date: Fri, 30 Jan 2009 11:41:01 +0000 from: Adrian Simmons subject: Re: CRUTEM3v and HadCRUH comparisons with ERA-40 and ERA-Interim to: P.Jones@uea.ac.uk Thanks for the message, Phil. I'm not in the office myself today. I've one hard copy of the whole thing with me, and I'm sure Stephan will print off some more copies for us. Good idea about consulting with Kevin and Phil next week - can't think why this did not occur to me. It's most likely we'll meet on Monday at breakfast. I won't get to the Mon Repos until 2030-2100 on Sunday, and will need an hour or two to gather thoughts as to what I'm going to say the next morning. I've not prepared for this meeting in advance, as I've already had a couple of sessions in Geneva on the review of progress of the current GIP, and decided to devote the present week to my FP6/7 projects and the humidity paper. All the best Adrian P.Jones@uea.ac.uk wrote: > Adrian, > Thanks for the email and the plots. I'm in Switzerland > already at an extremes workshop. I'll look through these > in more detail later. > Can you bring along a few (3-4) hard copy sets of the > pdf? It is easier for me to look at the hard copy. It might > also be useful to get the views of Kevin Trenberth and Phil > Arkin of your RH thoughts in Geneva next week. > I'm glad to see the precip in ERA-Interim behaving well > in the tropics. There is another precip dataset from GPCC > that we might want to try - again useful to get Phil Arkin's > thoughts on that. > See you on Monday - or maybe Sunday. > > Cheers > Phil > >> Hi everyone >> >> I've not got on as fast I would have liked with the writing, but at >> least I have an argument for the drop in relative humidity. Whether you >> can accept it is another matter.... >> >> Attached is a document that comprises an abstract, two tables and twelve >> figures, with captions. Doubtless there'll be further changes, >> especially to take into account the HadCRUH update. >> >> Figs 1 to 10 you have seen before in some form or other, though they are >> now updated to include ERA-Interim data up to June 2008, the latest >> month to be completed. I took Peter's comments on board, and simplified >> what I displayed in the regional plots, and also switched the colours >> for the humidity, so blue means moistening and red drying. >> >> Fig 11 is a new one, and I find it quite striking. It shows (a) that >> HadCRUH shows similar temporal variations in the averages over all land >> and all sea (maybe the point is also made in Kate's paper, which I need >> to reread), and (b) that in ERA, there is quite a reasonable correlation >> between temporal variations in the saturation specific humidity >> calculated using sea-surface temperature and surface pressure, averaged >> over all sea points, and temporal variations in the 2m specific humidity >> averaged over all land points. >> >> So I think the recent drop in relative humidity could well be real (to >> be confirmed by the HadCRUH extension, I hope!) and a consequence of the >> fact that in recent years the atmosphere has gone on warming just above >> the land surface, whereas temperatures over sea have not shown the same >> rise. With warmer temperatures over land, extra moisture has to be >> supplied if relative humidity is to stay fixed. But evaporation over sea >> does not increase commensurately because sea-surface temperatures have >> not risen recently in concert with those over land. So there is not the >> moisture supply from sea to land to maintain uniform relative humidity. >> >> Does the above make sense to you? I think Fig 11 supports the argument. >> There can be other effects - reduced transpiration due to increased >> stress on vegetation in areas that are already arid, and consequences of >> deforestation - that could cause drying (and there could be moistening >> at high latitudes due to a reduction in the space/time extent of frozen >> soils). But the drop in relative humidity seems intuitively to be too >> rapid and widespread for such other causes to provide the only >> explanation. >> >> Fig. 12 was an attempt to answer a question Dick raised when I tried the >> argument