Thursday, December 22, 2011

1176746137.txt

From: P.Jones@uea.ac.uk
To: "C G Kilsby" <c.g.kilsby@newcastle.ac.uk>
Subject: RE: Outputs from WG
Date: Mon, 16 Apr 2007 13:55:37 +0100 (BST)
Cc: david.sexton@metoffice.gov.uk, "Phil Jones" <p.jones@uea.ac.uk>, "Colin Harpham" <c.harpham@uea.ac.uk>, "H J Fowler" <h.j.fowler@newcastle.ac.uk>


Chris et al,
I'll sedn some more thoughts on Thursday when back from
the EGU. It is too hot in Vienna to sit through too many
talks !

I suspect we need a subset of indices. The program will
calculate all those recommended in various programs. One
possibility is to keep them all and let users decide.
We do need to make a series of checks though at some
stage to make sure they are OK.

I think you'll have some fruitful discussions on
some of these on April 24. I hope you can come to
closure on a few things.

Cheers
Phil

> All:
>
> Indices
>
> I had a session with UKCIP last week, and we did get on to dicsussing
> what outputs might come out of WG (as well as DDP etc.) and the issue of
> indices derived from daily data (i.e. requiring time series) came up,
> with the distinct possibility of confusion/inconsistency as David
> mentions!
>
> I would be happy to produce indices only from WG, as long as we can
> check they are sensible first of course!
> E.g. heatwave duration (various thresholds), drought duration, various
> accumulations of rainfall ?
> Less clear cut might be gale days (definition?), snow days, proportion
> of days above temp threshold etc.
>
> I think we will need to consider the list in detail, as far as what is
> included (STARDEX list?), how they are calculated/validated and also
> whether they can be calcualted from some other source and found to be
> inconsistent.
> E.g. is it planned to take the (17?) RCM runs and analyse/release these
> indices as well ?
>
>
> Rainfall stats - pdfs
>
> I think (hope?) lag1-ac and skewness will actually be quite well behaved
> (if not realistic) even when you convert/downscale. The more
> validation/analysis we do of these fields the better anyway.
>
>
> Separate topic: measures of reliability
>
> May be a can of worms, but I think we need to address it sooner rather
> than later: UKCIP02 had subjective measures of reliability attached to
> different variables/predicted changes. We must do better, and a case in
> point is the WG where we sidestep the bias issue by using change
> factors. We therefore need to provide some measure (per grid square, per
> varaible?) of reliability.
>
> For example: if control annual rainfall is more than (say) 10% biased,
> reduce reliability measure and inform the user when generating.
> Problem 1: which model runs to use for this check?
> Problem 2: how to assess more complex measures e.g. annual cycle in
> rainfall/temperature?
> Problem 3: need a common, easily understood scale of reliability
> Furthermore - WG procedure introduces more uncertinty, e.g. for wind
>
> Thoughts?
>
> Cheers, Chris
>
>
>
>>-----Original Message-----
>>From: david.sexton@metoffice.gov.uk
>>[mailto:david.sexton@metoffice.gov.uk]
>>Sent: 16 April 2007 08:07
>>To: Phil Jones
>>Cc: david.sexton@metoffice.gov.uk; C G Kilsby; Colin Harpham
>>Subject: RE: Outputs from WG
>>
>>Hi,
>>
>>we will try for lag-1 correlation and skewness but an issue
>>for us is whether something doesn't work when we convert the
>>equilibrium pdfs to time-dependent ones or we downscale to 25km.
>>
>>As Phil has said that you can do all the derived indices
>>except gale days, if we could get a decision from the project
>>management team to cut those variables from MOHC list of
>>outputs without making any extra work for you, then that would
>>free up some time for us to investigate this further.
>>
>>Looking forward to seeing Colin's results on 24th.
>>
>>Cheers, David
>>
>>
>>
>>
>>On Fri, 2007-04-13 at 17:16 +0100, Phil Jones wrote:
>>> Some more thoughts - keep in on the loop in case i get a chance
>>> to respond from Vienna or next Thursday.
>>>
>>> Phil
