tag:blogger.com,1999:blog-9959776.post4110060225847883627..comments2024-02-15T04:42:41.606+00:00Comments on James' Empty Blog: More on that recent sensitivity paperJames Annanhttp://www.blogger.com/profile/04318741813895533700noreply@blogger.comBlogger157125tag:blogger.com,1999:blog-9959776.post-90372267441276850282013-07-31T01:33:20.373+01:002013-07-31T01:33:20.373+01:00W, Glad to see you followed me here. I thought I...W, Glad to see you followed me here. I thought I wasn't worth following :-) Did you actually read the technical substance before judging it? It is technically correct and interesting to a lot of people without a political filter.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-70193263965248021272013-07-30T23:09:33.468+01:002013-07-30T23:09:33.468+01:00Sorry, my ejecting DY's confused trolling seem...Sorry, my ejecting DY's confused trolling seems to have pushed him over here.William M. Connolleyhttps://www.blogger.com/profile/05836299130680534926noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-91518676143207119102013-07-30T14:57:31.197+01:002013-07-30T14:57:31.197+01:00Continuation of previous comment:
There is an ev...Continuation of previous comment:<br /><br /><br />There is an even more disturbing phenomenon of the “pseudo-solution” described in the paper. All other RANS codes simply NEVER converge to more than 4-5 digits in the norm of the residual. Hey, its a tough problem to converge reliably. The paper documents the existence of flows whose residual is order 5-6 digits lower than freestream flow that ARE NOT TRUE SOLUTIONS. If the algorithm is allowed to find a true solution, the overall forces differ by 70%. Does this mean all other codes are called into question? You can be the judge.<br /><br />Further on the bad news front, the pseudo-solutions at least on a common test case are substantially closer to the test data than the true solutions. What does this mean? My guess is that the eddy viscosity models are incorrectly calibrated based on unconverged solutions. By the way, its commonly acknowledged by modelers themselves that the viscosity models are too dissipative in some common situations.<br /><br />So, climate is the Navier-Stokes equations with lots of subgrid models of everything from aerosols to clouds, to albedo changes. Making something more complex doesn’t usually make it more stable. Linear potential flow methods are much simpler and are absolutely stable. Navier-Stokes is not. Generally, if you add chemistry or combustion, or convection to a Navier-Stokes simulation it merely makes the problem stiffer and less well-posed, but its hard to generalize on this subject.<br /><br />I will generate a follow up comment on the relationship of numerical stability to well-posedness and sensitivity of results to compilers and other rounding error details. This subject is really pretty well covered in graduate school courses in numerical methods. Basically, if your problem is well-posed these rounding errors can be proven to not make much difference. For the ill-posed problems, they do make a difference and as discussed above. Of course if you add enough dissipation, you can make any problem well-posed.<br /><br />If you use poor methods, like the leapfrog scheme that was known to be bad when I was in graduate school, you rather shoot yourself in the foot from day one as Paul Williams has shown rather convincingly. I know, GISS doesn’t use the method, but NCAR does.<br />David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-58949997538209699382013-07-30T14:56:07.148+01:002013-07-30T14:56:07.148+01:00Just wanted to add a postscript for KarSteN and Ja...Just wanted to add a postscript for KarSteN and James' benefit. I took KarSteN seriously and tried to discuss this topic of multiple solutions and ill-posedness at Stoat, believing that people are reasonable until they prove otherwise. My comment summarizing the science, which was strictly technical in nature was consigned to the "burrow" because it was "boring." Just one more piece of evidence of the politization of this field. Of course Connolley is a partisan and very political, but the conversation did seem to have a lot of scientist participation. I'm not complaining, just reporting another piece of evidence of the nature of the debate in climate science.<br /><br />[At this point I got bored. Further comments from DY will just get trashed if they're off-topic or trolling -W]<br /><br />James and Jules run a more honest forum here it would seem. For those who are interested, here's the comment.<br /><br />I see from W’s in line response to my last comment that the witch hunt has begun on qualifications. The default assumption seems to be that as soon as someone says something controversial, the demand to qualify yourself follows and I understand that urge.