科学研究证明,沙源的形成是一个相当长的过成,其中自然力起的作用是主要的。据对深海岩心和冰盖沉积物的测定,早在白垩纪末(距今7000万年)就有风沙尘暴出现,我国最早的记录可以追溯到公元前205年。在漫长的地质历史中沙尘暴显示出周期性变化,它与地质时期气候变化和地面沙尘物质的消长有关,遇气候暖湿时期地面植被生长茂密,生态环境条件好,沙尘暴发生频率低;反之,在冷干气候时期,则沙尘暴发生频率高。我国从公元前205年以来有85%以上的沙尘暴都发生在3~5月份,而且多出现于春季的午后。这是由于春季是全年中空气冷暖变化最剧烈的季节,午后到傍晚之前又是一天中气温最高的时段,更容易造成空气层结的不稳定。沙尘的肆虐,就在于对流层低层存在着强烈的垂直方向的不稳定和强对流。另外,春季北方地区气温陡然回升,大地解冻,同时干旱少雨,地表干燥松软,不论是耕地还是荒漠草原,均无植被覆盖而裸露无遗,为沙尘暴的发生提供了丰富的沙尘源。
Scientific research has proved that the formation of sand source is a long-term over formation, in which natural forces play a major role. According to the determination of deep-sea cores and ice sheet sediments, sandstorms appeared as early as the end of Cretaceous (70 million years ago), and the earliest record in China can be traced back to 205 BC. In the long geological history, sandstorm shows periodic change, which is related to the climate change in geological period and the fluctuation of ground dust material. In the warm and humid climate period, the ground vegetation grows luxuriantly, the ecological environment conditions are good, and the frequency of sandstorm is low; on the contrary, in the cold and dry climate period, the frequency of sandstorm is high. Since 205 BC, more than 85% of sandstorms in China have occurred in March to may, and most of them occur in the afternoon of spring. This is because spring is the season with the most violent change of air temperature in the whole year. From afternoon to evening, it is the period with the highest temperature in the day, which is more likely to cause the instability of air stratification. The rampant of dust lies in the strong vertical instability and strong convection in the lower troposphere. In addition, in spring, the temperature in the northern region rises sharply, the land thaws, and the surface is dry and soft with little rain. No matter in cultivated land or desert grassland, there is no vegetation coverage and bare, which provides a rich source of sand and dust for the occurrence of dust storms.
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