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Factors Affecting Entrainment Rate in Deep Convective Clouds and Parameterizations
Journal of Geophysical Research: Atmospheres ( IF 4.4 ) Pub Date : 2021-07-22 , DOI: 10.1029/2021jd034881
Xiaoqi Xu 1 , Cheng Sun 1, 2 , Chunsong Lu 1 , Yangang Liu 3 , Guang Jun Zhang 4 , Qian Chen 1
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The parameterization of cloud entrainment rate has been problematic for many years, hindering the accurate representation of convective processes in large-scale models. Here, we extend our previous work on individual shallow convection to ensemble deep convection. Entrainment rate is estimated based on three-dimensional convective clouds from August 19 to 20, 1999, during the Kwajalein Experiment, simulated using a high-resolution cloud-resolving model. They are found to be negatively correlated with both vertical velocity and buoyancy, and positively correlated with the vertical divergence of the vertical velocity and with the reciprocal of cloud radii. The physical mechanisms underlying these relationships are interpreted. It is found that the parameterizations with multiple properties perform better than those with a single property. Entrainment rate and relative humidity of entrained air are positively correlated at temperature higher than 0°C, but negatively correlated at temperature lower than 0°C. Relative humidity is also included in the parameterization of entrainment rate, which differs from our previous work on shallow cumulus clouds and other studies. Finally, two forms of parameterization for entrainment rate are recommended. The first treats the entrainment rate as a function of the vertical velocity and buoyancy for temperature higher than 0°C, but as a function of relative humidity and buoyancy for temperature lower than 0°C. The second involves an equation that relates entrainment rate to vertical velocity and buoyancy regardless of temperature.

中文翻译:

影响深对流云中夹带率的因素和参数化

云夹带率的参数化多年来一直存在问题,阻碍了大规模模型中对流过程的准确表示。在这里,我们将之前关于单个浅对流的工作扩展到集合深对流。夹带率是根据 1999 年 8 月 19 日至 20 日在夸贾林实验期间使用高分辨率云解析模型模拟的三维对流云估算的。发现它们与垂直速度和浮力均呈负相关,与垂直速度的垂直发散度和云半径的倒数呈正相关。解释了这些关系背后的物理机制。发现具有多个属性的参数化比具有单个属性的参数化表现更好。夹带速率与夹带空气的相对湿度在温度高于 0°C 时呈正相关,而在温度低于 0°C 时呈负相关。相对湿度也包含在夹带率的参数化中,这与我们之前对浅积云和其他研究的工作不同。最后,推荐两种形式的夹带率参数化。第一种方法将夹带率视为温度高于 0°C 时垂直速度和浮力的函数,但视为温度低于 0°C 时相对湿度和浮力的函数。第二个涉及将夹带率与垂直速度和浮力联系起来的方程,而不管温度如何。但在低于 0°C 的温度下呈负相关。相对湿度也包含在夹带率的参数化中,这与我们之前对浅积云和其他研究的工作不同。最后,推荐两种形式的夹带率参数化。第一种方法将夹带率视为温度高于 0°C 时垂直速度和浮力的函数,但视为温度低于 0°C 时相对湿度和浮力的函数。第二个涉及将夹带率与垂直速度和浮力联系起来的方程,而不管温度如何。但在低于 0°C 的温度下呈负相关。相对湿度也包含在夹带率的参数化中,这与我们之前对浅积云和其他研究的工作不同。最后,推荐两种形式的夹带率参数化。第一种方法将夹带率视为温度高于 0°C 时垂直速度和浮力的函数,但视为温度低于 0°C 时相对湿度和浮力的函数。第二个涉及将夹带率与垂直速度和浮力联系起来的方程,而不管温度如何。推荐两种形式的夹带率参数化。第一种方法将夹带率视为温度高于 0°C 时垂直速度和浮力的函数,但视为温度低于 0°C 时相对湿度和浮力的函数。第二个涉及将夹带率与垂直速度和浮力联系起来的方程,而不管温度如何。推荐两种形式的夹带率参数化。第一种方法将夹带率视为温度高于 0°C 时垂直速度和浮力的函数,但视为温度低于 0°C 时相对湿度和浮力的函数。第二个涉及将夹带率与垂直速度和浮力联系起来的方程,而不管温度如何。
更新日期:2021-08-03
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