<br /><br />There are a couple of papers I mentioned on James’ place on the “more on that recent sensitivity paper’ thread. You will also see some very intense name calling and slanderous comments too, something which I’m sure W does not allow here. ;-) The references give some details of our recent work. We are not in the business of “getting people to read our papers” so they are not that visible unless you know what to look for.<br /><br />The doctrine that seems to me to be the basis of this whole thread and the previous one is the uniqueness of climate as a function of forcings. If this is false, pretty much everything else said here is questionable.<br /><br />In Navier-Stokes simulation of fluid flows, 15 years ago had there had developed a similar doctrine. It’s true the Navier-Stokes equations at high Reynolds numbers is essentially ill-posed. But people had developed this dissipation called eddy viscosity that “time averages” the effect of small scale eddies and gives their effect on the resolved scales and converts an ill-posed initial value problem into a boundary value problem that was claimed to be well posed. In this case, the RANS problem really is a boundary value problem. This doctrine was supported by tons of computational experience that seemed to confirm it. Of course, there is positive results bias and the placebo effect but that’s another story. To be fair, part of this experience was based on the easier flow problem, namely the attached flow cases where the methods perform reasonably well, but not much better than simpler and far less costly methods.<br /><br />F. Johnson with a team of top notch people set out to build a code that would embody this principle, use the latest methods, and would avoid the huge numbers of knobs used in existing codes. This effort went on for a long time and fell further and further behind schedule. Finally, people were forced to admit that the underlying assumption of well-posedness was probably wrong.<br /><br />If you read AIAA 2013-0063, you will find a rather convincing proof that in fact there are multiple steady state fully converged solutions to the RANS equations given identical forcings. Further, which one you find is dependent on the details of the numerics used to get there as well as the grid. In fact, pseudo-time marching techniques are required to find converged solutions reliably. It is unknown whether all of these solutions are physical but at least some of them are as was shown by very early testing many decades ago.<br /><br />David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-24679040031287561592013-06-30T00:40:24.469+01:002013-06-30T00:40:24.469+01:00OK, Maybe not able to withstand "any turbule...OK, Maybe not able to withstand "any turbulence so far encountered" but lets say 99.999% of all turbulence in the atmosphere. I can't tell without buying the article whether any of these accidents were due to structural failure (which is what I was talking about) or to pilot error or failure of other systems. You know commercial aviation is safer than virtually any other human activity. It's a remarkable achievement. I've actually been in severe turbulence on a commercial flight and while it was unsettling, everything worked fine and the pilot found another altitude. I've also been on a flight that was struck by lightening. Once again, not exactly fun, but everything worked. Apparently, the hot spot for severe clear air turbulence is over Wyoming & the Dakotas but I haven't checked into it recently.<br /><br />According to the Annan criterion, that makes me 99.999% right :-) Not even the Team is right all the time. ;-)David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-70114709500898249922013-06-30T00:07:47.347+01:002013-06-30T00:07:47.347+01:00> Airplanes are designed to withstand
> any ...> Airplanes are designed to withstand<br />> any turbulence so far encountered<br /><br />Since when? <br /><br />http://link.springer.com/article/10.1007/s00703-004-0080-0Hank Robertshttps://www.blogger.com/profile/07521410755553979665noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-47571455838193451782013-06-27T05:37:31.146+01:002013-06-27T05:37:31.146+01:00Yes, There are some good papers on the limits of ...Yes, There are some good papers on the limits of the GCM's. But I would claim that in general and in particular for the IPCC, there is a pretty pervasive positive results bias. Of course, GCM's are not completely useless, but I do have to wonder if appropriately constrained simpler models might be better. I have still not seen any substantive response to my challenges, however. Gerry Browning has been systematically ignored. Perhaps climate modelers don't read blogs or are too busy to respond. I have made some of them aware of this work. The response has been superficial. Paul Williams said basically that he was focused on getting modelers to pay attention. And that's the problem. Paul has some very good work that should be very interesting to them.