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

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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.