<div dir="ltr">Hi Gus,<div><br></div><div>I am using GFDL dynamical core. Since the output of "pk" from my simulation is "zero" so I assuming that the coordinate is sigma. Anyway, which interpolation technique do you think the best for <span style="font-size:12.8px">vinth2p:</span> "linear" or "logarithmic" (?)</div><div><br></div><div>Thanks</div><div>Xi</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Apr 28, 2017 at 12:42 PM, Gustavo Correa <span dir="ltr"><<a href="mailto:gus@ldeo.columbia.edu" target="_blank">gus@ldeo.columbia.edu</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hi Xi<br>
<br>
I am speaking about GFDL AM3/CM3, so if you're using AM2.1/CM2.1<br>
or older, you need to check if this is correct for those older versions.<br>
<br>
I just went through the same problem a couple of weeks ago.<br>
<br>
In the history/postprocessed files,<br>
GFDL renames as "pk" what is in fact "ak".<br>
<br>
Note however, that contrary to NCAR models,<br>
which uses this conversion formula:<br>
<br>
pressure(i,j,k,n)=ak(k)*p0 + bk(k)*ps(i,j,n)<br>
<br>
AM3 (maybe older versions as well) use<br>
<br>
pressure(i,j,k,n)=ak(k) + bk(k)*ps(i,j,n)<br>
<br>
<br>
where ak is just renamed<br>
to pk in the netCDF output files.<br>
<br>
In the formulas above, i,j,k,n are respectively the indices for longitude,<br>
latitude, level, and time, and p0 is the reference pressure (at the surface).<br>
Although the mean sea level pressure p0 is 1013hPa, models<br>
normally use p0=1000hPa.<br>
<br>
Note that in the NCAR scheme both ak and bk are<br>
non-dimensional.<br>
However, in the GFDL AM3 scheme bk is non-dimensional,<br>
but ak (renamed pk) has dimensions of pressure.<br>
Actually ak (or pk) is in Pascal (NOT mb or hPa).<br>
<br>
This is probably handled directly by vinth2p, or at most you need<br>
to rescale ak=pk/p0 before you use vinth2p.<br>
Please, check the vinth2p documentation before you use it.<br>
<br>
A good reference is the Donner et. al. 2013 Journal of Climate<br>
article about AM3.<br>
It has a table clarifying the meaning of ak, bk, etc, although<br>
it doesn't mention that in the output files ak is renamed pk.<br>
<br>
I hope this helps,<br>
Gus Correa<br>
<div class="HOEnZb"><div class="h5"><br>
On Apr 28, 2017, at 12:07 AM, Xi Chang wrote:<br>
<br>
> Hi NCL team,<br>
><br>
> I am currently running some simulations with GFDL model + topography.<br>
> So, I aware that pressure level_interpolation is needed when topography is non-zero due to terrain-following sigma coordinates. I know that I can use this function from NCL "vinth2p" but I only have "bk", "pk", and "ps". from the output file, but not the "ak". Can you suggest me how to solve this issue?<br>
><br>
> Thanks<br>
> Dr. Chang<br>
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