If the weather is always warm, such as sudden heavy snow in March and April, the temperature drops obviously, and frost will appear after the snow. In this way, crop seedlings can't stand the attack of low temperature and will wither and turn yellow. This is definitely harmful to crops; If at a certain time in spring, such as late spring and early spring, the weather is always cold and crops have certain cold resistance, then the Chun Xue under the tree can cover crops to keep warm. As soon as the sun came out, the weather became warmer. In this case, the damage to crops is not great.
So generally speaking, snow in early spring has little effect on crops; Snow after March-April has a great influence on crops. Spring is always warm. If there is a strong cold wave and heavy snow suddenly, it will do more harm to crops.
"Xue Rui heralds a bumper harvest year" is an agricultural proverb widely circulated in China. In the north, a thick layer of loose snow is like covering wheat with a quilt to keep out the cold. The cold nitrogen in snow is easily absorbed and utilized by crops. The low temperature of snow water can freeze the overwintering pests on the surface and bring benefits to agricultural production. So there is another agricultural proverb, "wheat covers three layers in winter and sleeps with steamed bread in the next year."
Snow has a wide range of functions, but it is of great benefit to mankind. First, it is beneficial to the growth and development of crops. Because of the poor thermal conductivity of snow, covering the soil surface with a layer of snow cover can reduce the diffusion of soil heat and block the invasion of cold air on the snow surface, so the crops protected by snow can survive the winter safely. Snow can also store water for crops. In addition, snow can enhance soil fertility. According to the determination, every 1 liter of snow water contains about 7.5 grams of nitride. Snow water permeates the soil, which is equivalent to applying nitrogen fertilizer once. Feeding livestock and poultry with snow water and irrigating crops can obtain obvious benefits.
Snow is both beneficial and harmful to people. In mid-spring in March and April, if it suddenly snows because of the cold wave. It will cause severe cold. Therefore, the agricultural proverb says, "La Xue is a treasure, but Chun Xue is not good."
Effects of Snow on Human Health
In winter, it snows endlessly. People often ignore the role of snow when watching Yushu Qionghua. Snow has many benefits to human health. Compendium of Materia Medica has long recorded that snow water can detoxify and cure the plague. There is a folk prescription for treating fire burns and frostbite with snow water.
Taking a bath with snow water often can not only enhance the resistance between skin and body, reduce diseases, but also promote blood circulation and enhance physical fitness. Drinking clean snow water for a long time can prolong life. This is one of the "secrets" of those who have lived in the deep mountains and forests for a long time.
Why does snow have such strange functions? Because snow water contains less heavy water than ordinary water 1/4. Heavy water will seriously inhibit the life process of living things. After testing, fish will die quickly in water containing 30-50% heavy water. The most basic condition for the formation of rain and snow is the existence of "condensation nuclei" in the atmosphere, and solid impurities such as dust, coal particles and minerals in the atmosphere are the most ideal condensation nuclei. If meteorological factors such as water vapor and temperature in the air reach certain conditions, water vapor will condense into snowflakes around these condensation nuclei. Therefore, snowflakes can clean a lot of pollutants in the air. So every time after the heavy snow, the air is particularly fresh.
According to the measurement, the density of new snow is generally 0.05-0. 10g per cubic centimeter. Therefore, the reflectivity of ground snow to sound waves is extremely low, which can absorb a lot of sound waves and help reduce noise.
Thermal insulation function of snow
Snow is like a wonderful carpet, covering the earth, so that the temperature of the ground will not drop too low because of the cold in winter. This heat preservation effect of snow is inseparable from its own characteristics.
As we all know, it is warm to wear a cotton-padded jacket in winter. Why is it warm to wear a cotton-padded jacket? This is because the porosity of cotton is very high, and the pores of cotton are filled with a lot of air, which has poor thermal conductivity. This layer of air prevents the heat of human body from spreading outward. The snow covering the breast of the earth is very similar to cotton, and the porosity between snowflakes is very high. It is this layer of air that drills into the pores of the snow to protect the ground temperature from falling very low. Of course, the thermal insulation function of snow changes with the density at any time. It's like wearing a new cotton-padded jacket, which is especially warm, and the old cotton-padded jacket is not very warm. The density of fresh snow is low, and there is a lot of air stored in it, so the heat preservation effect is particularly strong. Chen Xue is like an old cotton-padded jacket, with high density and weak heat preservation effect, because there is less air stored in it.
Why does the more air an object stores, the stronger the heat preservation effect?
This is because air is a bad conductor. As we know, any object itself can transfer heat, and this property of transferring heat is called the thermal conductivity of the object. Among several common substances in nature, air has the worst thermal conductivity. Therefore, the more air an object contains, the worse its thermal conductivity. Because the amount of air contained in snow changes greatly, the thermal conductivity of snow also changes greatly. Generally, the newly fallen snow has large pores and the best heat preservation effect. In the late stage of snow melting in spring, snow is soaked by water, and its thermal conductivity is closer to that of water, so the thermal insulation effect of snow tends to disappear.
nivation
Erosion caused by frequent melting and frost heaving of snowfields in periglacial climate. Snow erosion occurs in polar and sub-polar regions without ice sheets, as well as in alpine regions below the snow line and above the tree line. The annual average temperature there is about 0℃, which belongs to permafrost region. On the one hand, the alternate freezing and thawing of the edge of the snowfield destroys the surface material through ice cracking; On the one hand, snow melting will take away the crushed fine substances, so snow erosion includes two functions: denudation and transportation. With the deepening of the bottom of the snowfield and the expansion of its periphery, a wide and shallow basin-shaped concave land with small peripheral slope is gradually formed on the hillside, that is, the snow melting concave land. Its shape, origin and spatial distribution are different from those of ice buckets, but they are related. When the climate becomes cold and the snow line drops, the snow-eroded depression can develop into an ice bucket; On the contrary, when the climate warms and glaciers recede, ice buckets can degenerate into snow-melting depressions. Under different natural and geographical conditions, the way and speed of snow erosion are different. Where the latitude is low, the precipitation is high, and the freezing and thawing days are many, the snow erosion rate is faster, and the snow erosion is deep and large. For example, snow erosion is very common in Xiaoxing 'anling area of Northeast China. On the contrary, snow erosion is weak in places with high latitude, little precipitation and low temperature in summer. The influence of ground slope is: the slope is steep > 40, and the snow field is not easy to exist; Snow erosion on the flat land is slow; Snow erosion is most active on the slope of about 30.
Taking a bath with snow water often can not only enhance the resistance between skin and body, reduce diseases, but also promote blood circulation and enhance physical fitness. If you drink clean snow water for a long time, it will help you live longer. This is one of the "secrets" of the old people who have lived in the deep mountains and forests for a long time.
Why does snow have such strange functions? Because snow water contains less heavy water than ordinary water 1/4. Heavy water will seriously inhibit the life process of living things. According to experiments, fish will die quickly in water containing 30 ~ 50% heavy water. The most basic condition for the formation of rain and snow is the existence of "condensation nuclei" in the atmosphere, and solid impurities such as dust, coal particles and minerals in the atmosphere are the most ideal condensation nuclei. If meteorological factors such as water vapor and temperature in the air reach certain conditions, water vapor will condense into snowflakes around these condensation nuclei. Therefore, snowflakes can clean a lot of pollutants in the air. So every time after the heavy snow, the air is particularly fresh.
According to the measurement, the density of new snow is generally 0.05 ~ 0. 10g per cubic centimeter. Therefore, the reflectivity of ground snow to sound waves is extremely low, which can absorb a lot of sound waves and help reduce noise.