Determining Tropospheric Composition from Satellite Measurements
Lara Gunn(1), Martyn Chipperfield(1), Richard Siddans(2) and Brian Kerridge(3)
(1) University of Leeds, Leeds, LS2 9JT, United Kingdom
(2) CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon OX11 0QX , United Kingdom
(3) CCLRC Rutherford Appleton Laboratory, Chilton, Didcot, Oxon, OX11 0QX, United Kingdom
The direct measurement of tropospheric trace gases from space is difficult and so it is necessary to combine models and data to fully exploit the potential of observations. We present a new procedure for the quantitative determination of tropospheric total column amounts of trace gases from nadir viewing satellites such as the Global Ozone Monitoring Experiment (GOME) on-board the European Research Satellite 2 (ERS-2). The procedure constrains the stratosphere by assimilating chemical observations from the Halogen Occultation Experiment (HALOE) on-board the Upper Atmosphere Research Satellite (UARS) into the SLIMCAT/TOMCAT three-dimensional (3-D) chemical transport model (CTM). The chemical data assimilation method is performed using the sequential sub-optimal Kalman filter scheme and here we assimilate HALOE CH4, H2O, O3 and HCl. The assimilation scheme preserves tracer correlations and the overall effect is to produce a more realistic stratosphere in the CTM.
Using the stratospheric constraints from the CTM we then calculate tropospheric residuals. In the first instance we are applying this method to GOME observations of NO2, BrO, HCHO and SO2. Retrieved slant columns are usually converted to vertical column by an air mass factor. The calculated air mass factor is sensitive to surface albedo, cloud fraction and height and aerosol properties. Our method uses data on surface albedo, cloud and aerosol from the ERS-2 Along Track Scanning Radiometer 2 (ATSR-2). This data in conjunction with a multiple-scattering radiative transfer model (GOMETRAN) will enable a more accurate air mass factor calculation.
We will show preliminary quantitative results from July 1997 of derived tropospheric abundance of GOME-observed species using ATSR-2 cloud and aerosol data. We will discuss the advantages to this scheme, and the improvements obtained by including the model stratosphere and retrieved aerosol and cloud properties.
Keywords: ESA European
Space Agency - Agence spatiale europeenne,
observation de la terre, earth observation,
satellite remote sensing,
teledetection, geophysique, altimetrie, radar,
chimique atmospherique, geophysics, altimetry, radar,