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CableGotchas
This page is a place to post various gotchas that may trip up users when running CABLE
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It is recommended that a lower umin (0.1-0.5) value (turbulence param) is used in offline runs.
[INH] CABLE represents the turbulent exchange using bulk transfer relationships across a network of resistances/conductances which connects the soil and canopy to the atmospheric boundary-layer. The formulations for these resistances are based upon surface-layer theory (and extensions) and assume a quasi-linear dependence on wind speed and wind shear. If calm (or near-calm) conditions are experienced some resistances can become infinite (v. large) and CABLE crashes.
Calm conditions are readily experienced in the real world, however in these conditions turbulent exchange involves involves additional processes and the link between the resistances and wind speed becomes non-trivial. CABLE currently does not represent those additional processes. Instead a minimum value on the wind speed is enforced, above which the coded formulations are known to solve. The default value of umin = 1.0m/s (March 2018) is conservative and has been set for use within ACCESS (where this issue is more challenging). In offline simulations the user has more freedom to choose. However note that the underlying issue is the lack of process representation - retaining a higher umin may result in greater accuracy.