The terrain of the United States is mountainous in the west, low mountains in the east and plains in the middle. What effect does this terrain have on the climate?

(1) There are mountains in the west of North America, and the water vapor in the Pacific Ocean is not easy to penetrate eastward. The low mountains and plateaus in the east do not block the water vapor in the Atlantic Ocean, so the precipitation in North America mainly comes from the Atlantic Ocean, and the annual precipitation decreases from east to west and increases year by year along the Pacific coast. ?

(2) The central plain of North America is flat from north to south. In winter, cold air from the north may push southward, and in summer, warm air from the south may push northward, thus increasing the temperature annual range in North America and aggravating the continental characteristics of the climate in North America.

2. Professional explanation:

The topographic structure of North America is characterized by three north-south longitudinal zones, which is of great significance to the differentiation of continental climate. The most significant influence is the Cordillera mountain system in the west, which consists of triple mountains and a series of mountain plateaus and basins. It is not only quite high, but also very wide, and the coastal areas lack bays that go deep into the mainland. Therefore, on the one hand, the Cordillera mountain system has become an important obstacle to the eastward invasion of the polar Pacific air mass, limiting the mild and humid maritime climate to the west coast north of 40 north latitude, and the intermountain plateau and intermountain basin in the leeward position become semi-arid and arid climate; On the other hand, the polar Canadian air mass and the tropical Gulf of Mexico and Atlantic air mass can only move in the central and eastern parts of the mainland because the Cordillera Mountains cannot invade the west. The Rocky Mountain in the east of Cordillera Mountains is also an important climate dividing line between the east and the west of the mainland, which not only leads to a great difference in precipitation between the east and the west, but also has a certain impact on the temperature. Generally speaking, the annual precipitation in the western part of the Rocky Mountain is below 500 mm, with little rain or drought in summer, and the temperature in winter is higher than that in the eastern part of the same latitude, except for the coastal areas and windward slopes north of 40 north latitude. Except for the northern part of high latitude and parts of the great plains near the Rocky Mountains, the annual precipitation in the east of the Rocky Mountains is above 500 mm, and the proportion of precipitation in summer increases. The climate data of Spokane and Montreal can illustrate this problem. Of course, this difference is also related to factors such as atmospheric circulation and ocean currents.

To the east of the Rocky Mountain is the central plain, which is low and flat, and there is no east-west mountain barrier. It is open to the north and south, and the Hudson Bay, the Great Lakes, the Mississippi River system and the Gulf of Mexico are interconnected. Such terrain conditions are conducive to the smooth movement of air masses with different properties in the north and south. In winter, the dry and cold polar Canadian air mass can go straight to the south, resulting in cold wave weather and a sudden drop in local temperature; In summer, the warm and humid air masses in the tropical Gulf of Mexico and the Atlantic Ocean can freely go north to the coast of Hudson Bay, bringing sultry and rainy weather. The Central Plains has become a place where cold and warm air masses meet and compete with each other, and cyclone activities are frequent, especially in winter. Therefore, the weather in the central plain is changeable, which is the area with the biggest seasonal variation of temperature and precipitation in North America and strong mainland.

The Appalachian mountains in the east are not high or wide, and the continuity of the mountains is poor, which does not constitute a significant boundary in climate, but it still has a great impact on climate in some areas. For example, on the northwest slope of the Appalachian Mountains, the polar Canadian air mass passes through the Great Lakes region, which is slightly denatured in winter and often forms heavy snow; Due to the high altitude, the tropical Gulf of Mexico and Atlantic air mass swelled in the south of the mountain, forming topographic precipitation, with annual precipitation exceeding 65,438+500mm, making it one of the rainy areas in North America. ?

3. Look at this photo again: