Contribution of the Northeast Cold Vortex Index and Multiscale Synergistic Indices to Extreme Precipitation Over Northeast China

The northeast cold vortex (NECV) is one of the major synoptic systems affecting Northeast China. The activity of NECV is an important reason for severe convective storms. However, research on extreme precipitation over Northeast China and their associations with the northeast cold vortex index (NECVI) is limited. Based on nonstationary generalized extreme value models, we analyze and quantify the contribution of the NECVI and the multiscale synergistic indices. Then, we verify the necessity of the NECVI by the likelihood ratio test and the blank control experiment, and further verify the impact of the NECVI on the extreme precipitation over Northeast China in combination with the climate index atmospheric circulation analysis. Results suggest that the models established with East Asian summer monsoon index, Southern Oscillation Index, and NINO3.4 index as covariates the most common. The NECVI and the synergies also make significant contribution and have passed the likelihood ratio test at 80% confidence. Especially in late summer, accounting for 18.69% of the 10 selected best models and 29.41% of the nine selected best nonstationary models. Based on the blank experiments, the models with the NECVI have a maximum reduction of 4.72% than those without the NECVI in the Akaike information criterion values in late summer. In early summer and late summer, the center of the high values of the water vapor anomaly is mainly located in southwestern in the strong NECVI years. These findings help to understand the genetic mechanism of extreme precipitation over Northeast China and provide reference for risk management. Plain Language Summary Precipitation over northeast China is often influence by NECVI defined by monthly meteorological indices. We applied the methodology and the algorithm for calculating daily NECVI values in early summer and late summer, which is used as a parameter in nonstationary generalized extreme precipitation value models for the first time. Then, statistical analysis and case study show the significance of NECVI. The correlation between NECVI and humidity field anomalies, wind field anomalies and their divergences at 850 hPa helps to reveal the mechanism of the influence of NECVI on extreme precipitation over northeast China.