Characteristic modes of isotopic variations in atmospheric chemistry

Interacting chemical systems can be analyzed using the structures and lifet imes of characteristic modes of variation about a quasi-steady state. For t he atmospheric CH4-CC-OH system, characteristic modes of concentration vari ation involve predominantly a single species, but their lifetimes differ fr om the dominant species turnover times. Here a species turnover time is the species amount divided by its removal rate, whereas the characteristic mod e lifetime is the amplitude of a perturbation pattern divided by its rate o f change and includes feedback effects. Characteristic mode analysis is use d here to consider variations in both concentrations and isotopic ratios fo r such systems. New 'isotopic modes' are identified which are only weakly a ffected by feedbacks and have lifetimes very close to species turnover time s. This raises the possibility that analysis of variations in both concentr ation and isotopic ratios may provide a unique tool for resolving turnover times and chemical feedbacks in atmospheric chemistry.