Influence of the Stratospheric QBO on Seasonal Migration of the Convective Center Across the Maritime Continent

Abstract

Modulation of tropical convection by the stratospheric quasi-biennial oscillation (QBO) during the austral summer has become evident in recent studies. In this study, we show that the QBO affects the seasonal migration of the tropical convection from the equatorial Indian Ocean to the Western Pacific: large-scale convection over the Maritime Continent (MC) and western Pacific strengthens and moves eastward more effectively during easterly QBO (QBO–E) austral summers than during westerly QBO counterparts. This relationship is consistent with an enhanced Madden–Julian Oscillation (MJO) in the QBO–E. The monsoonal active convection over the Sumatra–Borneo region in December produces Kelvin wave-like low temperature anomalies in the tropical tropopause layer (TTL) over the eastern MC. These temperature anomalies strengthen when the lower stratospheric wind is easterly. We propose a hypothesis that the anomalous cooling associated with Kelvin wave-like response produces a favorable condition for the development of penetrating convection into the TTL over the eastern MC and a more effective seasonal march of deep convection across the MC occurs under the QBO–E. The implication of this process for the QBO modulation of the MJO crossing the MC is also discussed.