| Tropical cyclones are one of the most important extreme weather disasters in the world.And global warming in the 20th century is a hot issue.The state of the ocean and atmosphere will change under the global warming,increasing the uncertainty of the impact on the intensity of tropical cyclones.The previous conclusions about tropical cyclone activity under global warming have been controversial.Aiming at the problems existing in the previous work of the field,combined with the latest formula of maximum potential intensity of tropical cyclone,this paper uses historical observation data,SODA reanalysis data and the output of Coupled Model Intercomparison Project?CMIP5?,to systematically analyze how the MPI of tropical cyclone and the related variables(average temperature of mixed depth?9?,outflow temperature TO,the difference between convective available potential energy in the air-sea boundary?CAPE term?change,and assess changes of tropical cyclone intensity in the future.Firstly,the relationship between the historical observations and MPI and various related variables is analyzed to determine the critical value of MPI corresponding to each level of tropical cyclone.Based on this,we find that in the northwestern Pacific,the area trends of MPI-related variables that meet the strong tropical cyclones are different.The area of(?9?exceeding the critical value is increasing,and the stronger the climate warming,the larger the area;the area where the CAPE term exceeds the critical value remains basically unchanged;the area where the TO exceeds the critical value has a slight decrease,the more carbon dioxide emissions,the more obvious the decrease.This shows that under the background of global warming,although the area of(?9?in MPI exceeds the critical value is increasing,the area of MPI exceeding the critical value remains basically the same,mainly affected by the CAPE term.There is a significant seasonal variation of tropical cyclones intensity in the western North Pacific.High value central area of MPI in spring is small,and gradually expands to the north and extends northward in summer.In autumn,the intensity increases,and in winter,the area decreases.In view of the global warming scenarios of NCAR-CESM,we selected the tropical cyclone high-incidence zone?5°N-30°N,100°E-180°?as the research area,and found that the monthly mean change in this region of future MPI is also basic consistent with historical simulation.The maximum occurs in September or October,and the minimum occurs in February or March.There is a one-month lag or lead,and climate warming has no significant effect on seasonal changes.When performing EOF analysis on MPI to observe its interannual variation,it can be found that there is a positive high value center at 155°E-180°near the equator and a negative center exists in the South China Sea and 0°-10°N,130°E-155°E,and the time series has a period of 3-7 years.It is found that the spatial distribution of the first mode is consistent with the shape of ENSO by doing linear regression of MPI and the Ni?o 3.4 index in the same period.And the first modal time series is significantly correlated with the Ni?o 3.4 index,so the main mode of MPI interannual variation is affected by ENSO.The correlation between MPI and ENSO is getting stronger and stronger under the background of global warming,but there is no significant difference between the RCP8.5scenario and the RCP4.5 scenario in the same time period. |
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