<html><body style="word-wrap: break-word; -webkit-nbsp-mode: space; line-break: after-white-space;">Senja,<div class=""><br class=""></div><div class="">I noticed this line in the default KPP_OPTIONS.h:</div>#define KPP_SMOOTH_DBLOC<br class=""><br class="">I turned it off and found much better solutions in the first phase of high viscosities, but then it deterioriates. See attached plot of a timeseries at grid point i=39,j=51. Top is your original code (with default KPP_OPTIONS.h), second is with KPP_SMOOTH_DBLOC undefined, and third with GGL90 instead of KPP.<div class=""><br class=""></div><div class="">I guess it’s pretty clear what to use (o: It’s particularly unclear where there’s large viscosities below the actively mixed layer come from, the same with the enhance viscosities below 20m.</div><div class=""><br class=""></div><div class="">These instabilities in KPP need a more efficient test setup, before I can look into this further. Maybe we can construct something from your setup.</div><div class=""><br class=""></div><div class="">Martin<br class=""><div class=""><br class=""></div><div class=""><img apple-inline="yes" id="A084C906-5426-4F55-90BF-84037A14D021" src="cid:E354FE6D-D824-4F45-8FA1-07729D3D35BA@localdomain" class=""><br class=""><div class=""><br class=""></div><div class=""><br class=""><blockquote type="cite" class="">On 8. Apr 2020, at 15:32, Martin Losch <<a href="mailto:Martin.Losch@awi.de" class="">Martin.Losch@awi.de</a>> wrote:<br class=""><br class="">Senja,<br class=""><br class="">I reset the KPP_OPTIONS.h to the default version in pkg/kpp to see the full drama.<br class="">I can see that after about 16h of integration, the model becomes dynamically instable (more motion) and the described patterns appear, but they also disappear again when the forcing becomes weaker (right?)<br class=""><br class="">The phases with the vertical grid scale noise in the viscosities is associated with interersting surface field patterns (e.g. temperature and KPPdbloc, which is gravity*drho/rho). In my opinion this has got to do something with the way KPP handles the surface forcing. On the other hand, your surface forcing is fairly smooth and I don’t see how that should lead to this noise. There are so many thresholds and if statements/min/max function in the kpp-code that I find it hard to trace down the source of these instabilities.<br class=""><br class="">I have tried your configuration wih GGL90 instead of KPP. The surface forcing by wind is quite similar in that mixed layer model code, but the noise never appears. So if you don’t have to use KPP I would recommend to use GGL90 for your simulations.<br class=""><br class="">Martin<br class=""><br class=""><blockquote type="cite" class="">On 7. Apr 2020, at 21:40, Martin Losch <<a href="mailto:Martin.Losch@awi.de" class="">Martin.Losch@awi.de</a>> wrote:<br class=""><br class="">OK, got it to run, but how long does it take until these patterns appear?<br class=""><br class="">I am not at all certain that this matters: I assume that salinity is zero all the time, but I would suggest either setting a diffusive advection scheme for salinity (saltAdvScheme = 33) or turn salinity off (saltStepping = .FALSE.). With the default advection scheme (2) and the tiny diffusivities, there may be unexpected results.<br class=""><br class="">Martin<br class=""><br class=""><blockquote type="cite" class="">On 7. Apr 2020, at 19:18, Senja Walberg <<a href="mailto:senja.w@gmail.com" class="">senja.w@gmail.com</a>> wrote:<br class=""><br class="">Thanks Martin for moving this back to the support board. <br class=""><br class="">I haven't looked at all the fluxes and will output those next to see. I also haven't played with the time step, but I've changed the vertical grid spacing (dz). I'm using a 15 s timestep, when dz=1m I don't get any banding or artifacts. I've tried dz=0.5m and dz=0.25m and the banding is gridscale for both of those cases. <br class=""><br class="">My case is small enough to share, I've attached it in a zip file. Just run 'genbins.py' to get all the binary files and do the usual steps compiling to set up my configuration.<br class=""><br class="">Cheers,<br class="">Senja<br class=""><KPPIssueSetup.zip>_______________________________________________<br class="">MITgcm-support mailing list<br class=""><a href="mailto:MITgcm-support@mitgcm.org" class="">MITgcm-support@mitgcm.org</a><br class="">http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<br class=""></blockquote><br class="">_______________________________________________<br class="">MITgcm-support mailing list<br class=""><a href="mailto:MITgcm-support@mitgcm.org" class="">MITgcm-support@mitgcm.org</a><br class="">http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<br class=""></blockquote><br class="">_______________________________________________<br class="">MITgcm-support mailing list<br class=""><a href="mailto:MITgcm-support@mitgcm.org" class="">MITgcm-support@mitgcm.org</a><br class="">http://mailman.mitgcm.org/mailman/listinfo/mitgcm-support<br class=""></blockquote><br class=""></div></div></div></body></html>