[ncl-talk] vertical wavenumber FFT

[Xi Chang]

Hi Gehne, and NCL users,

Thanks for the hints, I knew this function, but I have following question
prior of using the ezfft:

1. How can I convert the vertical level in my data (which is in pressure)
to altitude (geometry) in order to get the vertical wavenumber with units
km? I dont have any idea for this using ncl.

2.  do I need to interpolat the vertical level (km) to equally space (per 1
km each) ?

3. Is there any function or hints that you may purpose if I want to get the
spectrum as a function as vertical wavenumber and frequency ?

Thank you for your experience and hints.

Dr. Chang.

On Tue, Feb 17, 2015 at 5:08 PM, Maria Gehne - NOAA Affiliate <
maria.gehne at noaa.gov> wrote:

> Hi Chang,
>
> the function ezfftf should do that.
>
> https://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftf.shtml
>
> It works for multidimensional arrays as well as one dimensional arrays,
> for more than one dimension you need to reorder so that the pressure levels
> are the right most dimension. So if x = (time,lev,lat,lon) you may need to
> transform y = x(time,lat,lon,lev).
>
> As with all FFT applications you probably need to taper the values you are
> trying to transform so that the end points are zero and you are essentially
> transforming a periodic sequence.
>
> Hope this helps,
>
> Maria
>
> On Sun, Feb 15, 2015 at 3:35 PM, Xi Chang <xi.chang01 at gmail.com> wrote:
>
>> Hallo NCL,
>>
>> is there any trick or function in ncl to decompose the data in pressure
>> level to vertical wavenumber (m) based on FFT filter?
>>
>> Thank you
>> Chang
>>
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