It is difficult for coarse‐resolution global models of the atmosphere to accurately simulate the observed distribution of low clouds. In particular, it is difficult for moist turbulence closure models to simulate sufficiently bright near‐coastal stratocumulus (Sc) without simulating overly bright marine shallow cumuli (Cu). To parameterize bright Sc, a turbulence parameterization must damp the turbulent fluxes of heat and moisture above cloud top in order to prevent excessive entrainment of dry air into cloud top. To parameterize dim shallow Cu, the subgrid variances of temperature and moisture must remain large, in order to permit partial cloudiness. However, damping the fluxes but not the variances just above cloud top is difficult if a parameterization uses a single “master” time scale to damp both. In nature, the above‐cloud fluxes are damped by pressure fluctuations, whereas scalar variances are damped by a different process, namely, turbulent dissipation. In a stably stratified inversion above cloud, pressure damping is large but turbulent dissipation is small. To avoid this problem, a multitime scale parameterization for damping has been developed. The damping parameterization has been implemented in a global model and evaluated. The parameterization is capable of dimming shallow Cu while producing adequately bright Sc.

中文翻译：

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稳定分层反演中湍流耗散和压力阻尼时间尺度的参数化及其在整体模拟中对低云的影响

粗略的全球大气模型很难准确地模拟观测到的低云分布。特别是，潮湿湍流闭合模型很难模拟足够明亮的近海岸平流层积云（Sc）而不会模拟过于明亮的海洋浅层积云（Cu）。为了参数化明亮的Sc，湍流参数化必须抑制云层上方的热和湿气的湍流，以防止干燥空气过多地夹带到云层中。为了参数化暗淡的Cu，温度和湿度的子网格变化必须保持较大，以允许部分混浊。但是，如果参数化使用单个“主”时间标度来同时衰减这两者，则很难衰减通量，而不能衰减仅在云顶上方的变化。在自然界，上面的通量受压力波动的影响而衰减，而标量方差受另一过程（即湍流耗散）的影响而衰减。在云层上方稳定分层的反演中，压力阻尼较大，但湍流耗散较小。为了避免这个问题，已经开发了用于阻尼的多次标度参数化。阻尼参数化已在全局模型中实现并进行了评估。参数化能够使浅铜变暗，同时产生足够明亮的Sc。阻尼参数化已在全局模型中实现并进行了评估。参数化能够使浅铜变暗，同时产生足够明亮的Sc。阻尼参数化已在全局模型中实现并进行了评估。参数化能够使浅铜变暗，同时产生足够明亮的Sc。