On the Direct Influence of the Stratospheric QBO on the Troposphere: A History of Observational Studies (1955–2003) (Invited Presentation)

An overview of observational studies during 1955-2003 is presented which investigated the direct influence of the stratospheric quasi-biennial oscillation (QBO) on tropical deep convection, with an emphasis on QBO differences in synoptic patterns in the upper troposphere / lower stratosphere (UTLS). Historical studies are highlighted which explored issues including depth of penetration into the troposphere, modulation of tropopause altitude, zonal asymmetry, effect on tropospheric weather phenomena, and the meridional extent of influence of the QBO mean meridional circulation into the extratropical UTLS. Proposed physical mechanisms for how the QBO can modulate deep convection, and therefore tropospheric circulation systems, include the effects of tropopause altitude, UTLS vertical wind shear, and UTLS inertial stability.

QBO differences in synoptic patterns of tropopause temperature, tropopause pressure, 70-150 hPa zonal wind shear, and 150 hPa relative vorticity are shown as a function of season for the 43-yr period 1958-2000. During QBO easterly shear, the tropical tropopause is ~0.5-1 K colder, at ~2-3 hPa lower pressure, and ~200-300 m higher altitude than during QBO westerly shear. The QBO temperature signal is largest over centers of deep convection. In the tropics, QBO easterly shear favors more intense deep convection, with effects being larger during boreal winter. QBO westerly shear reduces 70-150 hPa wind shear in the subtropical North Atlantic. Subtropical westerly jets are stronger and displaced equatorward during QBO westerly shear. This historical overview is a contribution to the Stratospheric Processes and their Role in Climate (SPARC) initiative Stratospheric and Tropospheric Influences on Tropical Convective Systems (SATIO-TCS).