Move a Tropical Cyclone with 4D-Var and Vortex Dynamical Initialization in WRF Model

Previous studies showed that 4 D-Var technique used for data assimilation could be modified for weather control. This study demonstrates the ability of 4 D-Var to influence the future path of a tropical cyclone by calculating perturbations in WRF simulation. Given the background error covariance matrix, the initial field is improved by the vortex dynamic initialization technique. Our results show that 4 D-Var can be applied to control the trajectory of simulated tropical cyclones by producing "optimal" perturbations. In the numerical simulation experiment of Typhoon Mitag in 2019, after this kind of weather control similar to data assimilation, the tropical cyclone moved obviously,and the damaging wind over the coastline weakened. The prediction results after the initial field modified by 4 D-Var have a great change, and the position of the tropical cyclone moved about 0.5° southeastward after assimilation,which misses the southeast coast of China. Moreover, the damaging wind is also weakened. Since the 4 D-Var is premised on the assumption that the model is perfect and does not consider the model error, then the research plan to consider model error and introduce new methods is discussed in the paper.

Improving Simulation of a Tropical Cyclone Using Dynamical Initialization and Large-Scale Spectral Nudging: A Case Study of Typhoon Megi (2010)

In this study, an approach combining dynamical initialization and large-scale spectral nudging is proposed to achieve improved numerical simulations of tropical cyclones （TCs）, including track, structure, intensity, and their changes, based on the Advanced Weather Research and Forecasting （ARW-WRF） model. The effectiveness of the approach has been demonstrated with a case study of Typhoon Megi （2010）. The ARW-WRF model with the proposed approach realistically reproduced many aspects of Typhoon Megi in a 7-day-long simulation. In particular, the model simulated quite well not only the storm track and intensity changes but also the structure changes before, during, and after its landfall over the Luzon Island in the northern Philippines, as well as after it reentered the ocean over the South China Sea （SCS）. The results from several sensitivity experiments demonstrate that the proposed approach is quite effective and ideal for achieving realistic simulations of real TCs, and thus is useful for understanding the TC inner-core dynamics, and structure and intensity changes.