Radiative Convective Equilibrium and Organized Convection: An Observational Perspective
Radiative Convective Equilibrium and Organized Convection: An Observational Perspective
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辐射对流平衡和有组织对流：观测视角
DOI：
10.1029/2018jd030092
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
L. Jungandreas
中科院分区：
文献类型：
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作者：
C. Jakob;M. S. Singh;L. Jungandreas
辐射对流平衡（RCE）描述了辐射冷却大气与潜热释放和表面热通量加热之间的平衡。虽然众所周知，RCE 在全球范围内对大气提供了能量约束，但人们对较小空间和时间尺度上的大气与 RCE 的接近程度知之甚少，尽管 RCE 在理想化建模研究中经常使用。在这里，我们对大气接近 RCE 的尺度进行了首次观测评估。我们进一步利用云特征的观测来研究有组织对流在 RCE 状态中所扮演的角色。虽然热带大气整体在每日时间尺度上接近 RCE 甚至更长，但对于任何给定位置而言情况并非如此。相反，必须考虑超过 5,000 × 5,000 km2 的区域，以确保大气层至少在 80% 的时间内保持在 RCE 附近，即使在月平均条件下也是如此。我们确认，RCE 是通过具有高降水和弱辐射冷却的活跃深对流区域与导致浅云状态的沉降运动区域（允许强辐射冷却但没有降水）的相互作用而建立的。最大辐射冷却和潜热加热的不对称导致了在热带地区观察到的众所周知的小面积降水和大面积沉降的比例。最后，我们表明，当 RCE 附近小于 1,000 × 1,000 km2 的区域时，不会发生有组织的深层对流。
Radiative convective equilibrium (RCE) describes a balance between the cooling of the atmosphere by radiation and the heating through latent heat release and surface heat fluxes. While RCE is known to provide an energetic constraint on the atmosphere at the global scale, little is known about the proximity of the atmosphere to RCE at smaller spatial and temporal scales, despite the common use of RCE in idealized modeling studies. Here we provide the first observational evaluation of the scales at which the atmosphere is near RCE. We further use observations of cloud characteristics to investigate the role played by organized convection in the RCE state. While the tropical atmosphere as a whole is near RCE on daily time scales and longer, this is not the case for any given location. Rather, areas in excess of 5,000 × 5,000 km2 must be considered to ensure the atmosphere remains near RCE at least 80% of the time, even for monthly averaged conditions. We confirm that RCE is established through the interplay of regions of active deep convection with high precipitation and weak radiative cooling and regions of subsiding motions leading to shallow cloud states that allow strong radiative cooling with no precipitation. The asymmetry in the maximum amount of radiative cooling and latent heating leads to the well‐known ratio of small areas of precipitation and large regions of subsidence observed in the tropics. Finally, we show that organized deep convection does not occur when regions smaller than 1,000 × 1,000 km2 are near RCE.