Overview of Advances in Synoptic Meteorology:Four Stages of Development in Conceptual Models of Frontal Cyclones

The advance of fluid dynamics may be divided into four stages： ancient, classical, neoteric, and contem- porary. A similar four-stage framework can be used to describe the advance of synoptic meteorology, such as the conceptual models of extratropical cyclones and their attendant fronts. The first conceptual model of extratropical cyclones was proposed by Admiral FitzRoy in 1863. Based purely on Admiral FitzRoy＇s personal experience （although it does contain some scientific essentials）, this model represents the “ancient” stage of synoptic meteorology. The Norwegian cyclone model was developed based on Newtonian mechanics about 100 yr ago, and represents the classical stage of synoptic meteorology. This model was based on the idea that weather changes are primarily caused by baroclinicity, but contain some serious flaws. In particu- lar, the Norwegian model regards fronts as zeroth-order discontinuities in density, which is inconsistent with the continuity principle of fluid dynamics. The Chicago three-dimensional conceptual model of fronts and cyclones, which was developed approximately 50 yr ago by using quasi-geostrophic theory, can be thought of as representing the neoteric stage of synoptic meteorology. The Chicago model was replaced in the late 20th century by a model of extratropical cyclones characterized by back-bent and wrap-up warm fronts. This model has been developed with massive numerical calculations, and represents the contemporary stage of synoptic meteorology. In the era of large data, contemporary synoptic meteorology should be careful to maintain and make full use of the profound physical understanding generated during the neoteric stage of synoptic meteorology.

The development of a powerful Mongolian cyclone on 14-15 March 2021:Eddy energy analysis

Intense and extensive dust,caused by a strong Mongolian cyclone,hit Mongolia and northern China on 14-15 March 2021.In this study,the development process of this cyclone is analysed from the perspective of highfrequency eddy energetics.During the low-frequency circulation field of early March of 2021,an amplified polar vortex intruding towards central Asia and a ridge straddling eastern and northeastern Asia worked in concert to comprise a strong baroclinic zone from central Asia to Lake Baikal.Under these favourable conditions,on 13 March,a migratory trough triggered the Mongolian cyclone by crossing over the Sayan Mountains.The downwards transfer of kinetic energy from the eddy at 850 hPa played a key role in the intensification and mature stage of the cyclone.This mechanism was primarily completed by the cold air sinking behind the cold front.The frontal cyclone wave mechanism became crucial once the cyclone started to rapidly develop.The authors emphasize that the anomalously large growth of high-frequency available potential energy,which characterized this super strong cyclone,was obtained by extracting energy first from the time-mean available potential energy and then from the low-frequency available potential energy.The interannual temperature anomaly pattern of"north cold south warm"facilitated the additional time-mean available potential energy,and the temperature anomaly pattern of"northwest cold southeast warm"conditioned the extra low-frequency available potential energy.The analysis results suggest that the interaction between high-and low-frequency waves was also important in the development of the intense cyclone.