Global long-lived chemical modes excited in a 3-D chemistry transport model: Stratospheric N2O, NOy, O3 and CH4 chemistry

The two longest-lived, major chemical response patterns (eigenmodes) of the atmosphere, coupling N2O and CH4, are identified with the UCI chemistry-transport model using a linearized (N2O, NOy, O-3, CH4, H2O)-system for stratospheric chemistry and specified tropospheric losses. As in previous 1D and 2D studies, these century-long 3D simulations show that the e-folding decay time of a N2O perturbation (mode-1: 108.4 y) caused by a pulse emission of N2O is 10-years shorter than the N2O atmospheric lifetime (118.2 y). This mode-1 can also be excited by CH4 emissions due to CH4-O-3 stratospheric chemistry: a pulse emission of 100 Tg CH4 creates a +0.1 Tg N2O perturbation in mode-1 with a 108-yr e-folding decay time, thus increasing the CH4 global warming potential by 1.2%. Almost all of the 100 Tg CH4 appears in mode-2 (10.1 y). Citation: Hsu, J., and M. J. Prather (2010), Global long-lived chemical modes excited in a 3-D chemistry transport model: Stratospheric N2O, NOy, O-3 and CH4 chemistry, Geophys. Res. Lett., 37, L07805, doi: 10.1029/2009GL042243.