Intercomparison of atmospheric carbonyl sulfide (TransCom-COS; Part
Two): Evaluation of optimized fluxes using ground-based and aircraft
observations
Abstract
We present a comparison of atmospheric transport models that simulate
carbonyl sulfide (COS). This is part II of the ongoing Atmospheric
Transport Model (ATM) Inter-comparison Project (TransCom–COS).
Differently from part I, we focus on seven model intercomparison by
transporting two recent COS inversions of NOAA surface data within
TM5-4DVAR and LMDz models. The main goals of TransCom-COS part II are
(a) to compare the COS simulations using the two sets of optimized
fluxes with simulations that use a control scenario (part I) and (b) to
evaluate the simulated tropospheric COS abundance with aircraft-based
observations from various sources. The output of the seven transport
models are grouped in terms of their vertical mixing strength: strong
and weak mixing. The results indicate that all transport models capture
the meridional distribution of COS at the surface well. Model
simulations generally match the aircraft campaigns HIPPO and ATom.
Comparisons to HIPPO and ATom demonstrate a gap between observed and
modelled COS over the Pacific Ocean at 0–40$\degree$N,
indicating a potential missing source in the free troposphere. The
effects of seasonal continental COS uptake by the biosphere, observed on
HIPPO and ATom over oceans, is well reproduced by the simulations. We
found that the strength of the vertical mixing within the column as
represented in the various atmospheric transport models explains much of
the model to model differences. We also found that weak-mixing models
transporting the optimized flux derived from the strong-mixing TM5 model
show a too strong seasonal cycle at high latitudes.