Connections between the stratospheric quasi-biennial oscillation and tropospheric circulation over Asia in northern autumn

摘要

We investigate the variations in tropospheric circulation over Asia associated with the stratospheric quasi-biennial oscillation (QBO) during Northern Hemisphere (NH) autumn (September-November) using the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) Reanalysis and NCEP-Department of Energy (DOE) Reanalysis II data sets for a 25 year period (1980-2004). The anomaly fields in this study are expressed as the easterly years minus the westerly years of the QBO. The zonal wind distribution at 200 hPa indicates easterly anomalies at low latitudes from India through Taiwan, statistically significant westerly anomalies at midlatitudes including the Tibetan Plateau to northern China, and significant easterly anomalies in the high-latitude Eurasia north of 50°N. A momentum balance analysis indicates that these anomalies over Asia are attributable to atmospheric waves and residual mean meridional flow. Significant northward and descending anomalies are observed in the lower stratosphere over Asia, with detectable signals in the troposphere around Tibet. The adiabatic heating due to descending motions in the region centering on India and Bangladesh is consistent with the distribution of rainfall anomalies. The formation of zonal wind anomalies over South Asia seems to be associated with not only wave activities but also adiabatic heating and thermal advection. We suggest that the QBO may be linked to tropospheric circulation over Asia through wave activities and convective activities in autumn, and the wave activities in the low latitudes associated with the QBO seem to be connected with the rainfall distribution over the Asian monsoon region. Key Points Relationship between QBO and troposphere over Asia in autumn Wave activity and meridional circulation with QBO Convective activity associated with QBO