Why is the climate in Zhangjiakou cold, dry and windy? It is the source of sandstorm. Thank you, God, for helping me.

Zhangjiakou Climate Zhangjiakou is located in the northern part of Hebei Province, starting from 1 15 E50 in the west, 1 16 E30 in the east, 39n30 in the south and 42 N 10 in the north. Its climatic characteristics are: distinct seasons throughout the year, long cold winter; Spring is dry and windy; Summer is hot and short, and precipitation is concentrated; Autumn is sunny, the temperature is moderate, and it is warm and pleasant. Zhangjiakou is high in the northwest and low in the southeast. Bashang area in the north is adjacent to Inner Mongolia Plateau, with an altitude of 1400~ 1600 meters and a wide and flat terrain. The mountains are undulating and the terrain is complex. The main peak of Xiaowutai Mountain in Yuxian County in the south is 2870 meters high, and the Sanggan River and Yanghe River in the middle form a narrow valley basin. Its complicated geographical conditions make the weather and climate in Zhangjiakou extremely complicated, and there are many local disastrous weather, such as hail, heavy precipitation, strong wind and sandstorm. 1. Winter is cold and long. Zhangjiakou is located in the continental monsoon climate zone of East Asia, and the dry and cold winter wind blowing from the mainland to the ocean prevails in winter. Zhangjiakou is adjacent to the Inner Mongolia Plateau, with high terrain and a northerly position. Siberian cold air only rushes south, and our city bears the brunt. Therefore, winter is characterized by cold, dryness, abundant sunshine and little precipitation. Under the influence of strong cold air, there are often strong cooling, cold wave and windy weather, and sometimes there will be "white hair wind" on the dam. The winter in our city is controlled by the strong Mongolian high pressure for a long time, so the winter is cold and long. If the average temperature is below 10℃, it is winter, and below 0℃ it is severe winter. The winter in Chongli and Chicheng in Bashang and Basha alpine areas lasts for more than 7 months, about 5 months is severe winter, while the winter in dapu county under Basha lasts for 6 months and the severe winter lasts for nearly 4 months. Second, spring is dry and windy. In spring, the atmospheric circulation in Zhangjiakou is in the transition season between winter and summer, and the cold air is active. At the same time, the position of solar radiation gradually moved northward, and the energy received by the ground increased rapidly. When there is cold air activity, the cold and warm advection is very strong, which leads to the increase of ground pressure gradient. Therefore, often weak cold air will also cause obvious strong winds and strong cooling weather. Spring is the season with the strongest wind in the whole year, and the number of windy days accounts for about 40% of the number of windy days in the whole year. The warming temperature in spring increases the solar radiation energy near the surface, which on the one hand accelerates the thawing of the surface soil and makes the soil loose; On the other hand, due to the rapid temperature rise in the lower layer, unstable air stratification often occurs in the middle and lower layers when there is strong cold air activity. Driven by strong winds, ground dust is blown into the air, resulting in dusty weather, especially in areas with wide and flat terrain, sparse vegetation and more sand on the dam. Spring is the frequent season of sandstorm, and the spring sandstorm weather station accounts for 60~80% of the annual sandstorm weather. Third, summer is hot and short, and precipitation is concentrated. In summer, due to radiation warming and obvious weakening of cold air, warm air is strong and the temperature is high. However, due to the geographical environment of Zhangjiakou, the temperature changes in a wide range, which is cool in the morning and evening and hot at noon. According to the average temperature above 22 is summer, and above 30 is extremely hot. In Zhangjiakou, July is the hottest month in a year. The average temperature on the dam is 18~ 19 degrees, and it is 20~2 1 in Chongli and Chicheng in the alpine area under the dam, and 23~26 in other counties. There is basically no extreme heat period. The main source of precipitation in our city is the warm and humid air flow from the Pacific Ocean. Therefore, under the control of the summer monsoon blowing from the ocean to the mainland in summer, the precipitation is concentrated, accounting for about 70% of the annual precipitation. But also mainly thunderstorms with uneven distribution. The annual rainfall is between 300-550 mm. Fourth, the weather in autumn is cool and pleasant. Autumn is the transition season from summer circulation to winter circulation. The atmosphere cools from the lower level, and the gas layer is stable, so it is not easy to wind. Formed a crisp autumn scenery. Especially the elevation difference between the upper dam and the lower dam, along the dam head, the leaves change from green to gold, feeling the difference in different seasons. Zhangjiakou is located in the northwest of Hebei province, east longitude113 50 ′ ~16 30, north latitude 39 34 ′ ~ 4210 ′. It connects Inner Mongolia Autonomous Region to the north, Baoding to the south, Shanxi Province to the west, Chengde and Beijing to the east, and is located between Inner Mongolia Plateau and North China Plain. The general trend of topography in this area is high in the northwest and low in the southeast, and the yinshan mountains passes through the middle, which divides the area into two parts: the upper dam and the lower dam. The dam is divided into valley basins and hilly areas. Bashang area: Kangbao, Guyuan, Zhangbei and shangyi county are located in Bashang area in the north of our city. Bashang area is a part of the Mongolian Plateau, with an altitude of 1400 ~ 1600 meters, with flat terrain and numerous inland lakes, accounting for one third of the total area of the area. The main climatic and agricultural characteristics of this area are: abundant light resources and large temperature difference between day and night. Conducive to the formation of crop carbohydrates and the accumulation of dry matter; Rain and heat are in the same season, and the climate is cool during the growing period, which is suitable for the growth of