Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field
Effects of 3-D thermal radiation on the development of a shallow cumulus cloud field
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DOI：
10.5194/acp-17-5477-2017
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发表时间：
2017-04
影响因子：
6.3
通讯作者：
C. Klinger;B. Mayer;F. Jakub;T. Zinner;Seung-Bu Park;P. Gentine
中科院分区：
文献类型：
--
作者：
C. Klinger;B. Mayer;F. Jakub;T. Zinner;Seung-Bu Park;P. Gentine
抽象。本文利用UCLA-LES模式研究了热辐射对云发展的影响。我们调查单个对流云（由温暖的气泡驱动）在50米的水平分辨率和一个大的积云场在50和100米的水平分辨率。我们比较了新发展的3-D相邻柱近似与独立柱近似和无辐射的模拟以及它们各自对云的影响。热辐射引起云顶强烈的局部冷却，伴随着云底的适度变暖，在三维方案的情况下，也有云侧冷却。当在模型域上平均时，3-D热辐射引起系统性更大的冷却。为了研究局部冷却对云的影响，并将这些局部影响与建模域中系统性较大的冷却效应分开，我们以不同的方式应用辐射传输解决方案。在第一次模拟中应用了云的加热和冷却的直接效果（局部热辐射）。此外，在每一层的1-D和3-D辐射的水平平均被用来研究当地云辐射的影响，而不是域平均的效果。这些平均辐射模拟显示出在多云层中具有更强冷却的冷却轮廓。在最后的设置中，我们用2.6 K day − 1的均匀冷却代替辐射模拟。为了关注辐射效应本身并避免可能的反馈，我们在模拟中固定了潜热和感热的表面通量，并省略了降雨的形成。局部热辐射通过引起更强的上升气流和更强的下沉壳来改变单云模拟以及浅积云场中的云环流。在我们的积云场模拟中，我们发现，本地辐射增强环流相比，平均辐射的应用。此外，我们发现热辐射以两种不同的方式触发云的组织。首先，局部相互作用的辐射导致细胞结构的形成;后来，更大的云发展。比较了三维和一维热辐射的组织效应，我们发现三维局部热辐射的组织效应通常比一维的强。水平平均辐射比没有辐射的模拟产生更多的云和更深的云，但一般来说，云的组织比当地辐射模拟少。在模拟中应用恒定的冷却会导致云场的类似发展，就像平均辐射的情况一样，但是在模拟中总体上凝结的水更少。一般来说，如果考虑到辐射，云含有更多的液态水。此外，热辐射增强了湍流和混合以及云的大小和寿命。局部的热辐射产生更大的云，具有更长的寿命。云场在100和50米的分辨率模拟发展相似，但是，3-D的本地效果更强的100米的模拟，这可能表明我们的3-D辐射参数化的限制。
Abstract. We investigate the effects of thermal radiation on cloud development in large-eddy simulations (LESs) with the UCLA-LES model. We investigate single convective clouds (driven by a warm bubble) at 50 m horizontal resolution and a large cumulus cloud field at 50 and 100 m horizontal resolutions. We compare the newly developed 3-D Neighboring Column Approximation with the independent column approximation and a simulation without radiation and their respective impact on clouds. Thermal radiation causes strong local cooling at cloud tops accompanied by a modest warming at the cloud bottom and, in the case of the 3-D scheme, also cloud side cooling. 3-D thermal radiation causes systematically larger cooling when averaged over the model domain. In order to investigate the effects of local cooling on the clouds and to separate these local effects from a systematically larger cooling effect in the modeling domain, we apply the radiative transfer solutions in different ways. The direct effect of heating and cooling at the clouds is applied (local thermal radiation) in a first simulation. Furthermore, a horizontal average of the 1-D and 3-D radiation in each layer is used to study the effect of local cloud radiation as opposed to the domain-averaged effect. These averaged radiation simulations exhibit a cooling profile with stronger cooling in the cloudy layers. In a final setup, we replace the radiation simulation by a uniform cooling of 2.6 K day−1. To focus on the radiation effects themselves and to avoid possible feedbacks, we fixed surface fluxes of latent and sensible heat and omitted the formation of rain in our simulations. Local thermal radiation changes cloud circulation in the single cloud simulations, as well as in the shallow cumulus cloud field, by causing stronger updrafts and stronger subsiding shells. In our cumulus cloud field simulation, we find that local radiation enhances the circulation compared to the averaged radiation applications. In addition, we find that thermal radiation triggers the organization of clouds in two different ways. First, local interactive radiation leads to the formation of cell structures; later on, larger clouds develop. Comparing the effects of 3-D and 1-D thermal radiation, we find that organization effects of 3-D local thermal radiation are usually stronger than the 1-D counterpart. Horizontally averaged radiation causes more clouds and deeper clouds than a no radiation simulation but, in general less-organized clouds than in the local radiation simulations. Applying a constant cooling to the simulations leads to a similar development of the cloud field as in the case of averaged radiation, but less water condenses overall in the simulation. Generally, clouds contain more liquid water if radiation is accounted for. Furthermore, thermal radiation enhances turbulence and mixing as well as the size and lifetime of clouds. Local thermal radiation produces larger clouds with longer lifetimes. The cloud fields in the 100 and 50 m resolution simulations develop similarly; however, 3-D local effects are stronger in the 100 m simulations which might indicate a limit of our 3-D radiation parameterization.