[R] correlation value and map

Jenny Barnes jmb at mssl.ucl.ac.uk
Wed Jan 10 17:24:34 CET 2007

Hi Zoltan,

Right, I have 30x32=960 data points per year (It is actually the mean febuary 
precipitation total in case you were wondering) at each grid point over the 
world, so I have 960 data points each of the 43 years. Therefore can I do 
anything with a trend and residuals? I don't think I can if it's just mean feb 
precipitation, one data point per grid square per year... I apreicate your help 
though very much.....although I do still need to perform a spatial correlation 
if anyone else can help?

Many thanks,


Hi Jenny!

So if i understand your datafile corect you have 960 case for a year. Any
you have 43 years.. Yes?

I'm not sure you should use correlation in this situation because of the
autocorrelation of the data. There are big autocorrelation on spatial data's
like what you use, and there are also a very big autocorrelation in time
series data. I think you have to decompose your time series, and you have to
cut down, the trend (and maybe some kind of sesonality), and than for the
residuals you should do a correlation. You have to filter out the
autocorrelation on the spatial data too, some way..

And because of the above problems, don't calculate correlation for the
entierly databases!


Jennifer Barnes
PhD student - long range drought prediction
Climate Extremes
Department of Space and Climate Physics
University College London
Holmbury St Mary, Dorking
01483 204149
07916 139187
Web: http://climate.mssl.ucl.ac.uk

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