We investigate how ocean feedbacks and the diurnal cycle impact convective aggregation using a slab ocean coupled to a cloud resolving model. With a 20 m mixed layer ocean, aggregation occurs after 25 days. Thinner ocean layers slow the onset of clustering, with a 1 m ocean layer needing around 43 days. The delay is due to anomalous solar radiation in clear sky regions, causing a relative surface warming balanced by a matching cooling in cloudy areas. The resulting gradient in surface heat fluxes opposes low level convergence into convecting regions. On aggregation, the convective regions are surrounded by moist, clear sky regions with the hottest SSTs, toward which convection migrates, while a cold SST patch forms under dry suppressed regions due to enhanced latent heat fluxes and longwave radiation. The next experiment allows a diurnal cycle of 2.5°C in the domain mean SST. This causes convective rainfall to shift from a weak morning maximum to a sharper evening peak, reminiscent of undisturbed tropical observations. However, convection reverts to a weak early morning maximum once aggregation starts due to spatially heterogeneous radiative forcing. This implies thin mixed ocean layers are a necessary but non-sufficient condition for an afternoon maximum of convection; limited spatial water vapor variability is also necessary. The imposition of the mean diurnal cycle has no statistically significant impact on the mean timing of clustering onset.

中文翻译：

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混合海洋层和日循环对对流聚集的影响

我们使用与云解析模型耦合的板状海洋来研究海洋反馈和日循环如何影响对流聚集。对于 20 m 的混合层海洋，25 天后会发生聚集。较薄的海层减缓了集群的开始，1 m 的海层需要大约 43 天。延迟是由于晴朗天空区域的异常太阳辐射，导致相对地表变暖被多云区域的匹配冷却平衡。由此产生的表面热通量梯度反对低水平会聚到对流区域。聚集时，对流区域被具有最热海温的潮湿、晴朗的天空区域所包围，对流向其迁移，而由于潜热通量和长波辐射增强，在干燥抑制区域下形成冷海温斑。下一个实验在域平均 SST 中允许 2.5°C 的昼夜循环。这导致对流降雨从较弱的早晨最大值转变为更尖锐的晚高峰，让人想起未受干扰的热带观测。然而，由于空间异质辐射强迫，一旦聚集开始，对流就会恢复到较弱的清晨最大值。这意味着薄的混合海洋层是下午最大对流的必要但不充分的条件；有限的空间水汽变异性也是必要的。平均昼夜周期的施加对聚类开始的平均时间没有统计学上的显着影响。由于空间异质辐射强迫，一旦聚集开始，对流就会恢复到较弱的清晨最大值。这意味着薄的混合海洋层是下午最大对流的必要但不充分的条件；有限的空间水汽变异性也是必要的。平均昼夜周期的施加对聚类开始的平均时间没有统计学上的显着影响。由于空间异质辐射强迫，一旦聚集开始，对流就会恢复到较弱的清晨最大值。这意味着薄的混合海洋层是下午最大对流的必要但不充分的条件；有限的空间水汽变异性也是必要的。平均昼夜周期的施加对聚类开始的平均时间没有统计学上的显着影响。