Area enclosed by isopleth

[Arindam Chakraborty]

hi Kristopher,
        if the area enclosed by a constant isopleth is nothing
but the sum of the grid areas having values more than that of the
isopleth, the solution is rather simple:
...
'dx=2*3.1416*6371*cos(lat*3.1416/180)/360.0*cdiff(lon,x)/2'
'dy=2*3.1416*6371/360.0*cdiff(lat,y)/2'
'area = dx*dy'
set time range
'd
tloop(asumg(maskout(area,sst-28),lon=lon1,lon=lon2,lat=lat1,lat=lat2))'
(in sq km)

where (lon1,lon2), (lat1,lat2) is the region over which the area is
being computed.

If it is required to find the area under only a specific isopleth
which is not possible to separate from the other same-valued
contours by a simple rectangle, you may need to carefully divide the
region around the required isopleth into smaller rectangles and sum
over all those will give the total area.

Hope this helps,

----------------------------
 ARINDAM CHAKRABORTY
 Department of Meteorology
 Florida State University
 Tallahassee, FL-32306, USA
 Tel: +001-850-6443524 (Off)
      +001-850-5758550 (Res)
 Fax: +001-850-6449642
____________________________

On Sun, 30 Oct 2005, Kristopher Karnauskas wrote:

> Dear GrADS users,
>
> Is there a command or script capable of computing the spatial area enclosed
> by a specified isopleth (e.g. the 28C isotherm of SST)?
>
> The archives show this question being asked twice.  The first (2002) doesn't
> appear to have been responded to.  The response to the second (May 2005) was
> to set gxout to grid and count the qualifying cells.  However, is there a
> way to do this automatically, as it could then be looped through hundreds
> of, say, weekly or monthly average maps?  This way a time series of the
> "area enclosed by the 28C isotherm" could be produced... for example.
>
> Thank you in advance,
> Kris Karnauskas
>