Fog - low stratus (FLS) regimes on Corsica with wind and PBLH as key drivers Atmospheric Research

The French Mediterranean island of Corsica is already today confronted with a clear tendency towards water shortage, leading not only to socio-economical, but also to ecological problems. A potential, but not very widespread source of water is the presence of near-ground clouds, mostly fog. In this study, we investigate fog-low stratus (FLS) frequencies in Corsica, derived from a data set of Meteosat Second Generation SEVIRI, whereby a distinction between fog and low stratus is hardly feasible using remote sensing data. The FLS frequency was studied with respect to its interaction with distinct locally-generated wind and its dependence on the planetary boundary layer height (PBLH) obtained by ERA5 reanalysis (the fifth generation of the European Centre for Medium-Range Weather Forecasts, ECMWF). Results show that radiation FLS is formed in coastal areas at sunrise, with low PBLH. On the other hand, in the interior of the island at sunset, a maximum of advection FLS is formed, fostered by locally-generated and related transport of moisture. On the east side of the island, FLS frequency is lower throughout the year due to frequent lee situations. This situation is reinforced by reduced synoptic moisture transport by westerly winds, so that westerly exposed slopes benefit from moisture input by FLS formation.

作为法国地中海岛屿的科西嘉岛，当前已面临显著的水资源短缺趋势，由此引发的不仅有社会经济问题，还包括生态层面的诸多困境。近地面云体（多为雾）是一种潜力未被充分发掘的非常规水资源。本研究依托第二代气象卫星（Meteosat Second Generation）SEVIRI的数据集，对科西嘉岛的雾-低云（fog-low stratus, FLS）出现频率展开探究；由于利用遥感数据难以区分雾与低云，因此本研究将二者统一归为FLS进行分析。本研究针对FLS出现频率与局地生成风场的相互作用，以及其对ERA5再分析资料（欧洲中期天气预报中心（ECMWF）第五代再分析产品）获取的行星边界层高度（PBLH）的依赖关系开展研究。研究结果表明，辐射型FLS多形成于日出时分的沿海区域，此时行星边界层高度较低。而在日落时分的岛屿内陆区域，平流型FLS的出现频率达到峰值，这类云体的形成得益于局地生成的水汽及其输送过程。在岛屿东侧，由于常年处于频繁的背风状态，FLS的全年出现频率均较低。西风带导致的天气尺度水汽输送减弱进一步加剧了这一状况，因此面向西风的坡地可通过FLS的形成获取水汽补给。