Abstract
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.
Highlights
Chemistry–climate models (CCMs), which calculate ozone interactively and include asymmetric ozone effects, have existed since the early 2000s (CCMVal, 2010)
To understand the differences in planetary wave propagation depending on the phase of the quasi-biennial oscillation (QBO), and how ozone waves modulate them, we look at the life cycles of individual events of upward wave propagation from the tropowww.atmos-chem-phys.net/18/6637/2018/
We examine the implication of these effects on the seasonal cycle of the autumn–winter season by inspecting the differences between our two simulations, with and without ozone waves passed onto the radiation code
Summary
Chemistry–climate models (CCMs), which calculate ozone interactively and include asymmetric ozone effects, have existed since the early 2000s (CCMVal, 2010). Due to their large numerical cost, CCMs have mostly been used to study stratospheric processes, and only in recent years have they been coupled to an interactive ocean for the purpose of performing multidecadal climate simulations, air pollution, and aerosol studies. The majority of the fifth Coupled Model Intercomparison Project (CMIP5) models (Taylor et al, 2012) do not use interactive atmospheric chemistry; instead, they prescribe a zonal mean monthly mean ozone field, neglecting the effects of zonal asymmetries in the ozone field (ozone waves). In order to compare and evaluate the performance of models using either interactive chemistry (including ozone waves) or prescribed zonal mean ozone (neglecting ozone waves), it is Published by Copernicus Publications on behalf of the European Geosciences Union
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