How spatial organization of clouds at the mesoscale contributes to the daily cycle of shallow cumulus clouds and precipitation is here explored, for the first time, using three years of high-frequency satellite- and ground-based observations. We focus on the four prominent patterns of cloud organization – Sugar, Gravel, Flowers and Fish – which were found recently to characterize well the variability of the North Atlantic winter trades. Our analysis is based on a simple framework to disentangle the parts of the daily cycle of trade-wind cloudiness that are due to changes in (a) the occurrence frequency of patterns, and (b) cloud cover for a given pattern. Our investigation reveals that the contribution of mesoscale organization to the daily cycle in cloudiness is largely mediated by the frequency of pattern occurrence. All forms of mesoscale organization exhibit a pronounced daily cycle in their frequency of occurrence, with distinct 24-hr phasing. The patterns Fish and Sugar can be viewed as daytime patterns, with a frequency peak around noon for Fish and towards sunset for Sugar. The patterns Gravel and Flowers appear instead as night-time patterns, with a peak occurrence around midnight for Gravel and before sunrise for Flowers. The cloud cover for a given pattern, however, always maximizes at night-time (between 0000 and 0300 hr), regardless of the specific pattern. Analyses of the role of large-scale environmental conditions shows that the near-surface wind speed can explain a large part of the diurnal variability in pattern frequency and cloudiness.

中文翻译：

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论冬季交易中尺度云组织的日周期

在这里，首次使用三年的高频卫星和地面观测，探索了中尺度云的空间组织如何影响浅积云和降水的日常周期。我们关注云组织的四种突出模式——糖、砾石、花和鱼——最近发现它们很好地表征了北大西洋冬季贸易的变化。我们的分析基于一个简单的框架，以分解由于 (a) 模式的发生频率和 (b) 给定模式的云量变化而导致的信风云量日周期部分。我们的调查表明，中尺度组织对云中日常周期的贡献在很大程度上取决于模式发生的频率。所有形式的中尺度组织在其发生频率上都表现出明显的每日周期，具有明显的 24 小时定相。鱼和糖的模式可以被视为白天模式，Fish 的频率峰值在中午左右，Sugar 的频率峰值接近日落。Gravel 和 Flowers 模式反而显示为夜间模式，Gravel 的峰值出现在午夜左右，而 Flowers的峰值出现在日出之前。但是，无论特定模式如何，给定模式的云量总是在夜间（0000 到 0300 小时之间）最大化。对大尺度环境条件作用的分析表明，近地表风速可以解释很大一部分模式频率和云量的日变化。