The Change Of Atmospheric Static Stability In The Western North Pacific And Its Relationship With Tropical Cyclone Frequency And Intensity

Under the scenario of global warming it is likely that the frequency of tropical cyclone decreases based on climate models. And some studies suggest that the increased static stability possibly contribute to the reduction in tropical cyclones. Multiple sets of reanalysis data are used to analyze the change of atmospheric static stability during tropical cyclone peak season(July-September) in the western North Pacific in this paper. After understanding the change characteristics of static stability, we further discuss the possible relationship between static stability and tropical cyclone frequency and intensity using reanalysis data and WRF model, respectively.MERRA, ERA-Interim and JRA-55 are assessed through a comparison with radiosonde data in CAPE and it turns out that MERRA outperforms in variation trend than ERA-Interim and JRA-55. Based on MERRA, we take advantage of CAPE, equivalent temperature and N2 to characterize the change of atmospheric static stability founding that CAPE increases in the western typhoon activity area (15°-30°N, 120°-145°E) and decreases in the eastern area (15°-30°N, 145°-180°E), and atmosphere of eastern area is also more unstable than the western area in two other parameters. It is suggested that the eastern tropospheric atmosphere over the typhoon activity ocean has unstable tendency and the western tropospheric atmosphere has stable tendency in the recent 36 years.It is worth noting that the trend of atmospheric static stability of the western and eastern regions of the main activity of tropical cyclones is not consistent with tropical cyclones in western North Pacific. There is no obvious link between tropical cyclone (reach tropical storm) frequency and static stability, but when we take the tropical disturbances into account, it shows a surprising significant inverse correlation between the two parameters. In this paper, the effect of static stability on the intensity of tropical cyclones is also simulated using WRF model. Keep the humidity be constant and simulate the development of tropical cyclones under three different temperature stratification structures and find that the initial atmosphere more stable, the more time the initial vortex will takes to reach the stable intensity of tropical cyclone. In this experiment the ultimate strength of tropical cyclone have nothing to do with the initial static stability.