Frost conditions

"Frost" doesn't fall from the sky, but the water vapor on the ground condenses when it meets cold weather. Frost will appear in autumn, winter and spring. Frost is formed by the condensation of water vapor in the air close to the ground directly on or near the ground; The lower the temperature, the greater the air density and the greater the specific gravity.

With the flow of air, the coldest and heaviest air will flow to the lowest place, and after reaching the lowest place (depression), it will gradually accumulate and condense into frost. Therefore, depressions are usually more prone to frost than ordinary places, and plants in depressions are particularly prone to frost. ?

The meteorological conditions for dew and frost are sunny and breezy nights. Clear skies at night are conducive to the rapid radiation cooling of the ground or ground objects. Breeze can fully cool radiation in the thick gas layer, and can also replace the air close to the ground to ensure sufficient water vapor condensation. When there is no wind, there is not much water vapor condensation. When the wind speed is too high, the turbulence is too strong, which makes the air close to the ground strongly mix with the warmer air in the upper layer, which leads to the slow cooling of the air close to the ground, which is not conducive to the formation of dew and frost.

For frost, besides radiation cooling, it is beneficial to its formation after cold advection or when cold air gathers at low pressure. This kind of frost is called advection frost or low pressure frost, and they are often strengthened by radiation cooling. Therefore, frost often occurs in depressions and valleys. Frost is not common in waterside plains and forest areas. ?

Ground condensation is an important part of weather phenomena. It is a phenomenon that water vapor condenses from the air and onto objects or the ground (China Meteorological Bureau, 2003). Common ground condensation phenomena include dew and frost. "first frost" and "first frost" and "first frost" are not the same thing, but three different concepts.

"Frost" refers to a white ice crystal formed by condensation of water vapor on the ground in cold weather; "Frost" refers to a common agricultural meteorological disaster phenomenon; The "first frost" solar term refers to the season that reflects the sudden drop of temperature, while the "first frost" does not mean "frosting", but refers to the cold weather. From a scientific point of view, the saying that "dew becomes frost" is not accurate.

The frozen dew formed by dew freezing is hard small ice beads. Frost refers to the phenomenon of crop freezing injury caused by the sudden drop of temperature, and its harmful temperature varies with crops, varieties and growth periods. To form frost, the temperature of the ground or ground objects must drop below 0℃, and the water vapor content in the air in the ground should reach a certain standard.

Therefore, there may not be frost in first frost, and there may not be frost in first frost. However, due to the low temperature during frost, if the temperature continues to drop, it will easily lead to frost.