From: Dave Allured <dave.allured_at_nyahnyahspammersnyahnyah>

Date: Wed, 24 Jun 2009 19:58:50 -0600

Date: Wed, 24 Jun 2009 19:58:50 -0600

Ibraheem,

Point to grid correlation is easy. At each grid point, just compute

the correlation between the single point time series and the time

series for the grid point. The output from this is a single grid of

correlation numbers. Just plot this field, using any generic

contour plot function from NCL.

How do you define correlation between two unequal regions? There

are various definitions. First you need to have a good mathematical

description of what you want, independent from any programming

considerations.

One definition is a simple cross correlation where single grid

points at matching coordinates are correlated. If the regions are

different sizes, then this makes a plot that is only the size of the

small region, and blank in the remainder of the large region. This

is the third example on the correlation example page:

http://www.ncl.ucar.edu/Applications/corel.shtml

Another definition is to reduce the small region to a single time

series by a method of your choice, such as weighted or unweighted

averaging. Then compute and plot the gridded correlation of the

average time series to the larger region, similar to the single

point case.

Yet another definition is to start at one grid point in the larger

region, and compute independent correlations to each point in the

smaller region. Then combine the resulting correlation numbers to a

single number by your choice of method, such as taking the mean or

median. Repeat over all grid points of the larger region, and once

again you have a single grid of numbers to plot in the usual way.

Once you have decided on the definition, NCL has good matrix

capability to help with the computations.

Dave Allured

CU/CIRES Climate Diagnostics Center (CDC)

http://cires.colorado.edu/science/centers/cdc/

NOAA/ESRL/PSD, Climate Analysis Branch (CAB)

http://www.cdc.noaa.gov/psd1/

Ibraheem Khan wrote:

*> Hi,
*

*>
*

*> I am thinking about drawing a correlation map. The correlation must be between a point value and gridded data. Also a correlation between two unequal gridded datasets (one covering a small region and the other a larger domain). Is it possible to do both correlations?
*

*> Thanks
*

*>
*

*> -Ibraheem
*

*>
*

*>
*

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Received on Wed Jun 24 2009 - 19:58:50 MDT

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