on him - "what does this imply for precipitation?". I'm not >> sure this figure will survive, and right now I'm puzzled by the shift in >> the ERA/GPCP comparison around 1999 for most regions. It's much the same >> for both ERA-40 and ERA-Interim. Could just be a mistake on my part, but >> I've used two different pieces of code and got the same result. So the >> jury is out on this one. But there are some similarities between the RH >> series in Fig 6 and the precip series in Fig 12, so I keep it in for now. >> >> Otherwise I've written just a handful of technical paragraphs. >> >> No chance of progress in the next couple of weeks due to two trips, but >> at least I'll get a chance to talk with Phil at the first of the meetings. >> >> All the best >> >> Adrian >> >> >> Adrian Simmons wrote: >>> Thanks for the comments, Peter. A few quick responses: >>> >>> (i) I'll check different tolerances for including CRUTEM3v data, but >>> doubt it will help coverage much. Actual numbers can be seen in the >>> attached plots. They shift mostly only on the decadal timescale, >>> consistent with the 10-year book explanation given by Phil earlier. >>> >>> (ii) For temperature, I could show the CRUTEM2v time series plus >>> differences. To see anything much though I would have to use a different >>> scale for differences, and that may detract from the main point, which >>> is that the time series are very similar indeed. I would argue that if >>> you can't see the differences, they can't be very significant. I've got >>> a couple of tables to quantify differences. I'll try out the alternative >>> nevertheless. This approach won't work for humidity, however, as none of >>> the time series spans the full period. >>> >>> (iii) If you could extend HadCRUH over land to the end of 2007, albeit >>> in provisional form, I would certainly be interested. >>> >>> (iv) I wondered myself about flipping the colour for the humidity plots. >>> But q increases as T increases. So I thought to use red colours both for >>> larger T (conventional) and larger q (unconventional, I know), so that >>> the correlation stands out. I guess it's a matter of taste. If we stick >>> with the current scheme, I would include a sentence explaining why blue >>> means dry. >>> >>> (v) I had a longish chat with June Wang when I visited NCAR in October. >>> She was then about to put in a proposal jointly with Aiguo Dai (who I've >>> not met) and Leo for funding for an attempt at homogenising radiosonde q >>> - something we're very interested in for future reanalysis. I've also >>> just looked at a paper of hers on the dry RS80 bias, as this may play a >>> part in the RH shift over Europe either side of ~1990 (generally, >>> radiosondes dry our boundary-layer analysis whilst SYNOPs moisten it). A >>> visit from them in the summer would be very welcome. >>> >>> Best regards >>> >>> Adrian >>> >>> >>> peter.thorne wrote: >>>> Dear Adrian, >>>> >>>> some comments below inter-leaved within the text. Hopefully they will >>>> be >>>> useful. >>>> >>>> >>>> On Fri, 2008-12-19 at 18:38 +0000, Adrian Simmons wrote: >>>>> Dear Phil, Kate and Peter >>>>> >>>>> I finally managed to spend some time over the past few days assembling >>>>> some provisional figures (attached) for a comparison of our reanalyses >>>>> with your data sets. Era-Interim is now in January 2008, and when it >>>>> completes 2008 (probably late next month or early February), we'll >>>>> have >>>>> 20 years of this reanalysis, and thirty years of combined >>>>> ERA-40/ERA-Interim reanalysis from the FGGE year onwards. My idea is >>>>> to >>>>> start writing something soon, with a view to finalising the figures >>>>> and >>>>> text once we have results up to the end of 2008. >>>> Sounds great. >>>> >>>>> Here are some comments on the figures (all of which are land-only). >>>>> >>>>> (i) Figs. 1-3 These cover the temperature comparisons, and simply >>>>> update >>>>> the picture from Simmons, Jones et al. (2004). In these and other >>>>> figures I have normalised everything to give zero anomaly for the >>>>> ten-year mean 1989-1998, which is convenient as I can then plot