Tropical Intraseasonal Variability in an "Aqua Planet" GCM

有强有力的理论证据表明，大气中的麦登-朱利安（30-60天）振荡是由于对流和环流之间的相互作用。PI将在一个海洋覆盖地球（“水行星”）的完全非线性环流模式中研究这些相互作用的特征。对该模式的初步试验表明，在10-15天的周期内，该模式向东方传播较强。振荡在对流层上层被赤道捕获，振幅最大。扰动似乎同时表现出开尔文波和罗斯比波的特征，这可能表明扰动是耦合的开尔文-罗斯比波。提出了一个假设，即对流加热的垂直剖面决定了模型和实际大气中观测到的传播相速度。结果表明，由糖尿病加热激发的相互作用的垂直模式导致传播波- cisk模式。PI将在“水行星”环流模型中严格检验这一假设。在观测中，最慢的模式对最温暖的水域的优先刺激是不能用假设充分解释的。pi还将研究振荡对海面温度纬向不对称的敏感性。对流的空间尺度很小，而环流中的振荡发生在行星尺度上。最后，pi将通过分析波数域的模型能量随时间的变化，研究纬向尺度的选择以及旋转动能和发散动能之间的耦合。本文的研究将有助于进一步认识大尺度大气环流与对流相互作用的特征。

There is strong theoretical evidence that the Madden-Julian (30-60 day) oscillation in the atmospheric is due to interactions between convection and circulation. The PI will study the characteristics of these interactions in a fully nonlinear general circulation model with an ocean covered earth ("aqua-planet"). Preliminary experiments with the model show strong eastward propagation at periods between 10-15-days. The oscillation is equatorially trapped with maximum amplitude in the upper troposphere. The disturbances appear to exhibit both Kelvin and Rossby wave characteristics, possibility suggesting that the disturbances are coupled Kelvin-Rossby waves. The hypothesis has been put forth that the vertical profile of convective heating defines the phase speed of propagation observed in the model and the real atmosphere. It is suggested that interacting vertical modes excited by the diabetic heating lead to propagating wave-CISK modes. The PI will critically examine this hypothesis in the "aqua-planet" general circulation model. The preferential excitement of the slowest modes over the warmest waters in the observations is inadequately explained by the hypothesis. The PIs will also study the sensitivity of oscillations to zonal asymmetries in the sea surface temperatures. The spatial scale of the convection is very small whereas the oscillations in the circulation occur on the planetary scale. Finally, the PIs will study the zonal scale selection and the coupling between the rotational and divergent kinetic energy by an analysis of the model energetics in the wave number domain as a function of time. It is expected that the proposed research will provide a better understanding of the characteristics of the interactions between convection and large scale atmospheric circulation.