence period between 30 and 90 days, consisting of surface westerly wind bursts, deep atmospheric convection, and heavy precipitation. The MJO generally originates in the Equatorial Indian Ocean, develops as it travels eastward at roughly 5 meters per second along the equator until reaching the central Pacific and then accelerates as it circumnavigates the globe, impacting global weather patterns. MJO prediction is unsatisfactory, especially at its initiation stage when the oceanic feedback to the atmosphere may be important. The DYNAMO (DYNAmics of the Madden-Julian Oscillation) experiment conducted in 2011-2012 in the central Tropical Indian Ocean was successful in capturing several initiations of the MJO. In that context, one of the goals of DYNAMO was to understand the effects of salinity stratification on the turbulent entrainment flux and Sea Surface Temperature in the Tropical Indian Ocean where salinity stratification plays a significant role in the heat, momentum and salinity budgets of the surface ocean mixed layer. Observations from the DYNAMO experiment confirm that the turbulent heat flux at the base of the surface mixed layer is a primary component in the heat budget. The turbulent heat flux, however, varies by amounts larger than 100 Watts per square meter at intra-seasonal (e.g., MJO) time scales under similar surface wind and buoyancy forcing, and is presumably modulated by the barrier layer processes. This study will evaluate the details of the surface mixed layer salinity budget and barrier layer properties, and their temporal and spatial variations. Results from this proposed study will quantify and increase understanding of salinity stratification effects on turbulent entrainment fluxes in order to improve parameterizations of turbulent fluxes in the central and eastern Tropical Indian Ocean. This analysis project will complete the training of a Ph.D. student.This project focuses on the surface mixed layer salinity budget in the central and eastern Tropical Indian Ocean and its modulation of Sea Surface Temperature and the evolution of the Madden-Julian oscillation. Comprehensive in-situ observations from ocean moorings deployed in the central and eastern Tropical Indian Ocean as part of the DYNAMO experiment, and remotely-sensed Sea Surface Salinity from the Aquarius satellite will be used for that purpose. The moorings collected meteorological variables, as well as temperature, salinity, and horizontal velocity measurements in the upper ocean. All the DYNAMO moorings and some RAMA moorings were equipped with microstructure sensors, allowing direct measurements of turbulent entrainment fluxes. These observations provide a unique opportunity to close the surface mixed layer salinity budget in the central and eastern TIO during different MJO phases in the period of the DYNAMO experiment. The air-sea salinity flux will be computed using mooring meteorological measurements. The advective salinity flux will be computed using mooring measurements, aided by the Aquarius measurements. The turbulent salinity flux will be computed using direct microstructure measurements. The dominant fluxes in the surface mixed layer salinity budget will be identified. The temporal (from days to intra-seasonal) and spatial (central to eastern Tropical Indian Ocean) variability of salinity fluxes and barrier layer properties, and their effects on shear instability and turbulent entrainment flux will be quantified in different MJO phases. This study will establish the basis for developing a physics based turbulence parameterization scheme that includes the effects of barrier layer process that can help improve model predictions of the initiation and evolution of the MJO.