cc: Fortunat Joos , plattner@climate.unibe.ch, Jonathan Overpeck , Stefan Rahmstorf , Anders Levermann , Eva Bauer , Eystein Jansen , Keith Briffa date: Tue, 21 Feb 2006 08:26:54 +0100 from: Anders Levermann subject: Re: Fwd: Re: Millennium Simulations to: Tim Osborn Dear Tim, Tim Osborn wrote: > Dear all, > > after talking with Keith about the exact wording to use in the text to > describe how the stronger solar forcing assumption raises the > variability of the simulated temperatures, I've realized that it might > be misleading to say that the standard deviation of natural > variability of NH temperature is 58-72% higher if the strong solar > forcing is assumed than if the weak solar forcing is assumed. The > reason is that these figures refer only to the natural variability > that is *forced* (unless these models have internally-generated > variability -- inspection of the control runs for Bern2.5CC and > Climber2 suggests that they don't). If internally-generated > variability had a standard deviation (for 30-year smoothed NH > temperatures) of, say, 0.08 K (from HadCM3), then the stronger solar > case would have total natural variability only 28-40% greater than the > weaker solar case. > > Is this right? If so, should we just change the text to indicate that > we only mean natural variability due to external forcings? This is probably a good idea. However, since also c3a doesnot have internal variability, none of the used models does and thus the percentage that you give refers to both forced and overall variability. With respect to your calculation for the HadCM3: If other models have internal variability that would also show in the forced simulations, I guess. This would increase the standard deviation not only of the control but also of the forced simulation. Apart from non-linear effects (which might be there, of course) this shouldn't change the result (i.e. the percentage) to much. Or am I missing something here ? Cheers, Anders > > Cheers > > Tim > > At 15:23 20/02/2006, Fortunat Joos wrote: > >> Thanks Tim. This sounds good. >> >> Tim Osborn wrote: >> >>> At 15:23 15/02/2006, Fortunat Joos wrote: >>> >>>> TIM can you please give us the appropriate number for the low-freq. >>>> NH T variability and specify the smoothin. >>> >>> >>> Hi Fortunat, >>> for the smoothing actually used on the Climber2/3a/Bern2.5CC figure >>> (30-year smoothing), these are the standard deviations of the >>> simulated NH temperatures for the "only natural forcings runs": >>> Bard08-WLS Bard25 Ratio of standard deviations >>> Bern 0.103 0.177 1.72 >>> Clm2 0.078 0.123 1.58 >>> Clm3a 0.092 0.147 1.60 >>> So, the multi-decadal variability in NH surface air temperature is >>> between 58% and 72% greater under the stronger solar forcing >>> (Bard25) than under the weaker solar forcing (Bard08-WLS). >>> This can go in the text where Fortunat indicated. OK everyone? >>> Cheers >>> Tim >>> >>> Dr Timothy J Osborn >>> Climatic Research Unit >>> School of Environmental Sciences, University of East Anglia >>> Norwich NR4 7TJ, UK >>> e-mail: t.osborn@uea.ac.uk >>> phone: +44 1603 592089 >>> fax: +44 1603 507784 >>> web: http://www.cru.uea.ac.uk/~timo/ >>> sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm >> >> >> -- >> >> Climate and Environmental Physics, >> Physics Institute, University of Bern >> Sidlerstr. 5, CH-3012 Bern >> Phone: ++41(0)31 631 44 61 Fax: ++41(0)31 631 87 42 >> Internet: http://www.climate.unibe.ch/~joos/ > > > Dr Timothy J Osborn > Climatic Research Unit > School of Environmental Sciences, University of East Anglia > Norwich NR4 7TJ, UK > > e-mail: t.osborn@uea.ac.uk > phone: +44 1603 592089 > fax: +44 1603 507784 > web: http://www.cru.uea.ac.uk/~timo/ > sunclock: http://www.cru.uea.ac.uk/~timo/sunclock.htm > > -- Anders Levermann phone: +49-331-288-2560 Potsdam Institute for Climate Impact Research fax: +49-331-288-2570 Telegraphenberg A26, 14473 Potsdam, Germany anders.levermann@pik-potsdam.de www.pik-potsdam.de/~anders