Changes between Version 1 and Version 2 of DevelopmentActivities/CMIP6/DevelopmentsCMIP6/soil_physic

Timestamp:

2015-02-02T17:18:17+01:00 (9 years ago)

Author:

aducharne

Comment:

--

DevelopmentActivities/CMIP6/DevelopmentsCMIP6/soil_physic

@@ -18 +18 @@
 === Discussions ===
 
+'''Jan Polcher, 13/01/15'''
+
+après notre discussion cet après-midi j'ai un peu réfléchi à comment "merger" les 4 points de Philippe dans le trunk, tout en permettant à tout le monde de suivre ce qui se passe et donc de construire une confiance commune dans ces changements.
+
+Je propose un plan en 4 étapes ou nous laissons quelques semaines entre chaque étape afin que tout le monde puisse faire des runs et des tests avec cette nouvelle version. Ceux ceux qui ont piloté les changement pourront écrire une documentation technique pendant ce temps. J'ai essayé aussi de séparer les changements structuraux des améliorations des paramétrisations actuelles. Donc voici mes 4 étapes :
+
+1) implémentation de la discrétisation verticale commune entre T et W. L'important est de garder la profondeur en T et W comme des paramètres indépendants afin qu'on soit libre de choisir plus tard ce qui convient.
+
+2) Enlever la neige de Thermosoil et la mettre en sandwich entre enerbil et thermosoil. Ceci est donc la partie thermodynamique de la neige que Thao vient d’implémenter dans MICT mais avec la l'interface neige/sol finalisée.
+
+Après ces deux changements on aura une version qui a la nouvelle structure et les nouvelles approches numériques. Les paramètre auront peu changés et donc à priori le comportement du modèle sera similaire au trunk. Un environnement idéal pour voir si tout marche bien techniquement.
+
+3) On rajoute les nouvelles capacité et diffusion thermiques de Fuxing avec le transport de la chaleur par l'eau.
+
+4) L'albedo de la neige et les autres composantes du modèle de neige de MF sont rajouté afin d'arriver à la même configuration que dans MICT aujourd'hui.
+
+Si on veut on peut rajouter une 5ème étape qui est l'activation du gel du sol et la vérification des processus dans la première couche.
+
+Je pense qu'après ce processus on sera au stade ou voulait en venir Philippe pour CMIP6. Si à chaque étape on échange sur ce qui a été fait, que tout le monde fait les tests qu'il pense important on aura tous la même compréhension des évolutions faites.
+
+Pour réaliser ce plan je suis disposé à travailler avec Fuxing et Thao sur les étapes 1 et 2. Je ne peux pas quantifier le travail pour chaque étape, mais une semaine me semble un bon first-guess. Je pense que pour la neige ce sera un peu plus long. Mais comme cela vient en second on peut préparer les choses en amont. 
+
+'''Philipe Peylin, 17/01/15'''
+
+Concernant la proposition de Jan:
+- De mon coté je vois un interêt au point 1) et à le traiter tout de suite en discussion avec ce qui va devoir être fait pour inclure le permafrost (déja inclus dans MICT (version de Charlie Koven)) car dans ce cas la discretisation pour la Temperature devra aller beaucoup plus profond.
+- Ensuite pour le point 2 et 4, personnellement j'aurais traiter cela ensemble (mais je ne suis pas le plus compétent pour juger de l'intéret de séparer)
+
+'''Agnès Ducharne, 23/01/15'''
+
+My opinion is that the main challenges are :[[BR]]
+1) to get the new snow scheme, as it improves the albedo, but in a way that fully respects the surface energy budget and the implicit coupling with LMDZ[[BR]]
+2) to define the best vertical discretizations for T and W, in a way that keeps them as close as possible for convenience.
+The new soil termal properties are an improvement that can be added even if we do not change the vertical discretizations compared to the present Trunk, and heat convection might probably be overlooked in CMIP6.v1 if we cannot achieve identical discretizations, as it has a small effect based on Fuxing's results.[[BR]]
+3) define "MODIS-like" reference albedos for the PFTs
+
+I focus today on the second point: define the best vertical discretizations for T and W.
+Again, we can identify several issues, and from my point of view, the main ones are:[[BR]]
+a) the deep soil required for T may be to deep to reasonable runoff values compared to observed river discharge[[BR]]
+b) the very thin top layer required for W may be too thin for T and induce numerical instabilities of Ts and the surface energy  fluxes[[BR]]