<br /><br />At a recent NASA workshop on these issues, a turbulence modeler said that our current methods are "post-dictive" and not really predictive. But the users of these turbuelence models (who build and maintain the codes) mentioned no such thing and presented their usual positive results and passed over in silence the negative ones. <br /><br />I really am interested in substantive debate on this. Can you suggest a forum for such a discussion or some people to contact? Please, don't give the names of communicators (such as Real Climate) or those politically invested in this (you know who I mean) or those who censor comments that disagree but allow the most vile insults and libels to stand. I don't need to deal with Carl C and his constant political insults and bigotry. Unless you are very dishonest, you know that this is a real problem.<br /><br />Airplanes are designed to withstand any turbulence so far encountered and there is a 50% safety factor. The airframe must withstand 150% of the maximum design load. Your challenge is not very interesting. You I am sure fly all the time and don't give it a second thought. Preference is given to observationally based models and actual data over Navier-Stokes models especially for design loads for which the models tend to be pretty poor. David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-8053643274345180412013-06-27T01:17:21.812+01:002013-06-27T01:17:21.812+01:00Speaking of appropriate challenges. Would you get ...Speaking of appropriate challenges. Would you get on an airplane which is bound to fly through severe<br />turbulences, turbulences so severe that no one could ever safely say it would withstand them damage-free?<br /><br />As an aside: I have yet to meet a colleague who is naive enough to blindly believe what the models are telling him. And believe it or not, I happen to know a few brilliant colleagues (apart from Paul) who devote their entire scientific career to challenge our models. Yet they are smart enough to realize that these very models are not completely useless.<br /><br />If you want to discuss details of the model dynamics, do it with those experts. I'm happy to put you in contact with them ...KarSteNhttps://www.blogger.com/profile/16117301462523147860noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-27612350810471585172013-06-26T02:23:16.984+01:002013-06-26T02:23:16.984+01:00KarSteN,
I guess it all depends on what the meani...KarSteN,<br /><br />I guess it all depends on what the meaning of the word 'match" is. Opinions will vary.<br /><br />What you say about models is not convincing to me. Paul Williams is doing good work but has already uncovered some rather bad examples of excessive dissipation that do affect skill. He has a fix for one of them, the notorous leapfrog scheme that 32 years ago I was taught is not a good method. He seems to be having trouble getting the modelers attention. I just hope he is continuing to get funding, hopefully a of it. A lot of the money goes into just "running" models which is not going to result in any breakthroughs.<br /><br />Modelers I have found are usually honest at least when they are not in "grant getting" mode. The models and the "communicators" are another story. Whether the models are "wrong" is not the issue. The issue is can they pass normal numerical tests and do they predict actual data, before the data is known. I've gone into the problems in great detail here on a couple of threads, including the Anthropogenic Data Point thread and this one. I'd welcome any real responses. So far its just the argument from expended effort (we've invested tens of thousands of man years in this so it can't be all wrong) or the honest Abe argument (you can't believe all the modelers are dishonest can you?) My main concern is just the artificial dissipation issue because everyone in this field has seen the documentation on how serious an issue it is.<br /><br />As to the airplane analogy, there are 2 things to be said.<br />1. The first paper I referenced earlier on this thread says it clearly. For attached flows, models are pretty good. Of course simple models are also pretty good and cost a lot less to run (paper in press). For separated flow, there are a lot of issues and testing is still critical and required by the FAA as it should be.<br />2. You must be extremely careful about the literature on this subject. A lot of it is "colorful fluid dynamics" and not meaningful at a quantitative level. Also, there is a pretty strong positive results bias just as in medicine for all the same reasons. The RANS models are not as good as one might be led to believe, Of course climate models use a very dissipative form of the RANS equations. One thing is clear however, adding explicit nonphysical dissipation requires great care and usually destroys the accuracy of the simulation by damping the dynamics. I've gone into the "dogma of the attractor" elsewhere, viz., that short term errors don't matter because we get "sucked into the attractor". It is just hand waving.<br /><br />A more appropriate challenge for you is. Would you get on an airplane designed with models before it was flight tested? If so, you are naive about issues on all airplane program exposed in flight test. They are all fixed of course and air travel is safer than virtually any other human activity, which is a track record to be proud of. Most of this is due to very careful testing and continuing in service monitoring.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-18179503762623681212013-06-26T00:06:16.324+01:002013-06-26T00:06:16.324+01:00@David Young
