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[GEMPAK #EEF-383663]: sfcntr

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  • Subject: [GEMPAK #EEF-383663]: sfcntr
  • Date: Tue, 03 Aug 2010 12:16:22 -0600
Hi David,

the barnes analysis and gempak terms can be confusing - what is called the 
weighting factor in barnes analysis is determined by station spacing "deltan": 

weight = 5.051457 * ( deltan * 2. / PI ) **2

now for the confusing part: what is called "WEIGHT" in SFCNTR is more aptly 
called "SEARCH" in OABSFC and is used as a multiplier for "weight" on the 
second pass to determine the search radius:

http://www.unidata.ucar.edu/cgi-bin/gempak/manual/variables_index?search

SEARCH controls the search radius in an objective analysis program.  
     The radius is the maximum distance that a station may be from a grid 
     point to be used in the analysis for that point.  The search radius 
     is set so that stations whose weighting factor is less than 
     EXP (-SEARCH) are not used.  SEARCH must have a value in the range 
     1 - 50.  If the value is outside this range, a default value of 20 
     is used.  If SEARCH is given a very small value, many grid points 
     will not have three stations within the search area, and consequently 
     will be set to the missing data value.

In Koch's "An Interactive Barnes Objective Map Analysis Scheme for Use with 
Satellite and Conventional Data":

http://www.dca.ufcg.edu.br/grads/gs/Barnes/Barnes_02.pdf

"SEARCH" (what is called "WEIGHT" in SFCNTR") would be the maximum usable value 
of r_m.


-Michael James
Unidata









> Hello.
> I'm trying to understand the Barnes analysis in SFCNTR, and specifially,
> the parameter WEIGHT.
> 
> Many web searches lead to this page:
> http://www.unidata.ucar.edu/software/gempak/tutorial/barnes.html.
> 
> I naively searched for the phrase "Barnes weighting parameter", as
> described in the GEMPAK help, but it isn't present on the page.   Could
> you tell me a more mathematical meaning of WEIGHT?   There are many
> references to "weight" on the aforementioned page, but I don't think any
> of these are the same "weight" as the "WEIGHT" parameter in SFCNTR.
> (correct me if I'm wrong).  I tried reading the journal article, but it
> was way over my head.
> 
> Thanks for your time.
> Dave
> 


Ticket Details
===================
Ticket ID: EEF-383663
Department: Support GEMPAK
Priority: Normal
Status: Open