Updating the Vertical Vorticity Constraint

[jgebauer44]

In Dahl et al. (2019) (https://doi.org/10.1175/JTECH-D-18-0211.1), the vorticity constraint for the DDA was updated so that instead of using Ut and Vt as a proxy for the vorticity tendency in the cost function, the vorticity tendency field was calculated before running the DDA and that field was then held constant for calculating the vorticity cost function during the DDA. This gave much better results than using the old method. Could this be implemented into PyDDA? If so, I think it would also be good to provide functions to calculate the vorticity tendency like it was done in Dahl et al. (2019).

I am one of the co-authors on the Dahl et al. (2019) paper and also worked with technique for my dissertation so I am very familiar with the changes. I could possibly try to work on this when I get the chance but I don't know when that would be.

[rcjackson]

We would welcome your updates on this. I do think this could be implemented in PyDDA with a little bit of modification to the vorticity cost function an an extra procedure to calculate the vorticity tendency. I see this being a wrapper function around the current wind_field function, since it looks like you have to do 3 provisional DDA's on t to t+2 to get the vorticity tendency, then one more final one on t.