Reassessment of causes of ozone column variability following the eruption of Mount Pinatubo using a nudged CCM 1NCAS-Chemistry-Climate, University of Cambridge, Cambridge, UK
2now at: National Institute of Water and Atmospheric Research, Private Bag 50061, Omakau, Central Otago 9352, New Zealand
Received: 09 Feb 2009 – Published in Atmos. Chem. Phys. Discuss.: 02 Mar 2009 Abstract. The eruption of Mount Pinatubo produced the largest loading of stratospheric
sulphate aerosol in the twentieth century. This heated the tropical lower
stratosphere, affecting stratospheric circulation, and provided enhanced
surface area for heterogeneous chemistry. These factors combined to produce
record low values of "global" total ozone column. Though well studied,
there remains some uncertainty about the attribution of this low ozone, with
contributions from both chemical and dynamical effects. We take a
complementary approach to previous studies, nudging the potential temperature and
horizontal winds in the new UKCA chemistry climate model to reproduce
the atmospheric response and assess the impact on global total ozone.
We then combine model runs and observations to distinguish between chemical and dynamical effects.
To estimate the effects of increased heterogeneous chemistry on ozone
we compare runs with volcanically enhanced and background surface aerosol density.
The modelled depletion of global ozone peaks at about 7 DU in early
1993, in good agreement with values obtained from observations.
We subtract the modelled aerosol induced ozone loss from the observed
ozone record and attribute the remaining variability to `dynamical' effects.
The remaining variability is dominated by the QBO.
We also examine tropical and mid-latitude ozone, diagnosing contributions
from El Niño in the tropics and identifying dynamically driven low
ozone in northern mid-latitudes, which we interpret
as possible evidence of changes in the QBO. We conclude that,
on a global scale, the record lows of extra-polar ozone
are produced by the increased heterogeneous chemistry, although there is
evidence for dynamics produced low ozone in certain
regions, including northern mid-latitudes.
Revised: 22 Jun 2009 – Accepted: 24 Jun 2009 – Published: 03 Jul 2009
Citation: Telford, P., Braesicke, P., Morgenstern, O., and Pyle, J.: Reassessment of causes of ozone column variability following the eruption of Mount Pinatubo using a nudged CCM, Atmos. Chem. Phys., 9, 4251-4260, doi:10.5194/acp-9-4251-2009, 2009.