Ed merely agrees that "models s...@David Young<br /><br />Ed merely agrees that "<i>models show a larger effect to Pinatubo than the observations</i>". There's plenty of literature available on that subject, which he might not have been fully aware of in that particular moment. In fact, many individual models get the response right and if you correct for ENSO. The observations even match the (CMIP5) ensemble: <a href="http://www.karstenhaustein.com/Dateien/Climatedata/R/Multimodel_ensemble_1870.png" rel="nofollow">CMIP5 vs GISS</a><br />Note that the ensemble does not suppress the magnitude of the response due to the synchronized response. Apart from that it shouldn't come as a surprise that some models show a stronger temperature response as they have higher sensitivites than others.<br /><br />Re model reliability: It's because we have people like Paul Williams that I wouldn't bet a penny on the vanishingly small chance that all models are wrong. They are trustworthy within the very well known limits intrinsic to each and every existing model. That's why it's called a model. Thousends of people are working on improving and understanding them better. If you don't trust the modellers, then you better never get on an airplane ...KarSteNhttps://www.blogger.com/profile/16117301462523147860noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-37232907963454040612013-06-25T06:00:30.119+01:002013-06-25T06:00:30.119+01:00KarSteN, What do you make of the response to the ...KarSteN, What do you make of the response to the Penatubo eruption? Ed Hawkins graph appears to show that GCM's badly overestimate the response and Ed says that is true and is the subject of continuing research.<br /><br />While it is true that GCM's include "nonlinear" responses, is there really any reason to suppose that those responses will be trustworthy given the huge levels of non physical dissipation in the models realization of the Navier-Stokes equations? See my previous comment.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-29610460365385012292013-06-22T17:09:21.141+01:002013-06-22T17:09:21.141+01:00As a late update to my comment on 25/5/13 12:01 pm...As a late update to my comment on <a href="http://julesandjames.blogspot.co.uk/2013/05/more-on-that-recent-sensitivity-paper.html?showComment=1369450871553#c8297220571300877639" rel="nofollow">25/5/13 12:01 pm</a>, let me add a few things in response to a quite lengthy chat I had with Alex Otto last week.<br /><br />First, I was wrong in assuming that their method would neglect the volcanic OHC imprint. Equ. 1 in their paper takes the volcanic forcing by means of a reduced decadal forcing explicitly into account. The only missing component is the long-term impact it will have on temperature in the future. This might otherwise well be balanced by the long-term impact of past eruptions (before the time interval in consideration). Assuming it is balanced, one shouldn't assume the decadal heat uptake in the reference period (1860-1879 in their case) to be positive (0.08W/m2). It's quite a stretch for which they didn't have a good reference (or justification for that matter). Assuming zero forcing in the reference period, I would rather set the heat content uptake to zero as well. Only GCM results can provide more reliable results. One would have to determine the fraction of the natural OHC at the beginning and at the end of the time interval in question, starting the simulation at least 500 years before. The difference would then have to be considered in the forcing estimate.<br /><br />Second, the aerosol forcing was deliberately chosen such that it fits the lower AR5 estimate. However, the references are simply wrong. Should have been picked up, but the whole thing had to be done a bit in a hurry. It was meant to be an confirmation exercise, aiming on demonstrating that the current forcing assumptions in AR5 are still consistent with the previous estimates. The list of co-authors does therefore comprise all AR5 lead authors. For aerosols, only Drew Shindell contributed. So Drew might not have double-checked what the final ACP version of ref 19 (Bellouin et al. 2013) actually says. I agree with Paul S, that half their aerosol forcing reduction (adding 0.15 instead of 0.3W/m2) would have been a smarter choice. Given that they performed the test for both results, ECS would be 2.2 everything else being equal.