In autumn and winter, due to the long nights, Feng Yun appears frequently, and the ground heat dissipation is faster than that in summer, which leads to a sharp drop in the ground temperature, so that the water vapor in the air near the ground can easily reach saturation in the middle of the night, condense into small water droplets and form fog. The morning temperature in autumn and winter is the lowest and the fog is the thickest.
Extended data:
And haze.
1, the horizontal visibility is different. The horizontal visibility of fog is less than 1000 m, and that of haze is less than 10 km.
2. The relative humidity is different. The relative humidity of fog is more than 90%, and that of haze is less than 80%. 80% ~ 90% of relative humidity is a mixture of haze and fog, but its main component is haze.
3, the thickness varies. The thickness of fog is only about tens of meters to 200 meters, and the thickness of haze can reach 3000 meters.
4. The boundary features are different. The boundary of fog is very clear, and the "fog area" may be clear Wan Li; There is no clear boundary between smog and clear sky.
5. Different colors. Fog is milky white and bluish white, haze is yellow and orange gray.
6. Different formation conditions. Although the formation of fog and haze requires a breeze or no wind, the atmospheric state is stable, that is, there must be an inversion layer, but fog needs certain water vapor and cooling conditions to make the air saturated and condense; The formation of smog does not need water vapor and cooling conditions, mainly because the (dry) particles in the air should reach a certain concentration and the relative humidity should not be large.
7. The ingredients are different. Fog is mainly composed of tiny water droplets or ice crystals, and the size of water droplets is generally 3 ~ 100 micron. Smog is composed of complex tiny particles invisible to the naked eye, and the diameter of smog particles is only 0.3 ~ 0.6 micron.
8. The changes are different every day. Fog usually appears most easily from midnight to early morning, and dissipates quickly after sunrise. The diurnal variation characteristics of haze are not obvious. When the air mass changes little and the atmospheric stratification is stable, it lasts for a long time.