Effects of Freshwater Flux Forcing on Interannual Climate Variability and Predictability in the Tropical Pacific

淡水通量（FWF）是大气对海洋的重要强迫，涉及地球水循环、海洋环流和气候之间的相互作用。最近的模拟研究表明，热带太平洋与fwf相关的海洋盐度对热带动力学和厄尔尼诺Niño-Southern涛动（ENSO）具有重要意义，并且对海平面的使用和解释以及海洋数据同化也具有重要意义。然而，在许多最先进的耦合气候模式中，热带太平洋的FWF强迫及其相关的盐度效应并没有得到实际的体现；在用于ENSO预报的大多数简化耦合模式中，甚至没有包括FWF强迫。本项目将利用观测数据和混合耦合模式（HCM）研究FWF强迫在调节热带太平洋气候系统年际变率和可预测性方面的作用。研究人员将验证热带太平洋的FWF强迫引起正气候反馈的假设，这为ENSO的调制和ENSO模拟和预测的重要热带偏倚源提供了新的机制。他们将根据历史降水和蒸发数据开发一个FWF年际变率的经验模型。这种依赖海温（SST）的异常海面暖流强迫的预测表示允许在ENSO周期中海面暖流和海温之间的交互反馈。然后，该FWF模式将被纳入热带太平洋的HCM，以考虑FWF强迫并代表FWF引起的气候反馈。在一个耦合的海洋-大气模式中实际地包括FWF强迫，预计将导致更好的ENSO模拟和预测。将进行各种数值试验，以量化FWF强迫对该地区季节至年际气候变率和可预测性的贡献程度。特别是，FWF强迫对ENSO调制的影响将是一个焦点。该项目的更广泛影响包括：(1)考虑到fwf引起的气候反馈，有可能直接改进ENSO模拟和耦合海洋-大气模式的预测；(2)对认识全球变暖导致的气候变化中的全球水循环具有重要意义；(3)本科生、研究生、博士后跨学科学习与培养经验；(4)透过刊物及会议/工作坊报告，广泛传播研究成果。

Freshwater flux (FWF) is an important atmospheric forcing to the ocean, involving interactions among the Earth's water cycle, ocean circulation, and climate. Recent modeling studies have shown that the FWF-related ocean salinity in the tropical Pacific is important to the tropical dynamics and El Niño-Southern Oscillation (ENSO), and also has important implications for the use and interpretation of sea level, and for ocean data assimilation. However, FWF forcing and its related salinity effects in the tropical Pacific have not been realistically represented in many state-of-the-art coupled climate models; the FWF forcing has not been even included in most simplified coupled models used for ENSO forecasts. This project will investigate the roles of FWF forcing in modulating interannual variability and predictability for the tropical Pacific climate system using observational data and a hybrid coupled model (HCM). The investigators will test a hypothesis that FWF forcing in the tropical Pacific induces a positive climate feedback, which presents a new mechanism for the modulation of ENSO and significant tropical bias sources for ENSO simulation and prediction. They will develop an empirical model for interannual FWF variability from historical precipitation and evaporation data. This Sea Surface Temperature (SST)-dependent, prognostic representation of anomalous FWF forcing allows for an interactive feedback between FWF and SST during ENSO cycles. Then, this FWF model will be incorporated into an HCM of the tropical Pacific to take into account FWF forcing and to represent FWF-induced climate feedback. The realistic inclusion of FWF forcing in a coupled ocean-atmosphere model is expected to lead to better ENSO simulations and predictions. Various numerical experiments will be conducted to quantify the extent to which FWF forcing can contribute to seasonal-to-interannual climate variability and predictability in the region. In particular, the effect of FWF forcing on the ENSO modulation will be a focus. The broader impacts of this project include (1) the potential for direct improvements in ENSO simulations and predictions in coupled ocean-atmosphere models by taking into account the FWF-induced climate feedback; (2) important implication for understanding global water cycle in a changing climate due to global warming; (3) interdisciplinary learning and training experience for undergraduate and graduate students, and postdoctoral researchers; (4) wide dissemination of the results through publications and meeting/workshop presentations.