Impact of a Mixed Ocean Layer and the Diurnal Cycle on Convective Aggregation.
Impact of a Mixed Ocean Layer and the Diurnal Cycle on Convective Aggregation.
复制标题
混合海层和昼夜周期对对流聚集的影响。
DOI：
10.1029/2020ms002186
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发表时间：
2021-12
影响因子：
6.8
通讯作者：
Semie AG
中科院分区：
文献类型：
--
作者：
Tompkins AM;Semie AG
我们研究如何海洋反馈和昼夜循环的影响对流聚集使用板状海洋耦合到云解析模式。对于20米的混合层海洋，聚集发生在25天后。较薄的海洋层减缓了集群的开始，1米的海洋层需要大约43天。这一延迟是由于晴朗天空区域的异常太阳辐射，导致相对的表面变暖，并被多云地区的匹配冷却所平衡。由此产生的地表热通量梯度会阻碍低层辐合进入对流区。在聚集，对流区域被包围的潮湿，晴朗的天空区域与最热的SST，对流迁移，而冷SST补丁下形成干燥的抑制区域，由于增强的潜热通量和长波辐射。下一个实验允许域平均SST的2.5°C的日周期。这导致对流降雨从一个微弱的早晨最大值转变为一个尖锐的晚上峰值，让人想起未受干扰的热带观测。然而，对流恢复到一个弱的清晨最大一旦聚集开始由于空间异质辐射强迫。这意味着薄的混合海洋层是下午对流最大值的必要但非充分条件;有限的空间水汽变率也是必要的。施加的平均昼夜周期没有统计学上的显着影响的平均时间集群发病。相互作用的SST通过短波云强迫和潜热通量减缓对流聚合的开始。减缓聚合的开始也是高度可变的，正如弱强迫双稳态随机系统所预期的那样。允许平均表面温度的日周期对聚合时间没有显着影响。
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. Interactive SSTs acts to slow the onset of convective aggregation, via shortwave cloud forcing and latent heat fluxes Slower aggregation onset is also highly variable, as expected for a weakly forced, bi‐stable stochastic system Allowing a diurnal cycle in the mean surface temperature has no significant impact on aggregation timing