VARIABILITY IN THE UPWARD PROPAGATING SEMIDIURNAL TIDE DUE TO EFFECTS OF QBO IN THE LOWER ATMOSPHERE

We report on a series of numerical experiments designed to investigate the effects of the quasi-biennial oscillation (QBO) in the stratosphere on upward propagating semidiurnal tides. Our results indicate that significant variability (5-20 m/s) in semidiurnal winds in the mesosphere is attributable to the QBO of stratospheric mean winds and temperatures. While QBO variability in the background atmosphere is largely confined to low latitudes in the lower atmosphere, the QBO signature in upward propagating semidiurnal tides during January is largely evident in the neutral wind field at high latitudes in the mesosphere. Subsequent Hough mode decompositions of our tidal calculations indicate that the QBO primarily affects the (2,2) and (2,3) modes. The absolute magnitudes of the effect on these modes are comparable but the largest percent change is evident in the (2,3) mode. Our results also show that the QBO of stratospheric ozone does not affect semidiurnal tidal forcing.