Fog is defined as a weather phenomenon in which small water droplets suspended close to the Earth's surface cause visibility to drop below 1000 meters (WMO, 1992). From a scientific and socioeconomic perspective, fog is of great importance as an internal regulator of the climate system, a barrier to traffic, and its association with compromised air quality [Jmark, 2008]. For example, fog disasters shorten the sunshine hours, reduce the light and efficiency of green plants, and reduce crop yields; urban fog contains a large amount of industrial pollutants, which contribute to the formation of acid fog [Wu et al, 2009]. In addition, the foggy weather also seriously affects the operation efficiency of many open-pit industrial and mining enterprises, causing huge losses [Li et al, 2008]. Fog also has a direct impact on human life. The occurrence of dense fog is often accompanied by the formation of a temperature inversion layer, which leads to the accumulation of pollutants in the air and aggravates the harm of air pollution. Long-lasting dense fog is conducive to the breeding and spread of viruses and bacteria [Li et al, 2008]. In addition to these negative effects, fog may also be beneficial to humans. For example, the high water vapor content of fog provides an important freshwater resource in the Atacama Desert along the coastline [Lukas et al, 2018]. Frequent fog is also critical for local human social activities because fog water is collected to meet industrial needs [Lukas et al, 2019]. In addition, fog also has certain ecological effects. For example, fog is an important driver and major prerequisite for epiphyte richness in tropical montane cloud forests (Obregon et al, 2014). As a water source for vegetation in arid regions (Pinto et al, 2001, Henschel et al, 2008, Lehnert et al, 2018), in Taiwan Montane Cloud Forest (MCF) as a major regulator of the entire ecosystem ( Li H. J. et al, 2015), and through the spatial and temporal patterns of fog that significantly affect species distribution and dynamics in California coastal ecosystems (Licia et al, 2015).
Due to all these factors, there is a growing need for spatially accurate data on fog distribution and for a more precise understanding of the various meteorological drivers that govern fog formation and dissipation processes. Especially considering human-induced climate change (IPCC, 2014) (e.g. urbanization, increased atmospheric drought due to the greenhouse effect), changes in the frequency distribution of fog and low-level clouds over time and space can be expected in the future, which is very important May vary by fog type, geographic location and meteorological conditions (Egli et al, 2019).
This study is an initial effort to use satellite imagery to understand the temporal and spatial variation of fog and low cloud observed in central and eastern China. For this, eight years of satellite data products were used. With hourly data of fog and low cloud cover (FLCC) stripped from the H8 cloud detection product, we generate an 8-year-long daytime FLCC product from 2015 to 2022. Explicit analyses on diurnal, monthly, seasonal and annual scales are further performed in this paper. In addition, seasonal/seasonal/annual climate data were taken into account to assess future trends in the FLCC.