QBO modulation of global monsoon systems with application to northern winter and summer for neutral to moderate ENSO conditions

Abstract. The influence of the stratospheric Quasi-biennial oscillation (QBO) on global monsoon systems and their extratropical teleconnections is investigated using 42 years (1979–2020) of monthly mean ERA-5 reanalyses data, excluding the ∼ 22 % of months with Niño 3.4 index above ±1.0 K. This study provides a unified perspective on how the QBO modulates the global monsoon system for neutral to moderate ENSO conditions, with applications to northern summer and winter. During JJA, QBO westerly (W) at 50 hPa coincides with enhanced rainfall over the Maritime Continent and less over the Western Pacific. For the same JJA and QBO W, the zonal mean cold anomaly in the subtropical UTLS associated with the QBO mean meridional circulation (MMC) acts to reduce static stability in the Northwest Pacific. This coincides with a weaker anticyclonic lower tropospheric circulation and eastward shift in convective rainfall from south of Japan. During DJF, QBO modulation of tropical deep convection alters the planetary wave train pattern emanating from the tropics along the UTLS. QBO W at 50 hPa promotes a positive North Atlantic Oscillation (NAO) phase, with an enhanced Azores High, stronger North Atlantic jet stream, and westward shift in precipitation toward North America. QBO W at 70 hPa promotes a positive Pacific North America (PNA) phase, with anomalous northeastward flow into Alaska and above average precipitation, accompanied by reduced precipitation along the west coast of the United States. In each case, the opposite effect is observed during QBO easterly (E).