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Volume 18, issue 9 | Copyright
Atmos. Chem. Phys., 18, 6637-6659, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 09 May 2018

Research article | 09 May 2018

Radiative effects of ozone waves on the Northern Hemisphere polar vortex and its modulation by the QBO

Vered Silverman1, Nili Harnik1, Katja Matthes2, Sandro W. Lubis3, and Sebastian Wahl2 Vered Silverman et al.
  • 1Department of Geophysics, Faculty of Exact Sciences, Tel Aviv University, Tel Aviv, Israel
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • 3Department of the Geophysical Sciences, The University of Chicago, Chicago, IL, USA

Abstract. The radiative effects induced by the zonally asymmetric part of the ozone field have been shown to significantly change the temperature of the NH winter polar cap, and correspondingly the strength of the polar vortex. In this paper, we aim to understand the physical processes behind these effects using the National Center for Atmospheric Research (NCAR)'s Whole Atmosphere Community Climate Model, run with 1960s ozone-depleting substances and greenhouse gases. We find a mid-winter polar vortex influence only when considering the quasi-biennial oscillation (QBO) phases separately, since ozone waves affect the vortex in an opposite manner. Specifically, the emergence of a midlatitude QBO signal is delayed by 1–2 months when radiative ozone-wave effects are removed. The influence of ozone waves on the winter polar vortex, via their modulation of shortwave heating, is not obvious, given that shortwave heating is largest during fall, when planetary stratospheric waves are weakest. Using a novel diagnostic of wave 1 temperature amplitude tendencies and a synoptic analysis of upward planetary wave pulses, we are able to show the chain of events that lead from a direct radiative effect on weak early fall upward-propagating planetary waves to a winter polar vortex modulation. We show that an important stage of this amplification is the modulation of individual wave life cycles, which accumulate during fall and early winter, before being amplified by wave–mean flow feedbacks. We find that the evolution of these early winter upward planetary wave pulses and their induced stratospheric zonal mean flow deceleration is qualitatively different between QBO phases, providing a new mechanistic view of the extratropical QBO signal. We further show how these differences result in opposite radiative ozone-wave effects between east and west QBOs.

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This study provides a quantified and mechanistic understanding of the radiative effects of ozone waves on the NH stratosphere. In particular, we find these effects to influence the seasonal evolution of the midlatitude QBO signal (Holton–Tan effect), which is important for getting realistic dynamical interactions in climate models. We also provide a synoptic view on the evolution of the seasonal development of the Holton–Tan effect by looking at the life cycle of upward-propagating waves.
This study provides a quantified and mechanistic understanding of the radiative effects of ozone...