cc: t.osborn@uea.ac.uk, Keith Briffa date: Mon, 01 Oct 2007 02:29:01 +0200 from: Bo Vinther subject: Re: 20th century to: t.kleinen@uea.ac.uk Hi Thomas Just looked a bit more into the SO2-emissions.... Based on fig. 1 in the attached paper on European/Russian SO2-emissions we might consider to reverse the forcing as late as 1975. Especially since modeling efforts suggest that Arctic sulphate comes mostly from Europe and Russia (see fig. 3 in the second attached paper). Greenland - being quite close to North America probably gets more of the North American SO2-emissions than does most of the Arctic (North American emissions peaked in the period 1965-75 - as seen in Greenland). Cheers.....Bo Thomas Kleinen wrote: Hi Bo. Thanks for sending that Greenland data. The volcanic aerosols are independent from the anthropogenic. Therefore it's no problem at all to keep them. I'll look into creating a suitable aerosol forcing timeseries during the next couple of days. Cheers, Thomas On Thursday 27 September 2007, Bo Vinther wrote: Hi Thomas I really like the idea of mirroring the sulphate - based on the Greenland data (see attached), I would go for reversing the forcing in 1970 (without reversing the sulphate from volcanoes - if we can avoid it?). If feasible, I do think it would be interesting to run the model a bit longer than 2007 - maybe to 2020 - to see what is ahead of us.... Cheers........Bo Thomas Kleinen wrote: Hi Tim. Well, control run is done with fixed orbital conditions (supposedly late 20th century), so I guess we can leave that. I have volcanic & solar timeseries until 1999/2000, and my original idea was to include those for as long as we have them to get the historical forcings right, and then not worry about the few years afterwards (doesn't matter in the volcanic case anyway). We can still update them later if we decide we need solar variability after 2000 (the volcano code assumes 0 aerosol optical depth after 2000). Since it will take a fortnight to reach 1990 anyway, we need to decide on the forcings for the earlier part now, though. I have Sulphate emissions / albedo change patterns until 2100 for the SRES A2 (the ozone file for some reason is for the B2, but that shouldn't make a big difference in those first years). So my idea was to run one experiment with the SRES forcings, and one with the forcings changed in the N Atlantic / Arctic area, just as you suggested. I'll have to look at the scenario data to decide on the best time for the switchover to reductions, though, I haven't quite made up my mind there yet. (As I indicated earlier, we still have time to decide on that). Cheers, Thomas On Thursday 27 September 2007, Tim Osborn wrote: Hmm. I think orbital doesn't matter either way, so whatever is easiest and also consistent with the initial conditions (i.e. if control run is NOT set up with 1860 orbital forcing, you would have an unwanted step in forcing if you began from that and suddenly switched to 1860 orbital forcing; on the other hand, if it has been run with 1860 orbital conditions, then clearly the orbital option becomes possible and the decision is yours!). Solar also probably won't have a large influence, though volcanoes might. But are you running up to 2000 or 2007 and do you have solar/volanic forcing up to that point? Of course, with little activity since Pinatubo, the volcanic forcing that you do have -- perhaps to 1999? -- might already have returned to low constant aerosol optical depth values which could be continued on at a constant level to 2007? Solar, if used, would need to be updated too, assuming you are running through to 2007. GHGs you will hopefully get from Sarah. Aerosols, did you think my suggestion of running with existing forcing through to ~1965 and then running reverse forcing (for N. Atlantic/Arctic region only?) 1965..1925 for 1966-2007 is workable? Would need some careful consideration, but since we cannot redo the sulphur transport and indirect effect modelling, we will do better with potential referees if we do something deliberately idealised rather than a poor attempt at a more realistic forcing. Also, presumably we will want to do 2 runs, one with all these forcings and the OLD too high aerosols, and then a second with all forcings identical except for the NEW lower aerosols in N. Atl. and Arctic. So, if running as far as 2007, we need OLD too high aerosols up to 2007 as well. Not sure how to get/extrapolate these? You might want to forward this to Bo & Keith in case they have different suggestions. Cheers Tim On Thu, September 27, 2007 12:21 pm, Thomas Kleinen wrote: Hi Tim. I still need to do a more detailed check, but right now it looks like the modern climate run might actually be working. Therefore I am wondering how to set it up exactly - should I include orbital, solar and volcanic forcing as well? I guess it might be best to do as realistic a run as possible. GHG I would start from control run levels - doing it from the Nat run would also involve adjusting the vegetation fields (and running from 1750, right now I am planning on running from 1860), and I'd prefer not to do that. What do you think? Cheers, Thomas Attachment Converted: "c:\eudora\attach\SO2transport.pdf" Attachment Converted: "c:\eudora\attach\Europe_emissionsSO2.pdf"