[Greenline] vertical grid coordinate

• Shaped by: Magdalena
• Appetite (FTEs, weeks):
• Developers:

Problem

The exclaim experiments use the SLEVE terrain following coordinate (ivctype == 2) . See

• ICON tutorial, section 3.4

• Schär, C., D. Leuenberger, O. Fuhrer, D. Lüthi, and C. Girard, 2002: A new terrain- following vertical coordinate formulation for atmospheric prediction models. Mon. Weather Rev., 130, 2459–2480.

Referential heights for each model level are encoded in tow KDim fields in ICON eference called vct_a and vct_b those are used throughout the model for computations. In icon4py we currently read these fields from serialized data.

In ICON vct_a and vct_b are either read from file (reference files are in icon/vertical_coords_table) or are computed at model setup. and are governed by a couple of namelist parameters from sleve_nml Together with vct_a and vct_b the computation of nflatlev and nflatlev_gradp should be adressed.

Appetite

1 cycle

Solution

Computation of the vct_a and vct_b are determined by a couple of namelist parameters in slevel_nml. EXCLAIM experiments use the SLEVE coordinate and itype_laydistr = 1 that is a stretched cosine function. The corresponding calculation of vct_a and vct_b and parameters that depend upon them should be ported to python: see mo_init_vgrid.f90: init_sleve_coord, prepare_vcoord

icon4py

see icon4py-common: vertical.py. Add needed namelist parameters to the config class, with the default values given in mo_slevel_nml.f90

• nshift_above_thcklay : can be left out and set to 0, no experiments overwrites that value
• itype_laydistr == 1 : everywhere. The other options (not currently used by EXCLAIM) can be added if needed later.

class VerticalGridConfig:
    (...)
    lowest_layer_thickness:float = 50.0 (aka min_lay_thckn )
    maximal_layer_thickness: float (aka max_lay_thckn)
    top_height_limit_for_maximal_layer_thickness = (aka htop_thcknlimit) 
    top_height:float = 23500.0
    stretch_factor: float = 1.0
    
    
class VerticalParams:
   (...)
    vct_b
    

• add vct_b to VerticalModelParams
• vct_a is currently passed as parameter into the constructor. If not passed, it should alternatively be upon construction from the namelist parameters according to init_sleve_coord. Passing as a parameter can be used if it is read from file or serialized input.
• compute nflatlev and vct from vct_a and vct_b

Computation can be tested against serialized vct_a, vct_b, nflatlev

add a __str__ function that can be used to write the VerticalModelParams to log. (see ICON run logs or print_vcoord_info)

Rabbit holes

leave out init_vert_coord which computes the full heigth fields, since we have no terrain yet.

This is exactly what Jacopo started in a port_z_ifc branch. This being a rabbit hole, it also requires (apparently even for analytically smooth hills) topography smoothing routines from mo_process_topo.

Progress

• Port v_grid which computes vct_a, vct_b
• Port init_vert_coord
  • Computation of z_ifc
  • Computation of topography smoothing
• Actually use all this stuff to compute metrics and derivatives
  • vct_a and vct_b
  • z_ifc
  • rearrange the icon4py_driver.initialization of the testcases such that there is only one if (jabw/gauss/serialized): which reads the grid, generates topography, generates ICs etc (rather than how it's done now with ifs hidden in specific methods for the above functions)