<br /><br />Third, as OHC is the dominating factor, the results are crucially dependent on the choice of the data set. On top of that, the ECS estimate for each decade varies widely in both directions due to internal variability or delayed responses. Four decades is therefore not too long an interval to make reliable statements. Keeping in mind that the evolution of the anthropogenic forcing over the last century also remains to be inflicted with uncertainties (GISS vs CMIP5 vs Skeie et al. 2011), one is left with a variety of options, covering the entire range of accepted forcing estimates. I personally think that Skeie et al. 2011 come closest to the truth. A crude estimate of their forcing (omitting O3 and land use changes), combined with the NODC/Levitus et al. 2012 (L12) and the most recent ORAS4/Balmaseda et al. 2013 (B13) decadal OHC trends, yields the following result: <a href="http://www.karstenhaustein.com/Dateien/Climatedata/R/Forcing_dOHC.png" rel="nofollow">Forcing vs L12/B13 dOHC</a><br />It is a 10 yr trailing average for all forcing equivalents. It seems, that at least the average of L12 and B13 over the last 50 years is not too far off. In any case, B13 looks more plausible than L12 to me. I remain unconvinced, that you can deduce a reliable ECS estimate with only those five decades of data.<br /><br />Finally, two more aspects which people should keep in mind. GISS temperature will produce slightly higher estimates than HadCRUT4 used in this study (GISS does not provide data for their reference period). Despite the fact that they call it ECS, it is actually the Charney sensitivity since non-linear feedbacks are excluded. Therefore their TCR/ECS ratio is lower than in most GCMs. They should have made this point clearer, as all GCMs will ultimately produce non-linear feedbacks which tend to increase ECS.<br /><br />Hope that helps ...KarSteNhttps://www.blogger.com/profile/16117301462523147860noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-13667163187876430232013-06-22T17:03:48.446+01:002013-06-22T17:03:48.446+01:00As a late update to my comment on 25/5/13 12:01 pm...As a late update to my comment on <a href="http://julesandjames.blogspot.co.uk/2013/05/more-on-that-recent-sensitivity-paper.html?showComment=1369450871553#c8297220571300877639" rel="nofollow">25/5/13 12:01 pm</a>, let me add a few things in response to a quite lengthy chat I had with Alex Otto last week.<br /><br />First, I was wrong in assuming that their method would neglect the volcanic OHC imprint. Equ. 1 in their paper takes the volcanic forcing by means of a reduced decadal forcing explicitly into account. The only missing component is the long-term impact it will have on temperature in the future. This might otherwise well be balanced by the long-term impact of past eruptions (before the time interval in consideration). Assuming it is balanced, one shouldn't assume the decadal heat uptake in the reference period (1860-1879 in their case) to be positive (0.08W/m2). It's quite a stretch for which they didn't have a good reference (or justification for that matter). Assuming zero forcing in the reference period, I would rather set the heat content uptake to zero as well. Only GCM results can provide more reliable results. One would have to determine the fraction of the natural OHC at the beginning and at the end of the time interval in question, starting the simulation at least 500 years before. The difference would then have to be considered in the forcing estimate.<br /><br />Second, the aerosol forcing was deliberately chosen such that it fits the lower AR5 estimate. However, the references are simply wrong. Should have been picked up, but the whole thing had to be done in quite a hurry. It was meant to be an confirmation exercise, aiming on demonstrating that the current forcing assumptions in AR5 are still consistent with the previous estimates. The list of co-authors does therefore comprise all AR5 lead authors. For aerosols, only Drew Shindell contributed. So Drew might not have double-checked what the final ACP version of ref 19 (Bellouin et al. 2013) actually says. I agree with Paul S, that half their aerosol forcing reduction (adding 0.15 instead of 0.3W/m2) would have been a smarter choice. Given that they performed the test for both results, ECS would be 2.2 everything else being equal.