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Envisat enables first global check of regional methane emissions   Derived from the TM3 three-dimensional chemical tranport model, this animation shows model results of the column-averaged methane volume mixing ratio (VMR) in parts per billion for the time period of August through November 2003. A University of Heidelberg and KNMI team compared these model results to actual SCIAMACHY methane observations during the same period, discovering unexpectedly high methane concentrations over tropical land regions. Note the particular high methane levels shown in the model above the Ganges plain in summer months.  SCIAMACHY measurements of column-averaged mathane volume mixing ratio (VMR) in units of parts per billion. The measurements are averged over the time period of August through November 2003 on a 1º x 1º horizontal grid. At least five (and up to 150) measurements are taken for each grid cells. Only a few observations are available over the ocean, since low ocean reflectivity substantially reduces the quality of the retrieval, leading in turn to unable measurements (standard deviation of the fit residual over 0.5%) that are discarded. Occasionally sun glint or clouds at low altitudes allow measurements over the ocean.  This image shows the residual difference between SCIAMACHY observations and TM3 results. The results are displayed in parts per billion by volume (ppbv), ranging in most pixels from -20 to 20 ppbv (+/- 1% relative difference). The largest discrepancies can be seen over tropical broadleaf evergreen forests in South America, central Africa and Indonesia. In these areas, measured values are persistently high than predicted by the model. Prevailing wind directions cause transport of these discrepant concentrations over the oceans (e.g northwest of South America or west of Africa).
Column-averaged methane volume mixing ratio (VMR) in parts per billion results were gathered from the TM3 model for the time period of August through November 2003. Only modelled values that are colocated in space and time with the respective SCIAMACHY measurements are used for the averaging. SCIAMACHY: sifting through sunlight  Residual differences between the model results and methane observed by SCIAMACHY were concentrated over the broadleaf evergreen forests of South America, central Africa and Indonesia. In these areas, measured values are persistently high than predicted by the model.  The high resolution and the wide wavelength range of the SCIAMACHY instrument makes it possible to detect many different trace gases.  Envisat instruments  SCIAMACHY is an imaging spectrometer whose primary mission objective is to perform global measurements of trace gases in the troposphere and in the stratosphere. The solar radiation transmitted, backscattered and reflected from the atmosphere is recorded at relatively high resolution (0.2 nm to 0.5 nm) over the range 240 nm to 1700 nm, and in selected regions between 2.0 µm and 2.4 µm. Release date: 22 February 2008 |