Multiscale characteristics and modeling of atmospheric methane

Methane influences the atmospheric radiative balance, ozone cycle, oxidizing capacity, and stratospheric water vapor abundance. Heightening concern, methane concentrations are increasing globally due to increasing emissions, predominantly from human activities.;Atmospheric methane measurements over 1983-1989 from twelve stations in the NOAA flask sampling network were used for statistical analysis and model calibration. Methane concentrations are greatest at high northern latitudes and decrease southward. Seasonal cycles are present at all latitudes but greatest at high northern latitudes. Concentrations are increasing at all latitudes, but the rates of increase are decreasing at most stations. Model studies suggest that hydroxyl radical concentrations are increasing in the northern hemisphere and decreasing in the southern hemisphere.;The rate of increase in the northern hemisphere is greater than the southern. The rate of increase decreased more rapidly in the northern hemisphere. A six month cycle exists in the northern hemisphere. The methane interhemispheric ratio oscillates annually, but shows no long-term trend. This, plus decreasing atmospheric methane residence times, suggests that the methane hemispheric source ratio decreased throughout the 1980s.;Global atmospheric methane concentrations continue to increase, although the rate of increase decreased throughout the 1980s. The global concentration record contains twelve and six month cycles. Removing the latter produces a much smoother seasonal cycle. A global methane mass balance model indicates increasing global hydroxyl radical concentrations contribute significantly to the decreasing methane rate of increase. Decreasing natural sources or increasing soil sinks are needed to achieve mass balance closure. Simulations suggest global methane concentrations will peak in twenty years.;Cryogenic Limb Array Etalon Spectrometer methane measurements delineate major transport mechanisms throughout the middle atmosphere. Seasonal patterns suggest the dominance of changing transport in the tropics and chemistry in the polar regions. Methane concentrations are increasing, but rates of increase are confounded by measurement uncertainty. Methanenitrous oxide correlations indicate temporal and spatial variability in stratospheric transport and photochemistry.;Fugitive methane emissions can be recovered at low cost or profit to lessen anthropogenic contributions to the global budget. Engineering is needed for successful policy implementation. Atmospheric policies must not be considered in isolation, as impacts may be offsetting.