7. Modeling of short-lived climate forcers Introduction - Modeling atmospheric methane (CH):

the difficulty in quantifying sources and sinks of CH4, model The atmospheric chemical sink of methane in the troposphere is simulations of CH4 often fail to closely match observed features of mainly due to reaction with the hydroxyl radical (OH), initiating the atmospheric CH4 distribution, such as the latitudinal gradient a reaction chain that ultimately leads to oxidation of CH4 to and seasonal. [...] The closer the model point is to the black the 1990–2015 (1995–2015 for GISS-E2.1) time period (see measurement point (located at 1 on the x-axis), the closer the Table A7.4 in the Appendix). [...] vertical levels in the free troposphere, there is a large range Figure A7.8 summarizes all of the ACE-FTS comparisons at in model results, particularly at the surface and in the the 150 hPa vertical level. [...] Unlike at the surface, discussed above, in the Arctic UTLS where ACE-FTS measures, this assumption is valid, as can be seen in the 1800 relatively smooth CH4 distribution of the top left panel of Figure 7.13, and the relatively small model biases of the order of +/-<10%. [...] There is a gradient in CH4 concentrations 1700 (higher in the northern hemisphere and lower in the southern hemisphere) that is seen in the measurements (top left panel of 1650 Figure 7.15) and reported in the literature (e.g., Dlugokencky et al., 1994).