maps >>>>> of >>>>> the anomalies for the decades 1979-1988 and 1999-2008. (Note that for >>>>> now the maps labelled 1999-2008 are actually for 1998-2007, and those >>>>> for 2004-2008 are actually for 2003-2007 - this will be fixed when we >>>>> actually have reanalysis data for 2008). For the maps I show all CRU >>>>> grid squares for which less than 5% of months are missing. >>>>> >>>> Is there any reason that the criteria is this tight? Is there any >>>> implication to loosening it to say 25%? You should find extra data in >>>> at >>>> least some relatively data sparse areas which may be worth the cost of >>>> the additional noise, or does it make no substantial difference to >>>> coverage for either dataset? >>>> >>>>> Basically we see excellent continuation of the ERA-40 results when we >>>>> sample ERA-Interim and ERA-40 in the same way as CRUTEM3v samples in >>>>> space and time. A point that might be emphasized is that the coverage >>>>> of >>>>> CRUTEM3v is much poorer for the last ten years than the first one. Any >>>>> comment on this? Are there many late-arriving CLIMATs that will change >>>>> the picture when I download a new version of CRUTEM3v? It is >>>>> noteworthy >>>>> that CRUTEM3v samples poorly the Arctic region where ERA indicates the >>>>> strongest warming (and ERA also shows strong warming over sea-ice - or >>>>> where sea-ice used to be!). Fig 1 shows a stronger trend in ERA that >>>>> in >>>>> CRUTEM3v when we use the complete ERA record rather than sampling it >>>>> as >>>>> CRUTEM3v. In other words ERA-Interim shows less recent cooling than >>>>> CRUTEM3v. Here we are treading on thin ice (sorry!) from a PR >>>>> viewpoint, >>>>> so I'm interested in your reaction to all this. >>>> For all the timeseries figures or at least those that you subsample to >>>> coverage mimicking can we consider a slightly different presentational >>>> style? I find it hard to ascertain what is going on because the lines >>>> are sufficiently thick to overlap substantially for much of the period. >>>> An alternative approach would be to show one dataset's (the >>>> "observations"? Open to argument and counter-vailing views here) actual >>>> timeseries and then offset from this the difference series to the other >>>> two timeseries. We know the datasets agree on the high frequency, its >>>> the low frequency behaviour that really interests us here. The >>>> difference series illuminates this directly and could be assessed for >>>> statistical trend significance probably without a d.o.f. correction to >>>> the uncertainty. This would very considerably strengthen this part of >>>> the analysis as it is actually really getting at a very thorough >>>> investigation of the inter-dataset differences which is key. >>>> >>>>> (ii) Fig. 4 shows excellent agreement between HadCRUH and ERA-40 time >>>>> series for q. After 2003, the "sampled as HadCRUH" means I sample >>>>> ERA-Interim for the grid squares for which HadCRUH gives values for >>>>> December 2003. Slightly less trend for the full ERA dataset. >>>>> >>>>> (iii) Fig. 5 and 6 are time series for RH. Generally good agreement >>>>> also. Two points. One is shift in ERA-40 around 1990 for Europe. I >>>>> think >>>>> this is a reanalysis problem. Hard to be sure, but could be explained >>>>> by >>>>> increased dry bias of sondes. No time to write more now, but Figs 10 >>>>> and >>>>> 11 relate to this, and also to second point - the relative dryness of >>>>> recent years. I cannot find a reanalysis problem to explain this, and >>>>> am >>>>> inclined to think for now it could be real - there is no fundamental >>>>> physical reason why relative humidity should not show a trend in a >>>>> climate that is shifting. But it is really frustrating that HadCRUH >>>>> stops at the end of 2003. What are the prospects for extending it? >>>>> Could >>>>> something quick be done as a check on the reanalysis result - omitting >>>>> homogenization and subtle QC checks for example. >>>> We could, in theory, update the series as we now have, just, >>>> unquarantined disk with the ISD source updated through the end of 2007 >>>> (wouldn't