[ncl-talk] Band-pass filter on a sphere

[Min-Woo Kim]

Dear NCL experts,

I'm looking for a method of band-pass filtering on a shpere using NCL.
"https://mailman.ucar.edu/pipermail/ncl-talk/2019-May/014800.html"
The above URL is the advice of that in ncl-talk.
Following the advice, I'm trying as below.
***------- ncl scripts

Gp = f->Z_GDS0_ISBL ; geopotential in ERA5(GRIB)


lon = tofloat(Gp&g0_lon_2)

Gp_w1  = Gp

Gp_w5  = Gp

Gp_a   = Gp


spec_harmonics = shaeC(Gp) ; to spherical harmonics domain

spec_w1  = tri_trunC(spec_harmonics,1) ; truncate

spec_w5  = tri_trunC(spec_harmonics,5) ; truncate

spec_a   = where(spec_w1.eq.spec_w5,0,spec_w5) ; band-pass filtering
(1<n<=5)


Gp_w1    = shseC(spec_w1,dimsizes(lon)) ; return to physical domain

Gp_w5    = shseC(spec_w5,dimsizes(lon)) ; return to physical domain

Gp_a     = shseC(spec_a ,dimsizes(lon))    ; return to physical domain

***-------

I want to remain only the wavenumber from 2 to 5 of geopotential(so
consider about n=2,3,4,5).

Is this the right process for band-pass filtering on a sphere?


Thank you,
Minwoo Kim

---------------
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