<br /><br />Third, as OHC is the dominating factor, the results are crucially dependent on the choice of the data set. On top of that, the ECS estimate for each decade varies widely in both directions due to internal variability or delayed responses. Four decades is therefore not too long an interval to make reliable statements. Keeping in mind that the evolution of the anthropogenic forcing over the last century also remains to be inflicted with uncertainties (GISS vs CMIP5 vs Skeie et al. 2011), one is left with a variety of options, covering the entire range of accepted forcing estimates. I personally think that Skeie et al. 2011 come closest to the truth. A crude estimate of their forcing (omitting O3 and land use changes), combined with the NODC/Levitus et al. 2012 (L12) and the most recent ORAS4/Balmaseda et al. 2013 (B13) decadal OHC trends, yields the following result: <a href="" rel="nofollow">http://www.karstenhaustein.com/Dateien/Climatedata/R/Forcing_dOHC.png</a><br />It is a 10 yr trailing average for all forcing equivalents. It seems, that at least the average of L12 and B13 over the last 50 years is not too far off. In any case, B13 looks more plausible than L12 to me. I remain unconvinced, that you can deduce a reliable ECS estimate with only those five decades of data.<br /><br />Finally, two more aspects which people should keep in mind. GISS temperature will produce slightly higher estimates than HadCRUT4 used in this study (GISS does not provide data for their reference period). Despite the fact that they call it ECS, it is actually the Charney sensitivity since non-linear feedbacks are excluded. Therefore their TCR/ECS ratio is lower than in most GCMs. They should have made this point clearer, as all GCMs will ultimately produce non-linear feedbacks which tend to increase ECS.<br /><br />Hope that helps ...KarSteNhttps://www.blogger.com/profile/16117301462523147860noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-73779629365479676182013-06-22T05:19:38.801+01:002013-06-22T05:19:38.801+01:00Just did a quick scan of the documentation of the ...Just did a quick scan of the documentation of the latest NCAR community climate model. I was able to verify that yes the leapfrog time marching scheme is still used despite Paul Williams having demonstrated that the filter used is vastly too dissipative. There is a nonphysical horizontal diffusion added. So regardless of grid resolution, there is Browning's nonphysical diffusion. The real diffusion is so small I suspect that it will never be resolvable in these methods. The spatial method is a spectral method. Forget about resolving sharp fronts and of course there is the usual eddy viscosity for the boundary layer with the usual hand waving as to why it isn't totally ad hoc.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-35988420048103807752013-06-19T14:59:17.446+01:002013-06-19T14:59:17.446+01:00Tom C: "Do I understand correctly that he is ...Tom C: "Do I understand correctly that he is an actual climate modeler"<br /><br />He says he is an IT specialist from PA, so that doesn't seem likely. <br /><br />He does seem to be an expert on paranoia.<br /><br />Resolution matters in weather models too. <br /><br />Duh. <a href="http://cliffmass.blogspot.com/2012/03/us-fallen-behind-in-numerical-weather.html" rel="nofollow">ECMWF for the win.</a><br /><br />I admit my knowledge of sewer-pipes is limited to what Hagen–Poiseuille tells me. Perhaps Carl is confused on that issue too. <a href="https://dl.dropboxusercontent.com/u/4520911/tower.jpg" rel="nofollow">This is my newest research tool</a> (went up yesterday), and does involve a pipe at least.<br />Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-84853218993090350352013-06-19T04:13:59.368+01:002013-06-19T04:13:59.368+01:00I'm going to perform a test here to see if Car...I'm going to perform a test here to see if Carl is anything more than an Al Gore bot. In any discrete realization of the Navier-Stokes equations or the hydrostatic approximation (which seems to rule out accurate simulation of cumulus convection) there is a numerical viscosity associated with the grid size. Now my research indicates that the Reynolds number for the atmosphere is quite large at the planetary scales and not small at smaller scales. If the grid doesn't resolve these viscous scales the real viscosity at the planetary scales, there is a very large nonphysical dissipation that will damp the dynamics. This is probably what Browning refers to in his papers as "unphysical dissipation". There is apparently even a "hyperviscosity" that is larger than the discrete viscosity. So, given this large artificial dissipation, why would you expect dynamics at any scale to be resolved?<br /><br />In terms of the "scale" of the dynamics, this is just a fiction Carl and Bloom have come up with. The dynamics is the same at large scales as at small scales, it involves vortex evolution and dissipation. If Carl has ever gotten in one of those "crashing" airplanes, he can see this vortex dynamics at take off if the humidity is very near the saturation point. There are shear layers and boundary layer too in climate. In climate, they must be unresolved, but that's another issue. They must be included if at all through subgrid models. The "scale" issue seems to me to be an unscientific gloss that can only be rooted in a schoolyard bullying tactic: "My problem is harder than your problem." Perhaps acceptable in the Al Gore world of political smears and untruths, but not a very scientific statement, unless of course there might be some actual substance behind the bluster.