from: Phil Jones <p.jonesatXYZxyz.ac.uk>

subject: Re: Fw: RE: Re: Urbanisation

to: <liqxatXYZxyz.gov.cn>

Dear Qingxiang,

Away all last week and Monday was a national holiday.

The formula David has sent by the email has the SE formula.

The bottom line has (n-2) in it.

This n should be reduced to allow for autocorrelation, so calculate

the lag-1 autocorrelation and then calculate n'.

The difficult point is to add in the effect of the bias adjustments.

There is more in

Brohan, P., Kennedy, J., Harris, I., Tett, S.F.B. and Jones, P.D., 2006: Uncertainty

estimates in regional and global observed temperature changes: a new dataset from 1850. J.

Geophys. Res. 111, D12106, doi:10.1029/2005JD006548.

but this is about errors on individual estimates, nt on how this affects standard errors

on trends.

I think as your bias adjustments have little effect overall on the overall 'China average'

then you can ignore this - and just use the formula and the adjustment of n.

Cheers

Phil

At 09:03 04/05/2009, you wrote:

Dear Phil,

I looked around, and find little help about how to calculate the 95% uncertainty

range of trend of the climate series. Dave's suggestion is asking for your help.

Would you give some instructions?

Best

Qingxiang

------------------

liqx

2009-05-04

-------------------------------------------------------------

�����ˣ�Parker, David

�������ڣ�2009-03-25 23:11:26

�ռ��ˣ�liqx@cma.gov.cn

��ͣ�p.jones@uea.ac.uk

���⣺RE: Re: Urbanisation

Dear Qingxiang

See

[1]http://www.okstate.edu/ag/agedcm4h/academic/aged5980a/5980/newpage24.htm

for a formula for the standard error of a least-squares trend.

But if the residuals are autocorrelated you will need to decrease n to

n' using the formula

n' = n(1-r)/(1+r) where r is the lag-1 autocorrelation of the residuals

from the regression line (Trenberth, 1984, reference cited below).

In addition you should really take account of the uncertainties in your

bias-adjustments, but I don't know how to do this other than by

Monte-Carlo experiments, creating lots of time series with each bias

adjustment varied by a random proportion of its own standard error.

Maybe consult Phil Jones too.

Regards

David

CITATION

Trenberth K. E. 1984. Some effects of finite sample size and persistence

on meteorological statistics. Part II: Potential predictability. Monthly

Weather Review, 112, 2369-2379.

David Parker, Climate Research scientist

Met Office Hadley Centre FitzRoy Road Exeter Devon EX1 3PB United

Kingdom

Tel: +44 (0)1392 886649 Fax: +44 (0)1392 885681

Email: david.parkeratXYZxyzoffice.gov.uk

Website: [2]www.metoffice.gov.uk

See our guide to climate change at

[3]http://www.metoffice.gov.uk/climatechange/guide/

-----Original Message-----

From: liqxatXYZxyz.gov.cn [[4]mailto:liqx@cma.gov.cn]

Sent: Wednesday, March 25, 2009 2:36 PM

To: Parker, David

Subject: RE: Re: Urbanisation

Dear david,

I cannot find any arithmetics here to calculate the 95% uncertainty

range of trend, can you give me some help?

Best

Qingxiang

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

----------------------------------------------------------------------------

## No comments:

## Post a Comment