Entrainment versus Dilution in Tropical Deep Convection
Entrainment versus Dilution in Tropical Deep Convection
复制标题
DOI：
10.1175/jas-d-16-0169.1
复制
发表时间：
2017-11-01
影响因子：
3.1
通讯作者：
Hannah, Walter M.
中科院分区：
文献类型：
--
作者：
Hannah, Walter M.
卷吸和稀释之间的区别进行了研究与云解析模拟在热带环境中的深对流。本文提出了一种估算卷吸和卷吸稀释率的方法，并计算了一系列具有一定初始半径的气泡模拟。卷吸通常对应于对流的稀释，但这两个量并没有很好的相关性。由于堆芯周围有一层湿空气，卷吸引起的堆芯稀释作用大大减少。夹带稀释也随着上升气流速度的增加而增加，但只有在足够强的上升气流下。夹带有助于显着的总净稀释，但去除和各种源/汇条款发挥很大的作用，取决于变量的问题。平均而言，分离具有浓缩效应，其抵消了夹带造成的稀释。实验还考察了卷吸或稀释尺度与云半径的关系.结果支持弱负相关的稀释，但不夹带。简要讨论了分辨率的敏感性。一个玩具拉格朗日热模式被用来证明云壳作为一个热力学缓冲，以减少稀释的核心卷吸的重要性。结果表明，显式云的异质性可能是一个有用的考虑未来的对流参数化的发展。
The distinction between entrainment and dilution is investigated with cloud-resolving simulations of deep convection in a tropical environment. A method for estimating the rate of dilution by entrainment and detrainment is presented and calculated for a series of bubble simulations with a range of initial radii. Entrainment generally corresponds to dilution of convection, but the two quantities are not well correlated. Core dilution by entrainment is significantly reduced by the presence of a shell of moist air around the core. Dilution by entrainment also increases with increasing updraft velocity but only for sufficiently strong updrafts. Entrainment contributes significantly to the total net dilution, but detrainment and the various source/sink terms play large roles depending on the variable in question. Detrainment has a concentrating effect on average that balances out the dilution by entrainment. The experiments are also used to examine whether entrainment or dilution scale with cloud radius. The results support a weak negative relationship for dilution but not for entrainment. The sensitivity to resolution is briefly discussed. A toy Lagrangian thermal model is used to demonstrate the importance of the cloud shell as a thermodynamic buffer to reduce the dilution of the core by entrainment. The results suggest that explicit cloud heterogeneity may be a useful consideration for future convective parameterization development.