Fog and clouds are condensation of small water droplets or ice crystals floating in the air, but fog is formed in the near-surface layer of the atmosphere, while clouds are formed in the upper layer of the atmosphere. Since fog is a condensation of water vapor, its cause should be found from the conditions that cause condensation of water vapor. There are no more than two reasons why water vapor in the atmosphere reaches saturation. The other is the cooling of the air itself. Cooling is more important for fog. Condensation occurs when there is a condensation nucleus in the air. Fog is formed when condensed water droplets reduce horizontal visibility to less than 1 km. That's why most mountain mists form.
At the same time, the mountain in winter is called valley fog. The weather turns cold, and the heavy cold air gradually accumulates in the valley. If the warm air passes through the mountain at this time, the temperature will increase in reverse, and the collision between the cold and warm air will form tiny water vapor that can float in the air, forming valley fog. Moreover, due to the weak air circulation in the valley, it tends to last for several days, which requires high humidity and sufficient moisture.
The reason for this cloud - shrouded scene, is not easy to see in the ordinary hillside, most occurred in the mountains. This is because a wide range of fog, the surrounding moist air must be stable, that is, the slope of the slope must be small, otherwise the formation of convection, mountain fog is difficult to form.
In addition, a kind of white smoke is formed because the mountain is rich in stone and minerals rich in calcium carbonate, magnesium carbonate and other substances. At the same time there is a certain amount of underground geothermal, from the cracks in the rock, cold formed fog. Finally formed, mountain mist wrapped around, like a fairyland scenery.