The chemical transport model Oslo CTM3 1Center for International Climate and Environmental Research – Oslo (CICERO), Oslo, Norway
Model Description Paper
21 Nov 2012
2Department of Earth System Science, University of California Irvine, California, USA
3Department of Geosciences, University of Oslo, Oslo, Norway
Received: 16 May 2012 – Published in Geosci. Model Dev. Discuss.: 19 Jun 2012 Abstract. We present here the global chemical transport model Oslo CTM3,
an update of the Oslo CTM2. The update comprises a faster
transport scheme, an improved wet scavenging scheme for large
scale rain, updated photolysis rates and a new lightning
parameterization. Oslo CTM3 is better parallelized and allows
for stable, large time steps for advection, enabling more
complex or high spatial resolution simulations.
A new treatment of the horizontal distribution of lightning is
presented and found to compare well with measurements. The
vertical distribution of lightning is updated and found to be
a large contributor to CTM2–CTM3 differences, producing
more NOx in the tropical middle troposphere, and less at
the surface and at high altitudes.
Compared with Oslo CTM2, Oslo CTM3 is faster, more capable and
has better conceptual models for scavenging, vertical transport
and fractional cloud cover. CTM3 captures stratospheric O3
better than CTM2, but shows minor improvements in terms
of matching atmospheric observations in the troposphere.
Use of the same meteorology to drive the two models shows that
some features related to transport are better resolved by the
CTM3, such as polar cap transport, while features like transport
close to the vortex edge are resolved better in the Oslo CTM2
due to its required shorter transport time step.
The longer transport time steps in CTM3 result in larger errors,
e.g., near the jets, and when necessary the errors can be
reduced by using a shorter time step.
Using a time step of 30 min, the new transport scheme
captures both large-scale and small-scale variability in
atmospheric circulation and transport, with no loss of
We present a version of the new transport scheme which has been
specifically tailored for polar studies, resulting in more
accurate polar cap transport than the standard CTM3 transport,
confirmed by comparison to satellite observations.
Inclusion of tropospheric sulfur chemistry
and nitrate aerosols in CTM3 is shown to be important to
reproduce tropospheric O3, OH and the
CH4 lifetime well.
Revised: 26 Oct 2012 – Accepted: 29 Oct 2012 – Published: 21 Nov 2012
Citation: Søvde, O. A., Prather, M. J., Isaksen, I. S. A., Berntsen, T. K., Stordal, F., Zhu, X., Holmes, C. D., and Hsu, J.: The chemical transport model Oslo CTM3, Geosci. Model Dev., 5, 1441-1469, doi:10.5194/gmd-5-1441-2012, 2012.