**To**:**Andreas Baumgaertner <andreas.baumgaertner@xxxxxxx>****Subject**:**Re: [ferret_users] EOF: area weighting?****From**:**"William S. Kessler" <william.s.kessler@xxxxxxxx>**- Date: Mon, 07 Dec 2009 16:17:50 -0800
- Cc: Ferret Usergroup <oar.pmel.ferret_users@xxxxxxxx>
- In-reply-to: <4B1CEADF.7030109@xxxxxxx>
- References: <4B1CEADF.7030109@xxxxxxx>
- Sender: owner-ferret_users@xxxxxxxx

Hi Andreas -

You should therefore do the weighting explicitly before computing EOFs.

The distance along latitude y1 from x1 to x2 is (x2-x1)*cos(y1). The area of a thin strip dy along y1 is (x2-x1)*cos(y1)dy. To find the area between y1 and y2, integrate this in y: A = (x2-x1)INT_y1^y2(cos(y))dy = (x1-x2)(sin(y2)-sin(y1)) Regards .... Billy K On Dec 7, 2009, at 3:45 AM, Andreas Baumgaertner wrote:

Hi ferret users,I am using the functions EOF_SPACE, EOF_TFUNC and EOF_STAT tocalculateEOF of geopotential height. This calculation requires equal-area gridbox sizes, i.e. a latitude weighting with cos(y/(180/pi))^(0.5). Isthisalready accounted for in these functions, or do I need to do thatbeforeusing them? Thanks, Andreas Baumgaertner

**Follow-Ups**:**Re: [ferret_users] EOF: area weighting?***From:*Andreas Baumgaertner

**[ferret_users] open-ended level in Ferret 5.7 (Mac)***From:*Iskhaq Iskandar

**References**:**[ferret_users] EOF: area weighting?***From:*Andreas Baumgaertner

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