MPAS: A GAP FLOW

Codes:
https://github.com/shimyook/DCMIP2025_SY

Regrid routine:

https://github.com/shimyook/DCMIP2025_SY/blob/main/other_scripts/run_regrid_all.bash

OUTPUT DIRECTORY:
/glade/work/simchany/dcmip25/

cases:

sy_dcmip2025_horiz_mount_flow_{resolution}_{experiment}

resolutions= mpasa60, mpasa120

experiments = cntrl, U0X2, T298, 

GAP1

cntrl-> control run

U0X2-> 20 m/s U0

T298->  T0=298 instead of 288 K

GAP1-> gap X 2

Useful information for MPAS:

https://www2.mmm.ucar.edu/projects/mpas/site/documentation/users_guide/appB_model_namelist.html

• Investigates the generation of meso-scale dynamics in the lee of a mountain. 

• Models a mountain chain with a gap. This leads to an acceleration of the zonal wind through the gap and the generation of lee vortices around the topography.

• Assumptions: isothermal atmosphere, constant static stability (Brunt–Väisälä frequency) and a zonal wind of u = u0 cos(lat), which is a solid body rotation.

Test cases:

1. Varying flow velocity - Change the wind speed, u0.

2. Change the isothermal temperature T0 (changes the Brunt-Vaisala frequency N). - vertical 

3. Note that both u0 and T0 & N variations impact the Froude number Fr = u0/(N h). Changing the Fr number changes the character of the flow (e.g. you might lose the vortex shedding signatures, try it out).

4. Increase the horizontal resolution from ~1 degree/5.5 km on the small Earth (ne30, C96, mpasa120) to ~0.5 degrees/2.75 km on the small Earth (ne60, C192, mpasa60).

5. Varying the mountain height (not possible as of now) or  changing distance of gap or gap location.

6.  With and without the Coriolis force (scaled for the small Earth).

7. Modify the diffusion settings - such as the order of divergence damping

   1. mpas_horiz_mixing: 

      1. '2d_smagorinsky' for a coefficient that varies as a function of the flow tension and shear. Default (control)

      2. '2d_fixed' for constant coefficient horizontal diffusion

   2.