The significant increasing of atmospheric bi-weekly disturbances over Northeast Asia during the global-warming hiatus

Abstract:

Based on daily 500 hPa heights from ERA-Interim reanalysis, this study analyzed the day-to-day circulation variance in cold season (October-March) during the global-warming hiatus by employing composite and correlation analysis. Two same-length time periods, i.e., the hiatus period (1999-2013) and the rapid warming period (1984-1998), are compared. Spectral analysis reveals that over the mid-high latitude northern hemisphere the most outstanding peak in the daily 500hPa height variance is of quasi bi-weekly (QBW) time scale (about 10-20d), which accounts for about 32% of the total variance. During the global-warming hiatus, the QBW disturbances have changed remarkably in Northeast Asia. On average in the domain of 128°E-142°E, 42°N-50°N the QBW variance has changed from 1860m² in the rapid warming period to 2475m² in the hiatus, increasing by about 33% and being statistically significant at the 95% level. The time-lag analysis shows that the QBW signal could be traced back to about 14 days ago with a origin around Ural Mountains, then the signals developed and moved southeastward, its location about 10 days ago was located in West Siberia, about 6 days ago located in Mongolian Plat. at finally move to Northeast Asia. Compared the propagation process between the two periods, we found that the path was basically the same, but there are evident difference in their signal intensity along its eastward propagation. Comparing with the rapid warm period, the QBW during the hiatus got much intensive as the signal move across the West Siberia. And the enhanced signal keeps its intensity till to Northeast Asia. The intensification of QBW may be related to the changes in the background circulation. During the hiatus period, there are anomalous large-scale changes in 500hPa heights, with a strengthened Ural ridge and a westward East Asia trough. Accordingly, there is a stronger east-west pressure gradient in western Siberia, being a condition beneficial to strengthen the QBW. The possible connection of the background circulation to the surface temperature cooling over Siberia during the hiatus and the underlying mechanisms, however, requires further investigation.