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Precipitation-generated oscillations in open cellular cloud fields

机译：在开放的细胞云场中降水产生的振荡

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摘要

Cloud fields adopt many different patterns that can have a profound effect on the amount of sunlight reflected back to space, with important implications for the Earth's climate. These cloud patterns can be observed in satellite images of the Earth and often exhibit distinct cell-like structures associated with organized convection at scales of tens of kilometres. Recent evidence has shown that atmospheric aerosol particles-through their influence on precipitation formation-help to determine whether cloud fields take on closed (more reflective) or open (less reflective) cellular patterns. The physical mechanisms controlling the formation and evolution of these cells, however, are still poorly understood6, limiting our ability to simulate realistically the effects of clouds on global reflectance. Here we use satellite imagery and numerical models to show how precipitating clouds produce an open cellular cloud pattern that oscillates between different, weakly stable states. The oscillations are a result of precipitation causing downward motion and outflow from clouds that were previously positively buoyant. The evaporating precipitation drives air down to the Earth's surface, where it diverges and collides with the outflows of neighbouring precipitating cells. These colliding outflows form surface convergence zones and new cloud formation. In turn, the newly formed clouds produce precipitation and new colliding outflow patterns that are displaced from the previous ones. As successive cycles of this kind unfold, convergence zones alternate with divergence zones and new cloud patterns emerge to replace old ones. The result is an oscillating, self-organized system with a characteristic cell size and precipitation frequency.
机译：云场采用许多不同的模式，这些模式可能对反射回太空的太阳光量产生深远影响，这对地球的气候具有重要影响。这些云模式可以在地球的卫星图像中观察到，并且通常在数十公里的尺度上表现出与有组织对流相关的独特的细胞状结构。最近的证据表明，大气气溶胶颗粒通过其对降水形成的影响，有助于确定云场是处于封闭的（反射率更高）还是开放的（反射率更低）细胞模式。然而，控制这些细胞形成和进化的物理机制仍然知之甚少6，这限制了我们实际模拟云对全球反射率的影响的能力。在这里，我们使用卫星图像和数值模型来显示降水云如何产生开放的蜂窝云模式，该模式在不同的弱稳定状态之间振荡。振荡是降水造成的结果，导致向下运动并从先前为正浮力的云中流出。蒸发的降水驱使空气向下流到地球表面，在那里它发散并与邻近的沉淀细胞的流出相撞。这些相撞的流出物形成了表面收敛带和新的云层。反过来，新形成的云产生降水和新的碰撞流出模式，这些模式与以前的模式不同。随着此类连续周期的展开，会聚区与发散区交替出现，并且出现了新的云模式以取代旧的云模式。结果是一个振荡的，自组织的系统，具有特征的细胞大小和沉淀频率。

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  • 来源
    《Nature》 |2010年第7308期|P.849-852ⅲ|共5页
  • 作者

    Graham Feingold; Man Koren; Hailong Wang; Huiwen Xue; Wm. Alan Brewer;

  • 作者单位

    NOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, Colorado 80305, USA;

    rnDepartment of Environmental Sciences, Weizmann Institute, Rehovot 76100, Israel;

    rnPacific Northwest National Laboratory, Richland, Washington 99352, USA;

    rnDepartment of Atmospheric Sciences, School of Physics, Peking University, 5 Yiheyuan Road, Beijing 100871, China;

    rnNOAA Earth System Research Laboratory (ESRL), Chemical Sciences Division, Boulder, Colorado 80305, USA;

  • 收录信息 美国《科学引文索引》(SCI);美国《工程索引》(EI);美国《生物学医学文摘》(MEDLINE);美国《化学文摘》(CA);
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