cc: Phil Jones <p.jones@uea.ac.uk>
date: Mon, 14 May 2007 17:25:44 +0100
from: Ian Harris <i.harris@uea.ac.uk>
subject: Re: cru ts2.1
to: Sandy.Harrison@bristol.ac.uk

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Hi Sandy,

Please see:

New, M., M. Hulme and P. Jones (1999). "Representing twentieth- 
century space-time climate variability. Part I: Development of a  
1961-90 mean monthly terrestrial climatology." Journal of Climate 12:  
829-856.

It's available as a PDF here:

http://www.ouce.ox.ac.uk/~mnew/research/publications/ 
new_et_al_20th_climate_part1_JoC.pdf

On page 832 they discuss the definition of a 'wet day' - the decision  
is to go with 0.1 mm.

However, do bear in mind that the CRU TS 2.1 'rd0' variable is, in  
part, derived from monthly precipitation - where the relationship to  
daily rain day definition is obviously more convoluted!

Our local precipitation expert tells me that, in effect, 'any'  
precipitation may be used to define a rain day. I think this is  
taking advantage of rain being measured to one decimal place!

Hope that helps,

Harry

On 14 May 2007, at 7:57, Phil Jones wrote:

>
>> Date: Sun, 13 May 2007 18:42:37 +0100
>> From: "SP Harrison, Geographical Sciences"  
>> <Sandy.Harrison@bristol.ac.uk>
>> To: p.jones@uea.ac.uk
>> Subject: cru ts2.1
>> Originator-Info: login-token=Mulberry:01SIcReq/ 
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>>  token_authority=postmaster@bristol.ac.uk
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>> Hi Phil,
>>
>> No, I am not bugging you about updates -- although it would be  
>> good to know where you are with this.
>>
>> Actually, I would like to know what threshold (if any) was applied  
>> in the definition of a wet day in the CRU TS2.1 data set. I have  
>> not been able to find this anywhere in the documentation. The  
>> reason I'm interested is that we are trying to derive wet days  
>> from GCM output, and I am wondering whether we can use/should use  
>> the sort of threshold that might be used with real climate data ..  
>> or whether we should deal with the drizzle problem by setting the  
>> threshold higher. So the first step is ... what is the threshold  
>> used in the CRU data sets.
>>
>> Any thoughts on this would be appreciated ...
>>
>> Cheers,
>> Sandy
>>
>> ----------------------
>> Professor Sandy P. Harrison
>> University of Bristol
>> School of Geographical Sciences
>> University Road
>> Bristol BS8 1SS
>> UK
>> Sandy.Harrison@bristol.ac.uk
>>
>> PA - Katie Pellicci
>> Katie.Pellicci@bristol.ac.uk
>
> 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  
> ---------------------------------------------------------------------- 
> ------

Ian "Harry" Harris
Climatic Research Unit
School of Environmental Sciences
University of East Anglia
Norwich NR4 7TJ
United Kingdom


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