date: Wed Nov 19 14:31:50 2008 from: Phil Jones subject: NI grid cells plus more to: C G Kilsby , Colin Harpham , "'vassilis glenis'" Chris et al, Below is an email from Dan Hollis of MOHC. It nicely explains why the grids differ for different periods. They are aware of it, regret it, but we now that we'll have to deal it. Colin knows what he has to do - this is to extend the MOHC mean T and DTR grids for the 5km buffer around the coastline of Britain. This is fine and won't take too long to do. Extrapolation is going to be not more than 10km and probably only 5km. The problem is Northern Ireland !!! The reason Colin asked Vaz to run the WG for the control period (1961-90) was to get the averages that the WG produces for mean T and DTR for all the UK points that the WG will simulate. With these we'll produce an offset file that will adjust these to what MOHC has for each 5km square. These offsets are mostly in the range +/- 2 deg C, but are slightly larger around some coasts. These offsets will be an additional number(s) to add to all generated data from the WG. The effect is to force the WG to get almost the same 1961-90 average as MOHC produces for each 5 by 5km square. If we'd been able to use daily grids on the 5km scale (which MOHC still have yet to produce) we wouldn't needed to have gone down the route with the interpolation from 115 stations. I explained why the 115 stations don't do as well as hoped at the Nov 3 PMG. Anyway - all this is background. We have time to do it, it won't take long so we're doing it. We're only doing it for Tmean and DTR. It's not an issue with sunshine, Vapour pressure etc. It related to frost hollows and coastal effects. It may be that MOHC isn't exactly right, but if we agree with them we can't be criticized on that score. Back to Northern Ireland! See the map that Colin sent earlier. There are 100s of points that are in your grid which are in Ireland (Eire)!! You have all of County Monaghan for example. I'm sure DEFRA wouldn't want the package to work beyond the NI border. There is one 5km point that should be in that you do not have. This is in the extreme west of Co. Fermanagh. Maybe we'll be lucky and no-one in Belleek will try and get any data! Colin reckons that if you remove the points wholly in Eire, then send him the revised set of co-ordinates he can produce the set of offsets needed. He can't extrapolate easily to your red circles (see earlier attachment) as some are way away for the true border. Also we shouldn't be offering points outside NI - even if they are part of cross-border catchments. Cheers Phil X-Authentication-Warning: ueamailgate02.uea.ac.uk: defang set sender to using -f X-IronPort-AV: E=Sophos;i="4.33,631,1220227200"; d="scan'208,217";a="45193" Subject: RE: 5km monthly temperature data Date: Wed, 19 Nov 2008 12:24:17 -0000 X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: 5km monthly temperature data Thread-Index: AclJiQ1hd1gn+26wTPmIVwvaOEGhqwAquvrw From: "Hollis, Dan" To: "Colin Harpham" Cc: "Phil Jones" , "Prior, John" X-Canit-CHI2: 0.00 X-Bayes-Prob: 0.0001 (Score 0, tokens from: @@RPTN, f028) X-Spam-Score: 0.00 () [Hold at 5.00] HTML_MESSAGE,SPF(none,0) X-CanItPRO-Stream: UEA:f028 (inherits from UEA:default,base:default) X-Canit-Stats-ID: 12919341 - 4a8d00af4c13 (trained as not-spam) X-Antispam-Training-Forget: [1]https://canit.uea.ac.uk/b.php?i=12919341&m=4a8d00af4c13&c=f X-Antispam-Training-Nonspam: [2]https://canit.uea.ac.uk/b.php?i=12919341&m=4a8d00af4c13&c=n X-Antispam-Training-Spam: [3]https://canit.uea.ac.uk/b.php?i=12919341&m=4a8d00af4c13&c=s X-Scanned-By: CanIt (www . roaringpenguin . com) on 127.0.0.1 Hello Colin, I admit that we have been inconsistent in our use of land/sea masks. Ian Simpson at UEA has highlighted similar issues with the monthly and daily rainfall grids, where three separate masks have been applied. I think this has come about because the various grids have been generated as a result of a several different projects and different decisions were made in each project. This is clearly unsatisfactory and something I'm trying to sort out. The short answer to your question is that the 1961-2000 data are not available for a larger area. The background to this is as follows: - When we initially generate our grids they actually cover a much larger area than just UK land areas. - However, we do not use any data for marine areas in the interpolation and therefore consider