How is the frost formed?

Freezing means that the temperature of soil or plant surface drops sharply to the temperature that causes crop injury or death during the growing season of plants.

There are frequent cold air activities in spring and autumn in Xinjiang, and the temperature changes are very unstable. Autumn frost often comes too early, and spring frost often ends late, which leads to different degrees of frost all over Xinjiang over the years. The main crops affected are corn, sorghum, rice, cotton, potatoes, vegetables and fruits.

I. Standards

Different crops or the same crop have different low temperature tolerance at different development stages, but the critical temperature of most thermophilic crops is around 0℃. In order to simplify the frost index, when analyzing the climate law of frost, the daily minimum temperature of 0℃ is used as the index.

Second, the occurrence time and geographical distribution

(1) First frost date

The first frost in Xinjiang is almost always related to the invasion of a strong cold air or cold wave. The average first frost days are generally in late September and early June 10 in Altay and Tacheng, northern Xinjiang, early June 10 in Ili Valley and along Tianshan Mountains, late June and first half of June 1 10 in northeastern Xinjiang, and late June in southwestern Xinjiang and Turpan. Maonaohu Depression in the south of Dongjiang River and Yiwu County is in the middle of 10, and Barkun Basin is in early September. The average first frost day in northern Xinjiang is about 1 month earlier than that in southern Xinjiang. The difference between the average date of the first frost and the earliest date can reach half a month to 1 month in northern Xinjiang and l0 ~ 20 days in southern Xinjiang and eastern Xinjiang. The longest difference between the earliest and latest dates of the first frost in northern Xinjiang is nearly 2 months, and the shortest difference is more than half a month, generally around 1 month, and the longest difference in southern Xinjiang is 1 month to 1 half a month (see Table 3-4 in Part III). When the first frost occurs, immature crops will be affected, such as cotton, late-maturing corn and replanted corn, fruits and vegetables. The influence of the first frost on crops is more serious than that of the last frost, and the loss is also greater.

(2) the date of the last frost

The final frost is mainly caused by cold air activity in northern Xinjiang, and it is caused by cold air activity and radiation cooling in southern Xinjiang. The average final frost date is early May in Altay and Tacheng, mid-April in Ili Valley and along Tianshan Mountains, mid-March in eastern southern Xinjiang, mid-late March in southwestern southern Xinjiang and Turpan, mid-April in Naomaohu depression in Yiwu county and mid-May in Barkun basin. The average final frost date in northern Xinjiang is about 1 month later than that in southern Xinjiang. The difference between the average date and the latest date of the final frost is generally from half a month to 1.5 months in northern Xinjiang and from 1 month to 1.5 months in southern Xinjiang. The difference between the earliest and latest dates of the final frost is even greater, with the longest 74 days and the shortest 29 days in northern Xinjiang, generally around 40 days. If the first day when the daily average temperature stably passes through l0℃ is taken as the start date of sowing date of warm-loving crops, the final frost date will appear before sowing of warm-loving crops in most areas and years in Xinjiang, and the final frost date will appear after sowing of warm-loving crops in a few areas, but the crops have not yet emerged.