Geography knowledge: Why is it sunny when the fog is heavy in the morning?

Does fog have anything to do with sunny days? What does it matter? To understand these problems, we must start with the causes of fog.

Fog refers to the ice crystals condensed by tiny water droplets or water vapor suspended in the air near the ground when the temperature drops. According to the data, according to the causes, fog is generally divided into four types: ① radiation dance. On a clear, windless or breezy night, ground radiation cooling condenses water vapor in the air layer near the ground. The fog is thickest before sunrise, and gradually dissipates or rises to stratus with the increase of ground temperature after sunrise. Its thickness is generally 100-200m, and the thinnest is only 2-3m. ② advection fog. Warm air moves to the colder underlying surface, and the water vapor under it condenses into fog. The emergence, disappearance and development of advection fog mainly depend on the characteristics of warm and humid advection. Generally speaking, it has a wider range, greater thickness, longer time and less obvious diurnal variation than radiation fog. Advection fog is formed when tropical warm and humid air mass migrates in high latitude and cold areas in winter. When the continental warm air mass moves to the colder sea surface in spring and summer; In winter and autumn, when the warm ocean air mass moves to the colder land; When the warm and humid air on the ocean moves to the intersection of the cold sea surface and the cold and warm ocean currents. ③ Evaporation fog. When the cold air moves to the warmer water surface, the water surface evaporates faster, making the water vapor saturated and forming fog. ④ frontal fog. It is a fog formed by the evaporation of rainfall before the warm front and the saturation of the lower air.

Obviously, the "fog" referred to here should be "radiation fog". It is formed because on a clear night, there is no cloud or partial cloudy, the atmospheric inverse radiation is weak, and the ground insulation effect is poor. The intense radiation cooling on the ground makes the water vapor in the atmosphere near the ground condense and form fog when it is cold. At the same time, because there is no cloud and it is partly cloudy, the weakening effect of the atmosphere on solar radiation is reduced, especially the reflection effect of clouds is weakened, and more solar radiation directly reaches the ground, so the temperature is higher and the weather is sunny in most days.