Quasi-biweekly oscillation of Northeast China cold vortex frequency in warm season
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Graphical Abstract
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Abstract
Northeast China cold vortex (NCCV) is the most important mid-latitude synoptic system for weather and climate anomalies in Northeast China in warm season. Many previous studies have focused on its synoptic and climatic variability. However, little is known about variability of the NCCV on the sub-seasonal timescales. In this study, we investigate sub-seasonal variability of the NCCV in the warm season (May to August) and its impact based on the NCEP/NCAR reanalysis dataset and observational climate data from 1981 to 2020. Results show that the NCCV frequency exhibits a significant quasi-biweekly oscillation (QBWO, 10−25 days). In 32 out of 40 years there is at least one significant period between 10 and 25 days. Our result provides the first direct evidence for significant QBWO signal in NCCV frequency. The QBWO circulation in the NCCV days features a cold low-pressure anomaly surrounding by warm high-pressure anomalies from northwest to southeast along a clockwise direction, which is related to an upstream wave train propagating southeastward from Ural Mountains into Northeast China and a downstream blocking high to the northeast. The NCCV QBWO causes more rainfall, with a quadrature phase shift as rainfall leading NCCV for approximately three days, and synchronized dropped surface air temperature in Northeast China.
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