terrestrial global means

There are a couple of fields on the land history file that should help
you with this question. They are "area" and "landfrac" (they might be
captitalized in the IPCC version of the land history files). Area is the
area of each gridcell in km**2 and landfrac is the fraction of the gridcell
that is land (range is 0-1).
If you want a global average of a land quantity (x) that has dimensions (lat,lon),
then you will need to do something like:

weight = area*landfrac/sum(area*landfrac)
avg_x = sum(weight*x)

In your case (e.g., x = surface runoff) this would give you global land average runoff in mm/s.

If you want total volume of runoff then you need something like:

vol_x = sum(x*area*landfrac*0.001*1.e6)

The 0.001 converts x from mm/s to m/s and the 1.e6 converts area from km**2 to
m**2.
This would give you global land volume of runoff in m**3/s.

You can also use the built-in function Dennis suggested below.

wgt_areaave_Wrap [wgt_areaave]

will do the areal average

http://www.ncl.ucar.edu/Document/Functions/Contributed/wgt_areaave_Wrap.shtml
http://www.ncl.ucar.edu/Document/Functions/Built-in/wgt_areaave.shtml

____________________________________________________________________________
Keith Oleson oleson_at_ucar.edu
Terrestrial Sciences Section Work Phone: 303-497-1332
Climate and Global Dynamics Division Fax: 303-497-1348
National Center for Atmospheric Research Express mail: NCAR
P.O. Box 3000 1850 Table Mesa Dr.
Boulder, CO 80307 Boulder, CO 80305

=++++++++++++++++++++++++++
+++++++++++++++++++++++++++
hi there,
 my first try to work with NCL. just got it installed and i've already got
 lots of
questions.

i've downloaded data from http://www.earthsystemgrid.org/. i got land only
data for surface and subsurface runoff for a T31 grid.

now i'm planning to calculate the global mean of these parameters.
unfortunately the data is in mm/s but i'll need km-3. this should be easy
but how do i generate a global mean of continental data only which are
normalized to the area of each grid cell (something you have to do when
transferring mm/s to volumes).

any ideas on how to proceed?

ciao sascha
_______________________________________________
ncl-talk mailing list
ncl-talk_at_ucar.edu
http://mailman.ucar.edu/mailman/listinfo/ncl-talk
Received on Mon Feb 05 2007 - 11:53:34 MST