Wrong MODIS-CDNC climatology in official Zonda rawdata path – need correct dataset + new icdnc_type=4

[jhelmert]

Problem

The MODIS-CDNC climatology currently available under the official Zonda rawdata path
modis_cdnc_climatology_BR17_37mu_adjusted.nc

is not the dataset that was requested and provided by Axel Seifert.

The official file therefore does not contain the intended climatology.

Impact (Quality Management)

• Data consistency: Experiments and operational EXTPAR runs may use different CDNC climatologies without this being visible.

Required Changes

1. Replace / add the correct MODIS-CDNC file in the official Zonda rawdata directory.
2. Introduce a new namelist switch in EXTPAR / Zonda:
   • icdnc_type = 4 → use the correct (Axel / ECMWF-adjusted) climatology
3. Update both repositories:
   • EXTPAR (namelist handling + consistency checks)
   • Zonda-Request (enable the new option)

Responsibility

The original introduction of the CDNC fields was done via a previous Merge Request.

Proposed next steps

• Confirm the correct file with Axel Seifert
• Create a branch and Merge Request for EXTPAR
• Create a corresponding Merge Request / update for Zonda-Request
• Document the new icdnc_type=4 option

Please assign this issue to the responsible persons for the previous CDNC Merge Request or to the EXTPAR SCA.

Thank you!

[stelliom]

Hi @jhelmert,

Not sure if this issue is intended for me, but I think Axel mentioned this to me already in an email conversation we had that started on 27.06.2025 until 22.08.2025. I report here the final messages:

From Axel Seifert:

Hi Mikael,

I think this works technically, but the data is not my most recent version. My latest version includes a combination with a CDNC climatology compiled by ECMWF. This help to reduce artifacts in high latitudes. I guess, I have to talk to Jürgen or whoever maintains these extpar data servers.

In my opinion, you could finish your implementation and we upgrade the data later.

Best regards, Axel

Answer:

Hi Axel,

No worries and thank you for looking into this!

Ok, then I will merge my PR to add support for this.

BTW, I am also maintaining the extpar-input-data repository. Currently, I added support for the datasets that were present there, but if you need to add or update some data, feel free to open a merge request there. Let me know if you need help there.

Cheers,
Mikael

As I wrote in my last message to Axel, if you need to add or update some data on extpar-input-data feel free to open a merge request there. The old datasets were added by Trang Van Pham ~2 years ago, thus I'm not sure if we should add a new CDNC option or just update the current BR17 data. Is Axel's data an improvement on the one already present or a completely different dataset? I.e. should we actually keep them both?

Finally, note that this is not a Zonda issue per se, but an EXTPAR one, Zonda simply calls EXTPAR.

Cheers,
Mikael

PS: I will be on holidays until 17.08.2026, so I might not answer quickly until then.