Midlatitude stratosphere – troposphere exchange as diagnosed by MLS O3 and MOPITT CO assimilated fields 1CNRM-GAME, Météo-France and CNRS, URA 1357, Toulouse, France
2Laboratoire d'Aérologie, Université de Toulouse, CNRS/INSU, Toulouse, France
3CNRM, Direction de la Météorologie Nationale, Casablanca, Morocco
4University of Maryland, Baltimore County, USA
5CERFACS, Toulouse, France
6Laboratoire de l'Atmosphère et des Cyclones, Université de La Réunion, France
Received: 05 Jun 2009 – Published in Atmos. Chem. Phys. Discuss.: 01 Oct 2009 Abstract. This paper presents a comprehensive characterization of a very deep
stratospheric intrusion which occurred over the British Isles on
15 August 2007. The signature of this event is diagnosed using
ozonesonde measurements over Lerwick, UK (60.14° N,
1.19° W) and is also well characterized using meteorological
analyses from the global operational weather prediction model of
Météo-France, ARPEGE. Modelled as well as assimilated fields of
both ozone (O3) and carbon monoxide (CO) have been used
in order to better document this event. O3 and CO from
Aura/MLS and Terra/MOPITT instruments, respectively, are assimilated
into the three-dimensional chemical transport model MOCAGE of
Météo-France using a variational 3-D-FGAT (First Guess at
Appropriate Time) method.
The validation of O3 and CO assimilated fields is done using
self-consistency diagnostics and by comparison with independent observations
such as MOZAIC (O3 and CO), AIRS (CO) and OMI (O3).
It particularly shows in the upper troposphere and lower stratosphere region
that the assimilated fields are closer to MOZAIC than the free model run.
The O3 bias between MOZAIC and the analyses is −11.5 ppbv
with a RMS of 22.4 ppbv and a correlation coefficient of 0.93, whereas
between MOZAIC and the free model run, the corresponding values are 33 ppbv,
38.5 ppbv and 0.83, respectively. In the same way, for CO,
the bias, RMS and correlation coefficient between MOZAIC and the analyses are −3.16 ppbv,
13 ppbv and 0.79, respectively, whereas between MOZAIC and the free model they are
6.3 ppbv, 16.6 ppbv and 0.71, respectively.
The paper also presents a demonstration of the capability of O3 and CO
assimilated fields to better describe a stratosphere-troposphere exchange (STE) event
in comparison with the free run modelled O3 and CO fields.
Although the assimilation of MLS data improves the distribution of
O3 above the tropopause compared to the free model run, it is not
sufficient to reproduce the STE event well. Assimilated MOPITT CO allows a better qualitative
description of the stratospheric intrusion event.
The MOPITT CO analyses appear more promising than the MLS
O3 analyses in terms of their ability to capture a deep STE event.
Therefore, the results of this study open the perspectives for using MOPITT CO in the STE studies.
Revised: 12 Feb 2010 – Accepted: 16 Feb 2010 – Published: 02 Mar 2010
Citation: El Amraoui, L., Attié, J.-L., Semane, N., Claeyman, M., Peuch, V.-H., Warner, J., Ricaud, P., Cammas, J.-P., Piacentini, A., Josse, B., Cariolle, D., Massart, S., and Bencherif, H.: Midlatitude stratosphere – troposphere exchange as diagnosed by MLS O3 and MOPITT CO assimilated fields, Atmos. Chem. Phys., 10, 2175-2194, doi:10.5194/acp-10-2175-2010, 2010.