The Influence of the QBO on the Propagation of Equatorial Waves into the Stratosphere

Abstract

The variation of stratospheric equatorial wave characteristics with the phase of the quasi-biennial oscillation (QBO) is investigated using ECMWF Re-Analysis and NOAA outgoing longwave radiation (OLR) data. The impact of the QBO phases on the upward propagation of equatorial waves is found to be consistent and significant. In the easterly phase, there is larger Kelvin wave amplitude but smaller westward-moving mixed Rossby-gravity (WMRG) and n 5 1 Rossby (R1) wave amplitude due to reduced propagation from the upper troposphere into the lower stratosphere, compared with the westerly phase. Differences in the wave amplitude exist in a deeper layer in summer than in winter, consistent with the seasonality of ambient zonal winds. There is a strong evidence of Kelvin wave amplitude peaking just below the descending westerly phase, suggesting that Kelvin waves act to bring the westerly phase downward. However, the corresponding evidence for WMRG and R1 waves is less clear.In the lower stratosphere there is zonal variation in equatorial waves. This reflects the zonal asymmetry of wave amplitudes in the upper troposphere, the source for the lower-stratospheric waves. In easterly winters the upper-tropospheric WMRG and R1 waves over the eastern Pacific region appear to be somewhat stronger compared to climatology, perhaps because of the accumulation of waves that are unable to propagate upward into the lower stratosphere. Vertical propagation features of these waves are generally consistent with theory and suggest a mixture of Doppler shifting by ambient flows and filtering. Some lower-stratosphere equatorial waves have a connection with preceding tropical convection, especially for Kelvin and R1 waves in winter.

Wave Forcing of the Quasi-Biennial Oscillation in the Max Planck Institute Earth System Model

“…1b) and, thus, favorable for the propagation of westerly waves (Ern et al 2008;Yang et al 2011). 1b) and, thus, favorable for the propagation of westerly waves (Ern et al 2008;Yang et al 2011).…”

“…Ern and Preusse (2009b) and Yang et al (2011) illustrated the underlying wave attenuation by the loss of spectral power of filtered wave modes with altitude. Ern and Preusse (2009b) and Yang et al (2011) illustrated the underlying wave attenuation by the loss of spectral power of filtered wave modes with altitude.…”

Idealized Quasi-Biennial Oscillations in an Ensemble of Dry GCM Dynamical Cores

“…13, which shows the temperature wavenumber-frequency analyses at 181, 94, 22, and 2 hPa for the SE dynamical core as an example. Similar absorption patterns were also found in Yang et al (2011) and Krismer and Giorgetta (2014). 1d and 3d.…”

“…The use of z in Eqs. It fosters the development of extratropical waves, which have been observed to trigger Kelvin waves in the equatorial region (Straub and Kiladis 2003;Yang et al 2007). The Richardson number serves two purposes.…”

“…Garfinkel and Hartmann (2011) used idealized dry model experiments with a forced QBO to discuss the impact of the QBO-induced meridional circulation on the tropospheric flow. Furthermore, it is well documented that the QBO acts as a filtering mechanism for upward-traveling waves (e.g., see Yang et al 2011Yang et al , 2012Krismer and Giorgetta 2014) and thereby modulates the wave composition in the mesosphere. Furthermore, it is well documented that the QBO acts as a filtering mechanism for upward-traveling waves (e.g., see Yang et al 2011Yang et al , 2012Krismer and Giorgetta 2014) and thereby modulates the wave composition in the mesosphere.…”