Global long-lived chemical modes excited in a 3-D chemistry transport model: Stratospheric N
2
O, NO
y
, O
3
and CH
4
chemistry
Abstract
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, NO y , O3, 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 CH4emissions due to CH4-O3 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).