Derivation of Tropospheric NO2 by Synergistic Use of Satellite Observations and a Chemical Transport Model

A contribution to ACCENT-TROPOSAT-2, Task Group 2

Thilo Erbertseder

DLR, Deutsches Fernerkundungsdatenzentrum (DFD), Oberpfaffenhofen
D-82234 Wessling, Germany
Tel.:  +49-(0)8153-28 3665
Fax:  +49-(0)8153-28 1363

Tropospheric NO2 columns can be derived by combining satellite observations and analyses of a chemical-transport model.

In the proposed method the tropospheric column is gained by subtracting the stratospheric column, obtained by CTM analyses, from NO2 vertical column density observations from GOME and SCIAMACHY. In order to account for the daily cycle of NO2 and the nitrogen family in general, the stratospheric analysis is derived for exactly the overpass time of the satellite-borne instrument. To avoid a bias the stratospheric analysis can be scaled to “clean” observation conditions. The tropopause is defined by thresholds of potential vorticity and temperature in the tropics. The cloudiness of the observations is considered.

Within the framework of TROPOSAT a number of contributions are envisaged.

1.      The derivation of tropospheric NO2 column densities will be applied to ESA SCIAMACHY Level 2 data and the latest version of ESA GOME Level 2 data (GDP 3.4) from 1995-2003.

2.      As it was shown recently by Thomas et al. (2003) CTM simulations of stratospheric NO2 distributions can be combined successfully with total column densities to derive tropospheric NO2 columns. Airborne measurements of nitrogen compounds during the SPURT campaign indicate a good coincidence with the retrieved tropospheric columns (Hegglin et al., 2004). Analyses of stratospheric nitrogen dioxide will be derived using the 3D global chemical-transport model DLR-ROSE 3.0 to account e.g. for zonal stratospheric variability. The model was significantly improved recently within the AFO 200 project INVERT (Bittner et al. 2004). The model is driven by ECMWF analyses and covers all relevant chemical and physical processes of the stratosphere.

3.      Besides the use of CTM results of stratospheric NO2, however, we also aim at assimilating ENVISAT-MIPAS observations of nitrogen compounds into the CTM DLR-ROSE 3.0. By using these observations an additional improvement of the stratospheric analysis is expected.

4.      Additional to the cloud fraction of each pixel, the cloud-top height information will be exploited, too. It will be investigated to what extent the cloud-top height information allows for tropospheric column slicing. Cloud fraction will be derived by the Optical Cloud Recognition Algorithm (OCRA) (Loyola, 1998) and cloud-top height will be determined by ROCINN (Retrieval of Cloud Information by a Neural Network).

5.      Additional application of 4D Var analyses of GOMOS, MIPAS and SCIAMACHY for improved stratospheric analysis of NO2

Time schedule

 

2004

2005

2006

2007

2008

Activity 1

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Activity 2

 

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Activity 3

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Activity 4

 

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Activity 5

 

 

 

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Aims for the first 18 months

·   Exploitation of ESA GDP NO2 vertical column densities (Version 3.4) from 1995-2003 and ESA SCIAMACHY NO2 vertical column densities (Version > 5)

·   Use of assimilated MIPAS observations for derivation of stratospheric NO2 column

Long term goals

·   Exploitation of cloud-top heights as derived by ROCINN for tropospheric column slicing

·   Validation by airborne measurements

·   Use of 4-D Var analyses of GOMOS, MIPAS and SCIAMACHY for derivation of stratospheric NO2 column

Approximate manpower and cost (travel costs only)

 

2004

2005

2006

2007

2008

Personnel / man-years

1

2

2

2

2

Yearly cost (kECU)

5

10

10

10

10

Likely funding agencies

Work is currently funded by SACADA (BMBF, Germany) and EVIVA (DLR)

Co-workers

 Frank Baier
DLR-DFD
 

Julian Meyer-Arnek,
 DLR-DFD
 

 


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