>>>
>>>
>>> At 16:32 13/04/2007, david.sexton@metoffice.gov.uk wrote:
>>> >Hi,
>>> >
>>> >On Fri, 2007-04-13 at 16:00 +0100, C G Kilsby wrote:
>>> > > Phil, David
>>> > >
>>> > > Briefly, and can respond fully next week when I have
>>some more time!
>>> > >
>>> > > Some crucial points here,
>>> > > 1. the one re 90%ile of one variable not same as for
>>other variables.
>>> > > Some simple restrictions need considering before diving off into
>>> > > full joint pdfs etc.
>>> > > Also, another dimension emerges with seasons, e.g. 90%ile winter
>>> > > rainfall, or 90%ile summer rainfall?
>>> >
>>> >Joint pdfs are just an issue for me in that I am giving you several
>>> >inputs to WG and they have to be consistent. For example, we are
>>> >finding we only get wetter summers for lower end of temperature
>>> >increases. Plus we already intend to provide sets of sampled values
>>> >for lots of variables that are consistent for any given point in
>>> >model parameter space.
>>>
>>> The joint pdfs are an issue for the WG as well. Not so much for
>>> Chris, but for us we have to reproduce the statistics for
>>> the other variables. Colin
>>> has solved the double counting issue for the means (for T etc),
>>> but we've yet to look at the variance.
>>>
>>> Colin should be able to show some of the results on the 24th
>>> as to how well the WG works. This fits the WG (with our rainfall
>>> component) to HadRM3 and then applies our modification
>>> technique to an A2 future (for comparison with the true RCM
>>> future for the 2070s). Sunshine is the only real problem.
>>>
>>> I don't think we need to repeat this with the NS rainfall,
>>> but discuss that once you've seen some preliminary results
>>> on the 24tjh.
>>>
>>>
>>> > >
>>> > > 2. Bit concerned to hear David talking of some precip
>>stats being
>>> > > secondary or optional - I would say mean, var and pdry days are
>>> > > all
>>> > > essential: from our experience autocorrelation and skewness are
>>> > > also pretty well behaved and we would rather have them
>>if at all possible!
>>> >
>>> >
>>> >Good. This discussion is throwing up a few discrepancies which need
>>> >clarifying. That some precip stats are of secondary
>>importance, is an
>>> >impression I was getting from Phil's earlier emails last month.
>>>
>>>
>>> I think there is some misunderstanding here. What I said earlier
>>> confirms what Chris has said - if they are available then Chris
>>> would like them. Chris will need to consider is they may be
>>> fully relevant due to the scale issue (25km squares vs points).
>>> Could be an issue for skew and r1.
>>>
>>> Checking this out a la fitting directly to HadRCM3 control
>>> data might be useful here. See Colin's plots though before
>>> deciding.
>>>
>>>
>>>
>>> >I look forward to the fuller response next week. I will be mainly
>>> >away then which is why I raise these issues now. It would
>>be good to
>>> >have a good chat about them on the 24th.
>>> >
>>> >Cheers, David
>>> >
>>> > >
>>> > >
>>> > > Cheers,
>>> > > Chris
>>> > >
>>> > > >-----Original Message-----
>>> > > >From: Phil Jones [mailto:p.jones@uea.ac.uk]
>>> > > >Sent: 13 April 2007 15:46
>>> > > >To: david.sexton@metoffice.gov.uk
>>> > > >Cc: david.sexton@metoffice.gov.uk; C G Kilsby; Colin Harpham
>>> > > >Subject: Re: Outputs from WG
>>> > > >
>>> > > >
>>> > > > David,
>>> > > > More thoughts embedded.
>>> > > >
>>> > > > Phil
>>> > > >
>>> > > >At 15:12 13/04/2007, david.sexton@metoffice.gov.uk wrote:
>>> > > >>Hi,
>>> > > >>
>>> > > >>I think we have clarified or converged on most of my points. I
>>> > > >>have some comments on points 2 and 4.
>>> > > >>
>>> > > >>Cheers, David
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>On Fri, 2007-04-13 at 14:42 +0100, Phil Jones wrote:
>>> > > >> > >2. WG will produce 100 versions of 30-yr sequences for
>>> > > >all (or just
>>> > > >> > >one?) WG variables for all months for a given combination
>>> > > >of 30-yr
>>> > > >> > >period, emissions scenario and location.
