Difference between revisions of "Vertical Coordinates"
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The [[Analysing_UM_outputs#Iris|Iris]] library can automatically work out altitude values from a UM file, provided it has access to orography. | The [[Analysing_UM_outputs#Iris|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 [https://code.metoffice.gov.uk/doc/um/latest/papers/umdp_F03.pdf | + | The full definition of UM height levels can be found in Appendix A of [https://code.metoffice.gov.uk/doc/um/latest/papers/umdp_F03.pdf UMDP F03] |
<pre> | <pre> | ||
| − | Z(i, j, k) = Zsea(k) + C(k) | + | Z(i, j, k) = Zsea(k) + C(k) * orography(i, j) |
Zsea(k) = eta(k) * top_level_height | 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 | C(k) = (1 - eta(k) / eta(first_constant_r_rho_level))**2 # for k <= first_constant_r_rho_level | ||
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</pre> | </pre> | ||
| − | 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 | + | 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${VN}/ctldata/vert/</code>. There are separate <code>eta</code> values for variables defined on theta or rho levels. |
| + | |||
| + | The values of Zsea and C are also available in the LOOKUP header of UM output files, as values <code>blev</code> and <code>bhlev</code> respectively. These header values can be accessed using [[Analysing_UM_outputs#Mule|Mule]] | ||
== WRF Vertical Coordinates == | == WRF Vertical Coordinates == | ||
WRF uses a hybrid pressure coordinate system | WRF uses a hybrid pressure coordinate system | ||
| + | |||
| + | <pre> | ||
| + | eta = (Ph - Pht)/(Phs - Pht) | ||
| + | </pre> | ||
| + | with <code>Ph</code> the hydrostatic pressure, and <code>Pht</code> and <code>Phs</code> the values at the topmost and surface levels respectively | ||
| + | |||
| + | [[Category:WRF]][[Category:Unified Model]] | ||
Latest revision as of 19:27, 31 August 2021
Climate models use a variety of vertical coordinate systems, here are the values for the models commonly in use in the Centre
UM Vertical Coordinates
The UM uses a hybrid height coordinate system, it is terrain following up to a specified height, above which it is regular height levels.
The Iris library can automatically work out altitude values from a UM file, provided it has access to orography.
The full definition of UM height levels can be found in Appendix A of UMDP F03
Z(i, j, k) = Zsea(k) + C(k) * orography(i, j)
Zsea(k) = eta(k) * top_level_height
C(k) = (1 - eta(k) / eta(first_constant_r_rho_level))**2 # for k <= first_constant_r_rho_level
= 0 # for k > first_constant_r_rho_level
The values of eta(k), top_level_height and first_constant_rho_level can be found in the UM vertical coordinate namelist, standard namelists are found on Gadi under ~access/umdir/vn${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
