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

麦登-朱利安涛动（MJO）是El Niño/La Niña-Southern涛动（ENSO）与日常天气之间最显著的热带变率。最近的理论和模型研究表明天气尺度（3-10天）变率（SSV）对MJO的高级反馈是重要的，但我们目前对这种高级反馈的理解非常有限。本项目旨在研究热带SSV对MJO的高档反馈。需要解决的具体科学问题是：SSV通过什么内部大气和海洋非线性过程以及表面通量过程反馈给MJO？正压/斜压能量转换如何依赖于MJO相？MJO对流与非线性整流表面热通量/视热源/涡流动量输运之间的相位关系是什么？这些问题将通过新一代再分析产品的分析来解决，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）现代研究与应用回顾性分析（MERRA）、和欧洲中期天气预报中心（ECMWF）的高分辨率YOTC（热带对流年）数据集，并通过数值模拟实验。本项目包括以下三个主要研究部分。首先，本文将应用新发展的涡动能预算诊断方法，研究天气涡旋与缓慢变化的背景平均状态和MJO流的相互作用对MJO各阶段正斜压能量转换的影响。其次，研究了非线性整流季节内地表潜热通量（LHF）的特征及其与MJO对流的时空相位关系。第三，研究SSV在多大程度上调节了季节内的视热和视湿源，以及非线性涡动量输送（包括2日波和中尺度对流系统的影响）如何对MJO施加高级反馈。通过一系列海洋环流模式实验，还将研究高频大气变率影响季节内海温的海洋“变红”过程。本文将重点研究两个非线性整流过程，即地面风应力/热通量非线性整流过程和海洋非线性平流过程。本研究的更广泛影响包括：在目前最先进的全球气候/天气模式中，改进了从天气尺度到季节内时间尺度的热带对流结构和变率的表示，这可能进一步提高热带和温带地区大范围天气和气候预报的技能，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.