The difference between the first frost and the first frost
On the surface, the first frost seems to be getting colder and colder, and it begins to frost. To be exact, frost does not fall from the sky, but is white loose ice crystals formed by condensation of water vapor in the air near the ground or on the ground. With the arrival of the first frost, crops that are not hardy have been harvested or will soon stop growing, and the vegetation has begun to turn yellow, showing a scene of late autumn.
Frost means that the surface temperature of soil or the temperature near plant canopy drops to zero in a short time at night during the growing season. Below c, the surface temperature of plants drops rapidly, the water in plants freezes, the metabolic process is destroyed, and cells are squeezed by ice cubes, causing damage.
When frost occurs, plants are hurt because of low temperature, not just because frost hurts plants. If the relative humidity of the air is low, you may not see the frost, and it will also frost. Usually, people also call frost-free frost black frost.
It can be seen that the first frost and first frost are two different concepts, and the first frost is only a solar term; Frost is related to plant damage. Where there are no plants, there will be no frost. According to the frost season, it can be divided into early frost and late frost.
Early frost, also known as autumn frost, refers to the frost that occurs when autumn crops are immature and vegetables are not harvested in the open field. As the season goes on, the frequency and intensity of autumn frost increase gradually.
Late frost, also known as spring frost, is the frost that occurs after spring sowing crops are in seedling stage, fruit trees are in flowering stage and overwintering crops turn green. With the increase of temperature, the frequency and intensity of late frost gradually decrease, but the later it appears, the greater the harm to crops.
Due to the difference of topography, altitude and latitude, the starting and ending time of frost varies from place to place. Generally speaking, the first frost (autumn frost) begins to appear. The higher the altitude, the earlier the latitude, and the earlier the low-lying (valley) land, and vice versa. The end time of late frost (that is, spring frost), the lower the altitude, the earlier the latitude, and the earlier the sloping land is than the low-lying land, and vice versa.
There are three forms of frost:
(1) advection frost. Cooling to 0 due to strong cold air intrusion? C or 0? Frost below c, wide attack range and large cooling range.
(2) radiation cream. On a clear, windless or breezy night, radiation cooling reduces the temperature of ground or near-earth objects to 0? C or 0? Below c, causing frost. This frost occurs in a relatively small area.
(3) Advection radiation cream. Frost caused by cold advection and radiation cooling. This frost has a serious impact. In addition, some areas also produce a depression (valley) frost. At night, the air near the surface layer cools down, and the cold air on the slope slides down, accumulating in depressions or valleys to form frost, which appears more than in autumn. This is consistent with the Qinghai agricultural proverb "Frost hits depression".