A linear CO chemistry parameterization in a chemistry-transport model: evaluation and application to data assimilation

Abstract

Abstract. This paper presents an evaluation of a new linear parameterization valid for the troposphere and the stratosphere, based on a first order approximation of the carbon monoxide (CO) continuity equation. This linear scheme (hereinafter noted LINCO) has been implemented in the 3-D Chemical Transport Model (CTM) MOCAGE (MOdèle de Chimie Atmospherique Grande Echelle). First, a one and a half years of LINCO simulation has been compared to output obtained from a detailed chemical scheme output. The mean differences between both schemes are about ±25 ppbv (part per billion by volume) or 15% in the troposphere and ±10 ppbv or 100% in the stratosphere. Second, LINCO has been compared to diverse observations from satellite instruments covering the troposphere (Measurements Of Pollution In The Troposphere: MOPITT) and the stratosphere (Microwave Limb Sounder: MLS) and also from aircraft (Measurements of ozone and water vapour by Airbus in-service aircraft: MOZAIC programme) mostly flying in the upper troposphere and lower stratosphere (UTLS). In the troposphere, the LINCO seasonal variations as well as the vertical and horizontal distributions are quite close to MOPITT CO observations. However, a bias of ∼ −40 ppbv is observed at 700 hPa between LINCO and MOPITT. In the stratosphere, MLS and LINCO present similar large-scale patterns, except over the poles where the CO concentration is underestimated by the model. In the UTLS, LINCO presents small biases Correspondence to: M. Claeyman (marine.claeyman@aero.obs-mip.fr) less than 2% compared to independent MOZAIC profiles. Third, we assimilated MOPITT CO using a variational 3D-FGAT (First Guess at Appropriate Time) method in conjunction with MOCAGE for a long run of one and a half years. The data assimilation greatly improves the vertical CO distribution in the troposphere from 700 to 350 hPa compared to independent MOZAIC profiles. At 146 hPa, the assimilated CO distribution is also improved compared to MLS observations by reducing the bias up to a factor of 2 in the tropics. This study confirms that the linear scheme is able to simulate reasonably well the CO distribution in the troposphere and in the lower stratosphere. Therefore, the low computing cost of the linear scheme opens new perspectives to make free runs and CO data assimilation runs at high resolution and over periods of several years.

Analysis of a rapid increase of stratospheric ozone during late austral summer 2008 over Kerguelen (49.4° S, 70.3° E)

“…MOCAGE is used for several applications: operational chemical weather forecasting in Météo-France (Dufour et al, 2004), tropospheric as well as stratospheric research studies (e.g. Claeyman et al, 2010;Ricaud et al, 2009a, b), and data assimilation research (e.g. Cathala et al, 2003;Semane et al, 2007;El Amraoui et al, 2008a, b;Semane et al, 2009).…”

Evaluating high-resolution forecasts of atmospheric CO and CO<sub>2</sub> from a global prediction system during KORUS-AQ field campaign

“…In particular, we use measurements of the main products of combustion (i.e., CO and CO 2 ; Gamnitzer et al, 2006) from the NASA DC-8 aircraft, along with observations from five ground sites, two research ships, and four satellites to assess the capability of CAMS to monitor anthropogenic combustion. Although CAMS CO and CO 2 forecasts and analyses have been evaluated previously (Agustí-Panareda et al, 2014Claeyman et al, 2010;Massart et al, 2016;Flemming et al, 2009Flemming et al, , 2015Flemming et al, , 2017, this study is unique for the following reasons.…”

A thermal infrared instrument onboard a geostationary platform for CO and O<sub>3</sub> measurements in the lowermost troposphere: Observing System Simulation Experiments (OSSE)

“…It has been validated during the assimilation of ENVISAT data project (ASSET, Lahoz et al, 2007) and has produced good quality results compared to independent data and other assimilation systems (Geer et al, 2006). Further details on the assimilation system can be found in Massart et al (2009), El Amraoui et al (2008b and Claeyman et al (2010). We use in this study an assimilation window of 1 h.…”