Analysis of magnitude, drivers, and mechanisms of salinity variability in the tropical Atlantic

海洋在全球水循环中起着至关重要的作用。在DFG Forschergruppe的第一阶段，重点是赤道大西洋，在第二阶段，它是热带北大西洋，一个受强降水影响的地区。该区域的海面盐度（SSS）在空间尺度上变化很大，从小尺度（与对流雨团相关）到流域尺度（例如与从南美洲到非洲的热带辐合带相关）。时间变率也与时间尺度为几小时的零星降雨事件、近地面层结和混合的日周期、时间尺度为几周到几个月的海洋中尺度动力学、主要与ITCZ季节性迁移相关的季节变率（图1）以及与热带大西洋变率的主要气候模态相关的年际到十年变率有关。拟议的项目依赖于卫星数据和在包括SFB 754在内的不同项目框架内在热带北大西洋获得的数据。在这里，我们使用了自2006年以来主要沿沿着23°W、15°N和5°S之间的断面（图2）采集的大量CTD剖面，以及在热带北大西洋更广泛区域采集的船上和滑翔机数据。大量的盐度分布图可以用来描述近地表盐度变化的特征，并将这一信息与卫星遥感的SSS联合收割机结合起来。滑翔机的数据，特别是包括大量的近表层海洋的微观结构配置文件是非常适合研究近表层淡水通量。拟议项目的主要目标是提高我们对热带北大西洋盐度最低区域水文循环的认识，重点是海洋淡水通量和近地表淡水收支，对认识长期气候驱动的变化有影响。具体而言，我们将讨论以下主题：1）ITCZ以下区域SSS的年际变化与大尺度气候模式有关，2）季节性混合层淡水收支，重点是穿透混合和ITCZ附近高度可变风强迫的近惯性波的作用，3）卫星遥感观测到的与降水事件和日至多日暖层相关的近地面层结变化及其对SSS的影响。所获得的知识和现有的数据集将用于评估有和没有数据同化的模型模拟的质量，并将有助于增加对SSS变异性的驱动因素和机制的理解。这项拟议的研究与SPURS-2国际计划密切相关，该计划将于2016-2017年重点关注热带太平洋东部的盐度最低区域。

The ocean plays an essential role in the global water cycle. While during the first phase of the DFG Forschergruppe, the focus was on the equatorial Atlantic, during the second phase it is on the tropical North Atlantic, a region affect by intense precipitation. Sea surface salinity (SSS) in this region is highly variable on space scales ranging from small scales, associated with convective rain cells, to the basin scale, associated for example with the Intertropical Convergence Zone (ITCZ) spanning from South America to Africa. Temporal variability again is associated with sporadic rainfall events with time scales of few hours, daily cycles in near surface stratification and mixing, ocean mesoscale dynamics with time scales of weeks to few months, seasonal variability mainly associated with the seasonal migration of the ITCZ (Fig. 1) and interannual to decadal variability associated with the dominant climate modes of Tropical Atlantic Variability. The proposed project relies on satellite data and on data acquired in the tropical North Atlantic in the frame of different projects, including the SFB 754. Here we use the large amount of CTD profiles taken since 2006 mainly along the 23°W section between 15°N and 5°S (Fig. 2), together with shipboard and glider data taken in the wider region of the tropical North Atlantic. The large amount of salinity profiles allows to characterize the near-surface salinity variability and to combine this information with SSS from satellite remote sensing. The glider data that particularly include a large amount of microstructure profiles of the near-surface ocean are ideally suited to study near surface diapycnal freshwater fluxes. Main goal of the proposed project is to improve our understanding of the hydrological cycle in the salinity minimum region of the tropical North Atlantic with focus on oceanic freshwater fluxes and near surface freshwater budgets with implications for the understanding of long-term climatedriven changes. More specifically we will address the following topics: 1) interannual variability of SSS in the region below the ITCZ associated with large-scale climate modes, 2) the seasonal mixed layer freshwater budget with focus on diapycnal mixing and the role of near-inertial waves forced by highly variable winds close to the ITCZ, and 3) the near surface stratification variability associated with rainfall events and diurnal to multi-diurnal warm layers and its effect on SSS as observed by satellite remote sensing. The gained knowledge and available datasets will be used to assess the quality of model simulations with and without data assimilation and will contribute to increase the understanding of drivers and mechanisms of SSS variability. The proposed study is strongly related to the international program SPURS-2 that will focus on the salinity minimum region of the eastern tropical Pacific in 2016-2017.