Partly hidden buildings are visible under a sea of fog in Qingdao city, East China's Shandong province, on the night of May 29, 2016. Advection fog, formed when warm and humid air is cooled after meeting cold land or water, often occurs in Qingdao city in spring. The advection fog, dense and usually covering a large area, can reach hundreds of meters. [Photo/chinadaily.com.cn]