[gradsusr] prolems with nested global area using const and atot

[Andrew Friedman]

Hi GrADS users,

I'm getting different answers in a global area calculation combining const with atot after setting x-values. This difference seems to depend on whether I do the calculation in 1 or 2 steps.

Following example 1 from atot (http://www.iges.org/grads/gadoc/gradfuncatot.html),
 I have a SST dataset (attached) with longitude dimensions of -180 to 180.

METHOD 1: one-step calculation
ga-> sdfopen sst_timeslice.nc
ga-> set lon -180 180
ga-> d atot(const(sst,1,-a),g)
Result value = 12.5664

METHOD 2: 2-step caclulation
ga-> sdfopen sst_timeslice.nc
ga-> set lon -180 180
ga-> sst1=const(sst,1,-a)
ga-> d atot(sst1,g)
Result value = 6.45772

Can anyone explain what is going on? Is this the intended behavior?

Thanks,
Andrew

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Andrew Friedman
Graduate student, UC Berkeley Geography
andfried at berkeley.edu