Low-Level Cloud Development and Diurnal Cycle in southern West Africa during the DACCIWA Field Campaign: Case Study of Kumasi Supersite, Ghana
Low-Level Cloud Development and Diurnal Cycle in southern West Africa during the DACCIWA Field Campaign: Case Study of Kumasi Supersite, Ghana
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DACCIWA 现场活动期间西非南部的低层云发展和昼夜周期：加纳库马西超级站点案例研究
DOI：
10.1002/essoar.10504072.1
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发表时间：
2020
期刊：
影响因子：
--
通讯作者：
Aryee J
中科院分区：
文献类型：
--
作者：
Aryee J
低层云的存在、空间范围和持续性在很大程度上影响着地面辐射和能量平衡以及区域气候。尽管如此，人们对其演变和进程的了解有限，特别是在西非南部。本文评价了低层积云的发展及其主要形成因素，以及它们与辐射和能量平衡的关系。首先，使用在DACCIWA(西非动力-气溶胶-化学-云相互作用)实地活动期间部署的Ceileter和无线电探空仪来识别有限责任公司。然后，用云分数来表征不同的LLC相。平均而言，LLC的分裂、消散和积聚分别出现在格林威治时间0900、1200GMT和2200GMT。此外，LLC的日演变及其与净辐射、能量储存和地表稳定性的关系的合成表明，LLCs通过减少下行短波辐射而显著影响净辐射通量。此外，LLC初始阶段的净辐射通量为近稳定状态，而低层的储能速率在平衡附近略有振荡。最后，通过对选定的密集观察期(IOP)的观察，评估了影响有限责任公司发展的主要因素。水平冷空气平流，加上夜间低空急流的加强，主要影响了研究期间低空急流的发展。这篇论文的发现对于改善对LLC特征、形成及其与表面属性的相互作用的理解是必要的，特别是在西非南部。
The presence, spatial extent and persistence of low-level clouds (LLCs) largely impact on the diurnal surface radiation and energy balance, as well as, the regional climate. Notwithstanding, there is limited understanding on their evolution and processes, particularly in southern West Africa. This paper assesses the development of LLCs and their dominant formative factors, as well as, their relationship with radiation and energy balance. Firstly, ceilometer and radiosondes deployed during the DACCIWA (Dynamics-Aerosol-Chemistry-Cloud Interactions in West Africa) field campaign were used in identifying the LLC. Afterwards, the cloud fraction was employed to characterize different LLC phases. Averagely, break-up, dissipation and build-up of LLC were marked at 0900 GMT, 1200 GMT and 2200 GMT respectively. Moreover, composites of LLC diurnal evolution and their relationship with net radiation, energy storage and surface stability showed that LLCs significantly impact on net radiation flux, by reducing downwelling shortwave radiation. Additionally, LLC onsets were characterized by a near-steady state in net radiation flux, whereas the rate of energy storage within the lower layers marginally oscillated about equilibrium. Finally, with observations from selected intensive observation periods (IOPs), the dominant factors influencing LLC development were evaluated. Horizontal cold air advection, with enhancement by nocturnal low-level jets, was observed to primarily influence the development of LLCs for the study period. Findings of this paper are necessary for improving the understanding of LLC characteristics, formation and interactions with surface properties, particularly over southern West Africa.