Clouds are one of the key factors influencing the evolution of the planetary boundary layer (PBL). Understanding the complex interactions between clouds and PBL height (PBLH) is essential for accurately simulating and predicting PBL processes. This study investigates the impact of clouds on PBLH evolution based on the lidar, radiosonde, ceilometer, and meteorological parameters observations at the Southern Great Plains site during the period January 2013 to December 2020. The findings indicates that the presence of clouds has an impact on the evolution of the PBLH. During the daytime, PBLH is lower under cloudy conditions than clear conditions, whereas during nighttime, PBLH is higher under cloudy conditions. This phenomenon arises because the intense solar radiation on clear days and strong turbulent mixing on cloudy nights contribute to the formation and maintenance of PBLH. Furthermore, during the daytime, clouds scatter and absorb solar radiation, leading to lower net radiation (NetR), sensible heat flux (SHF), surface temperature (TEM), and soil temperature (SoilT). These conditions, coupled with weaker turbulence intensity and high relative humidity (RH), leading to lower PBLH under cloudy conditions. Although TEM and SoilT are relatively high during clear nights, rapid surface radiative cooling and strong atmospheric stability inhibit the development of the PBLH. Consequently, during cloudy nights, clouds absorb and reflect longwave radiation from the surface, reducing surface radiative cooling rates, enhancing atmospheric instability and turbulence intensity. Furthermore, higher NetR and SHF, along with decreased RH, result in slightly deeper PBLH compared to clear conditions. Overall, this study systematically elucidates the influence of clouds on PBLH evolution and contributes to the understanding of the modulation of cloud on PBL structure.

中文翻译：

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云对行星边界层高度的影响：比较研究与因素分析


云是影响行星边界层 （PBL） 演变的关键因素之一。了解云与 PBL 高度 （PBLH） 之间的复杂相互作用对于准确模拟和预测 PBL 过程至关重要。本研究基于 2013 年 1 月至 2020 年 12 月期间南部大平原站点的激光雷达、无线电探空仪、云高仪和气象参数观测，调查了云对 PBLH 演变的影响。研究结果表明，云的存在对 PBLH 的演变有影响。白天，多云条件下的 PBLH 低于晴朗的天气，而在夜间，多云条件下的 PBLH 较高。之所以出现这种现象，是因为晴天时的强烈太阳辐射和多云夜晚的强烈湍流混合有助于 PBLH 的形成和维持。此外，在白天，云层会散射并吸收太阳辐射，导致净辐射 （NetR）、显热通量 （SHF）、表面温度 （TEM） 和土壤温度 （SoilT） 较低。这些条件，再加上较弱的湍流强度和高相对湿度 （RH），导致多云条件下的 PBLH 较低。虽然在晴朗的夜晚TEM和SoilT相对较高，但快速的表面辐射冷却和强大的大气稳定性抑制了PBLH的发展。因此，在多云的夜晚，云会吸收和反射来自表面的长波辐射，从而降低表面辐射冷却速率，增强大气不稳定性和湍流强度。此外，与清除条件相比，较高的 NetR 和 SHF 以及较低的 RH 导致 PBLH 略深。 总体而言，本研究系统阐明了云对 PBLH 演变的影响，并有助于理解云对 PBL 结构的调制。