Tropospheric vs. stratospheric chemistry

[thibaut_lurton@cnrs-orleans_fr]

Hello to all,

We've recently been working with the FSDWSF compset (involving WACCM with sulphur chemistry and CARMA sulphate), in order to monitor SO2 in the stratosphere after volcanic events.

We reckon we've managed to deal with the input of a SO2 burden at the grid points and altitudes needed (in the lower stratosphere). However, the simulation being still a bit slow, we were wondering whether it could be sped up in some way: our first idea was ---since we're only interested in stratospheric behaviour--- to switch off any tropospheric chemistry, in order to lighten the overall process.

Is there a way to draw a line and turn off tropospheric chemistry only, leaving stratospheric chemistry active? Or does it make no sense?

Any suggestion would be greatly appreciated.

Cheers,

Thibaut.

 

[mmills]

The chemistry in FSDWSF is tailored to the middle atmosphere. There are a few age-of-air (AOA) tracers that could be removed, but would not save much computing time. Other gas-phase chemical species are all likely necessary.CARMA sulfate is expensive because it has 30 sulfate size bins that require advection, spaced with a geometric volume ratio of 2.4 from one bin to the next. One could reduce the number of bins and increase the volume ratio to cover the same aerosol size space, at the expense of accuracy.Concerns about the cost of CARMA sulfate have motivated the current development of prognostic stratospheric sulfates in the modal aerosol model in CAM5 and WACCM5. Public release of that capability is not likely until 2016. If you might be interested in using the development code in collaboration with NCAR, please contact me via email, mmills@ucar.edu.