Stratospheric Variability at a glance – Analysis of the
intra decadal timescale and the QBO
Duy Cai1, Martin Dameris1, Hella Garny1, Felix Bunzel2, Patrick Jöckel1, and Phoebe Graf11Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany 2Max-Planck-Institut für Meteorologie, Hamburg, Germany
Received: 29 Sep 2016 – Accepted for review: 25 Oct 2016 – Discussion started: 26 Oct 2016
Abstract. In this study the stratospheric variability is analysed from decadal to seasonal timescales. Relevant processes for the decadal timescale are identified by means of power spectral analysis. The inspection of the ERA-Interim reanalysis data set shows considerably high variability at the 12 and 6 months period. But also in the extra tropical region at intra-annual to seasonal timescales clear peaks in the power spectrum arise. In addition to that, the quasi-biennial oscillation (QBO) obviously contributes to the stratospheric variability at decadal timescales. Regarding the power spectrum of EMAC 2.52 model simulations, only a model configuration with a vertical resolution smaller than 1 km in the stratosphere is capable to capture the relevant features of the spectrum. In particular, the model with a coarser distribution of vertical levels cannot reproduce the QBO signal. The analysis of the corresponding wave spectra reveals that, if the vertical resolution is insufficient, primarily the Mixed-Rossby-Gravity waves cannot be adequately reproduced. Estimates made by linear wave theory show that for reanalysis data the Mixed-Rossby-Gravity waves with equivalent depths between 50 m to 250 m are relevant for the QBO. In order to resolve these relevant waves, model simulations need to consider a vertical resolution of at least 1 km.
Cai, D., Dameris, M., Garny, H., Bunzel, F., Jöckel, P., and Graf, P.: Stratospheric Variability at a glance – Analysis of the
intra decadal timescale and the QBO, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2016-870, 2016.