Evolution and extinction of weather system

The weather system is always reborn, developing and dying. Various weather systems have different birth and death conditions and energy sources. Even if the characteristic scales belong to the same system, their birth and death conditions and energy sources are different. For example, the development conditions of extratropical cyclones are mainly determined by the intensity of air divergence caused by vorticity advection over them, and its energy comes from the effective potential energy stored in atmospheric baroclinic. The occurrence and maintenance of typhoon is due to the release of latent heat by tropical disturbance, which is related to the potential instability and convection instability of tropical atmosphere. Its energy mainly comes from the latent heat released by the water vapor supplied by the ocean during condensation. The mesoscale weather system with strong convection is mainly developed due to the sudden rise of air with unstable potential, and its energy also comes from the release of latent heat. Moreover, the weather system is often not closed, and the air in one system often exchanges with the air in the surrounding system. Through this exchange, momentum and energy between systems are exchanged, which leads to the birth and death of systems and the interaction between systems. Generally speaking, a large weather system restricts and breeds the occurrence and development of a small weather system, which in turn reacts to the maintenance and strengthening of the large weather system. It is one of the main tasks of meteorology to study the birth and death conditions, energy sources and their interaction of weather systems. Weather system and atmospheric circulation are not only related in flow pattern, but also related internally. For example, the activities of large-scale weather systems play an important role in maintaining atmospheric circulation through the north-south transport of heat and momentum and the conversion of energy. The thermodynamic state of atmospheric circulation and the characteristics of basic wind system, such as the horizontal and vertical changes of westerly airflow, in turn restrict large-scale weather systems and directly affect their development. The evolution of weather system combination, such as the recovery of zonal circulation, the propagation of wave group velocity, the development of planetary scale weather system, etc., can lead to the change of atmospheric circulation in a considerable range or even globally. The change of atmospheric circulation is the condition and mechanism that causes large-scale and long-term weather changes. In short-term weather forecast, we can mainly consider the change of a single weather system, while in medium-and long-term weather forecast, we need to study the evolution law of weather system combination and the evolution law of ultra-long waves and even the whole atmospheric circulation.