Transient Aggregation of Convection: Observed Behavior and Underlying Processes
Transient Aggregation of Convection: Observed Behavior and Underlying Processes
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对流的瞬态聚集：观察到的行为和潜在过程
DOI：
10.1175/jcli-d-19-0933.1
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发表时间：
2021
影响因子：
4.9
通讯作者：
Stein Thorwald H. M.
中科院分区：
文献类型：
--
作者：
Masunaga Hirohiko;Holloway Christopher E.;Kanamori Hironari;Bony Sandrine;Stein Thorwald H. M.
对流自聚集是辐射-对流平衡模拟中出现的最显著的特征之一，但它与在真实大气中观测到的对流扰动的相关性仍然存在争议。这项工作寻求云团生命周期中固有的对流聚集观测信号。为此，简单对流聚集指数(SCAI)和来自卫星测量的其他变量的合成时间序列是围绕降水量的时间极大值构建的。所有分析的参数都是10°×10°区域的大尺度平均值。强降水区域的合成演变表明，随着降水的增加，云团在±12h内聚集成较少的成员。随着星系团数量的减少，每个星系团的高云量也随之扩大，这意味着对流聚集的发生是暂时的。在弱降水区域，瞬时聚集的迹象不太明显或完全不存在。执行能量预算分析以搜索作为瞬时聚集基础的物理过程。柱状湿静力能量(MSE)在降水峰值前积累，之后消散，主要由水平MSE平流所占。区域平均柱体辐射冷却在聚集度较高的复合体中比在聚集度较低的复合体中更大，尽管辐射对流反馈在这背后的作用尚不清楚。
Convective self-aggregation is among the most striking features emerging from radiative–convective equilibrium simulations, but its relevance to convective disturbances observed in the real atmosphere remains under debate. This work seeks the observational signals of convective aggregation intrinsic to the life cycle of cloud clusters. To this end, composite time series of the Simple Convective Aggregation Index (SCAI), a metric of aggregation, and other variables from satellite measurements are constructed around the temporal maxima of precipitation. All the parameters analyzed are large-scale means over 10° × 10° domains. The composite evolution for heavy precipitation regimes shows that cloud clusters are gathered into fewer members during a period of ±12 h as precipitation picks up. The high-cloud cover per cluster expands as the number of clusters drops, suggesting a transient occurrence of convective aggregation. The sign of the transient aggregation is less evident or entirely absent in light precipitation regimes. An energy budget analysis is performed in search of the physical processes underlying the transient aggregation. The column moist static energy (MSE) accumulates before the precipitation peak and dissipates after, accounted for primarily by the horizontal MSE advection. The domain-averaged column radiative cooling is greater in a more aggregated composite than in a less aggregated one, although the role of radiative–convective feedback behind this remains unclear.