The effect of atmospheric radiative heating by clouds on the Madden-Julian Oscillation
The effect of atmospheric radiative heating by clouds on the Madden-Julian Oscillation
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DOI：
10.1002/2015ms000434
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发表时间：
2015-06-01
影响因子：
6.8
通讯作者：
Stevens, Bjorn
中科院分区：
文献类型：
--
作者：
Crueger, Traute;Stevens, Bjorn
本文探讨了由于云的存在而导致的大气辐射加热如何影响由四个综合大气环流模型模拟的马登-朱利安振荡 (MJO)。将云对电磁辐射透明的模拟（“云关闭”）与允许云与辐射相互作用的控制模拟（“云开启”）进行比较。使云层对辐射透明会导致平均状态的剧烈变化：赤道印度太平洋地区的西风减弱，降水显示从单热带辐合带转变为双热带辐合带。这些变化伴随着 MJO 的减弱。此外，降水的湿度敏感性会发生变化，但在我们的模型组中并不一致。进一步的分析表明，在季节内变化的活跃阶段，与无云相比，云辐射效应放大了加热剖面。非辐射过程的加热主要由参数化对流主导，但与作用在网格尺度上的云微物理过程相关的大规模加热改变了加热剖面的形状，在考虑云辐射效应时导致头重脚轻。云造成的辐射加热减慢了 MJO 的相速度。在整个 MJO 生命周期中平均，由云引起的柱积分辐射加热滞后于垂直积分湿静态能量 408-608 个经度（相当于 7-10 天，假设周期为 60 天）。研究的所有四个模型都显示，当云对辐射透明时，开尔文波更加明显，这表明云对大范围加热剖面的辐射效应会抑制较小规模或更快的开尔文波，并放大类似 MJO 的扰动。
This article explores how atmospheric radiative heating, due to the presence of clouds, influences the Madden-Julian Oscillation (MJO) as simulated by four comprehensive atmosphere general circulation models. Simulations in which clouds are transparent to electromagnetic radiation ("clouds-off'') are compared with control simulations in which clouds are allowed to interact with radiation ("clouds-on''). Making clouds transparent to radiation leads to robust changes of the mean state: the westerly winds in the equatorial Indo-Pacific area weaken and the precipitation reveals a shift from single to double Intertropical Convergence Zones. These changes are accompanied by weaker MJOs. Also, the moisture sensitivity of precipitation changes, however not consistently within our group of models. Further analyses show that within the active phase of intraseasonal variability, cloud-radiative effects amplify the heating profiles compared to clouds-off. Heating from nonradiative processes is dominated by the parameterized convection, but large-scale heating associated with cloud microphysical processes acting on the grid-scale modifies the shape of the heating profile, leading to a top-heaviness when cloud-radiative effects are accounted for. The radiative heating due to clouds slows down the phase speed of the MJO. Averaged over the entire MJO life cycle, the column-integrated radiative heating due to clouds lags the vertically integrated moist static energy by 408-608 of longitude (equivalently 7-10 days assuming a period of 60 days). All four models studied reveal more pronounced Kelvin waves when clouds are transparent to radiation, suggesting that cloud-radiative effects on large-scale heating profiles damp smaller scale, or faster, Kelvin waves and amplify MJO-like disturbances.