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reference height #240

Open penguian opened 4 years ago

penguian commented 4 years ago

keyword_maygit owner:bep599@nci.org.au type_model improvement | by Juergen.Knauer@csiro.au

In the current version of the code, reference height for wind speed (rough%za_uv) and temperature/humidity (rough%za_tq) is hardwired to 40m. For site-level runs (e.g. at eddy covariance (EC) sites) this might lead to a strong underestimation of wind speed at canopy height. One solution is to provide the measurement height as input within e.g. the forcing files. However, the measurement height at EC sites does not correspond to the reference height in CABLE (rough%zref_uv; rough%zref_tq), as the latter represents measurement height - displacement height. At the moment rough%zref_uv and rough%zref_tq are corrected for displacement height if cable_user%MetType is 'site':

rough%zref_uv = MAX(2.0, rough%za_uv - take_off_disp * rough%disp)

rough%zref_uv = MAX(rough%zref_uv, rough%hruff - rough%disp)

where take_off_disp = 1.0 if cable_user%MetType is 'site' and 0.0 otherwise. Same for rough%zref_tq. I am referring to branch https://trac.nci.org.au/svn/cable/branches/Share/NESP2pt9_BLAZE

It is currently unclear how to deal with this with other forcing types. In addition, the existing formulation might be subject to improvement.

Issue migrated from trac:240 at 2023-11-27 11:31:19 +1100

penguian commented 4 years ago

Juergen.Knauer@csiro.au set milestone to 6. Report

penguian commented 4 years ago

@mgk576@nci.org.au commented

Anna Ukkola has added "reference height" for almost all (maybe all) the FLUXNET2015 sites to the new PLUMBER met files.

penguian commented 4 years ago

@mgk576@nci.org.au commented

Part of the problem was that the Met File that was used originally had an incorrect name for the reference height %za - so was defaulting to 40m. I still think that there is a philosophical question around whether CABLE should provide a default value for %za for site runs (or just fail or create a big flashing light) which we should think through.

The science problem addressed in the ticket is subtly different – is the reference height %za provided above the ground or above the displacement height? For ACCESS, and possibly GSWP3 type runs, %za provided is above the displacement and d (while needed) should not be subtracted when evaluating %zref_uv and %zref_tq. However, my opinion, for single sites %za is usually above ground (i.e. is the known height of the sensors). There is then a difference in how CABLE should handle %za when in operating at single site or other configurations.

penguian commented 1 year ago

@ccc561@nci.org.au set keywords to maygit