>>> > > >> > >
>>> > > >> > >I am still not clear how to generate the 100.
>>Percentiles of
>>> > > >> > >PDFs is confusing me. I think Ag needs a clear procedure
>>> > > >outlined by us
>>> > > >> > >for 24th. I think the easiest way to make WG
>>consistent with
>>> > > >> > >MOHC pdfs is the following (assuming I am correct so far):
>>> > > >> > >
>>> > > >> > > a. User selects WG, 30-yr period, emissions
>>scenario and
>>> > > >> > > location
>>> > > >> > (up
>>> > > >> > >to 1000km^2).
>>> > > >> > > b. Work out which 25km x 25km box over UK is closest to
>>> > > >> > >this
>>> > > >> > multi-
>>> > > >> > >site location.
>>> > > >> > > c. For the 30-yr period, emissions scenario and
>>location
>>> > > >> > >in b),
>>> > > >> > DDP
>>> > > >> > >internally produces a table of changes in mean T, %
>>> > > >changes in mean
>>> > > >> > P,
>>> > > >> > >and changes in variance of P for each month for
>>100 randomly
>>> > > >> > >sampled different model variants. DDP ALREADY needs this
>>> > > >capability.
>>> > > >> > > d. So we have an internal matrix with 3*12=36
>>columns and
>>> > > >> > > 100
>>> > > >> > rows. WG
>>> > > >> > >loops through 100 rows, using each set of 36
>>numbers to drive WG.
>>> > > >> > User
>>> > > >> > >gets 100 WG's. Does what they like with it.
>>> > > >> >
>>> > > >> >
>>> > > >> > Sort of. The 100 versions of the WG I was talking
>>> > > >about will all
>>> > > >> > have
>>> > > >> > the same statistics. I thought these 100 would be from
>>> > > >one point
>>> > > >> > within
>>> > > >> > the pdf (or the joint pdf) - say the 10, 50 or 90th
>>> > > >percentile. We
>>> > > >> > could make
>>> > > >> > this percentile selectable.
>>> > > >> >
>>> > > >> > The 100 (or 1 or whatever) are representative of some
>>> > > >> > future 30-year period.
>>> > > >> > Your a) and b) are fine.
>>> > > >> >
>>> > > >> > Another option is like yours. There is a pdf
>>(or joint pdf).
>>> > > >> > The 100 could be
>>> > > >> > from each of the 100 percentiles? Does this make sense?
>>> > > >Or the 100
>>> > > >> > could
>>> > > >> > come from sampling the percentile space assuming a normal
>>> > > >> > distribution?
>>> > > >> >
>>> > > >> > Your 2) is an important aspect to sort out on the 24th.
>>> > > >>
>>> > > >>
>>> > > >>I agree that we need to discuss this but it would be good to
>>> > > >thrash it
>>> > > >>out a bit more before 24th. UKCIP08 needs the WG pdf to be
>>> > > >>consistent with the MOHC pdf. Your solution tries to
>>do this but
>>> > > >>a problem with selecting a percentile is that a model variant
>>> > > >>that is the 90th percentile for temperature is not
>>90th percentile for other variables.
>>> > > >>There is also a related issue about how you chose a model
>>> > > >variant near
>>> > > >>a given percentile. The solution I propose means these are
>>> > > >not issues.
>>> > > >>So we could sample M model variants and run N WGs for
>>each model
>>> > > >>variant. M has to be a good size to make sample
>>> > > >representative of MOHC
>>> > > >>pdf but N does not have to be large as internal variability
>>> > > >is already
>>> > > >>generated by using a different set of parameters and a
>>> > > >different seed for each WG.
>>> > > >>I think this solution is simpler than the percentile-based
>>> > > >solution. Do
>>> > > >>you agree?
>>> > > >
>>> > > >
>>> > > > Sounds OK. Let's see what Chris thinks.
>>> > > >
>>> > > >
>>> > > >
>>> > > >
>>> > > >> > >4. Phil has mentioned in the past that EARWIG produces some
>>> > > >> > diagnostics
>>> > > >> > >e.g. consecutive dry days, frost days etc. from WG. Will
>>> > > >> > >this be done for UKCIP08?
>>> > > >> >
>>> > > >> >
>>> > > >> > The plan is yes for this. Colin has the software
>>for this.
>>> > > >> > It just needs to be set
>>> > > >> > up carefully, as the base for all the diagnostics
>>(for the
>>> > > >> > future
>>> > > >> > runs) has to be
>>> > > >> > based on median run of the WG for the present (61-90).
