Multiscale interaction analysis of Landfall Typhoon Lekima(2019)based on vorticity equation diagnosis

To investigate the multiscale interaction characteristics of Landfall Typhoon Lekima(2019),this study analyzed the characteristics of the different scale vortex structure and interactions among different scales based on vorticity equation diagnosis.The analysis is based on the simulation results of the WRF model which has been thoroughly verified.The main results are as follows:the original vorticity dominated by the meso-αscale vorticity increases with height and then decreases,with maximum vorticity distributed at 900 hPa.The meso-βscale vorticity varies significantly with altitude,while the meso-γscale vorticityfield exhibits obvious positive vorticity below 850 hPa.The meso-αscale vorticity tendency primarily maintains negative,contributing significantly to the overall reduction in the original vorticityfield over time.The increase in mid-to-upper-level(above 550 hPa)original vorticity is mainly related to the variations in the meso-βand meso-γscale vorticityfields.The original vorticity dominated by the meso-αscale vorticity increases with height and then decreases,and the whole layer vorticity decreases over time.The meso-βscale vorticity varies significantly with altitude and time,while the meso-γscale vorticityfield consistently exhibits significant positive vorticity below 850 hPa.The vorticity equation diagnosis revealed that the primary source terms of the vorticity tendencies are the twisting and stretching terms,and the main sink terms being horizontal and vertical vorticity transport terms below 900 hPa.The source terms and sink terms exchange above 850 hPa.Scale separation results show that the primary contributions of all impact factors originate from the meso-αand meso-γscalefields(accounting for over 80%of the total),with the contribution of the meso-αscale being less than that of the meso-γscale and a notable contribution over 35.5%of the interactions between different scales.