397 | | == Snow coupling == |
398 | | |
399 | | === Presentation by Catherine and Tao (MICT version) === |
400 | | |
401 | | We had time only for a short presentation of the new snow module implementation: [https://forge.ipsl.jussieu.fr/orchidee/attachment/wiki/Meetings/CMIP6/Physic/Orchidee_snow_CMIP6.pdf][[BR]] |
402 | | |
403 | | Some features : |
404 | | |
405 | | - the number of layers of snow module (ES) is always 3 |
406 | | - when there is a snow fall the whole grid is covered by snow ; only the albedo is calculated with a fractional snow cover (standard linear fractional cover) |
407 | | - After "Enerbil" the "ES" module update the snow temp profile and accounts for melt, freezing, sublimation,... It then computes the coeficient for the next time step that is given to "Enerbil": the equivalent capacity "C" term that account in an implicit way the ground heat flux (here the flux through the snow pack); Then he provides "Thermosoil" with the lowest snow layer temperature. Thermosoil use that temperature to update its temperature profile and provide back a surface flux for "ES" for the next time step. |
408 | | - It seems thus that the scheme is not fully implicit with respect to the "flux from ground to the snow" that is provided in an explicit way from the previous time step value. |
409 | | - With the coupled simulation, Tao had to define a minimum snow depth (1 cm ?) to avoid "crashes"; possible problem of energy conservation ? |
410 | | |
411 | | === Discussion === |
412 | | |
413 | | We discussed the potential impact of the non fully implicit "soil-snow-atm" scheme. Catherine mentionned that in ISBA, Aaron B. had similar issues and that the change to fully implicit did not impacted much the results. |
414 | | |
415 | | However, we agreed that with very thin snow layers this could be a problem (see "trick" of Tao in coupled mode). |
416 | | |
417 | | We proposed that a first improvement is to account for fractional snow cover for the energy budget (not only for the albedo). For that the equavalent "C" term passed to "Enerbil" should be a mix between the standard one of "Thermosoil" and the one from "ES". But this needs some revision of the equation and calls of the routine (to be writen explicitely first). |
418 | | |
419 | | JP propose that we also split the fluxes from Thermosoil back to enerbil and ES with different values.. this would ensure also a full implicit scheme. |
420 | | |
570 | | == Testing roughness length for heat in LMDZOR == |
571 | | |
572 | | 01-Sep-2015 by Fuxing WANG, Frederique CHERUY. [[BR]] |
573 | | |
574 | | Background: |
575 | | The roughness length for heat (z0h) is generally not identical to roughness length for momentum (z0m). [[BR]] |
576 | | In LMDZOR, z0h = z0m. A short description of related code is (only in coupled mode): https://forge.ipsl.jussieu.fr/orchidee/attachment/wiki/Meetings/CMIP6/Physic/condveg_z0cdrag.pdf [[BR]] |
577 | | Objective: |
578 | | To test the sensitively of LMDZOR to z0h.[[BR]] |
579 | | Simulations: |
580 | | Two simulations (1-year) were done with LMDZOR after 20 years spin-up.[[BR]] |
581 | | (1) CTL: z0h = z0m; ORCHIDEE-rev 2664, LMDZ-rev 2287; new soil vertical discretization and soil thermodynamics [[BR]] |
582 | | (2) EXP: The same as CTL, but z0h = 0.1 * z0m. [[BR]] |
583 | | Results: |
584 | | Results are compared over different seasons (annual mean, JJA and DJF): https://forge.ipsl.jussieu.fr/orchidee/attachment/wiki/Meetings/CMIP6/Physic/z0mh_annual_jja_djf.pdf. [[BR]] |
585 | | The left side in the figures is "CTL: z0h = z0m", the right side is the 'EXP-CTL' (except the last row which is the " EXP/CTL"). [[BR]] |
586 | | The Ts (temp_sol) increases over most regions. The maximum increase is over 0N-90N in JJA (1-2K), while it is over 30N-60S in DJF (0.5-1.5K).(Fig b) [[BR]] |
587 | | The pattern of fluxsens is similar for different seasons. It increases over most regions (3 W/m2 for most regions).[[BR]] |
588 | | The variation of fluxlat (+/- 6 W/m2 over most regions) and precipitation (+/-0.5mm/d over most regions) is less systematic than Ts and fluxsens. [[BR]] |
| 539 | |