Difference between revisions of "Vertical Coordinates"
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WRF uses a hybrid pressure coordinate system | WRF uses a hybrid pressure coordinate system | ||
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| + | <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 | ||
Revision as of 20:23, 13 June 2019
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 UMDB 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 Raijin under /projects/access/umdir/vn${VN}/ctldata/vert/. There are separate eta values for variables defined on theta or rho levels.
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
