Main menu

Navigation

Near past glaciation: solution to POP instability

1 post / 0 new
flocolleoni@...
Near past glaciation: solution to POP instability

Dear all,

 

I feel it is also good to share positive experiences :-)

 

I computed new initial conditions, with great help from NCAR Paleo group, to prescribe LGM-like ice sheets in the Northern Hemisphere

for:

- CESM 1.0.5

- B compset

- fv 0.9x1.25 - gx1v6 resolution

 

I started the run from scratch, direclty taking as input the new initial conditions files and

setting GHGs values to very low glacial conditions (CO2 = 192 ppm for eg.).

I must say that I was surprised by the relatively good stability of the run at the beginning.

Still, atmosphere and land were not so happy with the completely different and extreme new forcing. But

the model kept running until the ocean crashed because of no convergence.

In that case it is advice to increase the timestep dt_count in POP namelist. But at somepoint, even

modulating this value was not enough to overcome instabilities.

 

Few years ago I was told to increase the levels on which was calculating tidal mixing if

set to "True" in POP namelist. This number can be modified from 2 to 6 in the vmix_kpp.F90 POP source code.

 

Finally to overcome all POP problems I did:

- increase by two the dt_count: from 23 to 46

- increase the vertical levels for tidal mixing parametrisation from 2 to 6

 

since then, it seems running more smoothly.

 

I hope that this message can be usefull to whom is trying to set new initial conditions for B case and hve set to "True" oveflows and tidal_mixing in POP namelist

 

Flo

 

 

Florence Colleoni
CMCC (Bologna, Italy)

Who's new

  • 20171204300@...
  • poornadurga.g@...
  • lina.boljka@...
  • nuistwangjing@...
  • vineetm@...