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Paul Leopardi edited this page Nov 4, 2024 · 21 revisions

Discussion page for reported CABLE deficiency: evaporation / latent heat

This page follows up part of the CABLE deficiencies discussion at the December 2014 CABLE workshop.

Claire Carouge reported: CABLE has an excessive evaporation problem, particularly in LIS/WRF applied to the Australian region. A -10^o^C bias in winter maximum temperatures is associated with the problem. The addition of a groundwater scheme (Mark Decker's work) appears to improve the problem but testing with/without the groundwater scheme at flux sites shows only a small impact. Does the online coupling amplify the response to adding the groundwater scheme?

A LIS/WRF test with the NOAH land model instead of CABLE also showed large temperature biases though not quite as large as CABLE. This could also suggest that LIS/WRF is amplifying a land surface bias, but tests have been done with a variety of boundary layer schemes in WRF.

Ruth Lorenz reported excessive latent heat flux in ACCESS-CABLE, especially over high vegetation.

![Picture1.jpg, width=800](/EvapIssue/Picture1.jpg, width=800)

Her paper, Lorenz et al, GMD, 2014 reports much lower diurnal temperature range than observed and Kowalczyk et al., AMOJ, 2013 also noted a lower diurnal temperature range over Australia for ACCESS1.3 (with CABLE) compared to ACCESS1.0 (with MOSES).

ACCESS does not appear to give the large winter maximum temperature biases seen in LIS/WRF (at least over Australia, some larger biases occur over South America). This figure shows the difference in DJF (left) and JJA (right) maximum temperature compared to Era-Iterim for an ACCESS1.1 simulation (same atmospheric settings as ACCESS1.0 but uses CABLE instead of MOSES).

![Picture2.jpg, width=800](/EvapIssue/Picture2.jpg, width=800)

Vanessa Haverd has not seen any evidence of evaporation / latent heat fluxes in BIOS2-CABLE Australian continent offline simulations. Has the data assimilation element of BIOS2 changed any parameter values that might be relevant to this problem?

Comments from Ian Harman (via email 17/12/14)

  1. and most definitely NOT a criticism of anybody's work: We must be mindful when comparing CABLE output with global observations in that most (all?) of these are actually products which involve some kind of LSM (either directly or via the reanalysis model). There is a risk of 'following the herd' e.g. if there are any structural issues within the LSMs used to derive the products.

  2. From the PLUMBER discussion Gab, Ned, Vanessa and I had following the meeting: It would be useful if we can assess whether any issue is due to errors in the short term (hour-day) sensitivities in the energy balance (especially when the carbon and water stocks are less, or not, relevant) or due to issues in the longer-term responses which inherently do rely on the carbon and water stocks or even due to issues in the atmospheric forcing. The LE figure suggests that all three maybe occurring.

  3. re tall canopies and the turbulence parameterisation: In CABLE 1.4 there are/were some in internal inconsistencies within the roughness & cbm modules in that the above canopy component varies with stability (zetar) yet there are no associated changes to the aerodynamic coefficients within the canopy. [I don't know whether this has been addressed in CABLE v2.0] This actually implies a discontinuous wind speed profile at canopy top!! In practice some of the other variables/parameters, rough%coexp springs to mind, should vary as well for consistency. Likely impact - during the day (unstable conditions) rough%coexp would increase -> increased conductances for sensible and latent heat with the sensible heat conductance increasing relatively more -> shift in the energy balance to more H, less LE and a little less outgoing longwave radiation. Having said that Eva K and I have done some tests around this issue (offline) and, from memory, we didn't see much impact - but perhaps worth thinking about whether to ticket this.

  4. Again from the PLUMBER discussions: Vanessa please correct me if I'm incorrect here - one of the parameters which the BIOS2 work considered was Ds0 (Leuning et al. 1995, Eq. 7 which I think translates to parameters d0c3 and d0c4 in the code). This clearly affects the balance between H, LE and radiation. Vanessa can you provide rough numbers for the impact?

Marcus -any comments from a CCAM or higher-res ACCESS perspective?

Ying-Ping - comments, 'known' issue with CABLE?

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