CICERO - Center for International Climate Research

Model resolution

The Oslo CTM3 standard vertical resolution is 60 layers (L60), as defined by the meteorological data driving the model. The vertical coordinate is defined by sigma-pressure hybrid coordinates extending from the surface up to 0.1 hPa (mass center of uppermost layer). Layer thickness above the surface is about 16 m, increasing to about 1 km at the tropopause and up to about 5 km at 60 km altitude. Horizontal resolution is more flexible and can be varied, also depending on the input resolution. Since late 2015, with the introduction of OpenIFS meteorological data, the standard horizontal resolution is 2.25°x2.25°, generated from 1.125°x1.125° (T159/N80) input by combining 2x2 grid boxes. It is also possible to reduce the number of layers by collapsing them.


Oslo CTM3 can in principle be set up to be driven by any meteorological data and resolutions, as long as the required fields are present.


The model relies of input of emissions from natural and anthropogenic sources. The OsloCTM3 can be run with different emission inventories and we have no recommendation of which to use. Emissions from lightning is perhaps the only exception, as will be described below. Emission datasets are usually given on a monthly basis and reading these into the Oslo CTM3 is quite straight-forward. Depending on the format of the input files, the code for emission input may need modification by the individual user.


For the most recent modeling studies, anthropogenic emissions (including from aircraft) of particles and precursor species from the Emissions Database for Global Atmospheric Research (EDGAR), ECLIPSE emissions from the GAINS model, and Community Emission Data System (CEDS) have been used. For the recent past, the Global Fire Emissions Database version 4 (GFED4) is the current default for biomass burning emissions, with an option of daily variability.


Biogenic emissions have traditionally been taken from offline datasets, such as MEGAN-MACC (Sindelarova et al., 2014). Recently, emission parameterization of the Model of Emissions of Gases and Aerosols from Nature version 2 (MEGAN2) (Guenther et al., 2012) was implemented in the model, enabling a direct link between land cover/vegetation and emissions (Lund et al. 2021, submitted). Other natural emission source that are input to the model include volcanic and oceanic sources of sulfur, marine organic matter, soil nitrogen oxides (NOx) and ammonia (NH3).


Lightning is an important source of NOx. The lightning source is based on convective mass fluxes calculated from the meteorological data. The parameterization combines the Price and Rind (1992) equations with scaling to lightning flash rates observed by Optical Transient Detector (ODT) and Lightning Imaging Sensor (LIS), as described by Søvde et al., (2012). Using the height of convection in a gridbox column, and a few other constraints, model flash rates are matched to climatological flash rates over land and ocean separately. Further, we impose climatological lightning emissions of 5 Tg(N)/year, allowing the lightning source to vary from year to year. Lightning emissions are distributed vertically within a column according to Ott et al. (2010), using the top of each convective cell.


The Oslo CTM3 can be driven by any suitable meteorological data, although it is set up to use 3-hourly forecast data generated by the European Centre for Medium-Range Weather Forecasts (ECMWF) OpenIFS or IFS models. These data are 36-hours forecasts produced with 12 hours of spin-up starting from an ERA-Interim analysis at noon on the previous day.

The resolution of the forecast data is denoted by three numbers: Spectral truncation as Txxx, Gaussian grid points on one hemisphere as Nyyy, and the vertical resolution as Lzz. What was previously often referred to as T42 is T42N32L60, while T159 is T159N80L60. This is typical numbers used by ECMWF. Using both T and N numbers is necessary since the ECMWF models can be run with higher spectral resolution than resolved by its grid resolution. The meteorological fields produced are listed in the ECMWF standard tables here, although not all of them are stored for use in the Oslo CTM3. We also retrieve some additional variables, such as convective mass flux into updrafts and downdrafts, the convective detrainment rates into updrafts and downdrafts, and 3D convective and large-scale precipitation fluxes. Meteorological data (T159N80L60) produced by the OpenIFS model are available for the years 1990–2017.



Guenther, A. B., X. Jiang, C. L. Heald, T. Sakulyanontvittaya, T. Duhl, L. K. Emmons, and X. Wang: The Model of Emissions of Gases and Aerosols from Nature version 2.1 (MEGAN2.1): an extended and updated framework for modeling biogenic emissions, Geosci. Model Dev., 5, 1471-1492, doi:10.5194/gmd-5-1471-2012, 2012.

Ott, Lesley E.; Kenneth E. Pickering, Georgiy L. Stenchikov, Dale J. Allen, Alex J. DeCaria, Brian Ridley, Ruei-Fong Lin, Stephen Lang and Wei-Kuo Tao: Production of lightning NOx and its vertical distribution calculated from three-dimensional cloud-scale chemical transport model simulations, J. Geophys. Res., 115, D04301, doi:10.1029/2009JD011880, 2010.

Sindelarova, K., C. Granier, I. Bouarar, A. Guenther, S. Tilmes, T. Stavrakou, J.-F. Müller, U. Kuhn, P. Stefani, and W. Knorr: Global data set of biogenic VOC emissions calculated by the MEGAN model over the last 30 years, Atmos. Chem. Phys., 14, 9317-9341, doi:10.5194/acp-14-9317-2014, 2014.

Søvde, O. A.; M. J. Prather, I. S. A. Isaksen, T. K. Berntsen, F. Stordal, X. Zhu, C. D. Holmes and J. Hsu: The chemical transport model Oslo CTM3, Geosci. Model Dev. Discuss., 5, 1561-1626, doi:10.5194/gmdd-5-1561-2012, 2012.