Temperate cyclones and meteorology

Extratropical cyclone Extratropical cyclone is a weather system active in temperate mid-latitude areas, also known as "extratropical depression" or "frontal cyclone". Temperate cyclone is a cold core system different from tropical cyclone. Its appearance is accompanied by a front, and its scale is generally larger than that of tropical cyclones, reaching hundreds or thousands of kilometers. Some extratropical cyclones are developed from waves on the front. Due to some reasons, waves are formed on the front, and a closed isobar appears near the peak of the waves, which gradually develops into a complete cyclone. There are also some extratropical cyclones moving into the temperate zone from tropical cyclones, which are transformed into extratropical cyclones by the influence of the westerly trough. Please refer to the explanation of cold front, warm front, stationary front and blocking front in the development stage of extratropical cyclone. In the initial stage, the front on the ground, which used to be a stationary front, fluctuated, resulting in a low-pressure area (shown as a closed isobar on the weather map), and a warm front and a cold front extended on both sides of the low-pressure area. During this period, the extratropical cyclone can be shown in the visible satellite cloud image as the front cloud band widens, bulges to the cold region, turns white in color, and the middle and high clouds increase. In the development stage, with the development of fluctuation, the lowest pressure in the center of extratropical cyclone continues to decrease (the closed isobar on the weather map increases). Because cold air moves faster than warm air, cold air pushes towards warm air. Rainfall or snowfall occurs near the cold front, and precipitation also occurs near the warm front. Generally speaking, the precipitation area has increased. With the development of extratropical cyclone, its thickness also develops from the lower layer to the middle and upper layer, and the airflow rises in a rotating way, and the low trough in the upper air gradually deepens. During this period, the extratropical cyclone shows that the frontal cloud belt rises more obviously on the satellite cloud image, and the back boundary of the middle and high clouds begins to sag inward. Mature stage In the mature stage, the temperate cyclone develops most vigorously, and it has become a circular closed circulation from the ground to the height of 500 HPA equipotential surface. On the ground, the cold front catches up with the warm front, forcing the warm air to rise, forming a trapped front. At this time, the temperate cyclone has the largest range, the strongest wind and the most dramatic weather changes. However, because the ground has been occupied by cold air and become a cold vortex, the extratropical cyclone will gradually weaken. During this period, the extratropical cyclone showed obvious dry tongue and obvious spiral structure at the back of the cloud system on the satellite cloud image. The cloud belt extends to the center of the vortex. The extinction stage is the last stage of the development of extratropical cyclones. At this time, the central pressure of the extratropical cyclone rises, and the extratropical cyclone has completely turned into a cold vortex, and the central part of the cyclone begins to be blocked. The closed circulation from the ground to the height of 500 HPA equipotential surface is weakened, and the upward movement of airflow disappears and eventually dies out. During this period, the extratropical cyclone is shown on the satellite cloud image, with the dry tongue extending to the cyclone center, the spiral cloud belt rotating around the center for more than one cycle, and the high and low circulation centers coincide with the vortex center of the cloud system.

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