Spring extratropical cyclones over the Mongolian region in the ERA5 reanalysis: climatology and variability

Mongolian extratropical cyclones (ETCs) play a crucial role in the weather and climate over East Asia, and the use of datasets with higher spatiotemporal resolutions can improve the understanding of Mongolian ETCs. Based on an automatic detection and tracking algorithm and the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis version 5 (ERA5) dataset, the characteristics of the frequency, lifetime, moving distance, moving speed, and intensity of Mongolian ETCs in spring during 1979-2021 are investigated. The results show that 92.6% of the Mongolian ETCs are locally formed. There were two decadal changes in the Mongolian ETC frequency in approximately 1993 and 2004, showing a "high-low-high" variation. In terms of ETC passages, there is an increasing trend from central Mongolia to Northeast China and a decreasing trend east of Lake Baikal, indicating that the Mongolian ETC tracks are located more southward. Based on the standard deviation ellipse method and K-means clustering, the Mongolian ETCs are clustered into three categories, namely, southern track (ST, accounting for 53.4% of Mongolian ETCs) ETCs, northern track (NT, accounting for 43.8%) ETCs, and long track (LT, accounting for 2.8%) ETCs. The ST ETCs have a significant increasing trend, while the NT ETCs show a significant decreasing trend. Moreover, the other properties of Mongolian ETCs also show significant decadal variability. The sequences of lifetime, moving distance, moving speed and intensity exhibit decadal changes in the 1990s, with longer lifetime and moving distance, faster moving speed, and stronger intensity after the abrupt change.