>>> > > >We shouldn't
>>> > > >> > allow users to change the 61-90 base period (or the
>>> > > >choice of the
>>> > > >> > median).
>>> > > >> >
>>> > > >> >
>>> > > >> >
>>> > > >>
>>> > > >>Good. I would like your opinion on a problem I am having with
>>> > > >>some of the variables we are providing pdfs for. Some
>>quantities
>>> > > >>are indices derived from daily model data e.g frost days but I
>>> > > >>think
>>> > > >there are two
>>> > > >>problems with this:
>>> > > >>
>>> > > >>1. Model bias e.g. a model that is too warm may have very few
>>> > > >>frost days and therefore the change looks small.
>>Effect will be
>>> > > >>a nonlinear function of bias based on shape of
>>distribution of daily data.
>>> > > >>
>>> > > >>2. WG and pdfs could provide two alternative routes to same
>>> > > >answer and
>>> > > >>they will obviously conflict for reasons we understand e.g.
>>> > > >model bias
>>> > > >>but the users won't understand.
>>> > > >>
>>> > > >>To avoid confusing user and potentially reducing their
>>> > > >>confidence in UKCIP products, I think it makes sense
>>for WGs to
>>> > > >>be the sole route towards a prediction of derived
>>indices. BTW,
>>> > > >>I have a handful of derived indices to do (hot days, wet days,
>>> > > >>gale days, heating and cooling degree days and frost
>>days) and I
>>> > > >>think you cover
>>> > > >some of these
>>> > > >>already. What do you think?
>>> > > >>
>>> > > >>Geoff wants to discuss issues connected to the three strands
>>> > > >of output
>>> > > >>(pdfs, WG, RCM) on the 24th.
>>> > > >
>>> > > >
>>> > > > Model biases will only be a problem with their data
>>used directly.
>>> > > > So this could be a problem with the larger regions
>>where the WG
>>> > > > won't work well. The WG won't have biases as it is based on
>>> > > > 61-90 as the base period. We will be perturbing these
>>with the
>>> > > > RCM-based pdfs.
>>> > > >
>>> > > > Maybe we need to show that the following will/should/must be
>>> > > > the same
>>> > > >
>>> > > > Model-based scenario for 2070s minus model present
>>(61-90) equals
>>> > > > WG scenarios for the 2070s minus WG present (61-90).
>>> > > >
>>> > > > Geoff will need to get this across as this is how the three
>>> > > >strands will
>>> > > > produce the same answers.
>>> > > >
>>> > > > The WG and the extremes software will do all the temp/precip
>>> > > > indices but won't do gale days.
>>> > > >
>>> > > >
>>> > > >>Cheers, David
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>
>>> > > >>--
>>> > > >>______________________________________________________
>>> > > >>David Sexton PhD Climate Research Scientist Met Office
>>> > > >Hadley Centre
>>> > > >>for Climate Prediction and Research FitzRoy
>>> > > >>Road Exeter EX1 3PB United Kingdom
>>> > > >>Tel: +44 (0)1392 886524 Fax: +44 (0)1392 885681
>>> > > >>E-mail: david.sexton@metoffice.gov.uk
>>http://www.metoffice.com
>>> > > >
>>> > > >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
>>> > > >---------------------------------------------------------------
>>> > > >-------------
>>> > > >
>>> > > >
>>> > > >
>>> >--
>>> >______________________________________________________
>>> >David Sexton PhD Climate Research Scientist Met Office Hadley
>>> >Centre for Climate Prediction and Research FitzRoy
>>> >Road Exeter EX1 3PB United Kingdom
>>> >Tel: +44 (0)1392 886524 Fax: +44 (0)1392 885681
>>> >E-mail: david.sexton@metoffice.gov.uk http://www.metoffice.com
>>>
>>> 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
>>>
>>---------------------------------------------------------------
>>-------------
>>
>>--
>>______________________________________________________
>>David Sexton PhD Climate Research Scientist Met Office
>>Hadley Centre for Climate Prediction and Research FitzRoy
>>Road Exeter EX1 3PB United Kingdom
>>Tel: +44 (0)1392 886524 Fax: +44 (0)1392 885681
>>E-mail: david.sexton@metoffice.gov.uk http://www.metoffice.com
>>
>

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