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Stratospheric Distribution of CO 2 from the MIPAS High-resolution Full Mission

Stratospheric Distribution of CO 2 from the MIPAS High-resolution Full Mission. Massimo Carlotti Enzo Papandrea Dip.to di Chimica Fisica e Inorganica Università di Bologna (Italy). Bianca Maria Dinelli Istituto di Scienze dell'Atmosfera e del Clima CNR (Italy). Fabrizio Niro

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Stratospheric Distribution of CO 2 from the MIPAS High-resolution Full Mission

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  1. Stratospheric Distribution of CO2 from the MIPAS High-resolution Full Mission Massimo Carlotti Enzo Papandrea Dip.to di Chimica Fisica e Inorganica Università di Bologna (Italy) Bianca Maria Dinelli Istituto di Scienze dell'Atmosfera e del Clima CNR (Italy) Fabrizio Niro SERCO -Itala Spa

  2. INTRODUCTION (1/2) • Carbon dioxide is very important for the energy balance of the Earth’s atmosphere. • CO2 concentration in the troposphere is steadily increasing (1–2 ppmv per year) due to anthropogenic influences. • The increase of CO2 near the surface propagates upwards reaching the upper stratosphere after about 5–6 years. • In the mesosphere the CO2 VMR is depleted through molecular diffusion and photochemically destroyed by solar UV radiation and by collisions with O+.

  3. INTRODUCTION (2/2) • CO2 is supposed to have a nearly constant Volume Mixing Ratio (VMR) in the stratosphere owing to the absence of significant sources or sinks. • Due to its low variability in the stratosphere, CO2 is commonly used to derive Temperature (T) and Pressure (p) from stratospheric infrared spectra assuming its VMR as well known. • However there is a lack of measurements of CO2 vertical distribution in the stratosphere, so the used VMR values come from theoretical models. • Can MIPAS provide information about CO2 in stratosphere?

  4. DATA ANALYSIS • MIPAS observations have been analyzed with the open source GMTR retrieval system (Carlotti et al. Appl. Opt. 45, 716-727(2006) ). • The main characteristics of GMTR are: • The horizontal inhomogeneities of the atmosphere are modelled using a 2-D discretization of the atmosphere. • Observations of a full orbit can be simultaneously analyzed • The (2-D) retrieval grid is fully independent from the measurement grid. • Target species can be retrieved simultaneously (Multi-Target-Retrieval) in order to suppress the systematic error due to spectral interferences.

  5. DATA ANALYSIS • For the CO2 retrieval, GMTR has been upgraded with: • CO2 new line-mixing modeling (Niro et al. JQSRT, doi:10.1016 (2006) ) • Target-dependent vertical retrieval grid. • The MTR strategy has been exploited for the simultaneous retrieval of p, T and CO2 VMR • 10 MicroWindows (MWs) have been selected with the program MWMAKE (Dudhia et al., Appl. Opt., 41, 3665(2002)).

  6. p, T, CO2 MicroWindows

  7. O3 CO2 systematic error budget

  8. DATA ANALYSIS • Ozone and water give the main contributions to the systematic error. • MW selection for p, T, H2O, O3 and CO2 retrieval not successful. • RETRIEVAL STRATEGY • GMTR of p, T, H2O, O3 • GMTR of p, T, CO2 using H2O and O3 from step 1. • Check on consistency of p, T retrieved in the two steps

  9. Temperature from p, T, H2O, O3 and from p, T, CO2

  10. RESULTS • The entire MIPAS full resolution mission (July 2002 – March 2004) has been processed. • To reduce ESDs the vertical retrieval grid of CO2 has been degraded to 6 km steps. • The accuracy obtained for the individual CO2 VMR values is comparable with the one obtained for other well-determined MIPAS targets (such as ozone). • For most applications the accuracy requirements for CO2 are much more stringent. • The too big random component of the error can be reduced by averaging. • Monthly averages have been performed over 10 deg Latitude bins and altitude intervals of 6 km.

  11. July 02 Sept. 02 Jan. 03 March 03 July 03

  12. 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 CO2 retrieval.

  13. 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 CO2 fields in the same direction (i.e. spectroscopic errors) can be neglected.

  14. 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 CO2 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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