Thermodynamic and Dynamic Changes in the Japan Sea Polar Air Mass Convergence Zone and Its Associated Heavy Snowfall Under Warmer Climate

The Japan Sea polar air mass convergence zone (JPCZ) has the potential to cause heavy snowfall events several times per year in the west side of the Japanese archipelago. The associated severe snowfall can cause adverse effects on the social, economic, and ecological well-being in the affected areas. Therefore, understanding the changes of JPCZ and its associated snowfall under warmer climate conditions is of high importance. In the present study, pseudo global warming (PGW) experiments, considering the 2050s under SSP5-8.5 scenario, were carried out to evaluate these thermodynamic and dynamic changes. The amount of PGW experiment-simulated snowfall in 13 historical cases during 2015–2024 were in good agreement with ground observations. Warmer climate conditions can potentially reduce the amount of heavy snowfall as statistically supported by the t test, though increase the rainfall mainly due to the shift in hydrometeors in the convective zone. On the other hand, total precipitation does not significantly change, likely due to almost no changes in the sum of latent and sensible heat fluxes. Further, dynamic changes are not significant as the position of the convergence zone seems not to be different between PGW and historical climate, though local shifts in the convergence zone were simulated probably due to the changes in the geopotential fields and perturbed wind velocity in the lateral boundary. Our study shows that thermodynamic changes of the JPCZ can be significant, and it has the potential to change the ratio of snowfall within the total precipitation from 57.7% under historical condition to 34.7% under warmer climates.