Page 1 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 1 Stratospheric Distribution of CO 2 from the MIPAS High-resolution Full Mission Bianca Maria Dinelli Istituto di Scienze dell'Atmosfera e del Clima CNR (Italy) Massimo Carlotti Enzo Papandrea Dip.to di Chimica Fisica e Inorganica Università di Bologna (Italy) Fabrizio Niro SERCO -Itala Spa

Page 2 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 2 INTRODUCTION (1/2) w Carbon dioxide is very important for the energy balance of the Earth’s atmosphere. w CO 2 concentration in the troposphere is steadily increasing (1–2 ppmv per year) due to anthropogenic influences. w The increase of CO 2 near the surface propagates upwards reaching the upper stratosphere after about 5–6 years. w In the mesosphere the CO 2 VMR is depleted through molecular diffusion and photochemically destroyed by solar UV radiation and by collisions with O +.

Page 3 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 3 INTRODUCTION (2/2) w CO 2 is supposed to have a nearly constant Volume Mixing Ratio (VMR) in the stratosphere owing to the absence of significant sources or sinks. w Due to its low variability in the stratosphere, CO 2 is commonly used to derive Temperature (T) and Pressure (p) from stratospheric infrared spectra assuming its VMR as well known. w However there is a lack of measurements of CO 2 vertical distribution in the stratosphere, so the used VMR values come from theoretical models. w Can MIPAS provide information about CO 2 in stratosphere?

Page 4 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 4 DATA ANALYSIS wMIPAS observations have been analyzed with the open source GMTR retrieval system ( Carlotti et al. Appl. Opt. 45, (2006) ). wThe main characteristics of GMTR are: wThe horizontal inhomogeneities of the atmosphere are modelled using a 2-D discretization of the atmosphere. wObservations of a full orbit can be simultaneously analyzed wThe (2-D) retrieval grid is fully independent from the measurement grid. wTarget species can be retrieved simultaneously (Multi-Target- Retrieval) in order to suppress the systematic error due to spectral interferences.

Page 5 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 5 DATA ANALYSIS wFor the CO2 retrieval, GMTR has been upgraded with: wCO2 new line-mixing modeling ( Niro et al. JQSRT, doi: (2006) ) wTarget-dependent vertical retrieval grid. wThe MTR strategy has been exploited for the simultaneous retrieval of p, T and CO 2 VMR w10 MicroWindows (MWs) have been selected with the program MWMAKE ( Dudhia et al., Appl. Opt., 41, 3665 (2002) ).

Page 6 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 6 p, T, CO 2 MicroWindows

Page 7 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 7 CO 2 systematic error budget O3O3

Page 8 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 8 DATA ANALYSIS wOzone and water give the main contributions to the systematic error. wMW selection for p, T, H 2 O, O 3 and CO 2 retrieval not successful. wRETRIEVAL STRATEGY wGMTR of p, T, H 2 O, O 3 wGMTR of p, T, CO 2 using H 2 O and O 3 from step 1. wCheck on consistency of p, T retrieved in the two steps

Page 9 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 9 Temperature from p, T, H2O, O3 and from p, T, CO2

Page 10 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 10 RESULTS w The entire MIPAS full resolution mission (July 2002 – March 2004) has been processed. w To reduce ESDs the vertical retrieval grid of CO 2 has been degraded to 6 km steps. w The accuracy obtained for the individual CO 2 VMR values is comparable with the one obtained for other well-determined MIPAS targets (such as ozone). w For most applications the accuracy requirements for CO 2 are much more stringent. w The too big random component of the error can be reduced by averaging. w Monthly averages have been performed over 10 deg Latitude bins and altitude intervals of 6 km.

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Page 12 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 12 July 02Sept. 02Jan. 03July 03March 03

Page 13 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 13 Discussion  The random error has been reduced by the averaging process and is negligible  The systematic component is significant: ~ 8%.  We have evaluated the contributions to the systematic error of water and ozone uncertainties by propagating their retrieval errors in the CO 2 retrieval.

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Page 15 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 15 Discussion  As a consequence of the averaging process, part of the remaining systematic components can be scaled down: a careful estimate of the individual systematic errors is in progress  For internal comparison the effect of systematic errors that affect the CO 2 fields in the same direction (i.e. spectroscopic errors) can be neglected.

Page 16 ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 16 Conclusions  No correlation found with the retrieved temperature and pressure  The observed altitude and time variations that exceed the range of the systematic error need to be explained.  The low CO 2 VMR at high altitudes is consistent with its reduction for diffusion and destruction by photo dissociation.  Not clear the origin of the low values consistently found at ~36 km (3.6 hPa )  The magnitude of the systematic errors still prevents absolute conclusions (i.e. age of stratospheric air)

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