There are four seasons of dew, only a special winter. Early in the morning, look at the rice tops in the fields; the roadside fields will detect the glittering dew. Especially on the spider web, the dewdrops are as shimmering as a string of pearls.
In the old days, people thought that dew water was very precious. They think that dew is not only falling from the sky but also coming from distant stars. But ancient monopolists paid attention to collecting dew. They believe that it is essential to be trained in precious stones or longevity pills. Some people even take dew water as medicine; drink a lot of dew can ward off diseases to increase longevity.
Later the truth of the mist was clarified. The dew water is not falling from the sky, not even from distant stars, but they are just steam in the cold lower air that forms. In everyday life, we often see the following phenomenon, in winter, when you breathe into the glass on the window, you will see tiny water droplets on the glass. In the summer, if you put ice cream in a glass cup, you will find that there is a small layer of water droplets on the inside of the cup. These water droplets are caused by water vapor in the cold air that condenses to form.
On bright nights with no clouds, the ground heat is lost very quickly; the humidity of the air in the field quickly drops. If the air temperature is reduced, the air’s ability to hold water vapor becomes weaker. The water vapor in the lower air will cling to the tops of grass and leaves into tiny water droplets. Dew was formed like that.
Why is the weather clear when there is fog? This is because dew formation requires certain weather conditions, i.e., high-pressure control, small wind, clear sky, little clouds, and heat loss on the ground very quickly. When the temperature is lowered, when steam hits cold places, mist forms.
Why is there no fog on cloudy or windy nights? On cloudy nights, the ground seems to be covered with a cotton blanket, so it is difficult for the heat to diffuse into the air, moreover one part of the heat that rises meets the cloud and returns to the ground, the other absorbed by clouds. The amount of heat absorbed by clouds is then gradually radiated back to the ground. So clouds are like the ceiling of a room; it protects the heat. Therefore, on cloudy nights, the air temperature near the ground is difficult to cool down, so no mist can form.
Windy nights cause the upper and lower air to exchange with each other, increasing the air layer’s temperature near the ground, and at the same time, diffusing water vapor, making it difficult for the mist to form.
In agriculture, dew is very beneficial to plants and crops. Dew water is like rainwater that loosens the soil, allowing plants to grow.