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，而在第二阶段，重点是受强烈降水影响的热带北大西洋。该地区的海面盐度（SSS）在空间尺度上变化很大，从小尺度（与对流雨单体有关）到盆地尺度（例如与横跨南美洲到非洲的热带辐合带（ITCZ）有关）。时间变率同样与时间尺度为几小时的零星降雨事件、近地面分层和混合的每日周期、时间尺度为几周至几个月的海洋中尺度动力学、主要与ITCZ的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式相关的年际至年代际变率有关。拟议的项目依靠卫星数据和在北大西洋热带地区在不同项目框架内获得的数据，包括SFB 754。在这里，我们使用了自2006年以来主要沿着15°N和5°S之间的23°W剖面拍摄的大量CTD剖面（图2），以及在北大西洋热带更广泛地区拍摄的船载和滑翔机数据。大量的盐度剖面可以表征近地表盐度变化，并将这些信息与卫星遥感的SSS相结合。滑翔机数据尤其包含了近地表海洋的大量微观结构剖面，非常适合研究近地表底冲淡水通量。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的水文循环的了解，重点是海洋淡水通量和近地表淡水预算，这对了解长期气候驱动的变化具有影响。更具体地说，我们将讨论以下主题：1) ITCZ以下区域SSS年际变率与大尺度气候模式的关系；2)ITCZ附近高变化风所迫的季节混合层淡水收支，重点是纵向混合和近惯性波的作用；3)与降雨事件和日至多日暖层相关的近地面分层变率及其对SSS的影响。所获得的知识和现有数据集将用于评估有无数据同化的模式模拟的质量，并将有助于增进对SSS变率的驱动因素和机制的理解。拟议的研究与国际计划sprs -2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小区域。

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.