Quasi-Biennial Oscillation Modulation of Global Monsoon Systems and Regional Teleconnections

Abstract. This study investigates the influence of the stratospheric Quasi-biennial oscillation (QBO) on global monsoon systems and their extratropical teleconnections using 42 years (1979–2020) of monthly mean ERA-5 reanalyses data. QBO modulation of precipitation and circulation variables is examined in the context of downward-progressing QBO phase, separately for JJA and DJF. It is found that QBO teleconnections act primarily by modulating regional circulations. During JJA, QBO westerly (W) at 50 hPa coincide with an intensified Pacific Walker Circulation, with enhanced rainfall over the Maritime Continent and less over the Western Pacific. In the Northen Hemisphere subtropics for same QBO W, the anticyclonic lower tropospheric circulation in the northwest Pacific is reduced, with rainfall south of Japan shifting eastward. During DJF, QBO teleconnections with the North Atlantic Oscillation (NAO) and the Pacific North America (PNA) pattern are observed. QBO W at 50 hPa promotes a positive NAO, which enhances the anticyclonic circulation associated with the Azores High, resulting in a stronger North Atlantic jet stream and a westward shift in precipitation toward the east coast of North America. As QBO phase progress, QBO W at 70 hPa promotes a positive PNA phase, with a trough over the Gulf of Alaska and ridge over the eastern Pacific. This promotes northeastward flow into Alaska and above average precipitation, with less along the west coast of the United States. In each of these examples, the opposite effect is observed during QBO easterly (E) relative to QBO W, suggesting the dominance of linearity in QBO modulations.