page 1 envisat symposium - montreux – 23/27 april 2007 page 1 stratospheric distribution of co 2...

ENVISAT SYMPOSIUM - Montreux – 23/27 April 2007 Page 1

Stratospheric Distribution of CO2 from the MIPAS High-resolution Full

Mission

Bianca Maria Dinelli

Istituto di Scienze dell'Atmosfera e del Clima CNR (Italy)

Massimo CarlottiEnzo Papandrea

Dip.to di Chimica Fisica e InorganicaUniversità di Bologna (Italy)

Fabrizio NiroSERCO -Itala Spa


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+.


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?


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.


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) ).


p, T, CO2 MicroWindows


CO2 systematic error budget

O3


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


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


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.


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


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.


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.


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)

page 1 envisat symposium - montreux – 23/27 april 2007 page 1 stratospheric distribution of co 2...

Documents