Minimal Mechanisms Responsible for the Dispersive Behavior of the Madden–Julian Oscillation

IF 3 Q2 METEOROLOGY & ATMOSPHERIC SCIENCES Climate Pub Date : 2023-11-29 DOI:10.3390/cli11120236
Kartheek Mamidi, Vincent Mathew
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Abstract

An attempt has been made to explore the relative contributions of moisture feedback processes on tropical intraseasonal oscillation or Madden–Julian Oscillation (MJO). We focused on moisture feedback processes, including evaporation wind feedback (EWF) and moisture convergence feedback (MCF), which integrate the mechanisms of convective interactions into the tropical atmosphere. The dynamical framework considered here is a moisture-coupled, single-layer linear shallow-water model on an equatorial beta-plane with zonal momentum damping. With this approach, we aimed to recognize the minimal physical mechanisms responsible for the existence of the essential dispersive characteristics of the MJO, including its eastward propagation (k>0), the planetary-scale (small zonal wavenumbers) instability, and the slow phase speed of about ≈5 m/s. Furthermore, we extended our study to determine each feedback mechanism’s influence on the simulated eastward dispersive mode. Our model emphasized that the MJO-like eastward mode is a possible outcome of the combined effect of moisture feedback processes without requiring additional complex mechanisms such as cloud radiative feedback and boundary layer dynamics. The results substantiate the importance of EWF as a primary energy source for developing an eastward moisture mode with a planter-scale instability. The eastward moisture mode exhibits the highest growth rate at the largest wavelengths and is also sensitive to the strength of the EWF, showing a significant increase in the growth rate with the increasing strength of the EWF; however, the eastward moisture mode remains unstable at planetary-scale wavelengths. Moreover, our model endorses that the MCF alone could not produce instability without surface fluxes, although it has a significant role in developing deep convection. It was found that the MCF exhibits a damping mechanism by regulating the frequency and growth rate of the eastward moisture mode at shorter wavelengths.
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导致马登-朱利安振荡分散行为的最基本机制
人们试图探索水汽反馈过程对热带季内振荡或马登-朱利安涛动(MJO)的相对贡献。我们重点研究了水汽反馈过程,包括蒸发风反馈(EWF)和水汽辐合反馈(MCF),它们将对流相互作用机制纳入了热带大气。这里考虑的动力学框架是一个赤道β平面上的水汽耦合单层线性浅水模型,具有带状动量阻尼。通过这种方法,我们旨在认识导致 MJO 基本弥散特征存在的最基本物理机制,包括它的向东传播(k>0)、行星尺度(小的地带性波数)不稳定性和约≈5 m/s 的慢相速。此外,我们还扩展了研究范围,以确定每种反馈机制对模拟的向东扩散模式的影响。我们的模式强调,类似 MJO 的东向模式是水汽反馈过程综合作用的可能结果,而不需要额外的复杂机制,如云辐射反馈和边界层动力学。研究结果证明了 EWF 作为主要能量源对形成具有植物尺度不稳定性的东向水汽模式的重要性。东向水汽模式在最大波长处表现出最高的增长率,而且对 EWF 的强度也很敏感,随着 EWF 强度的增加,增长率显著增加;然而,东向水汽模式在行星尺度波长处仍然不稳定。此外,我们的模型还证实,虽然 MCF 在发展深对流方面具有重要作用,但如果没有表面通量,MCF 本身并不能产生不稳定性。研究发现,在较短波长上,MCF 通过调节东向水汽模式的频率和增长率,表现出一种阻尼机制。
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来源期刊
Climate
Climate Earth and Planetary Sciences-Atmospheric Science
CiteScore
5.50
自引率
5.40%
发文量
172
审稿时长
11 weeks
期刊介绍: Climate is an independent, international and multi-disciplinary open access journal focusing on climate processes of the earth, covering all scales and involving modelling and observation methods. The scope of Climate includes: Global climate Regional climate Urban climate Multiscale climate Polar climate Tropical climate Climate downscaling Climate process and sensitivity studies Climate dynamics Climate variability (Interseasonal, interannual to decadal) Feedbacks between local, regional, and global climate change Anthropogenic climate change Climate and monsoon Cloud and precipitation predictions Past, present, and projected climate change Hydroclimate.
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