help with '08). We could, as an interim measure, update >>>> through 2007 by simply plonking it on the end for now (not quite that >>>> simple as we'd have to convert to required res and format but the hard >>>> yards are done). Adding 2008 would be technically feasible but a heck >>>> of >>>> a lot of work and is probably outside the time remit. We were going to >>>> produce a 2nd gen product for end of '09 through 2007 then worry about >>>> instigating updates. That's quite a lot to do, but I guess in theory we >>>> have the data through 2007 so could update the land component thru >>>> then. >>>> Not sure about marine, but that's not your problem ...! >>>> >>>>> (iv) Fig 7 shows ten-year anomaly maps. Don't have HadCRUH for >>>>> 1999-2008 >>>>> of course. RH map for 1999-2008 show good temporal continuity - >>>>> generally drying (relatively) in tropics and mid latitudes, and >>>>> moistening (relatively) at high latitudes. Perhaps not implausible - >>>>> for >>>>> RH to stay uniform as T increases the water has to come from >>>>> somewhere. >>>>> That could be difficult over dry soils. And easier over melting >>>>> soils?? >>>>> Is anything like this seen in the Hadley Centre climate runs? >>>>> >>>> In the humidity maps can you flip the colour scheme so that red is >>>> drier >>>> and blue is wetter? That is more intuitive to me at least. >>>> >>>> We haven't had an in depth look at climate model output in this >>>> respect. >>>> We should have some HadGEM1 fields that we could dig out, but Kate's >>>> been doing some HadCRUH-climate model work and we want to ensure we >>>> don't duplicate so suggest Kate updates you on status. >>>> >>>>> (v) Fig 8 shows consistency across boundary layer (level 49 is close >>>>> to >>>>> 850hPa, where analysis in influenced more strongly by sondes rather >>>>> than >>>>> SYNOPs). >>>>> >>>>> (vi) Fig 9 shows some 5-year means, comparing ERA-INT and HadCRUH for >>>>> 1999-2003. >>>>> >>>>> (vii) Figs 10 and 11 are fits of background and analysis to >>>>> assimilated >>>>> observations. There are subtleties I don't have time to explain right >>>>> now, but basically a flat line is a good thing from the viewpoint of >>>>> trend analysis. It is the drop in the background RH curves and rise in >>>>> the background Q curves for the northern hemisphere between 1988 and >>>>> 1993 that makes me think the RH shift between the 1980s and 1990s in >>>>> ERA >>>>> relative to HadCRUH is a reanalysis problem. Equally though, there is >>>>> nothing in these curves (or some others I've looked at) that points to >>>>> the lowering of RH in the reanalyses for the last few years as being >>>>> spurious. >>>> Which makes it more appealing to do a quick and dirty fix to update >>>> HadCRUH through at least 2007 as that would be the clincher. Of course, >>>> in this era we also have the GPS-PW network from June Wang at NCAR. >>>> Perhaps this would be a useful addition? Aiguo Dai also has an >>>> alternative observational dataset of surface q and RH which could be a >>>> useful addition. I think his is updated through 2006. It has no >>>> homogeneity adjustments but because its a compilation of synops >>>> probably >>>> better coverage (swings and roundabouts). We have both of them visiting >>>> here in the summer for 2 months and 3 months respectively so >>>> opportunity >>>> to do some collaborative work on this. I know they were keen to visit >>>> CRU and Reading institutes. If you want their email addresses so you >>>> can >>>> send some enquiries just let me know. >>>> >>>> I hope you have a relaxing christmas >>>> >>>> Peter >> -- >> -------------------------------------------------- >> Adrian Simmons >> European Centre for Medium-Range Weather Forecasts >> Shinfield Park, Reading, RG2 9AX, UK >> Phone: +44 118 949 9700 >> Fax: +44 118 986 9450 >> -------------------------------------------------- >> > > -- -------------------------------------------------- Adrian Simmons European Centre for Medium-Range Weather Forecasts Shinfield Park, Reading, RG2 9AX, UK Phone: +44 118 949 9700 Fax: +44 118 986 9450 --------------------------------------------------