![Fog shrouds among many cities around China](../../images/attachement/jpg/site1/20110222/0023ae6cf3690ecd6ce110.jpg)
Redisential buildings stand among the advection fog in Yantai city, east China's Shandong province, Feb 21, 2011. The advection fog occurs when moist air passes over a cool surface by advection (wind) and is cooled. It is common as a warm front passes over an area with significant snowpack. [Photo/CFP] |