# [ncl-talk] ERA Interim [SEC=UNCLASSIFIED]

Dennis Shea shea at ucar.edu
Tue Dec 15 13:34:08 MST 2015

```Hello,

Sorry for the delay....

As indicated in the documentation, the uv2dvF functions uses the
fortran based 'Spherepack' (spherical harmonics) to calculate the
divergence. See:
http://www2.cisl.ucar.edu/resources/legacy/spherepack

The code is not 'simple' and for 'casual' viewing.   :-(
In addition, NCL uses a C-based interface to the fortran subroutines.
More complicated!

===

The NCL function *requires* that the data be ordered South->North. I
think ERA-Interim is ordered North->South. You can use NCL syntax to
reverse the order quite easily.

u = f->U            ; ? (time,level,lat,lon) ?

u = u(:,:,::-1,:)   ; reorder

Same for 'v'

====
There is a simple finite difference based function that could be used

http://www.ncl.ucar.edu/Document/Functions/Built-in/uv2vr_cfd.shtml

Assorted examples are at:
http://www.ncl.ucar.edu/Applications/wind.shtml
See:
Example 5

Hope this helps.

D

On Mon, Dec 7, 2015 at 9:57 PM, Eun-Pa Lim <E.Lim at bom.gov.au> wrote:
> Hi Sandy,
>
>
>
> Have you tried the comparison for one day?
>
>
>
> I can't find the actual code for uv2dvF. If you really need it, you can send
> an email to ncl-talk at ucar.edu.
>
>
>
> Also, if I were you, I would try to calculate the divergence manually
> du/dx+dv/dy.
>
>
>
>
>
> Sorry, I'm not very helpful !!
>
>
>
> Eun-Pa Lim
>
> Research Scientist
>
> Seasonal Prediction Science Team
>
> Centre for Australian Weather and Climate Research (CAWCR)
>
> Bureau of Meteorology
>
> Tel: +61-3-9669-4636
>
> http://www.cawcr.gov.au/staff/elim/index.php
>
>
>
> From: Sandra Richard
> Sent: Tuesday, 8 December 2015 3:33 PM
> To: Eun-Pa Lim
> Subject: ERA Interim
>
>
>
> Hi Eun Pa,
>
>
>
> Sorry, I got another question for you...
>
>
>
> I understand that there is "divergence" field in ERA Interim dataset. I
> guess it must be showing horizontal divergence (du/dx+dv/dy)right?
>
> I tried to compare the output of January 1979 divergence plot (which have
> been calculated in ERA Interim) and the calculation using NCL (uv2dvf) for
> the same data (Jan 79). I've attached the script I use for calculating
> divergence using uv2dvf. However the output is totally different. Any
> thoughts?
>
> Do you know where I can get the script for this NCL function uv2dvf to see
> what it is calculating?
>
>
>
> Thanks.
>
>
>
>
>
>
>
>
>
>
>
> ________________________________
>
> From: Eun-Pa Lim
> Sent: Monday, December 7, 2015 7:23 PM
> To: Sandra Richard
> Subject: RE: Hello from Kota Kinabalu, Malaysia [SEC=UNCLASSIFIED]
>
>
>
> Ah, that's sweet!!   You take care of yourself, too :-D
>
>
>
>
>
> Eun-Pa Lim
>
> Research Scientist
>
> Seasonal Prediction Science Team
>
> Centre for Australian Weather and Climate Research (CAWCR)
>
> Bureau of Meteorology
>
> Tel: +61-3-9669-4636
>
> http://www.cawcr.gov.au/staff/elim/index.php
>
>
>
> From: Sandra Richard
> Sent: Monday, 7 December 2015 7:20 PM
> To: Eun-Pa Lim
> Subject: Re: Hello from Kota Kinabalu, Malaysia [SEC=UNCLASSIFIED]
>
>
>
> Hi EunPa,
>
>
>
> Yes, this is the website I'm looking for.
>
>
>
> I don't think I've seen you work "less than hard" :)
>
>
>
> Take care. I miss you already!
>
>
>
>
>
> ________________________________
>
> From: Eun-Pa Lim
> Sent: Monday, December 7, 2015 7:08 PM
> To: Sandra Richard
> Subject: RE: Hello from Kota Kinabalu, Malaysia [SEC=UNCLASSIFIED]
>
>
>
> Hi Sandy!!
>
>
>
> It's nice to hear from you!  Is it nice to be back?? Your family and
> colleagues must be excited to see you :-D
>
> I'm glad you liked Max Lucado's book – I liked it as it has many analogies I
> can associated with.
>
>
>
> Is this what you are after? - climate explorer: http://climexp.knmi.nl/
>
>
>
> If you need any help you think I could offer, please feel free to send me
> emails. This week is not a social week, so I'll be here working "hard"!
>
>
>
> Cheers
>
>
>
> Eunpa
>
>
>
> Eun-Pa Lim
>
> Research Scientist
>
> Seasonal Prediction Science Team
>
> Centre for Australian Weather and Climate Research (CAWCR)
>
> Bureau of Meteorology
>
> Tel: +61-3-9669-4636
>
> http://www.cawcr.gov.au/staff/elim/index.php
>
>
>
> From: Sandra Richard
> Sent: Monday, 7 December 2015 6:57 PM
> To: Eun-Pa Lim
> Subject: Hello from Kota Kinabalu, Malaysia
>
>
>
> Hi EunPa,
>
>
>
> How are you? Hope everything is well with you there. Thank you for the
> birthday treat and the present. I love that book you gave me.
>
>
>
> I'm starting to do my work at the Malaysian Meteorological Department today.
> Expected to come in  the office every day. It's a bit harder because I do
> not have a walking library/reference (you!) here. Hahaha!
>
>
>
> Anyway, I wanted to ask you about the website where I can see the output of
> the reanalysis. I remember the other day you show me a website that shows
> the SST during each month. I lost the link when my laptop was formatted by
> uni staff :(.
>
>
>
> Thanks!
>
>
>
> Keep in touch.
>
>
>
> Cheers, Sandy
>
>
> _______________________________________________
> ncl-talk mailing list
> ncl-talk at ucar.edu
> List instructions, subscriber options, unsubscribe:
> http://mailman.ucar.edu/mailman/listinfo/ncl-talk
>
```