the values over the sea to be of low quality. Consequently, prior to releasing the data to users, we apply a land/sea mask to remove the sea data points from the grid (albeit inconsistently!). - Grids that have been produced in the last few years have been archived without any masking. The mask is applied at the time the data are extracted from the archive. In the case of the pre-1961 and post-2000 temperature grids this mask included a 5km buffer around the coastline. - Unfortunately, all of the monthly and annual grids for 1961-2000 (i.e. the datasets produced 6 years ago for UKCIP02) were archived with a land/sea mask already applied. A coastal buffer was not included so consequently the area is smaller than for the more recent data (but should still cover all land areas). Short of re-running all of the UKCIP02 analysis (which we have no plans to do in the near future), there is no way to 'unmask' these grids. At some point in 2009, hopefully to coincide with the eventual release of UKCIP08, we will be upgrading the gridded data download page on our web site. The main enhancements will be the addition of daily temperature grids for 1960-2006, daily rainfall metrics for the same period (the daily rainfall grids themselves are a commercial product and will not be available for download) and time series versions of both the monthly and daily data. As the lack of a consistent land/sea mask is clearly causing users such as yourself and Ian some headaches, my intention is to ensure that all of the data available for download covers tha same area. Given that we are tied to the UKCIP02 mask for the 1961-2000 monthly data I am therefore using this for all other datasets. You will see from this that the area of the pre-1961 and post-2000 grids will actually decrease in order to achieve this rationalisation. Given the concerns raised in your email I suspect you will find this unsatisfactory but I hope you will understand why we are making these changes. On a related topic, if either you or any of your colleagues at UEA have requirements for European-wide gridded climate data then you may be interested in the Showcase-EUROGRID project. This is a demonstration project looking at the practicalities of generating and distributing European-wide gridded data. Part of the work is a requirements-gathering exercise and there is a short questionnaire available for download on the project website ([4]http://www.e-grid.eu/public/ - the link is near the bottom of the page). If you or anyone else at UEA would like to fill in the questionnaire then that would be much appreciated. Please send them to our group inbox ([5]NCIC@metoffice.gov.uk) rather than to me, ideally by the end of next week. Thanks. If you have any further questions then please get in touch. Regards, Dan Dan Hollis Climatologist Met Office Hadley Centre FitzRoy Road Exeter Devon EX1 3PB United Kingdom Tel: +44 (0)1392 886780 Fax: +44 (0)1392 885681 E-mail: dan.hollis@metoffice.gov.uk [6]http://www.metoffice.gov.uk ___________________________________________________________________________________ From: Colin Harpham [[7]mailto:c.harpham@uea.ac.uk] Sent: 18 November 2008 14:22 To: Prior, John Cc: Hollis, Dan; Phil Jones Subject: 5km monthly temperature data Dear John, I am working on the UKCIP08 weather generator which is interpolated to a 5km OSGB grid using 115 station data. In order to provide improved urban accuracy (our 115 stations include few if any urban) I have calculated offsets from the 5km MO monthly temperature data to adjust the weather generator runs, this works well. Unfortunately we have a problem, the 1961-2000 temperature data covers less land area than our grid. I have scrutinised earlier and later MO 5km data and both have larger areas of land coverage than the 1961-2000 data by as much as two extra cells round the coast. Has the 1961-2000 been updated in line with the earlier and later data format? If so how could I obtain it? Regards, Colin Harpham Dr Colin Harpham Senior Research Associate Climatic Research Unit School of Environmental Sciences University of East Anglia Norwich NR4 7TJ UK Tel: +44 -1603 593857 Fax: +44 -1603 507784 Prof. Phil Jones Climatic Research Unit Telephone +44 (0) 1603 592090 School of Environmental Sciences Fax +44 (0) 1603 507784 University of East Anglia Norwich Email p.jones@uea.ac.uk NR4 7TJ UK ----------------------------------------------------------------------------