Runs required

This is largely my summary from Colin Jones's e-mail on 26 August 2014. The runs needs to be ready by the January 2018.

Minimum years of model run time

The minimum number of years that we are required to run the model for is

  • 500 years of pre-industrial
  • 160 years of historical run (1850-2010)
  • 90 years of the Reprensentive Concentration Pathway (RCPs) (2010-2100). This includes several runs, including 1% increase in CO2 and 4 * CO2.
so 750 years.

UKESM1-Hi

Ideal

The sub-models we probably want to run are

  • IO server
  • ATMOS + JULES (N216)
  • Miniature ATMOS + JULES + GLOMAP-mode full chemistry (N96)
  • NEMO-CICE (ORCA025)
  • Miniature NEMO-CICE + MEDUSA (?)
where each point is a separate executable. At time of writing (8 September 2012), the miniature versions don't exist and won't for a while.

Offline oxidants option

Instead of the miniature ATMOS + JULES + GLOMAP-mode full chemistry, this is

  • IO server
  • ATMOS + JULES + GLOMAP-mode simplified chemistry (using offline oxidants) (N216L85)
  • Miniature ATMOS + JULES + GLOMAP-mode full chemistry (N96L85)
  • NEMO-CICE (ORCA025), and MEDUSA here or extra executable as above.
where the input for the offline oxidants would be come from a N96 run.

Further options

If the above options are still too expensive, further options for the very long pre-industrial run are

  • we could use simplified chemistry
  • 500 years at N96 + a further 100 years at N216

And further options are

  • Use N144/ORCA025 instead of N216/ORCA025. Richard Wood is particularly against this, because there's much more experience of N216 than N144, such as more work in tunning N216. N144 would require a lot of work from Richard's AOIL team.

UKESM1-Lo

Ideal

The sub-models we probably want to run are

  • IO server
  • ATMOS + JULES + GLOMAP-mode full chemistry (N96)
  • NEMO-CICE + MEDUSA (ORCA1)

Pre-industrial spin up

When determining how much spin-up, it's necessary to consider the time scales different parts of the Earth System work on. For a boundary layer this might be of order of a day, whereas for the deep oceans this is much longer, say of order a 100 years (?).

It is for the deep oceans that we require the longest spin-up. Fortunately, the deep oceans aren't that sensitive to fine detail in the atmosphere and so don't require 500 year of coupling with the full UKESM1 at N216.

The spin-up of the ocean is likely to be something like the stages below

  1. Take 30 years of data from N96 run (I'm guessing mostly SSTs), and use this input repeatedly on a ORCA1 run without MEDUDA for maybe 1000 years. 30 years is chosen, so that it's not biased by any one freak year. (I'm not sure why a climatology is not used, but maybe the variability is important.)
  2. Attach a N96 run to this and run with MEDUSA for say 500 years
  3. Increase resolution of ocean to ORCA025, and run for several hundred years but less than years in previous stage.
  4. Attach a N216 run to ocean (ORCA025) and run for even less years
The reality is that the spin-up will probably never be quite as long as we'd like. So we'll take branches of our spin-up, while keeping the spin-up going, and use results from the one the latest branches.