Freshwater flux (FWF) at the sea surface, defined as precipitation minus evaporation, is a major atmospheric forcing to the ocean that affects sea surface salinity (SSS) and buoyancy flux (Q_B). Physically, there exist two pathways through which interannual FWF variability can affect the ocean: one through SSS and the other through Q_B. The roles of the interannual FWF variability in modulating the El Niño-Southern Oscillation (ENSO) through its effects on SSS or Q_B are separately examined using a hybrid coupled model (HCM) of the tropical Pacific; its ocean component is a layer model in which the topmost layer (the first layer) is treated as a mixed layer (ML) whose depth (H_m) is explicitly predicted using an embedded bulk ML model with H_m being directly affected by Q_B, whereas in level ocean models, Q_B does not have a direct and explicit effect on H_m. Four experiments are conducted using the HCM that is designed to illustrate the effects of these processes on coupled simulations systematically. It is demonstrated that interannual FWF variability serves as a positive feedback on ENSO through its collective effects on both SSS and Q_B. Individually, the interannual FWF effect through SSS accounts for about 80% in terms of ENSO amplitude in the Niño 3.4 area, while that through buoyancy flux accounts for about 26%. This indicates that ocean models without explicitly taking into account the direct FWF effect on Q_B (typically in level ocean models) could underestimate the positive feedback on ENSO compared with layer ocean models in which the FWF effects are collectively represented on both SSS and Q_B. Further implications for model biases associated with FWF effects are discussed.

海面的淡水通量（FWF）定义为降水量减去蒸发量，是对海洋的主要大气强迫，会影响海面盐度（SSS）和浮力通量（Q _B）。在物理上，存在两个途径，通过它的年际变化FWF会影响海洋：一个通过SSS和其他到Q_乙。使用热带太平洋的混合耦合模型（HCM）分别检查了年际FWF变异性通过其对SSS或Q _B的影响来调节厄尔尼诺-南方涛动（ENSO）的作用；它的海洋成分是一个层模型，其中最顶层（第一层）被视为深度（H _m）是使用嵌入式批量ML模型明确预测的，而H _m直接受Q _B影响，而在海平面模型中，Q _B对H _m没有直接和显着的影响。使用HCM进行了四个实验，该实验旨在系统地说明这些过程对耦合模拟的影响。结果表明，年际FWF变异性通过对SSS和Q _B的集体影响而对ENSO起到正反馈作用。就Niño3.4地区的ENSO振幅而言，通过SSS的年际FWF效应约占80％，而通过浮力通量的年际FWF效应约占26％。这表明，与在SSS和Q _B上共同表示FWF效应的层状海洋模型相比，没有明确考虑到Q _B的直接FWF影响（通常在水平海洋模型中）的海洋模型可能会低估ENSO的正反馈。。讨论了与FWF效应相关的模型偏差的其他含义。