Tell me about the whirlwind.

In the northern (southern) hemisphere, the horizontal airflow in the atmosphere is a large vortex rotating counterclockwise. The northern hemisphere leans to the right, and vice versa. At the same height, the air pressure in the center of the cyclone is lower than that around it, which is also called low pressure. Cyclones are similar to circles or ellipses, and their sizes vary greatly. Small cyclones have a horizontal scale of several hundred kilometers, and large ones can reach three or four thousand kilometers. In cyclones, the weather often changes dramatically, which is the weather system that people are most concerned about and studied at the earliest. Usually classified according to the main areas or thermal structures where cyclones are formed and active. According to the region, it can be divided into temperate cyclone, tropical cyclone and polar cyclone vortex According to the thermal structure, it can be divided into cold air rotation and hot low pressure.

There are vortex motions in the atmosphere similar to those in rivers, and there are two kinds of rotating motions: clockwise and counterclockwise: cyclone and anticyclone, both of which are large horizontal vortex motions in the atmosphere. Cyclone, in the northern hemisphere, the air moves counterclockwise, the central air pressure is the lowest, and it gradually increases outward, and the air continuously flows into the center, forming an updraft, also known as low air pressure. Its diameter: tens of kilometers small, thousands of kilometers big. When affected by hurricanes, rainy weather and strong winds often occur.

There are all kinds of eddies in the atmosphere, some rotate counterclockwise and some rotate clockwise. Among them, the larger horizontal vortex is called cyclone and anticyclone respectively, that is, low pressure and high pressure.

Related terms

Cyclone: Cyclone is also called low-pressure cyclone. A large vortex that occupies three-dimensional space and has a closed isobaric (high) line at the same height (isobaric surface) and the central pressure (height) is lower than the surrounding pressure (height). In the northern hemisphere, air rotates counterclockwise; In the southern hemisphere, it rotates in the opposite direction.

Anticyclone: Anticyclone is also called high pressure. Cyclone and anticyclone are two aspects of a system.

Jianghuai cyclone: refers to the cyclone in Jianghuai area now.

Northeast cyclone: also known as northeast depression. Cyclone active in northeast China. It is one of the important weather systems affecting China.

Frontal cyclone: also known as polar front cyclone, wave cyclone and baroclinic cyclone. Strong fluctuation baroclinic cyclone produced in the development of temperate polar front. In China, there are frontal cyclones entering trough, shallow depression or typhoon.

Cold vortex: short for cold vortex. The vortex strength with the center temperature lower than the ambient temperature increases with the height.

Northeast Cold Vortex: A large-scale cold vortex moving at high altitude in or near the northeast of China. It is a deep system that can last for 3-4 days or longer.

Southwest vortex: also known as southwest vortex. Under the combined action of special topography and certain circulation in the Qinghai-Tibet Plateau and southwest China, a shallow vortex is generated at low altitude in southwest China.

frontal cyclone

Surface cyclones are generally related to the frontal surface, which we call frontal cyclones. It is a common weather system in the middle and high latitudes of northern China.

Let's first look at the formation of frontal cyclone from the knowledge of frontal and cyclone. The front is the interface formed by the intersection of cold and warm air, and it is a narrow and inclined transition zone. Cyclones are low pressure. In the northern hemisphere, it is a weather system in which air flows counterclockwise from the periphery to the center.

As shown in the figure, this is a low pressure area. According to the wind map of the northern hemisphere, it can be determined that the south wind blows in the east and the north wind blows in the west. The narrow area where low pressure extends outward is called low pressure trough, just like the valley on the terrain. AB and CD are two slot lines in the figure.

Fronts are usually formed in the trough of low pressure of surface cyclones. In the picture, the southerly wind to the east of the cyclone comes from lower latitude and the temperature is higher. When moving northward, it meets cold air at higher latitudes, forming a warm front (near CD in the picture). Similarly, the airflow in the west of the cyclone comes from the northerly wind at high latitude in the north, and it will meet warm air at low latitude in the south to form a cold front (near AB in the figure), thus forming a frontal cyclone in the surface weather system. The cyclone in the northern hemisphere is a vortex that flows counterclockwise, and it also moves counterclockwise with the generated front.

After the formation of frontal cyclone system, what impact will it have on the weather controlled by the original single weather system?

As we know, because the airflow flows into the cyclone center from all directions, the central airflow is forced to rise and condense into rain. Therefore, when cyclones cross the border, the cloud cover increases, and rainy weather often occurs, that is, cyclone rain. In the frontal weather system, whether it is a cold front or a warm front, the warm air mass above the frontal surface rises along the frontal surface, which will form cloudy and precipitation weather, that is, frontal rain. When the two systems combine to form a frontal cyclone, it will converge into a stronger updraft, and the weather will change more violently, often causing clouds, rain and even heavy rain, thunderstorms and windy weather.

The precipitation area in cold and warm fronts will be slightly different. Because the density of the cold air mass is greater than that of the warm air mass, the cold air mass is always under the warm air mass, the front is always biased to the side of the cold air mass, and the precipitation area is always on the side of the cold air mass on the front. In the picture, a wide warm front cloud system and continuous precipitation weather will be formed in front of CD, and a narrow cold front cloud system and precipitation weather will be formed behind AB. The central part of the cyclone (between the cold front rain area and the warm front rain area) is sunny under the control of a single warm air mass.

Development of frontal cyclone

Frontal cyclones also have their processes of occurrence, development and extinction. There are two understandings of frontal cyclone: one is that a cover (quasi-static front and active cold front) is disturbed, gradually forming a low-pressure center and evolving into a frontal cyclone, which can be simply understood as an existing front and then forming a cyclone; Another view is that the ground depression first forms, then produces a front and develops into a frontal cyclone. Although the initial development conditions of the two frontal cyclones are different, the development process after their formation is very similar.