Wednesday, November 30, 2011

0229.txt

date: Wed Nov 19 14:31:50 2008
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: NI grid cells plus more
to: C G Kilsby <c.g.kilsbyatXYZxyzcastle.ac.uk>, Colin Harpham <c.harphamatXYZxyz.ac.uk>, "'vassilis glenis'" <vassilis.glenisatXYZxyzil.com>

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

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Subject: RE: 5km monthly temperature data
Date: Wed, 19 Nov 2008 12:24:17 -0000
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Thread-Topic: 5km monthly temperature data
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From: "Hollis, Dan" <dan.hollisatXYZxyzoffice.gov.uk>
To: "Colin Harpham" <c.harphamatXYZxyz.ac.uk>
Cc: "Phil Jones" <p.jonesatXYZxyz.ac.uk>,
"Prior, John" <john.prioratXYZxyzoffice.gov.uk>
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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]NCICatXYZxyzoffice.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.hollisatXYZxyzoffice.gov.uk [6]http://www.metoffice.gov.uk
___________________________________________________________________________________

From: Colin Harpham [[7]mailto:c.harphamatXYZxyz.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.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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