What is the principle of frontal weather?

Frontal cyclone is a combination of frontal cyclone and surface cyclone. Frontal cyclones, also known as extratropical cyclones, are mainly active in middle and high latitudes, and are more common in temperate regions.

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.

Frontal cyclones also have their processes of occurrence, development and extinction. There are two understandings of frontal cyclone: one is that a front (quasi-static front or 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.