crops that like cool and cool; High temperature, high humidity and hot weather are few, agricultural products diseases are less polluted, and vegetables in wrong season have high yield and good quality. The annual total solar radiation in this area is about (130 ~ 150) kcal/cm2, and the annual sunshine hours are 3000 hours. May-September is the active growth period of various vegetables and grasses in Bashang area. The average monthly temperatures are May 10 ~ 13℃, June 14 ~ 17℃, July 16 ~ 20℃, and August15 ~/kloc-0. The annual rainfall is 360 ~ 430mm. Suitable for the growth and development of Chinese cabbage, cabbage, celery, carrots, potatoes and other vegetables. The optimum temperature for the growth period of Chinese cabbage is 12 ~ 26℃. If it is higher than 30℃, it will grow poorly and be prone to pests and diseases. The suitable daily average temperature for the whole growth period of Chinese cabbage is 10 ~ 24℃, and the optimum temperature is about 17℃. Temperatures higher than 24℃ and lower than 10℃ are not conducive to the growth and development of Chinese cabbage. The suitable relative humidity is 50 ~ 70%. Celery is not resistant to high temperature, and its growth is hindered above 20℃, and it stops growing above 26℃. Because of the dry and cold climate in Bashang area, the diseases of crops in the whole growth period are light, there are few pesticides and no pollution. The produced anti-season vegetables have high yield and good quality and are sold all over the country. Baxia valley basin: distributed in the central area of our city. The runoff of Sanggan River and Yanghe River forms the valley basin under the dam, with an altitude of 500-800 meters and low terrain. It mainly includes Huailai, Zhuolu and Xuanhua counties, with large temperature difference between day and night, abundant light resources, long frost-free period, sufficient heat and the same season of rain and heat. Frost-free period 120 ~ 150 days, daily range 12.0 ~ 13.8℃, effective accumulated temperature ≥ 10℃, sunshine hours of 2600 ~ 3300 hours, and annual rainfall of 380. The soil is mostly sandy soil or sandy loam, which is very suitable for the growth of grapes, apples and other fruits. The grapes produced here are big, full and high in sugar content (above 16 degrees), which is an ideal wine-making product. Fruit has high yield and good quality. "Northern Pearl" longan grape, white milk grape and "Great Wall" dry red and white wine have won international and domestic gold medals for more than ten times. The wine produced here is famous all over the country. It is a famous land of fruits. At present, the largest high-quality grape planting base in North China has been built in the Sangyang River basin, and the grape industry has become the first of the dragon economy in the agricultural industry of our city and one of the top ten dragon economies in the province. Semi-Sichuan hilly area in Zhongshan: The hills under the dam are undulating and the terrain is complex. In the south is Xiaowutai Mountain, and the highest peak of Xiaowutai Mountain in Yuxian County is 2882 meters, which is the highest peak in our region. The mountains in northern Malaysia are generally at an altitude of 1300 ~ 1700 meters; Between the mountain and the valley basin, it is a hilly region composed of Yinshan residual vein and Hengshan residual branch. Distributed in Yuxian, Zhuolu, Huai 'an, Yangyuan and other places. Its climatic characteristics are: distinct seasons, great climate difference, abundant rainfall, long illumination time, large annual and daily temperature difference and moderate heat resources. The annual rainfall in this area is 400 ~ 550 mm, sunshine hours are 2700 ~ 3 100h, the average minimum temperature in10/6℃ in October, the average maximum temperature in July is 26 ~ 30℃, and the daily range is12.0 ~. Apricot production, corn and potato seed production are the specialties here. Apricot flat produced by Yuxian and Zhuolu is famous all over the country, and its export volume ranks first in the country. It has become the largest apricot producing area in China, and the apricot area here will grow to nearly one million mu. Zhangjiakou has a vast territory and complex terrain. From a large geographical background, our city is located in Nanlu, the Mongolian Plateau, on the west coast of the Pacific Ocean. The precipitation vapor mainly comes from the western Pacific Ocean, and the monsoon climate is remarkable. In summer, under the action of the southerly airflow of the subtropical high in the western Pacific, the water vapor reached our city after a long journey and was blocked by Xiaowutai Mountain and Dujun Mountain. After the airflow passes through the mountain, the water vapor content is very low. Therefore, the annual precipitation in our city is between 330-550 mm, which is only 2/3 of that in North China Plain. It can be clearly seen from the precipitation distribution map for many years that the geographical distribution of precipitation in our city mainly depends on the terrain. The effect of mountains on airflow uplift and the effect of airflow sinking after crossing mountains to increase temperature and reduce rain are obvious in our region. Because of the high terrain on the dam, warm and humid air is blocked by Jundu Mountain and the dam head twice, and the water vapor source is not rich, and the precipitation is less, with an annual precipitation of 330 ~ 400 mm The distribution trend of precipitation under the dam is closely related to the terrain, with great differences between regions. Due to the uplift of warm and humid air by topography, there is a lot of precipitation in mountainous areas, with an annual precipitation of 400 ~ 500 mm Chongli to Longguan in the north and deep wells in the south form two relatively rainy centers in the whole region. The annual precipitation in a rainy center in the north is more than 450 mm, and that in a rainy center in the south is more than 500 mm The precipitation in the valley area is less than that in the surrounding area, and the annual precipitation is below 400 mm. The first line from Xuanhua to Zhuolu is a relatively dry center, and the annual precipitation is less than 400 mm. In the surrounding area of Yangyuan Xicheng, the annual precipitation is only 340 mm because there are many branches in Hengshan in the southeast, which blocks the transportation of water vapor.