Re: [ferret_users] EOF weight

[Ansley Manke <ansley.b.manke@xxxxxxxx>]

Ah, ok. The ferret EOF functions don't take the underlying geographic units into account; if you want a cosine-latitude weighting to be applied, you will need to apply them yourself to the data. 

Other Ferret functionality - such as many of the transformations on the globe do handle this; see:
http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/XPRESSIONS#GeneralInfo

On 4/23/2015 9:52 AM, Douglas Lindemann wrote:

Dear Ansley,

I understood what you said. But for the Ferret is no need to calculate the weights? As in the cases of Grads and NCL (examples below)?

Grads:

• The data are not weighted. Use sqrt(cos(lat*3.141/180)) for a simple area weight.

NCL:

create weights:  sqrt(cos(lat))   [or sqrt(gw) ]
; =================================================================
  rad    = 4.*atan(1.)/180.
  clat   = f->lat           
  clat   = sqrt( cos(rad*clat) )                 ; gw for gaussian grid

Thank you for helping so far.

Douglas Lindemann

2015-04-23 18:07 GMT+02:00 Ansley Manke <ansley.b.manke@xxxxxxxx>:

Doug,
In Ferret, you can define a mask to pick out a region of a grid and work just on it.

yes? let mask = if  [condition] then 1

then you mask your variable,

yes? let masked_temp = temp* mask

and what you have is your original variable, but with missing values everywhere outside the region of your mask.  Here's the documentation about masks,
http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/XPRESSIONS#_VPID_181

You could define a masked variable and send that into the EOF calculation. Does this sound like what you need?

Ansley

On 4/23/2015 2:11 AM, Douglas Lindemann wrote:

Dear ferret users,
I'm trying to calculate EOF, but do not know how to declare the weights to calculate a specific area (ENSO, for example).
Does anyone know what are the equations of the weights and the equations are fixed for any area?
Could someone give some help on this?
Regards,

Douglas Lindemann

--
Douglas da Silva Lindemann
Mestre em Meteorologia
Doutorando em Meteorologia
Departamento de Meteorologia Agrícola
Universidade Federal de Viçosa-MG
Fone: DEA - (31) 3899-1901
         Cel. - (31) 8581-8602 (OI)
                  (31) 9379-7865 (TIM)

--

Douglas da Silva Lindemann
Mestre em Meteorologia
Doutorando em Meteorologia
Departamento de Meteorologia Agrícola
Universidade Federal de Viçosa-MG
Fone: DEA - (31) 3899-1901
         Cel. - (31) 8581-8602 (OI)
                  (31) 9379-7865 (TIM)