Re: questions about interpolation by NCL

Xuguang:

In general, interpolation is not going to be monotonic using
spherical harmonics. These values are largest near regions of
gradients? In addition, because spherical harmonics are not "local"
functions (like using lagrange polynomials), these Gibbs oscillations
are likely to be distributed across the domain. For interpolating
terrain, I would try to use more local interpolants, and then
constrain the output to be physical.

regards,

Lou Wicker

On Dec 6, 2006, at 6:28 AM, Xuguang Sun wrote:

> Hi, everyone,
>
> I'm trying to interpolate topography by f2fsh_Wrap
> into a lower resolution one, however, the interpolated
> topography in ocean has some positive and negative
> values which cross the whole ocean where the original
> values are all zeros. So when I turn back to the
> arithmetic, I find that the f2fsh_Wrap, f2gsh_Wrap and
> so on are all using the spherical harmonics.
> Therefore, I think the whether some pseudo waves or
> results are generated by using the NCL interpolation
> functions.Or in another words, the rank data cannot be
> interpolated simply by the NCL functions, right?
>
> Thanks in advance.
>
>
>
>
> SUN Xuguang
> Department of Atmospheric Sciences, Nanjing University
> 22 Hankou Road,Nanjing,P.R.China (210093)
> Tel: +86-025-83597203 (O)
> Email: sunxg007_at_yahoo.com.cn
>
>
>
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| Dr. Louis J. Wicker
| NSSL/WRDD
| National Weather Center
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Received on Wed Dec 06 2006 - 08:57:19 MST