In this manuscript, the author proposes the "upper westerly trough-middle NECV-lower extratropical cyclone" model, which provides a solid scientific explanation for the stratospheric ozone intrusion event that occurred in Northeast China in May 2019. Model simulations and observational analyzes provide substantial evidence supporting the authors' hypotheses. This is a paper worthy of acceptance and publication. Below are some specific comments and questions.

Line 107: “The portion of tropospheric O3 concentrations originating from the stratosphere (O3S)”, The author may need more description to substantiate this claim

Line 125 to 127: “The differences in --- in the SI event”, How sensitive is the "quantitative effect" to the ozone lateral boundary conditions used in the control experiments? It is best to provide information on how to set the ozone lateral boundary conditions at the top level of the model in WRF-CHEM.

Line 130: “Fig.S2”, Is it the average of all observations in domain 03? Please explain in detail

Line 138 to 139: “Therefore, our simulation results are available and convincing.”, Please see the first question above

Line 148: “Fig. S4b”, Is the value of air temperature in the picture negative or positive?

Line 172 to 176: “the intense --- to the near-surface layer”, Since both subsidence and ascending motion occur in extratropical cyclone systems, stratospheric intrusion ozone reaching the surface will rapidly diffuse and be carried back to the upper troposphere. Therefore, such events are difficult to observe.

Line 215: “week”, weak??

Line 225: “Figure 5”, How many weather observatories are there and how many ozone and carbon monoxide observatories are there? Why do the authors use regionally averaged observations? Have the authors looked at single-site observations of ozone in particular?

Line 258: “vertical mixing (VMIX) --- vertical advection (ADVZ)”, What is the difference between VMIX and ADVZ?

Line 266: “Fig. 6”, How did the authors choose the IPR times shown in Figure 6 for SJZ and JN?

Line 280: “without o3 pollution”, confused

Line 290: “Figure 7”, Is it the model simulation result on domain 03?

Please see the attached file. Thanks.