![]() The rest of the study is organized as follows. Such high-spatiotemporal-resolution measurements allow us to study spatiotemporal features, intensity, and mechanisms of SFP. Here, we use 22 automatic weather stations (AWSs) to obtain hourly SFP distribution in the Qingdao region for the first time. Detailed processes associated with SFP need further studies, preferably using high-resolution observations. However, the former cannot describe the spatial distribution of SFP and the latter can neither detect fog under higher cloud covers nor accurately separate fogs from low clouds ( Zhang and Yi, 2013). On the other hand, previous studies used sparse observations to explore SFP in Qingdao (e.g., Diao, 1992), such as data from a single sounding station ( Fu et al., 2008) or satellite ( Yi et al., 2015). However, how the winds modulate the SFP processes in the Qingdao region remains unclear. If the southerlies are persistent and strong enough, the fog or the moist air parcel may be advected northward to the Qingdao area, causing the occurrence of SFP. The Yellow sea fog is typical advection fog, occurring when prevailing southerlies transport moist and warm air from low latitude northward to the sea surface ( Sugimoto et al., 2013 Gao et al., 2016). Previous studies show that springtime fog in Qingdao is often associated with sea fog over the Yellow Sea ( Fu et al., 2008 Gao et al., 2007 Zhang et al., 2012). ![]() Considering different atmospheric circulations and features of fog from spring to summer, we only focus on spring in this study. The fog in Qingdao exhibits distinct seasonal variations that are highest during spring and summer. Qingdao ( Figure 1), a coastal city with a population of close to 10 million, experiences a high fog frequency in spring, for about 50 days every year ( Zhang et al., 2009). Moreover, many works studied coastal fog and synoptic meteorological conditions and its life cycle, also improving the understanding of SFP ( Dorman et al., 2021 Fernando et al., 2021 Gultepe et al., 2021). In addition to topography effects, SFP is affected by the land environment because a dry, warm, and unstable atmosphere over land tends to dissipate SFP ( Koračin et al., 2014). Along the coasts of California and Chile, SFP is promoted by persistent onshore wind but blocked by mountain ranges further inland ( Cereceda et al., 2002 Johnstone and Dawson, 2010). Over the Korean Peninsula, when cold sea fog penetrates into warm land, a weak land–sea temperature contrast promotes SFP ( Lee and Chang, 2018). In Scotland, the sea breeze determines SFP strength and dissipation ( Findlater et al., 1989). ![]() SFP occurs in coastal regions worldwide, though its causes may differ. The accuracy of predicting SFP events could reach 50–80%, which highlights the predictability of intensity of SFP in Qingdao. Considering that moistening leads SFP by about a day, we use this relationship to predict the intensity of SFP. The strength of SFP depends on the strength of daytime anomalous moistening. The daytime anomalous moistening, together with the following diurnal cooling at night, saturates the surface atmosphere and, hence, facilitates SFP. We further use reanalysis data to reveal that during the daytime before SFP, strong moisture advection at 925–975 hPa brings sufficient water vapor from the Yellow Sea to Qingdao the water vapor then transfers downward to the surface via background descending motion and turbulent mixing. Results show that these SFP events often penetrate inland areas from southeast to northwest and last 5–8 h at night. Based on hourly observations from buoys and automatic weather stations distributed in Qingdao and its adjacent islands, we composite SFP events to reveal their spatiotemporal features and to investigate the mechanisms involved. Qingdao, an international port city with a dense population, suffers from SFP originating over the Yellow Sea in the boreal spring (March–May) the process, however, is not well-studied. SFP can cause traffic accidents and other economic losses. Sea fog often penetrates adjacent coastal areas, a process called sea fog penetration (SFP). 6National Meteorological Centre, Beijing, China.5Qingdao National Laboratory of Marine Science and Technology, Qingdao, China. ![]() 4Ocean-Atmosphere Interaction and Climate Laboratory, Ocean University of China, Qingdao, China.3Qingdao Meteorological Bureau, Qingdao, China.2Physical Oceanography Laboratory, Ocean University of China, Qingdao, China.1Frontiers Science Center for Deep Ocean Multispheres and Earth System, Ocean University of China, Qingdao, China.Shu-Tong Song 1,2 Xiao-Meng Shi 3 Su-Ping Zhang 2,4 Xian-Yao Chen 1,2,5 Yun-Chuan Xue 3 Wei Zhao 6 Chao Yang 6 Bin Huang 6 Li Yi 1,2*
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