Upscale Feedback of Tropical Atmospheric Synoptic-Scale Variabilities to Intraseasonal Oscillations

马登-朱利安涛动（MJO）是日常天气和厄尔尼诺/拉尼娜-南方涛动（ENSO）之间最重要的热带变率。最近的理论和模拟研究表明，天气尺度（3-10天）变率（SSV）的高档反馈MJO是重要的，但我们目前的知识，在理解这种高档反馈是非常有限的。该项目阐述了一个奋进，调查高档反馈的热带SSV MJO。要解决的具体科学问题是：通过什么内部大气和海洋的非线性过程和表面通量过程的SSV反馈到MJO？正压/斜压能量转换如何依赖于MJO位相？MJO对流和非线性校正的表面热通量/视热源/涡动量输送之间的相位关系是什么？这些问题将通过分析新一代再分析产品来解决，如国家环境预测中心（NCEP）气候预报系统再分析（CFSR）、地球系统研究实验室（ESRL）百年历史再分析、美国国家航空航天局（NASA）现代研究和应用回顾分析（MERRA）、和欧洲中期天气预报中心（ECMWF）高分辨率的热带对流年（YOTC）数据集，并通过数值模拟实验。该项目包括以下三个主要研究部分。首先，一个新开发的涡动动能（EKE）收支诊断将被应用于调查的天气涡与缓慢变化的背景平均状态和MJO流的相互作用，在影响正压和斜压能量转换在不同阶段的MJO的作用。其次，研究者将研究非线性校正的季节内地面潜热通量（LHF）的特征及其与MJO对流的时空相位关系。第三，研究人员将研究到什么程度的SSV调制季节内的表观热量和水分来源，以及如何的非线性涡动动量输送（包括2天波和中尺度对流系统的影响）施加一个高档的反馈MJO。还将通过一系列海洋环流模型试验，研究高频大气变率影响季节内SST的海洋“红化”过程。以下两个非线性校正过程，即地面风应力/热通量的非线性校正和海洋非线性平流过程，将得到特别的研究。更广泛的影响包括：在当前最先进的全球气候/天气模式中，改进了从天气到季节内时间尺度的热带对流结构和变率的代表性，这可能会进一步提高热带和热带以外地区的长期天气和气候预报技能，促进亚季节尺度的预报潜力。

The Madden-Julian Oscillation (MJO) is the most significant tropical variability between day-to-day weather and El Niño/La Niña-Southern Oscillation (ENSO). Recent theoretical and modeling studies suggested that the upscale feedback of synoptic-scale (3-10-day) variability (SSV) to MJO is important but our current knowledge in understanding this upscale feedback is very limited. This project articulates an endeavor to investigate the upscale feedback of the tropical SSV to MJO. Specific scientific questions to be addressed are: Through what internal atmospheric and ocean nonlinear processes and surface flux processes does the SSV feed back to the MJO? How do the barotropic/baroclinic energy conversions depend on the MJO phases? What are the phase relationships between MJO convection and nonlinearly rectified surface heat fluxes/apparent heat sources/eddy momentum transport? These questions will be addressed through the analysis of new-generation reanalysis products such as National Centers for Environmental Prediction (NCEP) Climate Forecast System Reanalysis (CFSR), Earth System Research Laboratory (ESRL) 100-year Historical Reanalysis, National Aeronautics and Space Administration (NASA) Modern Era Retrospective-analysis for Research and Applications (MERRA), and European Centre for Medium-Range Weather Forecasts (ECMWF) high-resolution YOTC (Year of Tropical Convection) datasets and through numerical modeling experiments. This project consists of the following three major research components. Firstly, a newly developed eddy kinetic energy (EKE) budget diagnostics will be applied to investigate the role of synoptic eddy interactions with the slowly varying background mean state and the MJO flow in affecting barotropic and baroclinic energy conversions at various phases of MJO. Secondly, the investigator will examine the characteristics of nonlinearly rectified intraseasonal surface latent heat flux (LHF) and its temporal and spatial phase relationships with MJO convection. Thirdly, the investigator will examine to what extend SSV modulates intraseasonal apparent heat and moisture sources and how the nonlinear eddy momentum transport (including the effect of 2-day waves and mesoscale convective systems) exerts an upscale feedback to MJO. The ocean "reddening" process through which high-frequency atmospheric variability affects the intraseasonal SST will be also investigated through a series of ocean general circulation model experiments. The following two nonlinear rectification processes, the nonlinear rectification of the surface wind stress/heat flux and the ocean nonlinear advection process, will be particularly examined.Broader impacts of the research include the contribution to improved representation of the structure and variability of tropical convection from synoptic to intraseasonal timescales in the current state-of-art global climate/weather models, which may further lead to improved skills of extended-range weather and climate forecasts both in the tropics and extratropics, facilitating the forecast potential at the sub-seasonal scale.