Difference between revisions of "Vertical Coordinates"

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The values of <code>eta(k)</code>, <code>top_level_height</code> and <code>first_constant_rho_level</code> can be found in the UM vertical coordinate namelist, standard namelists are found on Raijin under <code>/projects/access/umdir/vn${VN}/ctldata/vert/</code>. There are separate <code>eta</code> values for variables defined on theta or rho levels.
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The values of <code>eta(k)</code>, <code>top_level_height</code> and <code>first_constant_rho_level</code> can be found in the UM vertical coordinate namelist, standard namelists are found on Gadi under <code>~access/umdir/vn${VN}/ctldata/vert/</code>. There are separate <code>eta</code> values for variables defined on theta or rho levels.
  
 
The values of Zsea and C are also available in the LOOKUP header of UM output files, as values <code>blev</code> and <code>bhlev</code> respectively. These header values can be accessed using [[Analysing_UM_outputs#Mule|Mule]]  
 
The values of Zsea and C are also available in the LOOKUP header of UM output files, as values <code>blev</code> and <code>bhlev</code> respectively. These header values can be accessed using [[Analysing_UM_outputs#Mule|Mule]]  

Latest revision as of 19:27, 31 August 2021

Climate models use a variety of vertical coordinate systems, here are the values for the models commonly in use in the Centre

UM Vertical Coordinates

The UM uses a hybrid height coordinate system, it is terrain following up to a specified height, above which it is regular height levels.

The Iris library can automatically work out altitude values from a UM file, provided it has access to orography.

The full definition of UM height levels can be found in Appendix A of UMDP F03

Z(i, j, k) = Zsea(k) + C(k) * orography(i, j)
Zsea(k) = eta(k) * top_level_height
C(k) = (1 - eta(k) / eta(first_constant_r_rho_level))**2 # for k <= first_constant_r_rho_level
     = 0                                                 # for k > first_constant_r_rho_level

The values of eta(k), top_level_height and first_constant_rho_level can be found in the UM vertical coordinate namelist, standard namelists are found on Gadi under ~access/umdir/vn${VN}/ctldata/vert/. There are separate eta values for variables defined on theta or rho levels.

The values of Zsea and C are also available in the LOOKUP header of UM output files, as values blev and bhlev respectively. These header values can be accessed using Mule

WRF Vertical Coordinates

WRF uses a hybrid pressure coordinate system

eta = (Ph - Pht)/(Phs - Pht)

with Ph the hydrostatic pressure, and Pht and Phs the values at the topmost and surface levels respectively