ABSTRACT: Cloud amounts, their spatial distribution, and the sky view factor (SVF) all have effects on the nocturnal upwelling longwave radiation and result in different degrees of urban-rural radiation cooling, which are widely investigated in studies of the urban heat island phenomenon. Currently, most research studies discuss the influence of synoptic conditions and urban geometric morphology on urban heat islands. Here we attempted to determine the influence of cloud cover on the relationship between the SVF and nocturnal urban heat islands by calculating the SVF considering the cloud amount and its distribution. The Adelaide central urban area of South Australia was selected as the study area, and we used urban 3-dimensional building data with a spatial resolution of 1 m and field measurement meteorological data, as well as ceilometer-observed cloud data. We sequentially analyzed the influence of cloud amount on the instantaneous nocturnal urban heat island intensity (UHII), SVF, and SVF-UHII relationship. The SVF-UHII feature space was then constructed to explain the nocturnal urban heat island. The results reveal that there are high negative correlations between the total cloud amount and UHII, while the correlations change with site location. The cloud amount has an effect on the defined SVF. SVFs at all sites gradually increase with the cloud amount, and the SVF differences between various sites decrease with increasing cloud amount. The SVF-UHII feature space can be preliminarily used to explain and simulate the UHII at some sites under different cloud cover conditions, and the mean relative error of the simulated UHII for the example data was 20%.

中文翻译：

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云量对夜视因子与夜间城市热岛关系的影响

摘要：云量，其空间分布和天空视野因子（SVF）均会影响夜间上升流的长波辐射，并导致不同程度的城乡辐射降温，这在城市热岛现象研究中已得到广泛研究。 。当前，大多数研究都讨论天气条件和城市几何形态对城市热岛的影响。在这里，我们尝试通过考虑云量及其分布来计算SVF，从而确定云量对SVF与夜间城市热岛之间关系的影响。选择南澳大利亚州阿德莱德市中心地区作为研究区域，我们使用了空间分辨率为1 m的城市3维建筑数据和实地测量气象数据，以及云高仪观测到的云数据。我们依次分析了云量对瞬时夜间城市热岛强度（UHII），SVF和SVF-UHII关系的影响。然后构造了SVF-UHII特征空间来解释夜间的城市热岛。结果表明，总云量与UHII之间存在很高的负相关性，而相关性随站点位置而变化。云量会对定义的SVF产生影响。所有站点的SVF随着云量的增加而逐渐增加，各个站点之间的SVF差异随着云量的增加而减小。可以使用SVF-UHII特征空间初步解释和模拟不同云量条件下某些站点的UHII，对于示例数据，模拟的UHII的平均相对误差为20％。