Significant Enhancement in Atmospheric Biweekly Disturbance over Northeast Asia during the Recent Warming Hiatus

Based on daily 500-hPa geopotential height from ERA-Interim reanalysis data, this study analyzed the day-to-day circulation variance in cold season (October-March) by composite and correlation analysis. Two same-length time periods were compared, namely, the hiatus period (1999-2013) and the rapid warming period (1984-1998). Spectral analysis revealed that over the mid-high latitudes of the Northern Hemisphere, the most outstanding peak in the daily 500-hPa geopotential height variance was of quasi-biweekly timescale (about 10-20 days), accounting for about 32% of the total variance. During the warming hiatus, quasibiweekly disturbance (QBD) changed remarkably in Northeast Asia. On average, within the domain 42-50N, 128-142E, the QBD variance changed from 1860 m2 in the rapid warming period to 2475 m2 in the hiatus period, increasing by about 33% and statistically significant at the 95% confidence level. Lead-lag analysis showed that the QBD signal could be traced back by about 14 days, with an origin around the Ural Mountains. Then, the signal developed and propogated southeastward, with its location about 10 days prior to its peak in West Siberia, and about 6 days prior to its peak in the Sayan Mountains, and finally moving to Northeast Asia. By comparing the propagation process between the two periods, we found that the propagation paths were basically the same, but there were evident differences in the intensity of the signals. The intensification of QBD may have been related to the increased energy conversion from mean flow to QBD transients. The frequency of low-temperature extremes in negative QBD phases was much higher than under normal conditions or in positive phases. Associated with the enhanced QBD, the probability of extreme low temperature increased from 19% during the rapid warming period to 27% during the warming hiatus.