Is there a quasi‐biennial oscillation in tropical deep convection?

Abstract

We investigate the possibility that the stratospheric Quasi‐Biennial Oscillation (QBO) modulates deep convection in the tropics. Interannual variations of outgoing longwave radiation (OLR) in the tropics during 1975–87 are compared with stratospheric zonal winds at Singapore (a measure of the QBO), and with the Tahiti‐Darwin sea level pressure difference (the Southern Oscillation Index, or SOI). A monthly time series of anomalous OLR was constructed for regions of consistently low OLR, thus targeting areas of chronic deep convection. This “chronic cold” index and the SOI correlate at −0.6 for zero lag. The “chronic cold” index correlates with 30 hPa Singapore winds at +0.3 and with 50 hPa‐70 hPa wind differences at +0.4, both near zero lag. These results are not inconsistent with the hypothesis that deep convection may be enhanced in chronically cold areas when QBO westward shear exists in the lower stratosphere, and diminished during eastward shear.