<br />David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-6124112967699099172013-06-17T05:40:04.118+01:002013-06-17T05:40:04.118+01:00Back from our extended break, will resume usual se...Back from our extended break, will resume usual service shortly - or at least, some sort of service :-)<br /><br />But I think this thread has pretty much run its course anyway...James Annanhttps://www.blogger.com/profile/04318741813895533700noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-30823515389850365762013-06-17T03:51:22.019+01:002013-06-17T03:51:22.019+01:00James and Steve Bloom, There is a new paper in Sc...James and Steve Bloom, There is a new paper in Science that seems to confirm our results on complexity of models.<br /><br />Rather than reducing biases stemming from an inadequate representation of basic processes, additional complexity has multiplied the ways in which these biases introduce uncertainties in climate simulations. – Bjorn Stevens and Sandrine BonyDavid Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-52683453087039372072013-06-07T03:49:42.736+01:002013-06-07T03:49:42.736+01:00My, my, Carl C is quite the class act. Do I under...My, my, Carl C is quite the class act. Do I understand correctly that he is an actual climate modeler? Ironic that Lewandowsky et al. are publishing papers about how skeptics are paranoid conspiracy nuts, while every other post from Carl mentions the Koch brothers, Sarah Palin, and every other mental tic of the Left. Maybe Carl should refrain from insults re religion and politics and hike over to Roy Spencers latest post. Seems to me there is something that must be dealt with honestly at this point and vulgar bluster will not help.Tom Chttps://www.blogger.com/profile/03793192912187740419noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-64403746535032821492013-06-05T00:52:47.540+01:002013-06-05T00:52:47.540+01:00James, is this thread still open for comments?James, is this thread still open for comments?David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-59690892504353108392013-06-03T19:00:00.155+01:002013-06-03T19:00:00.155+01:00Carrick, thanks. What little I've read of He...Carrick, thanks. What little I've read of Held seems excellent. As to why there isn't more interest in these issues, I have a hypothesis. In a highly competitive field there is constant pressure to get the "right" answer from your code. This has both professional and monetary sides to it. Since the codes are complicated and have many knobs, there are a large number of witches to be hunted in case of a negative result. We make the case that this situation has lead to a lack of progress and also incorrect heuristics for interpreting model results. It is impossible to come up with a predictive subgrid model if there is no clear understanding of numerical convergence issues. You already know this I suspect.<br /><br />As to the ____ on the floor, my apologies for using he who must not be named as a teaching foil. He illustrates my point perfectly.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-53841879295332606422013-06-03T18:13:20.060+01:002013-06-03T18:13:20.060+01:00This comment has been removed by the author.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-30046352660405085182013-06-03T14:58:06.001+01:002013-06-03T14:58:06.001+01:00*sigh* I'll try to make it simpler for you dop...*sigh* I'll try to make it simpler for you dopes. Climate modellers are not trying to model via CFD as you do on your sewer pipe studies in Mississippi or your crashing plane studies in Seattle (ie specific, small time & dimensional scales). What would the friggin' Reynolds number of engineering mean at even a high resolution .1 degree climate model?<br /><br />Climate models are basically weather models run for long periods of time to glean stats on temperature, precipitation etc. They are not trying to predict exact weather patterns, but they use the same/similar models. And these models nowadays are doing pretty good jobs. I mean, when you hear a weather forecast on Faux News of "90% rain tomorrow" -- do you similarly screech BS about how it's not modelling the resolution you want etc?Carl Chttps://www.blogger.com/profile/14717209873111026574noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-204402808548092822013-06-03T06:40:43.414+01:002013-06-03T06:40:43.414+01:00This comment has been removed by the author.David Younghttps://www.blogger.com/profile/17029429374522399227noreply@blogger.comtag:blogger.com,1999:blog-9959776.post-47648556943944478342013-06-03T05:03:54.495+01:002013-06-03T05:03:54.495+01:00When I say "modeling community" I don...When I say "modeling community" I don't mean global circulation modeling community. I've limited experience talking to climate modelers... speaking from my own areas of expertise in physics & acoustics.Carrickhttps://www.blogger.com/profile/03476050886656768837noreply@blogger.com