Methane boundary conditions for EC-Earth
For the EC-Earth version of TM5, the boundary conditions for methane at the surface and in the stratosphere should be using concentrations from the CMIP6 data set.
#3 Updated by Twan van Noije almost 5 years ago
I have completed the implementation of the CMIP6 methane concentrations in TM5 for the historical period.
The following flags were introduced in the rc-file:
input.conc.ch4.cmip6 : T
input.conc.ch4.cmip6.dir : <directory containing the files with CMIP6 zonal monthly mean and global annual mean mixing ratios>
input.natemis.year : 2000
input.ch4.fixyear : F
input.ch4.year : <year>
When input.conc.ch4.cmip6 is switched on, the CMIP6 data are used to constrain the methane mixing ratios in both the lower troposphere and stratosphere. In both cases, the interpolation between consecutive months and the nudging time scales are unchanged compared to the existing code.
In the lower troposphere, mixing ratios are nudged to zonal mean values provided by CMIP6. As before, it is recommended to combined the nudging with the use of methane emissions (using with_ch4_emis), in which case nudging is applied up to 500 hPa.
In the stratosphere, zonal mean mixing ratios from the HALOE climatology are scaled based on global annual mean surface mixing ratios from the previous year. This one-year delay between the surface and the stratosphere is in line with the CMIP6 recommendation from Meinshausen et al. (GMDD, 2016).
For climate integrations, it is recommended to set input.natemis.year to 2000. This will fix the methane emissions and/or uptake data provided by LPJ to their values for 2000. The same flag will later be used to fix natural emissions of other species, provided by the MACC and MEGAN data sets.
Switching on input.ch4.fixyear will fix the methane concentrations and emissions to a specific year, specified by input.ch4.year (e.g. 1850).
At the moment, CMIP6 has only released the mixing ratios for the historical period (1850-2014). This means that the model can run up to December 2014. As soon as the scenario files become available, it will be straightforward to include those. Methane emissions for this historical period are still based on CMIP5 and will be replaced once the CMIP6 emissions are available.
#4 Updated by Twan van Noije almost 5 years ago
- File CMIP6_surface_CH4_2010.png View added
- File ncview.vmrch4_CMIP6.png View added
- File ncview.vmrch4_GMD.png View added
To test the new implementation, I have carried out a simulation with the new flag "input.conc.ch4.cmip6" switched on (denoted by "TM5 w/ CMIP6") and reference simulation where this flag was switched off ("TM5 w/ GMD"). Both simulations started from the same initial conditions in February 2009. After a spin-up period of 11 month, I have compared the resulting budgets and surface mixing ratios for the year 2010. (To calculate the tropospheric contributions, a simplified tropopause definition is used.)Table 1. Global budget of methane
|TM5 w/ CMIP6||TM5 w/ GMD|
|Atmospheric burden (Tg)||4936||4951|
|Tropospheric burden (Tg)||4223||4225|
|Emissions + nudging (Tg/yr)||671.5||680.0|
|Stratospheric loss (Tg/yr)||41.5||30.6|
|Atmospheric burden change (Tg/yr)||21.9||41.1|
|Tropospheric burden change (Tg/yr)||16.8||34.8|
|Atmospheric lifetime (yrs)||7.38||7.40|
|Tropospheric chemical lifetime||8.26||8.29|
|CMIP6||TM5 w/ CMIP6||TM5 w/ GMD|
Attached is a plot of the seasonal cycles in the surface mixing ratios in the CMIP6 data set and the two TM5 simulations, as well as maps of the simulated surface mixing ratios for the month of January.
#5 Updated by Twan van Noije over 4 years ago
The files required to simulate the historical period with CMIP6 methane concentrations are:
They contain the annual global and monthly zonal (at 0.5 degree resolution) mixing ratios from year 0 up to and including 2014.
These file are available from
#8 Updated by Twan van Noije almost 3 years ago
I have added the reading of the future scenarios for SSP3-7.0 and SSP3-7.0-LowNTCF, which will be run for CMIP6 as part of ScenarioMIP and AerChemMIP, both the annual global means for scaling concentrations in the stratosphere and the monthly zonal means for constraining the surface concentrations.