Midlatitude stratosphere – troposphere exchange as diagnosed by MLS O<sub>3</sub> and MOPITT CO assimilated fields

Abstract

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 (O 3 ) and carbon monoxide (CO) have been used in order to better document this event. O 3 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 O 3 and CO assimilated fields is done using selfconsistency diagnostics and by comparison with independent observations such as MOZAIC (O 3 and CO), AIRS (CO) and OMI (O 3 ). 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 O 3 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 Correspondence to: L. El Amraoui (laaziz.elamraoui@meteo.fr) 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 O 3 and CO assimilated fields to better describe a stratosphere-troposphere exchange (STE) event in comparison with the free run modelled O 3 and CO fields. Although the assimilation of MLS data improves the distribution of O 3 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 O 3 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.

Validity of satellite measurements used for the monitoring of UV radiation risk on health

“…The meteorological analyses of Météo-France ARPEGE Numerical Weather Prediction Model (Courtier et al, 1991) have been used to initialize and constrain the dynamics of the model every 3 h (with linear interpolation in between). The simulations presented here have also assimilated AURA/MLS stratospheric ozone profile information using a variational 3d-fgat method as in El Amraoui et al (2010).…”

Diagnosing the transition layer at extratropical latitudes using MLS O<sub>3</sub> and MOPITT CO analyses

“…MOCAGE-PALM has been used to assess the quality of satellite O 3 measurements . The MOCAGE-PALM, assimilation products have been used in many atmospheric studies in relation to the O 3 loss in the Arctic vortex (El Amraoui et al, 2008a), tropics-midlatitudes exchange , STE , exchange between the polar vortex and the midlatitudes (El Amraoui et al, 2008b) and diagnosing STE from O 3 and CO fields (El Amraoui et al, 2010).…”

“…Data assimilation has the capability to overcome possible deficiencies of the MOCAGE model in the UTLS (see, e.g., Semane et al, 2007;Barret et al, 2008;El Amraoui et al, 2010;Barré et al, 2012). The aim of this study is to quantify the impact of the assimilation of O 3 and CO data on the UTLS at extratropical latitudes.…”

“…The aim of this study is to quantify the impact of the assimilation of O 3 and CO data on the UTLS at extratropical latitudes. We use the same case study as presented by El Amraoui et al (2010) that considers a deep stratospheric intrusion on 15 August 2007 over the British Isles (50 • N, 10 • W). In this previous study, detailed validation demonstrated the capability of CO and O 3 analyses to better represent the STE.…”

“…Section 2 provides the description of the model, the remotely sensed data and the assimilation system. Section 3 provides a brief description of the STE event in August 2007 that was fully evaluated by El Amraoui et al (2010). A set of diagnostics proposed by Pan et al (2007) are used on this case study for the different assimilation experiments.…”