date: Wed, 17 Oct 2007 14:03:32 +0100
from: Ian Harris <i.harris@uea.ac.uk>
subject: CRU TS Secondaries Strategy
to: Phil Jones <p.jones@uea.ac.uk>, Tim Osborn <t.osborn@uea.ac.uk>

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Hi,

I've been mulling over a strategy issue.

CRU TS Secondary parameters are currently derived from:

1. One or more Primary parameters, gridded (to 2.5°, for some reason)
2. Normals for the Primary parameter(s)
3. Normals for the Secondary parameter

The IDL routines do not allow for genuine observations of the  
secondary parameter to be incorporated.

The problem is that we should be moving towards using secondary  
observations where available. If we just pick a changeover point,  
there are likely to be noticeable discontinuities - also we probably  
don't have enough observations to do that yet!

So, what I propose is this:

1. Produce Secondaries as Secondaries (using synthetically-generated  
data from Primaries)
2. Produce Secondaries as if they were Primaries (ie using direct  
observations of Secondary values)
3. Let the output from 2 overwrite the output from 1 WHERE the actual  
station count is >=1.

In other words, the synthetic data is replaced with 'genuine' data if  
there is at least one station reporting within the cell at that  
timestep.

How does that sound? Any better ideas? It has the advantage that it  
doesn't require a great deal of coding ;-)

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


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