Changes between Version 4 and Version 5 of DevelopmentActivities/CMIP6/DevelopmentsCMIP6/zo_evaporation


Ignore:
Timestamp:
10/26/15 11:27:11 (5 years ago)
Author:
jpolcher
Comment:

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  • DevelopmentActivities/CMIP6/DevelopmentsCMIP6/zo_evaporation

    v4 v5  
    118118Within the Earth2Observe project a paper on the Tier 1 simulations has been submitted by Schellekens et al.. it include the following table : 
    119119 
    120 [[Image(Table3.png, 80%)]] 
     120[[Image(Table3.png, 60%)]] 
    121121 
    122122For this dataset it was the Trunk of July 2014 which was run but with the new driver. This meant a more accurate calculation of ETP from the WFDEI_CRU forcing. One immediately notes that evaporation is too high in ORCHIDEE and thus sets us apart from the other models. In order to test how much this is the result of years of accepting too high turbulence in order to compensate for too low ETPs produced the old driver, I re-ran the same code but dividing z0 by 10. The simulation is not yet finished so only the 90s are analysed. 
     
    124124The change in z0 is pictured below : 
    125125 
    126 [[Image(Z0_Diff.png, 80%)]] 
     126[[Image(Z0_Diff.png, 60%)]] 
    127127 
    128128This modification leads to a weak but significant reduction of evaporation as pictures below : 
    129129 
    130 [[Image(Evap_Diff.png, 80%)]] 
     130[[Image(Evap_Diff.png, 60%)]] 
    131131 
    132 Globally this translate into a reduction of evaporation of about 4%. 
     132Globally this translate into a reduction of evaporation of about 3.9%. 
    133133 
    134 If we consider that the 90's are a representative sample in the 34 WFDEI_CRU forcing, then we can apply this reduction to the mean ORCHIDEE number of 609 kg/m²/y and obtain 585kg/m²/y. With this reduction, ORCHIDEE is still in the higher evaporating models but very close to HTESSEL and SURFEX.  
     134The analysis is performed over 34 WFDEI_CRU forcing years (1979-2012). We can apply this reduction to the mean ORCHIDEE number of 598 kg/m²/y and obtain 574 kg/m²/y. With this reduction, ORCHIDEE is still in the higher evaporating models but very close to HTESSEL and SURFEX.  
    135135 
    136136This suggests to me that indeed we have been using Z0h=Z0m for years as a compensation for errors in the forcing. This is corroborated by analysis of the water cycle of the Mediterranean basin where ORCHIDEE systematically shows too much water in the rivers and thus too little evaporation. Choosing lower Z0h values in ORCHIDEE will allow to differentiate Z0m and Z0h in LMDZ, lowers evaporation and probably prepare us for a more complete parametrisation for estimating Z0h, like the one proposed by Su et al.