Modulation of the connection between boreal winter ENSO and the South Asian high in the following summer by the stratospheric quasi-biennial oscillation

Abstract

This study investigated the modulation effect of boreal winter quasi-biennial oscillation (QBO) on the connection between winter El Niño-Southern Oscillation (ENSO) events and the variability of the following summer’s South Asian high (SAH) by using European Centre for Medium-Range Weather Forecasts Interim Reanalysis data for the period of 1979-2013. The results suggest that the boreal summer SAH is more significantly influenced by preceding ENSO events in the easterly phase of the QBO than in the westerly phase. The change in the ENSO-SAH relationship in the different QBO phases may be attributable to the change in the ENSO-induced sea surface temperature (SST) anomalies over the tropical Indian Ocean (TIO). Specifically, ENSO’s influence on the following summer’s TIO SST is more significant when the QBO is in its easterly phase than westerly phase. Further analysis showed that the change in the connection between ENSO and the TIO SST in the different QBO phases may be attributable to change in the anomalous tropical Indian Ocean cell (IOC) associated with ENSO. In particular, the anomalous IOC induced by anomalous Walker circulation over the tropical Pacific is stronger and located further west in QBO easterly than westerly phase. This leads to stronger descending motion and larger SST anomalies over the TIO in the QBO easterly phase. These larger SST anomalies over the TIO in the QBO easterly phase could exert a more significant influence on the tropospheric temperature through moist adjustment, which subsequently results in stronger SAH variability.