Abstract:Numerical prediction models often encounter difficulties in predicting the intensity changes of tropical cyclones (TCs),particularly in the case of super typhoons and the progression of TC intensification.This study aims to investigate the large-scale environmental factors influencing the generation and development of super typhoons in the western North Pacific (WNP).We analyze the effects of thermodynamic and dynamic environmental factors on the intensity of TCs with tracks similar to Super Typhoon Haiyan (2013),the strongest TC in the past century in the WNP.Typhoons with tracks resembling Haiyan (2013) are categorized into two groups:super TCs and regular TCs.The Lanczos method is utilized to filter out synoptic-scale disturbances and typhoon disturbances,and mean composite differences are used to compare the composite environmental factors of the two groups.Observational analysis results indicate that,compared to dynamic factors,thermodynamic factors play a more significant role in strengthening TCs,such as higher temperatures and more abundant vapor in the lower troposphere,along with higher relative humidity in the middle troposphere.This configuration facilitates the release of a large amount of latent heat,which is beneficial for ascending motion.Meanwhile,low-level Ekman pumping enhances TC strength through positive feedback.To quantitatively assess the relative importance of environmental conditions in regulating TC intensity,a box difference index (BDI) analysis method is used to rank the environmental factors.Accordingly,925 hPa moist static energy (MSE),950 hPa specific humidity,and 900 hPa temperature are selected as the top-3 predictors for estimating TC intensity.Furthermore,we calculate the values of ocean heat content (OHC) and TC moving speed for each case,which are found to be larger for super TCs compared to regular TCs and may contribute to an increase in TC intensity.As the typhoon moves faster,the cold water upwelling caused by the typhoon leads to a smaller cooling effect,allowing the OHC to increase and facilitating typhoon intensity strengthening.Additionally,OHC and TC moving speed can also serve as additional predictors.Lastly,idealized numerical model experiments with the Weather Research and Forecasting (WRF) model are conducted to reveal the relative importance of environmental temperature and moisture vertical profiles in affecting TC intensity.The control experiment,identified as CTRL,and a set of sensitivity experiments,identified as Axel_SH,Axel_T,and Axel_SH+T,respectively,are designed.The sensitivity experiments Axel_SH,Axel_T,and Axel_SH+T indicate that the vertical profile of the area-averaged specific humidity,temperature,and specific humidity plus temperature of Typhoon Alex is replaced by that of Tyhpoon Haiyan.The sensitivity experiment results indicate that the relative contribution of environmental moisture and temperature profiles is 1∶4,suggesting that the environmental static stability parameter is the most important factor regulating super TC formation.Overall,the study confirms the significant impact of thermodynamic factors on typhoon intensity with tracks similar to Typhoon Haiyan (2013),providing quantitative insights into the contributions of different environmental factors.Given the challenges in predicting TC intensification,numerical modeling efforts should focus on understanding the interaction with the entire upper-ocean column and improving physical parameterization.