Cirrus clouds triggered by radiation, a multiscale phenomenon
Cirrus clouds triggered by radiation, a multiscale phenomenon
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由辐射引发的卷云，一种多尺度现象
DOI：
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发表时间：
2010
期刊：
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通讯作者：
P. Spichtinger
中科院分区：
文献类型：
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作者：
F. Fusina;P. Spichtinger
抽象的。在这项研究中，辐射冷却和小涡旋对卷云形成的影响进行了研究。为此目的，非流体静力学，滞弹性模型EULAG与最近开发和验证的冰微物理方案（Spichtinger和Gierens，2009年a）。此外，我们实现了一个快速辐射传递代码（Fu等人，1998年）。在理想化的剖面中，冰的过饱和度高达144%，而在过饱和层中，布伦特-维萨拉频率低至0.0018 s−1，辐射对卷云形成的影响是显著的。由于冰过饱和层顶部的辐射冷却，冷却速率降至−3.5 K/d，冰过饱和层内部的稳定性随时间而降低。在不稳定过程中，由高斯温度波动引起的小涡流开始生长并触发第一次成核。由于辐射不稳定，这些第一次成核事件然后诱导对流单体的生长。由于辐射和绝热抬升的冷却，增加当地相对湿度的影响导致形成的卷云IWC高达33毫克/立方米，平均光学厚度高达0.36。在更稳定的环境中，辐射冷却不足以在8小时内使过饱和层不稳定;在这种情况下不会发生成核。只有当过饱和层因辐射冷却而不稳定时，通过辐射的卷云的整体触发才会起作用，这样小涡旋的振幅可以增长，最终初始化冰核。这两种不同尺度的过程，小尺度涡旋和大尺度辐射冷却都是必要的。
Abstract. In this study, the influence of radiative cooling and small eddies on cirrus formation is investigated. For this purpose the non-hydrostatic, anelastic model EULAG is used with a recently developed and validated ice microphysics scheme (Spichtinger and Gierens, 2009a). Additionally, we implemented a fast radiative transfer code (Fu et al., 1998). Using idealized profiles with high ice supersaturations up to 144% and weakly stable stratifications with Brunt-Vaisala frequencies down to 0.0018 s−1 within a supersaturated layer, the influence of radiation on the formation of cirrus clouds is remarkable. Due to the radiative cooling at the top of the ice supersaturated layer with cooling rates down to −3.5 K/d, the stability inside the ice supersaturated layer decreases with time. During destabilization, small eddies induced by Gaussian temperature fluctuations start to grow and trigger first nucleation. These first nucleation events then induce the growth of convective cells due to the radiative destabilization. The effects of increasing the local relative humidity by cooling due to radiation and adiabatic lifting lead to the formation of a cirrus cloud with IWC up to 33 mg/m3 and mean optical depths up to 0.36. In a more stable environment, radiative cooling is not strong enough to destabilize the supersaturated layer within 8 h; no nucleation occurs in this case. Overall triggering of cirrus clouds via radiation works only if the supersaturated layer is destabilized by radiative cooling such that small eddies can grow in amplitude and finally initialize ice nucleation. Both processes on different scales, small-scale eddies and large-scale radiative cooling are necessary.