+c) this behavior might be exacerbated in case of freezing
+
+Attached is a series of plots by Fuxing illustrating point b.
+
+    ''Explanations of the plots:
+    If we look at the temperature at each time step, we can find oscillations over the upper 1.4cm soil depth, but the oscillations are not too large.
+    Three simulations were compared (only 5-day simulation, at point: 25E,0N) (see attachment):
+    CTL: the standard vertical discretization is used (2-meter for moisture, 5-meter for temperature), 7.5-min time step (black line)
+    EXP: the revised vertical discretization (8-meter for both moisture and temperature), 7.5-min time step (red line)
+    EXP2: same as EXP, but 15-min time step (green line)
+    Main conclusions include:
+    (1) in the revised soil layer (8-meter), the oscillations appear at upper 4 layers (0.5mm, 2mm, 6mm, 14mm). the oscillations disappear at 5th layer (29mm) (see Figs. c-g).
+    But there is no very large or very small strange temperature in the sub-surface (Figs. a-b).
+    (2) There are also oscillations in the FLUXLAT, FLUXSENS, SOILFLX, RAIN, QAIR (Figs. h-l), but the variations are in normal range.
+    Besides, there are also oscillations by using the standard discretization.''
+
+The good thing is that there seems to be solutions to the above issues:[[BR]]
+a) if pb a is proven (we are still waiting for an answer about this), we could do as in SURFEX-ISBA and only consider the same discretization over 2-m, below which T is solved under the assumption of a uniform W profile (consistent with teh gravitational drainage assumption).
+After talks with Jan, Frédérique and Philippe, I feel it's a solution anyone could agree on if cannot make deep W discretization work.[[BR]]
+b) we know  we have a pb here (Fuxing grahs), but Jan mentioned several times that numerical solutions exist.
+It's about filtering the variability, but I personnaly have no idea what is recover in practice, and it woud be nice if Jan could give us more information on this.
+Another solution might be to lump the 4 top layers of the W discretization to define the first layer for T
+It's seems rather easy, especially if we agree on eth proposition made by Aurelien during his PhD: stick to the present W discretization in the top 25cm, even we allow to change it below.[[BR]]
+c) this still needs to be assessed, and we need to do it for CMIP6.v1 if we want to activate soil freezing.
+
+'''Summary of a talk between Fuxing Wang and Aaron Boone at the AMA2015 in Toulouse'''
+
+(1) Potential problem with the too deep soil depth: A. BOONE said that not only the annual mean discharge changes by using very deep soil layers, the seasonal cycles of discharge (phase and amplitude) are changed a lot by using very deep soil layers in ISBA model. And the second situation may be more serious that the first problem. It seems the hydrology model in MPI also has this problem mentioned by A. BOONE. Currently, the soil depth is 2-3m (changing for different regions) for hydrology,and it is 12m for thermal (constant) in ISBA model. The soil moistures below 2-3m are computed by Darcy's law.
+    Decharme, B., A. Boone, C. Delire, and J. Noilhan (2011), Local evaluation of the interaction between soil biosphere atmosphere soil multilayer diffusion scheme using four pedotransfer functions, J. Geophys. Res., 116, D20126, doi:10.1029/2011JD016002.
+
+    Decharme, B., E. Martin, and S. Faroux (2013), Reconciling soil thermal and hydrological lower boundary conditions in land surface models, J. Geophys. Res. Atmos., 118, 7819–7834, doi:10.1002/jgrd.50631.
+
+(2) Spinup: For the spin up in the ISBA model, it is about 10 years (or more) for dry conditions, and it is much shorter for humid regions (2 year). And it is confirmed that the spinup length for temperature is shorter than that for moisture. For our revised model, A. BOONE commented that it maybe take several decades to get soil moisture equilibrium (but A. BOONE is also not sure exactly how many years are necessary).
+
+(3) 1st layer depth It is 1cm for the 1st soil layer in ISBA. A. BOONE's opinion is that the 1mm soil depth is too thin, and A. BOONE's suggested it better to use at least 1 cm for the 1st layer.
+
 
 === Agreed actions and Agenda ===