Changes between Version 77 and Version 78 of Documentation/Forcings


Ignore:
Timestamp:
2018-02-21T15:15:43+01:00 (6 years ago)
Author:
aducharne
Comment:

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  • Documentation/Forcings

    v77 v78  
    5151 
    5252(b) '''Two versions of the driver are available''' to do do both the reading and the inter/extrapolation of the forcing datasets. They differ in the way they interpret the time at which the diffrent variables are read in the forcing dataset (further called the timestamp, while the interval refers to the period between two succesive timestamps): 
    53 * '''the old driver (src_driver/dim2driver)''', which assumes that scalar variables (Tair,Qair,Psurf) are instantaneous values at the timestamp, while flux variables (Rainf,Snowf, SWdown, LWdown) are mean values over the interval ending at the timestamp.  
    54 * '''the new driver (src_driver/orchideedriver.f90) is more flexible''' and can normally deal with any temporal structure of the forcing datasets, provided the required attributes are inserted in the forcing files. This document [attachment:Description_Forcing_Files.pdf] provides detail of how forcing files need to be prepared. It addresses in particular the issues one may face when the fluxes are averaged and scalar variables instantaneous. The driver needs to take this into account else the diurnal cycle needs to be misplaced. Some data providers have different convention for representing averaged fluxes and this type of details matter.  
     53* '''the old driver (src_driver/dim2driver)''', which assumes that scalar variables (Tair,Qair,Psurf,Wind) are instantaneous values at the timestamp, while flux variables (Rainf,Snowf, SWdown, LWdown) are mean values over the interval ending at the timestamp. This driver also requires that the first value of the annual files corresponds to 00UTC+dt_forcing (for insatnce 03UTC for a 3hourly forcing), and that the last value is for Dec 31st at 24UTC = 00UTC on Jan 1st of the following year.     
     54* '''the new driver (src_driver/orchideedriver.f90) is more flexible''' and can normally deal with any temporal structure of the forcing datasets, provided the required attributes are inserted in the forcing files. Yet, orchideedriver is not yet compatible with libIGCM. This document [attachment:Description_Forcing_Files.pdf] provides details of how forcing files need to be prepared. It addresses in particular the issues one may face when the fluxes are averaged and scalar variables instantaneous. The driver needs to take this into account else the diurnal cycle can be misplaced. Some data providers have different convention for representing averaged fluxes and this type of details matter.  
    5555 
    5656A longer discussion on the differences between the two drivers (dated in 2016) can be found on https://forge.ipsl.jussieu.fr/orchidee/wiki/Branches/Driver_Improvements. 
     
    7070Read more about the shared accounts and IGCM repository here [http://forge.ipsl.jussieu.fr/igcmg_doc/wiki/DocBenvEcommonfiles] 
    7171 
    72 (d) '''Tips and script examples when building meteorological forcing files''': 
     72(d) '''Tips and script examples when building/using meteorological forcing files''': 
    7373* '''Land compressed files''':  
    74    - The '''missing_value''' attribute is mandatory in forcing files containing only land points, with a value outside of the valid range of the variables, for example missing_value=1.e+20. In flinget_mat, the default value is set to 0, if this value is kept, oceanic points will be filled with it and treated as land points because 0. is a valid value for some fields (Qair) but ORCHIDEE will crash because it's not valid for others (PSurf), causing the usual problems in qsatcalc. 
     74   - The spatial structure of ORCHIDEE forcing files can either be 2D, or 1D if we exclude the sea points to construct a vector of land points. In both cases, this imposes a land-sea mask, to define the land points on which ORCHIDEE will run if we use 2D files, or to construct the 1D files.  
     75   - To define the sea points, the '''missing_value''' attribute is mandatory in forcing files containing only land points, with a value outside of the valid range of the variables, for example missing_value=1.e+20. In flinget_mat, the default value is set to 0, if this value is kept, oceanic points will be filled with it and treated as land points because 0. is a valid value for some fields (Qair) but ORCHIDEE will crash because it's not valid for others (PSurf), causing the usual problems in qsatcalc. 
    7576   - FORTRAN 90 script to create a land points only forcing file (use of the compress attribute) [attachment:mk_grid.f90] 
     77* '''SPRED_PREC''' for forcings at 3 and 6 hourly time step:  
     78   - This externalizable keyword defines the nb of orchidee time steps on which the precipitation total of the forcing time step is spread. It can induce significant chnages on the model's behavior (interception and interception loss, infiltration, runoff and ET), although this hasn't been assessed in a systematic way.  
     79   - By default, we spread the precipitation over half the forcing time step (1.5h and 3h respectively for 3-hourly and 6-hourly files).  
     80* '''New driver''': you need to add a time attribute to each variable, e.g. "time: instantaneous" our "time: mean(end)", further details in [attachment:Description_Forcing_Files.pdf].    
     81* '''Old driver''':  
     82   - The above time attributes are optional but recommended so the files can also be used by the new driver. 
     83   - This time attributes should be "time: instantaneous" for the scalars (Tair,Qair,Psurf,Wind), and "time: mean(end)" for the fluxes (Rainf,Snowf, SWdown, LWdown). If the physical definitions of your forcing variables do not fit this scheme, then you should avoid using this forcing with dim2driver, unless you manage to adapt your files to these constraints.  
     84   - dim2driver also requires that the first value of the annual files corresponds to 00UTC+dt_forcing (for instance 03UTC for a 3hourly forcing), and that the last value is for Dec 31st at 24UTC = 00UTC on Jan 1st of the following year. Your files must be prepared accordingly. 
     85* '''Physical definition of the forcing variables''': both drivers follow the same conventions. In particular, the following measurement heights are assumed by default: 2m for Tair and Qair; 10m for Wind. Further details in [attachment:Description_Forcing_Files.pdf]. 
    7686 
    7787=== 1.1 CRU-NCEP* ===