The Tropospheric Response to Stratospheric Quasi-Bienniel Oscillation during Boreal Summer

The possible impact of stratospheric quasi-bienniel oscillation (QBO) on the tropospheric circulation during boreal summer is examined by using the NCEP-NCAR reanalysis, outgoing long-wave radiation and tropical cyclone track data. It is found that the QBO modulates convective activities over the western North Pacific by changing vertical wind shear in the upper troposphere. The resulting latent heating then influences extratropical circulations by exciting Rossby wave trains. A series of simple model integrations confirm this finding.

The QBO-induced circulation has a significant impact on the low-frequency variability in the boreal summer. For instance, it modifies the tropical cyclone track over the western North Pacific. In general, more tropical cyclones approach the East China Sea during the westerly phase than the easterly phase of the QBO. Although relatively weak, it also affects the PNA and MJO.