<div dir="ltr"><div><div><div>Not sure what information you have available.<br><br></div>[1] not geometric altitude but if you have temperature and surface geopotential, you could use the hydrostatic equation.<br> <a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/hydro.shtml">https://www.ncl.ucar.edu/Document/Functions/Built-in/hydro.shtml</a><br><br></div>[2] then interpolate (int2p_n) the results of [1] to fixed geopotential height<br> <a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/int2p_n.shtml">https://www.ncl.ucar.edu/Document/Functions/Built-in/int2p_n.shtml</a><br><br>===<br></div>Else ... maybe ...<br><br><a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/stdatmus_p2tdz.shtml">https://www.ncl.ucar.edu/Document/Functions/Built-in/stdatmus_p2tdz.shtml</a><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Thu, Feb 19, 2015 at 1:37 PM, Xi Chang <span dir="ltr"><<a href="mailto:xi.chang01@gmail.com" target="_blank">xi.chang01@gmail.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi Gehne, and NCL users,<div><br></div><div>Thanks for the hints, I knew this function, but I have following question prior of using the ezfft:</div><div><br></div><div>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.</div><div><br></div><div>2. do I need to interpolat the vertical level (km) to equally space (per 1 km each) ?</div><div><br></div><div>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 ?</div><div><br></div><div>Thank you for your experience and hints.</div><div><br></div><div>Dr. Chang.</div></div><div class="HOEnZb"><div class="h5"><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Feb 17, 2015 at 5:08 PM, Maria Gehne - NOAA Affiliate <span dir="ltr"><<a href="mailto:maria.gehne@noaa.gov" target="_blank">maria.gehne@noaa.gov</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr">Hi Chang,<div><br></div><div>the function ezfftf should do that. </div><div><br></div><div><a href="https://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftf.shtml" target="_blank">https://www.ncl.ucar.edu/Document/Functions/Built-in/ezfftf.shtml</a><br></div><div><br></div><div>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).</div><div><br></div><div>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.</div><div><br></div><div>Hope this helps,</div><div><br></div><div>Maria</div></div><div class="gmail_extra"><br><div class="gmail_quote"><div><div>On Sun, Feb 15, 2015 at 3:35 PM, Xi Chang <span dir="ltr"><<a href="mailto:xi.chang01@gmail.com" target="_blank">xi.chang01@gmail.com</a>></span> wrote:<br></div></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div><div><div dir="ltr">Hallo NCL,<div><br></div><div>is there any trick or function in ncl to decompose the data in pressure level to vertical wavenumber (m) based on FFT filter?</div><div><br></div><div>Thank you</div><span><font color="#888888"><div>Chang</div></font></span></div>
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