Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E) 1Laboratoire de l'Atmosphère et des Cyclones, UMR CNRS 8105, Université de La Réunion, France
2CNRM-GAME, Météo-France and CNRS, URA 1357, Toulouse, France
3Laboratoire Atmosphères, Milieux, Observations Spatiales, Université Versailles St-Quentin, CNRS-INSU, Verrières-le-Buisson, France
*now at: Jet Propulsion Laboratory, Pasadena, California, USA
Received: 11 Apr 2010 – Published in Atmos. Chem. Phys. Discuss.: 23 Jul 2010 Abstract. This paper reports on an increase of ozone event observed over Kerguelen
(49.4° S, 70.3° E) in relationship with large-scale isentropic
transport. This is evidenced by ground-based observations (co-localised
radiosonde and SAOZ experiments) together with satellite global
observations (Aura/MLS) assimilated into MOCAGE, a Méteo-France model.
Revised: 08 Nov 2010 – Accepted: 30 Nov 2010 – Published: 14 Jan 2011
The study is based on the analyses of the first ozonesonde experiment never
recorded at the Kerguelen site within the framework of a French campaign called
ROCK that took place from April to August 2008.
Comparisons and interpretations of the observed event are supported by
co-localised SAOZ observations, by global mapping of tracers (O3,
N2O and columns of O3) from Aura/MLS and Aura/OMI experiments, and
by model simulations of Ertel Potential Vorticity initialised by the ECMWF
(European Centre for Medium-Range Weather Forecasts) data reanalyses.
Satellite and ground-based observational data revealed a consistent increase
of ozone in the local stratosphere by mid-April 2008. Additionally, Ozone
(O3) and nitrous oxide (N2O) profiles obtained during January–May 2008 using the Microwave Limb Sounder (MLS) aboard the Aura satellite are
assimilated into MOCAGE (MOdèle de Chimie Atmosphérique à Grande
Echelle), a global three-dimensional chemistry transport model of
Météo-France. The assimilated total O3 values are consistent
with SAOZ ground observations (within ±5%), and isentropic
distributions of O3 match well with maps of advected potential
vorticity (APV) derived from the MIMOSA model, a high-resolution advection
transport model, and from the ECMWF reanalysis.
The event studied seems to be related to the isentropic transport of air masses
that took place simultaneously in the lower- and middle-stratosphere,
respectively from the polar region and from the tropics to the mid-latitudes.
In fact, the ozone increase observed by mid April 2008 resulted
simultaneously: (1) from an equator-ward departure of polar air masses
characterised with a high-ozone layer in the lower stratosphere (near the
475 K isentropic level), and (2) from a reverse isentropic transport from
the tropics to mid- and high-latitudes in the upper stratosphere (nearby the
700 K level). The increase of ozone observed over Kerguelen from the 16-April
ozonesonde profile is thus attributed to a concomitant isentropic transport
of ozone in two stratospheric layers: the tropical air moving southward and
reaching over Kerguelen in the upper stratosphere, and the polar air passing
over the same area but in the lower stratosphere.
Citation: Bencherif, H., El Amraoui, L., Kirgis, G., Leclair De Bellevue, J., Hauchecorne, A., Mzé, N., Portafaix, T., Pazmino, A., and Goutail, F.: Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E), Atmos. Chem. Phys., 11, 363-373, doi:10.5194/acp-11-363-2011, 2011.