The causes of climate in North America

The influence of topography on climate

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.

Folding volcano and earthquake

The west coast of North America is part of the volcanic belt along the Pacific coast. There are more than 90 active volcanoes in North America, including 28 in Aleutian Islands, 20 in Alaska and more than 40 in Central America. The western part of North America is also a region with frequent and strong earthquakes in the world.

Folding drainage system

The outflow area of North America accounts for about 88% of the whole continent, of which 48% belongs to the Atlantic basin and 20% belongs to the Pacific basin. Except the St. Lawrence River, all major rivers originate in the Rocky Mountains. Rivers to the east of the Rocky Mountains flow into the Atlantic Ocean and the Arctic Ocean respectively, and rivers to the west flow into the Pacific Ocean. Inflow areas (including non-inflow areas) account for about 12% of the whole continent, mainly distributed in great basin and Greenland in the western United States. Mississippi River is the largest river in North America and the fourth largest river in the world. Followed by Mackenzie River, yukon river River, St Lawrence River and Rio Grande. There are many waterfalls on rivers in North America. The waterfall with the biggest drop is the yosemite falls in Yosemite National Park in the western United States, with a drop of 700 meters. Niagara Falls, with a drop of 5 1m and a width of1.240m.. North America is a continent with many lakes, and the total area of freshwater lakes is about 400,000 square kilometers, ranking first among all continents. Lakes are mainly distributed in the northern half of the mainland. The Great Lakes in the Central Plateau: Lake Superior, Lake Huron, Lake Michigan, Lake Erie and Lake Ontario, with a total area of 245,273 square kilometers, are the largest freshwater lakes in the world and are known as the "Mediterranean of North America". Among them, Lake Superior is the largest freshwater lake in the world.

Folding climate

North America spans tropical, temperate and frigid zones, and its climate is complex and diverse. The north is in the Arctic Circle, which is a world of ice and snow. The southern Caribbean benefited from the equatorial warm current, but was hit by tropical hurricanes. The vast area in the middle of the mainland is located in the north temperate zone. Because all the mountains are north-south or close to north-south, the humid air from the Pacific Ocean only reaches the western coastal areas; Cold air from the Arctic Ocean can cross the central plain to the south; The humid air blown from the tropical Atlantic can also penetrate deep into the north through the central plain, so the climate in North America is very unstable, sometimes cold and sometimes thawed in winter, while in the subtropical areas along the Gulf of Mexico, it will be cold and snowy in winter. The average temperature in Leng Yue (65438+ 10) in North America is below 0℃, accounting for about 3/4 of the whole continent. The entire Arctic Islands (collectively referred to as the islands north of the North American continent and west of Greenland) and most parts of Greenland are below -32℃, and the central part of Greenland is as low as 0℃, which is a cold polar region in the western hemisphere. In summer, the whole continent is generally warming, and the average temperature in the hottest month (July, mostly August along the coast) is 0~3℃, which is the coolest area in the northern hemisphere in summer. The rest of the vast areas are between 0 and 32℃, of which the area above 20℃ accounts for more than half of the whole continent, and the area above 30℃ is small. Death Valley in the southwestern United States, with an extreme maximum temperature of 56.7℃, is the hottest area in the whole continent. There is more precipitation in eastern North America. The annual precipitation in the Pacific coast of Canada and Greenland, the eastern United States, Canada and Alaska is about 500~300 mm; The Pacific coast of Canada and Alaska is more than 2000 mm high, which is the most rainy area in North America. The annual precipitation in the Florida Peninsula, the eastern foothills of the Rocky Mountains, the Great Plains and the Yukon Plateau is 250 mm; The Caribbean belongs to the tropical rainforest climate, with high temperature and rainy all year round. The areas with the least precipitation are the southwest of great basin, the lower reaches of the Colorado River, the Arctic Islands and the northern part of Greenland. The annual average precipitation is less than 100 mm, and it is from May to 10 every year. Southeastern North America is often hit by hurricanes, which often causes serious disasters. Cold, strong storms and tornadoes often blow in winter in central and northern North America. After crossing the Rocky Mountains, the westerly wind forms Chinnock Foehn at the eastern foot.