# Re: [ferret_users] regarding ocean area

Dear Ansley

Thank you for your email i understood that ferret use to do weighted averages and neglect the no data grid such as land point in some ocean data. But i also asked that how to get the ocean basin area for the multiplication with the ocean variable.

as is put an example of Total Ocean Heat Content
let OHC=heat[z=0:700@ave]       !! units are j/m^2
let TOHC=OHC*( ocean basin area )                        !! units are j, TOHC=total OHC

suppose for global ocean area is the complete box (i.e. x=360*110*1000, y=180*110*1000) if it is so then this is covering land region also for the area calculation along with ocean region but our variable is defined over ocean only not on land. is there a way such that we can get the ocean area over which the ocean variable is defined so that we can multiple only the area of valid cell rather than the whole box?

regards, saurabh

On Tue, Nov 29, 2016 at 5:09 AM, Ansley C. Manke wrote:

Hi,

Ferret's averages are weighted averages, using only valid data, weighted by the grid-cell size. For grids that represent longitude and latitude, the average (and integrals) use correct area on the surface of the earth.  Here is the documentation about how transformations are done:

http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/variables-xpressions/XPRESSIONS#GeneralInfo  Scroll down in that section to see the specific defintion of @AVE.

A general technique for understanding how Ferret makes, is to set up a simple example, such as a variable whose value is 1 everywhere, and apply the operations you are using to that variable, perhaps on a very coarse grid so you can more easily study the values.  There's an example of that sort of thing, using a time average operation, in this FAQ, How can I determine the averaging weights when regridding with @AVE?

Ansley

On 11/27/2016 11:36 PM, saurabh rathore wrote:
Dear Ferreters

i am have one small doubt (just for the sake of confirmation) that while making zonal/meridional/box averages of ocean data lets say SST for the region x=20E:140E and y=90S:90N so does the ferret considering land region also for averaging or it is just averaging the ocean region in that box area. Because if ferret is making the averages considering the land part then the zonal/meridional/box averages of ocean data is wrongly calculated and interpreted.
i hope the land values (NAN if no data) are automatically taken care by the ferret while making zonal/meridional/box averages. is it so?

Apart from that how to get the area of ocean basin ? suppose i want to calculate total heat content of global ocean in joules (a line plot) so how to get the global ocean area only such that
let OHC=heat[z=0:700@ave,x=@ave,y=@ave]  !! units are j/m^2
let TOHC=OHC*(global ocean area)                   !! units are j, TOHC=total OHC

​is global ocean area is the complete box (i.e. x=360*110*1000, y=180*110*1000) if it is so then this is covering land region also along with ocean region but our variable is defined over ocean only not on land.  how to get the desired result for ocean area only ? please help me to get rid out of this puzzle.

regards saurabh​

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REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434

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REGARDS

Saurabh Rathore
Research Scholar (PhD.)
Centre For Oceans, Rivers, Atmosphere & Land Science Technology
Indian Institute Of Technology, Kharagpur
contact :- 91- 8345984434