I am seeing some unusual behaviour with Zgrid when running VERIFICATION.
When I kick off the VERIFICATION run, the input observation file is altered. It then has incorrect Zgrid, so the observations are rejected and hence incorrect values are output to the mod file (NLmodel_value output in the mod file).
In my input obs.nc file I have Zgrid=50 and depth=-2 for SST obs (my model has 50 layers).
When I run the VERIFICATION, the obs file is first written to and altered. For the first day (of 6 daily times for which I have SST data) the Zgrid is altered from 50 to zero in some places and to range from 30-50 in others. At all following days Zgrid is left at 50.
The SST values that are output to the mod file are incorrect when the newly written Zgrid=50 or 0, and only make ‘some’ sense when Zgrid is between 30 and just under 50 i.e. on day 1.
I tried writing Zgrid as 49.8 rather than 50 but I still get the same error. I also tried leaving Zgrid at 50 and changed depth to 0 for SST, same error. I also tried swapping Zgrid and depth in the obs file, as I have done in 4D-Var applications in the past, but still get the same error.
I am wondering what is causing the obs file to be altered. How can I look at the code to see where (and why) this is happening? The obs file is altered right at the beginning when I kick off the run for the entire 6 day window, then is not altered as the model runs the course of the 6 days (writing to the history file). But the mod file is subsequently incorrect (with observations rejected) because of this initial altering of the obs file.
