沙塵暴的形成需具備4個條件.
一是地面上的沙塵物質.它是形成沙塵暴的物質基礎.
二是大風.這是沙塵暴形成的動力基礎,也是沙塵暴能夠長距離輸送的動力保證.
三是不穩(wěn)定的空氣狀態(tài).這是重要的局地熱力條件.沙塵暴多發(fā)生于午后傍晚說明了局地熱力條件的重要性.
四是干旱的氣候環(huán)境.沙塵暴多發(fā)生于北方的春季,而且降雨后一段時間內不會發(fā)生沙塵暴是很好的證據(jù).
春季沙漠的邊緣地區(qū),由于長期干旱,而且地表少有植被覆蓋,當有大風來臨的時候地表的沙塵很容易被吹起且被輸移,但由于沙子粒徑較大,不易形成懸移(懸浮移動,是小顆粒物質保證長距離輸移的必要條件),因此不能長距離輸移,這也是距沙塵較遠的地區(qū)只有降塵而少見揚沙的主要原因.如果風持續(xù)的時間很長,形成懸移的浮塵能夠被輸送到很遠的地方,所經(jīng)過的地區(qū)就會出現(xiàn)沙塵暴；當風速減弱到一定程度后,浮塵就會降落,該地就會出現(xiàn)降塵天氣.如果此時降水,就會形成所謂的“泥雨”.
從沙塵暴形成過程所需的4個條件看,黃土高原、廣袤的沙漠及由人為因素的破壞正處于荒漠化過程中的土地,北方春季末耕種的土地及處于施工過程中的基礎設施(如高速公路等)為沙塵暴的發(fā)生提供了充分的物質源；而春季北方地區(qū)的干旱,又使沙塵暴發(fā)生的可能性增強；大風的產(chǎn)生是一種復雜的大氣現(xiàn)象,主要是冷鋒活動或經(jīng)緯向環(huán)流調整作用的結果.由此可見沙塵暴的產(chǎn)生是多種復雜因素共同作用結果,人類活動對自然界的破壞導致土地荒漠化的加劇,對沙塵暴發(fā)生產(chǎn)生了極其重要的作用,而近幾年全球干旱(其原因目前尚未知)等異常天氣現(xiàn)象也對沙塵暴的發(fā)生起了不可估量的作用.所以說人類活動對沙塵暴的產(chǎn)生只起到一定作用,并不能說沙塵暴就是人為因素造成的.
The formation of the sandstorm to have the four conditions.
One is the dust on the ground material.It is the material basis of form sandstorm.
2 it is winds.This is the power of the formation,is fundamental to the power of the sandstorm long-distance transport of guarantee.
Three is not stable air condition.This is an important local thermal conditions.Sandstorm occurs more often in the afternoon that incorporates the evening the importance of thermal condition.
Four is the dry weather environment.Born in the north of the sandstorm multiple spring,and rain after a period of time within a won't happen very good evidence is dust storms.
The edge of the desert in the spring,due to long drought,and surface vegetation cover,when there is little wind comes on the surface of the earth is easy to be blowing dust and sand,but due to lose move large particle size,is formed not easily movable (suspension movement,it is small particle material guarantee to lose the necessary conditions of long distance move),and therefore can not move long lost,this is far from the dust in the dust and rare only micrometeorology main reason.If the wind last time is very long,form the dust suspended loads can be transported to a very far place,through which areas will appear sandstorm; When the winds weaken to certain degree,floating dust will the landing,the dust weather will appear.If the precipitation,can form the so-called "NiYu".
The formation process from the four conditions look,the loess plateau and vast desert and by the destruction of the human factors in the process of desertification is in the land of the north,at the end of the spring farming land and in the construction process of infrastructure (such as high speed road,etc.) for the dust storm occurrence providing full source material; And the spring drought in the north,and the likelihood of the sandstorm strengthened; The winds generated is a complex phenomenon,mainly is the cold air activities or to the circulation of the regulatory role longitude results.This shows the generation of sandstorm is DuoZhong complex factors results of human activity on the natural world to disruption of the desertification intensifies,dust storms happen to have an important role,and in recent years the global drought (the cause isn't yet known) abnormal weather phenomenon also to the dust storm occurrence have played an important role.So that human activities for the generation of dust storms only play a role,and can't say dust storms are caused by human factors.