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Using the European Centre for Medium-Range Weather Forecasts (ECMWF) Interim Reanalysis (ERA-Interim) dataset and the Specified Chemistry Whole Atmosphere Community Climate Model (WACCM-SC), the impacts of sea ice reduction in the Barents-Kara Seas (BKS) on the East Asian trough (EAT) in late winter are investigated. Results from both reanalysis data and simulations show that the BKS sea ice reduction leads to a deepened EAT in late winter, especially in February, while the EAT axis tilt is not sensitive to the BKS sea ice reduction. Further analysis shows that the BKS sea ice reduction influences the EAT through the tropospheric and stratospheric pathways. For the tropospheric pathway, the results from a linearized barotropic model and Rossby wave ray tracing model reveal that long Rossby wave trains stimulated by the BKS sea ice loss propagate downstream to the North Pacific, strengthening the EAT. For the stratospheric pathway, the upward planetary waves enhanced by the BKS sea ice reduction shift the subpolar westerlies near the tropopause southward. With the critical lines displaced equatorward, the poleward transient eddies break at lower latitudes, shifting the eddy momentum deposit throughout the troposphere equatorward. Tropospheric westerlies maintained by eddy momentum deposit are also shifted southward, inducing the cyclonic anomalies over the North Pacific and deepening the EAT in late winter. Nudging experiments show that the tropospheric pathway only contributes to around 29.7% of the deepening of the EAT in February induced by the BKS sea ice loss, while the remaining 70.3% is caused by stratosphere-troposphere coupling.

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As a long-distance discharge phenomenon in nature, lightning not only poses serious risks to human beings but causes wildfires as well, which in turn affect the evolution of species and ecosystems (He et al., 2022;Hessilt et al., 2022). Lightning is the only natural source of nitrogen oxides (NOx) in the troposphere which regulates the oxidation ability in the upper troposphere and modulates tropospheric chemistry (Brune et al., 2021;Mao et al., 2021).Lightning activity shows large spatial heterogeneity on the globe with several lightning chimney regions around the equator (

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