Linkage Between a Dominant Mode in the Lower Stratosphere and the Western Hemisphere Circulation Pattern
Xin Tan, Ming Bao
Abstract
Abstract Based on the statistical analyses using ERA data sets, this study reveals a significant linkage between the tropospheric Western Hemisphere (WH) circulation pattern and the stratospheric EOF1 mode (North America [NA] pattern) of the wintertime daily height field at 50 hPa, which exhibits the displacement of the polar vortex to NA. The results of composite analysis indicate that the WH pattern leads the NA pattern at about 5 days. This time‐lagged linkage between the two patterns is further confirmed by the results of time‐lagged singular value decomposition (SVD) analyses. Through the linear interference with climatological waves, the WH pattern contributes to the enhanced (suppressed) wave‐2 (wave‐1) activity propagating into the stratosphere. The characteristics of planetary waves, with opposite sign of anomalous wave‐1 and wave‐2 activity, lead to the formation of the stratospheric NA pattern. We suggest the need for caution in interpreting the stratospheric influences on cold air outbreaks over NA.